The drive is worth the wait. Get the ring and pinion gear happy. 500 miles to go. That whine is a nice purr to me. Love seeing that smile on your face.
Great video. For those watching... it's really better if you give yourself room by taking the axles and driveshaft all the way out, clean and inspect. U-joints are cheap, I just assume they need to be replaced and keep the used as a spare. (As I get older I write "good spare" on the box, and "can be thrown away" so my wife knows what to ditch if I'm not around anymore.)
I just put 3.55 gears in the open end 8 inch housing in my 65 convy. It sounded in the video like you have a 4 spd, in it. I had a 66 coupe that I put a 5 spd in. I installed a tach before the changeover to see the delta. With the 4, in 4th gear my tach was at ~ 3500 RPM doing about 70, while with the 5spd, the tach sat at 2200 RPM doing 70. I'm going with the T5 in this car also, shortly.
You can use a plastic bottle, like an old bleach bottle and some tubing to pull the oil out. Drill a hole in the top and then put a tube in and then glue it shut. I had a 65' as a kid, and we bought a parts car to pull the four speed in it. I didn't swap the rear end at first and it was really high geared. I checked the parts car and it had a 3.55. It seriously woke the car up. Drove much better, had a lot more kick.
On my 66 I got ahold of a 9in axle tube and put a limited slip with 3:25 gears. Even got an original tag for it! I do some highway driving and don't want the transmission screaming at me at 60-70 mph. Ålso did rear disc brakes.
I'm going to be slightly nit picky about this...it's not a "posi". Posi is short for PosiTraction which is what GM calls that type of rear end. When I switched from the 2.80 to a 3.55, it was a TractionLock, which is the Ford name. Good video, and when you dropped those rear gears from the jack, I did the same thing and realized just how heavy that 3d member is. Can't wait to see more.
Yeah but, Posi is more fun to say. :) The sucker was heavier than I was expecting, and when you're on camera you know that you get one chance at this. That day I did it a little safer, but I make no claims about other days. :)
You can do it! Just make sure you get the correct part, or you'll be banging on things for a while. :) Thankfully they sell complete kits. I almost bought separate pieces, but buying the kit was the easiest way to go.
Thanks for the video. I have been thinking I need to put a posi my 66 but honestly had no idea what that would take so now I know and think I will giving it a shot.
A small caution Mike, if you change the gear while installing the lsd, you will likely require longer gear bolts which are not included in the installation kit. As well Summit racing is offering free shipping to Canada currently. I did this recently and it was about 550 cdn when done. Cheers.
Hey hind sight is 29 20 and to me every thing is simpler when I get done and it turns out fine thanks for the information and your time cool car I have a 65 coupe it's is a solid car work in progress lol lol but it's mine
This is awesome! I was actually looking at their kits also. Maybe for a Fall /winter project. I've always wanted to upgrade mine to a posi and maybe 3.25 gears. I only have a C4 so don't want RPMs to be that high while going 60+.
For the money, I think this is one of the best mods we can do to our cars. Looking at all the work you've done so far, I think you could easily replicate what I've done! :)
Just a FYI, should never allow the weight of the axle on the seals.. Will stretch the seal spring enough to allow it to leak.. May have caused your issue.. Anyway, I enjoyed watching the video.. Thanks again..
Swap the 4-speed out to a 5-speed and it will be more highway friendly. Running the same gear in my Mll. The 5-speed made mine much more highway friendly.
Awesome vid. Have a 66 Fairlane 390 4spd Open 8” rear not sure on my gears. How did you pick what ratio to go with? And how to pick proper Speedo gear? Im in Canada & GPS the car it’s not in Kms or MPH. Reading is off for both. Thanks for any help
Picking the gear ratio is dependent on what you're wanting from the car. If fuel economy and cruising speeds are your priority, then something below 3.00:1 is for you. If you want the car to accelerate faster, but at the cost of higher RPMs at highway speeds, then something in the 3.55:1 or 3.83:1 ratio is more for you. You need to know the tooth count of the speedo gear (inside the transmission) on the output shaft, gear ratio in your rear axle, and the tire diameter in order to calculate which speedo gear you need to buy. There are websites that can help with that too.
