# 64 GTO Axle Width



## pbearly (Apr 18, 2013)

I have a 64 GTO and the current axle has 256 gears and a posi. Well behind my four speed this gear ratio is horrible however I get great mileage. Well I found a complete replacement axle that is setup with a new posi and 390 gears. Well I removed my current axle and placed it next to the new one I discovered there are some differences. The new axle is 1inch wider which tells me it is out of a 67 or newer car. It also has more webbing on the center section which should make it stronger. My question is has anyone done this and did they have any issues with this swap? I'm currently running 255/60R-15 tires on 10 inch wheels.


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## geeteeohguy (Feb 2, 2008)

Deja-vu??


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## pbearly (Apr 18, 2013)

geeteeohguy said:


> Deja-vu??


Thank you for your reply on the other thread. After I got accused of hijacking an old post I thought I better start a new one. I did go back and read what you said and I kind of agree. I did get the new axle at a great deal. My current carrier has a posi that doesn't work, one wheel peel all day long. I also did some checking and was told I could only go to a 308 gear on that carrier. I had read one of you other posts on gear choices prior to buying this one and want to go to your gearset if this one is too low. If my information the 390 carrier will accept the same gear ratio you're running, please tell me if I'm correct. With my current 256 gears I can easily go 50 mph in first gear so I'm way too high.


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## geeteeohguy (Feb 2, 2008)

Yes, with a 4 speed, a 2.56 is a terrible choice. You'll burn up clutches. The '4 series' 8.2 ten bolt you have in 3.90 is the most desirable carrier, and you can gear it in 3.36, 3.55, 3.90, or 4.33. I switched the 3.55's out in my '65 for 3.36, and 3.36 works very well as an all-around, do-everything gear on a 4 speed car. My advice would be to run the 3.90 as is if you're not driving the car a lot, or if you just want to have fun in town. If you want to re-gear it to a 3.36, have a pro set it up. It's a precise job that requires special tools and knowledge if you want a long lasting and quiet rear end. 3.36 gears can be hard to find, I ended up with a cherry used GM set, and had a pro (Larry Woltzen) set up my rear end 23 years ago. I think he's in Illinois or Michigan now. With the 2.56 carrier, the only other gear you can use is the 2.78. A 3.08 will not fit.


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## pbearly (Apr 18, 2013)

So I did the right thing with the purchase, that's good to know. I appreciate your help, you have always been very knowledgeable on the site. I'm wondering what size tires you're running and what width rim? I stated my size earlier in the post and my current rims are 10 inch. They do fit with my old axle width but I think the 1/2 inch wider will make a difference. I do plan to change my wheels and was thinking of going to the 8 inch wide rallye II wheels or maybe the Torq Thrush.


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## geeteeohguy (Feb 2, 2008)

On the back of my '65 I am running 15X7 rally one repops. 235/70/15 tires. All of these early GTO's like wheels with a lot of backspacing. A lot of room between the axle flange and the frame channel. Not so much the other way. I'd get some torque thrust's that fit...they look wicked on the early goats.


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## pbearly (Apr 18, 2013)

well I go the rear axle installed and finally got to take it out for a little spin. I have a wicked vibration in 4th gear about 3000 rpm. I'm pretty sure it's a driveshaft issue, I mean I went t from 256 gears to 390 so the shaft is spinning a lot faster. The driveline was in the car when I bought it so I'm unsure about the driveshaft. I have nearly 2 inches of the slip yoke showing at the transmission so I'm wondering if anyone can tell me how much should be exposed?


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## Instg8ter (Sep 28, 2010)

do you still have the 2:56 posi carrier, i may be interested in buying it off you?


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## pbearly (Apr 18, 2013)

Instg8ter said:


> do you still have the 2:56 posi carrier, i may be interested in buying it off you?


I have the complete axle.


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## geeteeohguy (Feb 2, 2008)

Your u joints may be out of phase...try unbolting the driveshaft, turning it 180 and bolting it back up. Also make SURE that the rear u joint is centered on the yoke. 2"--4" of slip yoke at the front is normal.


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## pbearly (Apr 18, 2013)

Well the problem ended up being the driveshaft, there were a few things wrong with it. The driveshaft was about 3/4 of an inch short, someone had shortened as a do it yourself project and did a horrible job, the actual driveshaft was bent and had too much run out plus the front yoke was warn out. Lucky for me I have an excellent shop near me that made me a new shaft. They do excellent work and they even make shafts for NASCAR.


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## geeteeohguy (Feb 2, 2008)

Thanks for posting the solution. Goes to show that one can never assume _anything_ with a 40-50 year old car that's been through a bunch of owners. Modified driveshaft....who'd of thought? Glad you nailed it.


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## pbearly (Apr 18, 2013)

Yeah I nailed it and the car launches like a rocket. I can finally confirm my rev limiter is working. LOL. I'll run the 3.90 gears and see how they work but I'm betting I will go to some 3.23 for better driveability


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