Availability of a 65 3.90 rearend?
 

I have a chance to buy a 65 Tri-Power 4speed GTO. It originally had a 3.90 rearend. It was replaced somewhere along the way with a 3.23. I am wanting to see if there might be a rearend out there and if so, how much it might cost. Thanks for your help or input.

If you already have the 3:23's in there you can just buy the gear set & have them installed. The 3:90's are an easy set to find & buy. They will run about $ 250-300 for the gears set & depending where you live it may cost anywhere between $ 250 -600 to have them installed.

Hi Rex. The car is numbers matching and the rearend housing is the only major part that's not original. It even has the correct notched fan. That is an alternative but I hope I can find a correct rearend. Thanks for the response.

Not 100% sure , but I don't think 3:90's will fit in the 3:23's housing.
Check that before buying.

fitment??
 

Done that!

PM sent. Also, I think the 3.90 will fit the housing, but it will need a different carrier. Need to double check.
Tony

Need different carrier--or a ring gear spacer.

What code is the rear that's in the car now?

I'm not sure on the code. I have not purchased it yet.

I am hoping to find a correct housing with the correct code not just change the gears. Thanks for all of the input! I appreciate the help!

My 73 came with 3:08's in it new & all i had to do was change the gears to the 3:73's that are in there now. As long as it's a 3 series carrier you can bolt up to the 3:90's in it with no other parts . When you go to the 4 series gears then you will need a different carrier or a ring gear spacer. That has been my experience so far with changing gears.

As stated, in an 8.2 '65 rear end, 3.90 gears will not bolt to a 3.23 carrier, which works for 2.93, 3.08, and 3.23 gears. A 3.36-3.55-3.90-4.33 carrier is needed. When I re-geared the 3.55 in my own '65, 3.36 was as low as I could go numerically. Spacers are not a good idea in this already weak rear end. The OP's logic of finding a complete original 3.90 housing with gears intact is the best way to go, and will add value to his car.

8.5 vs 8.2
 

But that is for an 8.5" rear end where the 3 series carrier works with 2.73 3.08 3.23 3.42 and 3.73 OEM gear sets as well as the aftermarket 3.90 and 4.10 ratios. Not the case on the 8.2" carrier discussed by the original poster.

Were the original 65 3.90 rearends nodular cases with the large "N" on top of the case?
Thanks.

I have a 8.2 limited slip for a 3.90 and a new set of gears if you're interested.

Thanks but, I am looking for an original 3.90 axle with the correct codes and stamps for this car. I could possibly use it for another car though. PM me with a price if you don't mind.

I understand what you want. the housing you want is casting #9779822. these are also date coded to make your hunt even harder. the gear codes you can change. they are only stamped in axle tube. the gears as stated are not a issue.

the casting # and date code are on the bottom of pinion area of case.

you may be able to play with changing date code with some art work.

you are going to need a lot of luck finding this. so good luck!

Thanks for the great information! That's what I need. Another member gave me a heads up on a possible axle. Now I can look for the correct casting.

the correct date is the harder part. if your not critical on that it makes it easier. the 64 housing is different in that the upper eyes in the housing for bushings for upper control arms mount are smaller. the 66 case is wider ( some don't think so). i will get gruff on that. but the casting number will be different even if i'm wrong most likely.

The guy with the axle is checking the casting and date codes for me. It came out of his brothers car years ago. He says he has the PHS report that shows it was a tri power, 4spd, 3.90 car. So, I'm hoping it's real. My car was an April build so maybe I'll get lucky. Thanks for your help. I'm pretty fair with the 68-72 GTO's but not so much on the older ones.