@@AndyKruseChannel thanks for the reply. I’ll be crawling under car this wknd. I didn’t see a diff tag so I’ll have to try rotating tires & count turns on driveshaft. And I’ll look up what 4 spd is in the car & pull the Speedo gear
@@Yamadeere For the tooth count on the output shaft of the transmission, you'll want to look up the transmission you have online, it should tell you. The tooth count in the speedometer cable is a different number (although it is important too). You probably have a 7 tooth gear on the output shaft, but you'll want to confirm that. :)
@@AndyKruseChannel thanks Andy. I did some looking and I have an open 8” rear with 2.80 gears. 205/70R14 tires = 25.4" 4spd trans is wide ratio with 28 spline tail shaft 16 tooth Speedo gear. I’m thinking I’ll go with the 3.55 gears & locker. Then I’ll just have to figure out what Speedo gear to get things reading right. Keep up the great show. Live the car build I’m gonna be trying to do a lot of that this winter. And the truck build is looking good too
are you in the Spokane Wash area? I just did this swap on my 66. I had 2.80 gears with T5 and 351 Windsor, the car was a T code 6 cyl. I found what appeared to be a good used third member with 3.55 gears and the swap only took two hours. Have not got it out on the road yet, Iam hoping it is going to handle better with the lower gears.
Sorry Boss, it has been quite a while since I had those parts installed and it’s been a few years since I sold that Mustang. I went with slightly better parts on my current 8” upgrade and there is no noticeable whining from the rear end. I think 3.70 gears would be more fun on the back roads, but 3.50 gears are more fuel friendly and RPM friendly on the highway. I think it comes down to where you’ll drive the car more. 🙂
Andy, great video. I know you went to 3.55 gears with your 5 speed. I am thinking of changing my gears out. Currently 2.80 with a C4. What would you suggest to get faster off the line and still be able to take it on the freeway? Thanks,
As you're aware, any number higher than 2.8 will improve your acceleration times, but at the cost of higher RPM at highway speeds. Some say a 3.0:1 gear is a good compromise if you have to spend a lot of time at 60mph or higher. But if you're like most of us and are on a budget (don't have the money to try different gears), I'd say the 3.55 will put a bigger smile on your face for most of the driving you'll do compared to a lower numbered gear (taller gear). You'll be around 2600rpm at 60mph because in this video I had a 4 speed but the 4th gear is a 1:1, which is the same as your 3rd gear in your C4. :)
I paid about $300, about 2-1/2 years ago when I had the work done for assembling the third member for the car in this video. About 1-1/2 years ago I took my third member of my Fastback to the same shop and paid about $450, but I had to buy a used housing from them as mine was cracked. So with all that, I'd expect today's prices to be between $400 - $450 for a shop to assemble your third member. :)
@@AndyKruseChannel Aha, thanks. So Quick sells a preassembled third with the options I want and other upgrades for 1.1k. Seems the better option, thanks!
It depends on how much highway driving you do, and what your first gear ratio is. If you have the less desirable 3.35:1 first gear, then anything above a 3.55:1 rear end will make that first gear almost unusable. If you have the taller first gear (numerically smaller number), then you could go up to something like a 4.11:1 rear end and still be fine. The other end of the conversation is the RPMs at highway speeds. The shorter the rear end (numerically larger numbers), the higher your RPMs will be in a given gear for a given speed. On the highway it's nice to have that 5th gear for cruising speeds, but the a shorter rear will begin to eat into those RPMs and you begin to lose out on the advantage. Now, with that in mind, I think something in the 3.70s to 3.90s for the rear end will be both fun and still practical for highway speeds. :)
Any recommendations for a great gear ratio? I have a 66’ Mustang, I installed a 2004 Mustang GT rear end I got from pick-a-part. (Original GT was totaled) already has Posi.
I find the 3.55 is great for a little extra pep off the line, but also manageable RPMs when you're cruising at highway speeds. I think something between 3.80 and 4.10 would be more fun to drive, but it comes at the cost of higher RPMs when you're on the highway. If you rarely ever get the car up to 60+ mph, then looking at those shorter gears (numerically high numbers) might be right for you. :)
Wow!!! Andy Kruse is responding to me!! That’s awesome, wasn’t expecting that. Love your builds and ideas for the Mustang. I thought a 3.73 gear would be the best for mine. I wouldn’t lose much on the top end, but I would gain acceleration and a better throttle response, which is what I want. For some reason my 66’ just has a lot of lag on takeoff. Not looking to drag race. It’s my weekend car, but I wanted to have some snap, some Pep when I give it the Gas.
Haha, I'm a nobody, but I appreciate the excitement. I respond to all the comments, hoping to provide that extra bit of help to those that ask. :) 3.73 would be more fun than 3.55 than the really tall (numerically smaller number) gearing you are currently working with.
Depends on the application. For super sensitive stuff I use my digital Gearwrench unit, for everything else that can be + or - 5%, I use a generic unit I purchased from a pawn shop a long time ago.
In this video I have a generic set of Tri-Y headers. The rest of the exhaust is 2.5" tubing with generic 40 Series mufflers. I have since upgraded the headers to a set of Summit Racing 4-to-1 ceramic coated units. They hang down really low, I wouldn't recommend them on that aspect, but the fitment everywhere else is good.
Hi Andy. You raised my curiosity when you said “ with a mild bump” you could raise the power of the 289. I assume that would be a major effort /expense( pull engine, change displacement, etc) Am I correct?
Assuming someone has already done the intake/header/exhaust parts on these cars (good for 10-20 hp), the next step in pumping the power is a Cam. This can easily be done with the engine in the car, but the radiator will have to be pulled. The next step is upgrading the heads. Again, this can be done with the engine in the car. After that, they'd have t pull the motor to change the displacement. I imagine that a "mild bump" is different for each of us, but that seems to be the mod path when working with these 289s. :)
Correct, it's the factory 8 inch that comes with the V8 cars. Upgrading the rear gear will improve acceleration numbers for your car, but unfortunately I don't know what gear ratio you should buy. I had a 2.80:1 in there and went to a 3.55:1 and it was fantastic! However, I have since upgraded the trans to a 5 speed T5 and I think I need to go back in there and change the gearing again, maybe to 3.80:1? :)
I read your parts list and realized it is an 8inch diff. If I am not changing the gear ratio do I just need the Yukon Limited slip diff part and nothing else? Thanks
You can reuse your stock ring gear on the new Diff as the bolt pattern and fitment is essentially the same. While it's not hard to do, it does take special tools and a specific installation procedure to put all that together in the third member (tolerances and gear lash adjustments), so I'd recommend having a shop do that part of the assembly. The removal and installation of the third member can easily be done in you garage, much like I did in the video. :)
@@AndyKruseChannel Hi Andy: Thank you for the quick reply. My gear ratio is 3:00 ( probably that way from the factory) I have the 225 HP (A code) engine. What is the HP of your engine? I ask as I am considering going to a 347 Stroker which would definitely need a limit slip differential. This may require 9” rear end if the HP is more than 300. I am just a street cruiser, don’t need to lay rubber so the 289 is ok but there are some advantages to the larger engine… Again, ,Thanks Dennis
@@dennisparass5531 There's a couple ways you could go here. Do a mild bump to the internals in that 289 and get it closer to 300HP and add the LSD you were thinking about. Changing the gearing will improve acceleration but at the cost of higher RPMs at highway speeds. If you go the 347 route, you'll be at the limits of the 8 inch diff, but since you don't have a manual transmission, the shock to the rear diff will be lower when you put the pedal down (clutch drops are the hardest on these components, but since you have an auto....). Upgrading to a 9 inch rear with an LSD and better gearing will set you back about $2000+ in parts. Leaving the 8 inch there but upgrade its guts will be about $500 in parts. Labor for any of that stuff can be all over the map. I too would like some more displacement in my motor, but not only does it come at a higher cost to get there, it's the cost of all the other components that need upgrading that kills it for me. With all the parts and upgrades I've added to the car in the past year, I've sort of forced myself into a small window of wheel power as these new drivetrain parts are limited to something around 300HP. I did this as I'm still trying to figure out where I want to go with this car. I upgrade parts as I go and whatever the budget allows. Having a plan for big HP numbers would be great, but I should have done that at the beginning so the parts I purchase along the way are ideal for that HP scenario. Good luck!!
Man oh man! I wanted to do this mod to my 65 back in the day. I hated the one tire burn out. My next ride will get this upgrade for sure! How did it turn out?
Initially it was fantastic on that car, until I replaced the stock manual trans with the T5. The new rear gearing was perfect for that original trans, but the gearing with the T5 took away some of the "zip". But other than that, it's a must-need part for these cars, that's why I did it rather early on the Fastback build. :)
Correct, the stock 8" that comes on all the V8 cars. With the 4 speed I had in the car at the time of the install, the 3.55 gear was perfect. But I upgraded to a T5 trans not too long after this rear end swap and suddenly I wished I did the 3.80 gear. Just something to think about when considering the mods you are planning for your car. :)
What transmission do you have in this car ? I have a 65 mustang and I swapped a t5 transmission into it. Looking to possibly get 3.80’s or 3.55’s. Great video!
T10 4spd. With the gearing in that box, the 3.55 is about as high as I would go because the RPMs at highway speeds is almost too high. However, with overdrive gear you have in your T5, that 3.80 might be the sweet spot with fantastic acceleration in the first few gears, but usable at highway speeds without revving the motor too high at 60 mph. The 3.55 gear in a T5 will be about 2000 rpm at 60mph. I may or may not know this........ ;)
@@AndyKruseChannel I have 69 mustang where I want a crazy engine and transmission swap in it and upgrading the differential. Engine from 2006 Lexus Transmission toyota R155 Do you recommend the T5 from newer mustangs differential ? From what years you would suggest to look for if I would like the limited slip as well. Thanks
@@thaieralawadh2223 To make it easier and cheaper, I'd stick with the 1983 - 1993 T5 because it has the speedometer gear and not the electronic speedometer signal port. That right there will save you $350 for the converter box and anything else you need to finalize that install. Then, there's the issue with the input shaft on the 1999-2004 T5 where it is longer, which means you need to purchase the correct length input shaft, bearing retainer, and have someone put it together for you. That's even more money saved. However, depending on the motor you have in you '69, the T5 might not be strong enough for the Torque you're creating, and you might need to jump up to the Tremec TKO or some other newer trans. At that point it will be more money regardless. Happy modding!! :)
@@AndyKruseChannel thanks for the replay. I am sure of the engine and transmission set up. We do it a lot in here in 4X4 SUV's but wanted to try in in my classic mustang. Will produce around 300-400 of howerspower and torque. ( It is cheap in here like 1000$ for such engine and transmission ) ( 3UZ+ R155 ) But wanted to upgrade my old 8.8 differential and brakes. Thus, trying to find good option which I can pull from a wrecked car in the local junkyard. Unfortunately, I am in Dubai and not interested to order from the states due to cost and waiting time.
![Noob To Max With DRAGON REWORK In Blox Fruits [FULL MOVIE]](http://i.ytimg.com/vi/LnBMOinoOvA/mqdefault.jpg)
I remember upgrading to 3.80s last year. Wow what a difference gears make!
What trans do you have? Would you go with a different gear knowing what you know now?
Im really curious go from 3.25 to 3.80 with a mild 302 and c4
I have a 1967 mustang with a 289 engine and C4 transmission. This is a new world for me. Which kit should I get? Thx guys!
Thank you for the torque specs. I’m know i can always count on you for that when I’m working on my car! 💯
Any time!
The drive is worth the wait. Get the ring and pinion gear happy. 500 miles to go. That whine is a nice purr to me. Love seeing that smile on your face.
I actually made the video over a month ago, I've put some more miles on there, the whine is definitely not as noticeable.
Great video. For those watching... it's really better if you give yourself room by taking the axles and driveshaft all the way out, clean and inspect. U-joints are cheap, I just assume they need to be replaced and keep the used as a spare. (As I get older I write "good spare" on the box, and "can be thrown away" so my wife knows what to ditch if I'm not around anymore.)
You're assuming she's just not going to pitch the whole garage when you're not around anymore. :)
I just put 3.55 gears in the open end 8 inch housing in my 65 convy. It sounded in the video like you have a 4 spd, in it. I had a 66 coupe that I put a 5 spd in.
I installed a tach before the changeover to see the delta. With the 4, in 4th gear my tach was at ~ 3500 RPM doing about 70, while with the 5spd, the tach sat at 2200 RPM doing 70. I'm going with the T5 in this car also, shortly.
Yeah, that overdrive gear can really help with the highway RPMs. I did put a T5 in this car before I sold it, by current Mustang also has a T5. :)
You can use a plastic bottle, like an old bleach bottle and some tubing to pull the oil out. Drill a hole in the top and then put a tube in and then glue it shut. I had a 65' as a kid, and we bought a parts car to pull the four speed in it. I didn't swap the rear end at first and it was really high geared. I checked the parts car and it had a 3.55. It seriously woke the car up. Drove much better, had a lot more kick.
Great tip!
On my 66 I got ahold of a 9in axle tube and put a limited slip with 3:25 gears. Even got an original tag for it! I do some highway driving and don't want the transmission screaming at me at 60-70 mph. Ålso did rear disc brakes.
Nice! Upgrading to the 9 inch would be great, that way there's no holding back on the power plans for the motor! :)
@@AndyKruseChannel Yes , especially with that 347 roller motor I built for it. Wish I could send you pictures of it.
I'm going to be slightly nit picky about this...it's not a "posi". Posi is short for PosiTraction which is what GM calls that type of rear end. When I switched from the 2.80 to a 3.55, it was a TractionLock, which is the Ford name. Good video, and when you dropped those rear gears from the jack, I did the same thing and realized just how heavy that 3d member is. Can't wait to see more.
Yeah but, Posi is more fun to say. :)
The sucker was heavier than I was expecting, and when you're on camera you know that you get one chance at this. That day I did it a little safer, but I make no claims about other days. :)
I've seen some mechanics put a thin layer of oil resistant silicone or RTV (not sure which) around that axle seal to prevent leaks.
That won't hurt anything. :)
Great video Andy, can’t wait to do the same to my ‘66
You can do it! Just make sure you get the correct part, or you'll be banging on things for a while. :) Thankfully they sell complete kits. I almost bought separate pieces, but buying the kit was the easiest way to go.
Thanks for the video. I have been thinking I need to put a posi my 66 but honestly had no idea what that would take so now I know and think I will giving it a shot.
Overall a project like this is fairly simple and somewhat affordable. Good luck!!
Andy thanks for giving the cost, i have to shop in Canadian $, plus shipping, SO please and thank you for giviing that .out.
Any time!
A small caution Mike, if you change the gear while installing the lsd, you will likely require longer gear bolts which are not included in the installation kit. As well Summit racing is offering free shipping to Canada currently. I did this recently and it was about 550 cdn when done. Cheers.
Hey hind sight is 29 20 and to me every thing is simpler when I get done and it turns out fine thanks for the information and your time cool car I have a 65 coupe it's is a solid car work in progress lol lol but it's mine
Thanks!
Happy New Year!
Happy holidays!
Same to you!
This is awesome! I was actually looking at their kits also. Maybe for a Fall /winter project. I've always wanted to upgrade mine to a posi and maybe 3.25 gears. I only have a C4 so don't want RPMs to be that high while going 60+.
For the money, I think this is one of the best mods we can do to our cars. Looking at all the work you've done so far, I think you could easily replicate what I've done! :)
Remember C4 final drive ratio is 1:1...same as a 4 speed toploader
@@babygrand1100 I actually swapped out the C4 for an AOD then upgraded to limited slip diff w 3.55 gears. Fun to drive!
Just a FYI, should never allow the weight of the axle on the seals.. Will stretch the seal spring enough to allow it to leak.. May have caused your issue.. Anyway, I enjoyed watching the video.. Thanks again..
Thanks for the info!
Swap the 4-speed out to a 5-speed and it will be more highway friendly. Running the same gear in my Mll. The 5-speed made mine much more highway friendly.
I did, and I made a video about it. Check it out!! :)
Great video! I couldn't really hear the gears so much on the audio. I did hear what sounded like your lifters though.
Probably, that motor was getting tired and probably could have used a good rebuild. :)
Love your work
Thank you so much 😀
Jeez, at about the 1:49 mark, you can see the whole entire quickjack move. What's going on there? I have quickjacks and never seen it so unstable.
It adds to the sense of danger I like to put in my videos. :)
Awesome vid. Have a 66 Fairlane 390 4spd
Open 8” rear not sure on my gears.
How did you pick what ratio to go with? And how to pick proper Speedo gear?
Im in Canada & GPS the car it’s not in Kms or MPH. Reading is off for both. Thanks for any help
Picking the gear ratio is dependent on what you're wanting from the car. If fuel economy and cruising speeds are your priority, then something below 3.00:1 is for you. If you want the car to accelerate faster, but at the cost of higher RPMs at highway speeds, then something in the 3.55:1 or 3.83:1 ratio is more for you.
You need to know the tooth count of the speedo gear (inside the transmission) on the output shaft, gear ratio in your rear axle, and the tire diameter in order to calculate which speedo gear you need to buy. There are websites that can help with that too.
@@AndyKruseChannel thanks for the reply. I’ll be crawling under car this wknd. I didn’t see a diff tag so I’ll have to try rotating tires & count turns on driveshaft. And I’ll look up what 4 spd is in the car & pull the Speedo gear
@@Yamadeere For the tooth count on the output shaft of the transmission, you'll want to look up the transmission you have online, it should tell you. The tooth count in the speedometer cable is a different number (although it is important too). You probably have a 7 tooth gear on the output shaft, but you'll want to confirm that. :)
@@AndyKruseChannel thanks Andy.
I did some looking and I have an open 8” rear with 2.80 gears.
205/70R14 tires = 25.4"
4spd trans is wide ratio with 28 spline tail shaft
16 tooth Speedo gear.
I’m thinking I’ll go with the 3.55 gears & locker. Then I’ll just have to figure out what Speedo gear to get things reading right.
Keep up the great show. Live the car build I’m gonna be trying to do a lot of that this winter. And the truck build is looking good too
Love that thumbs up. I am so jealous. Beautiful
Thank you so much!
Looking to do this swap in my 69 mustang. Do I need to change my axel shafts if I go to 3.80? I also have the 8” on 2.79 I believe
No, you can use your same stock units. The 8" rear uses 28 spline, so just make sure your new Diff has the same spline count. :)
are you in the Spokane Wash area? I just did this swap on my 66. I had 2.80 gears with T5 and 351 Windsor, the car was a T code 6 cyl. I found what appeared to be a good used third member with 3.55 gears and the swap only took two hours. Have not got it out on the road yet, Iam hoping it is going to handle better with the lower gears.
Sounds like you've got quite the setup on your Mustang. It will be great to get behind the wheel once the weather gets better. :)
Andy, did you have whining noise with the excel gears?
Would you choose 3.55 over 3.73 gears again?
Sorry Boss, it has been quite a while since I had those parts installed and it’s been a few years since I sold that Mustang.
I went with slightly better parts on my current 8” upgrade and there is no noticeable whining from the rear end. I think 3.70 gears would be more fun on the back roads, but 3.50 gears are more fuel friendly and RPM friendly on the highway. I think it comes down to where you’ll drive the car more. 🙂
Andy, great video. I know you went to 3.55 gears with your 5 speed. I am thinking of changing my gears out. Currently 2.80 with a C4. What would you suggest to get faster off the line and still be able to take it on the freeway? Thanks,
As you're aware, any number higher than 2.8 will improve your acceleration times, but at the cost of higher RPM at highway speeds. Some say a 3.0:1 gear is a good compromise if you have to spend a lot of time at 60mph or higher. But if you're like most of us and are on a budget (don't have the money to try different gears), I'd say the 3.55 will put a bigger smile on your face for most of the driving you'll do compared to a lower numbered gear (taller gear). You'll be around 2600rpm at 60mph because in this video I had a 4 speed but the 4th gear is a 1:1, which is the same as your 3rd gear in your C4. :)
Great info 👍👍👍
Thanks 👍
I know it's been a couple of years, but what did labor end up being? I'm torn between replacing mine or just getting a fully built third member.
I paid about $300, about 2-1/2 years ago when I had the work done for assembling the third member for the car in this video. About 1-1/2 years ago I took my third member of my Fastback to the same shop and paid about $450, but I had to buy a used housing from them as mine was cracked. So with all that, I'd expect today's prices to be between $400 - $450 for a shop to assemble your third member. :)
@@AndyKruseChannel Aha, thanks. So Quick sells a preassembled third with the options I want and other upgrades for 1.1k. Seems the better option, thanks!
Man I never knew those gears were so tiny on the speedometer cable
Yup, there's not much to them. I'm just glad the gear inside the trans is good to go, don't want to have to replace that.
Hi Andy, I just installed a T5 in my 67 mustang. It has a 289 motor and 280 gears. Do you recommend going with the 380 gears?
It depends on how much highway driving you do, and what your first gear ratio is. If you have the less desirable 3.35:1 first gear, then anything above a 3.55:1 rear end will make that first gear almost unusable. If you have the taller first gear (numerically smaller number), then you could go up to something like a 4.11:1 rear end and still be fine. The other end of the conversation is the RPMs at highway speeds. The shorter the rear end (numerically larger numbers), the higher your RPMs will be in a given gear for a given speed. On the highway it's nice to have that 5th gear for cruising speeds, but the a shorter rear will begin to eat into those RPMs and you begin to lose out on the advantage.
Now, with that in mind, I think something in the 3.70s to 3.90s for the rear end will be both fun and still practical for highway speeds. :)
Thanks Andy. I think the 3.8 is where I while wind up.@@AndyKruseChannel
Any recommendations for a great gear ratio? I have a 66’ Mustang, I installed a 2004 Mustang GT rear end I got from pick-a-part. (Original GT was totaled) already has Posi.
I find the 3.55 is great for a little extra pep off the line, but also manageable RPMs when you're cruising at highway speeds. I think something between 3.80 and 4.10 would be more fun to drive, but it comes at the cost of higher RPMs when you're on the highway. If you rarely ever get the car up to 60+ mph, then looking at those shorter gears (numerically high numbers) might be right for you. :)
Wow!!!
Andy Kruse is responding to me!! That’s awesome, wasn’t expecting that. Love your builds and ideas for the Mustang.
I thought a 3.73 gear would be the best for mine. I wouldn’t lose much on the top end, but I would gain acceleration and a better throttle response, which is what I want. For some reason my 66’ just has a lot of lag on takeoff. Not looking to drag race. It’s my weekend car, but I wanted to have some snap, some Pep when I give it the Gas.
Wish I could show you my 66’
20 years in the making.
Haha, I'm a nobody, but I appreciate the excitement. I respond to all the comments, hoping to provide that extra bit of help to those that ask. :)
3.73 would be more fun than 3.55 than the really tall (numerically smaller number) gearing you are currently working with.
What torque wrench are you using?
😊
Depends on the application. For super sensitive stuff I use my digital Gearwrench unit, for everything else that can be + or - 5%, I use a generic unit I purchased from a pawn shop a long time ago.
can you tell me what kind of headers and what size of pipes and what kind of mufflers you have have on your car
In this video I have a generic set of Tri-Y headers. The rest of the exhaust is 2.5" tubing with generic 40 Series mufflers. I have since upgraded the headers to a set of Summit Racing 4-to-1 ceramic coated units. They hang down really low, I wouldn't recommend them on that aspect, but the fitment everywhere else is good.
Hi Andy. You raised my curiosity when you said “ with a mild bump” you could raise the power of the 289. I assume that would be a major effort /expense( pull engine, change displacement, etc) Am I correct?
Assuming someone has already done the intake/header/exhaust parts on these cars (good for 10-20 hp), the next step in pumping the power is a Cam. This can easily be done with the engine in the car, but the radiator will have to be pulled. The next step is upgrading the heads. Again, this can be done with the engine in the car. After that, they'd have t pull the motor to change the displacement. I imagine that a "mild bump" is different for each of us, but that seems to be the mod path when working with these 289s. :)
Maybe I missed it , is your rear differential an 8 inch? I have an 8 inch and a C4 transmission so I presume I would not do any gear ratio change?
Correct, it's the factory 8 inch that comes with the V8 cars. Upgrading the rear gear will improve acceleration numbers for your car, but unfortunately I don't know what gear ratio you should buy. I had a 2.80:1 in there and went to a 3.55:1 and it was fantastic! However, I have since upgraded the trans to a 5 speed T5 and I think I need to go back in there and change the gearing again, maybe to 3.80:1? :)
I read your parts list and realized it is an 8inch diff. If I am not changing the gear ratio do I just need the Yukon Limited slip diff part and nothing else? Thanks
You can reuse your stock ring gear on the new Diff as the bolt pattern and fitment is essentially the same. While it's not hard to do, it does take special tools and a specific installation procedure to put all that together in the third member (tolerances and gear lash adjustments), so I'd recommend having a shop do that part of the assembly. The removal and installation of the third member can easily be done in you garage, much like I did in the video. :)
@@AndyKruseChannel Hi Andy:
Thank you for the quick reply.
My gear ratio is 3:00 ( probably that way from the factory)
I have the 225 HP (A code) engine. What is the HP of your engine? I ask as I am considering going to a 347 Stroker which would definitely need a limit slip differential. This may require 9” rear end if the HP is more than 300.
I am just a street cruiser, don’t need to lay rubber so the 289 is ok but there are some advantages to the larger engine…
Again, ,Thanks
Dennis
@@dennisparass5531 There's a couple ways you could go here. Do a mild bump to the internals in that 289 and get it closer to 300HP and add the LSD you were thinking about. Changing the gearing will improve acceleration but at the cost of higher RPMs at highway speeds. If you go the 347 route, you'll be at the limits of the 8 inch diff, but since you don't have a manual transmission, the shock to the rear diff will be lower when you put the pedal down (clutch drops are the hardest on these components, but since you have an auto....). Upgrading to a 9 inch rear with an LSD and better gearing will set you back about $2000+ in parts. Leaving the 8 inch there but upgrade its guts will be about $500 in parts. Labor for any of that stuff can be all over the map. I too would like some more displacement in my motor, but not only does it come at a higher cost to get there, it's the cost of all the other components that need upgrading that kills it for me. With all the parts and upgrades I've added to the car in the past year, I've sort of forced myself into a small window of wheel power as these new drivetrain parts are limited to something around 300HP. I did this as I'm still trying to figure out where I want to go with this car. I upgrade parts as I go and whatever the budget allows. Having a plan for big HP numbers would be great, but I should have done that at the beginning so the parts I purchase along the way are ideal for that HP scenario. Good luck!!
Man oh man! I wanted to do this mod to my 65 back in the day. I hated the one tire burn out. My next ride will get this upgrade for sure! How did it turn out?
Initially it was fantastic on that car, until I replaced the stock manual trans with the T5. The new rear gearing was perfect for that original trans, but the gearing with the T5 took away some of the "zip". But other than that, it's a must-need part for these cars, that's why I did it rather early on the Fastback build. :)
@@AndyKruseChannel I can't wait to see that video! Thanks for posting.
What book di you use for the torque specs? Service manual or Haynes?
I use the '66 Service Manual for the car. It has an orange cover and the title is "1966 Comet, Falcon, Fairlane, and Mustang Shop Manual". :)
@@AndyKruseChannel perfect that’s what I just got for my 67. Thanks Andy for all the vids. I binged last night when I couldn’t sleep haha
Nice new haircut. Looked like you have lost a little weight as well. All the car renovation 😅😅
😁 Thanks! Cutting out the sweets and snacks goes a long way.
@@AndyKruseChannel keep it up!!!
what engine tran combo?
At the time this video was made, I had the 4 Speed T-10 Sideloader and some bolt on parts for the 289.
I’m probably going to do the same thing. Is your rear end an 8 inch?
Correct, the stock 8" that comes on all the V8 cars. With the 4 speed I had in the car at the time of the install, the 3.55 gear was perfect. But I upgraded to a T5 trans not too long after this rear end swap and suddenly I wished I did the 3.80 gear. Just something to think about when considering the mods you are planning for your car. :)
Hey Andy. Do you remember how much your shop charged you to install the trac loc and gears?
$320, this was two years ago, so this kind of work is likely a bit more, maybe $350 now?
Another great video. Thanks for posting. I plan on doing this to my 66 soon too. How do you like the new gears ?
Thanks!
This is a must do on two levels: better gearing for acceleration and no more one legged wheels spinning. :)
What transmission do you have in this car ? I have a 65 mustang and I swapped a t5 transmission into it. Looking to possibly get 3.80’s or 3.55’s. Great video!
T10 4spd. With the gearing in that box, the 3.55 is about as high as I would go because the RPMs at highway speeds is almost too high. However, with overdrive gear you have in your T5, that 3.80 might be the sweet spot with fantastic acceleration in the first few gears, but usable at highway speeds without revving the motor too high at 60 mph.
The 3.55 gear in a T5 will be about 2000 rpm at 60mph. I may or may not know this........ ;)
@@AndyKruseChannel perfect thank you so much!
@@AndyKruseChannel I have 69 mustang where I want a crazy engine and transmission swap in it and upgrading the differential.
Engine from 2006 Lexus
Transmission toyota R155
Do you recommend the T5 from newer mustangs differential ? From what years you would suggest to look for if I would like the limited slip as well.
Thanks
@@thaieralawadh2223 To make it easier and cheaper, I'd stick with the 1983 - 1993 T5 because it has the speedometer gear and not the electronic speedometer signal port. That right there will save you $350 for the converter box and anything else you need to finalize that install. Then, there's the issue with the input shaft on the 1999-2004 T5 where it is longer, which means you need to purchase the correct length input shaft, bearing retainer, and have someone put it together for you. That's even more money saved. However, depending on the motor you have in you '69, the T5 might not be strong enough for the Torque you're creating, and you might need to jump up to the Tremec TKO or some other newer trans. At that point it will be more money regardless. Happy modding!! :)
@@AndyKruseChannel thanks for the replay.
I am sure of the engine and transmission set up. We do it a lot in here in 4X4 SUV's but wanted to try in in my classic mustang. Will produce around 300-400 of howerspower and torque. ( It is cheap in here like 1000$ for such engine and transmission ) ( 3UZ+ R155 )
But wanted to upgrade my old 8.8 differential and brakes. Thus, trying to find good option which I can pull from a wrecked car in the local junkyard.
Unfortunately, I am in Dubai and not interested to order from the states due to cost and waiting time.