First Generation Firebird

Rear End Interchangeability Question

Posted By: thedad

Rear End Interchangeability Question - 08/02/19 12:37 PM

I have a '67 Firebird and wonder if I can swap out my rear end for one out of a 1977 TA. I know I've seen this around here somewhere but I can't find it. Too, I've been traveling extensively for the last several years and have probably asked about this before, but I'm about 6 months from retirement and am refocusing my life on my life and not my [censored] job so please, forgive me for repeating myself and thanks in advance for your help!
Posted By: Firebob

Re: Rear End Interchangeability Question - 08/02/19 01:11 PM

Dad, congrats on making to retirement. I, myself, have 3 1/2 weeks left and frequently tell people who ask, what are you going to do then?, that I have so much to do that I don't have time for a job anymore.

As to your question...of course you can swap a later assembly in but of course there are adjustments that must be made. Mounting points and spring position have to be modified. Also it is more than likely a different width rear so possible wheel change and back spacing has to be considered. Definitately not a direct bolt in.
Posted By: Hank350

Re: Rear End Interchangeability Question - 08/02/19 01:23 PM

The 2nd gen rear will only require having the spring perches repositioned. The width difference is only a quarter inch or so.
I'm retired a couple of years now and loving it. Enjoy!
Posted By: firebird69racer

Re: Rear End Interchangeability Question - 08/02/19 03:15 PM

The strongest BOLT IN rearend for out 1st Gen Firebirds is the Chevy 12 bolt from a 67-69 Camaro, 68 - 71 Nova. The next best is the GM 8.5" 10 bolt from a 72-79 Nova, Ventura, or other GM X bodies. Just be careful from 76 to 79 as they also had a 7.5" which I would stay away from. When I put the 8.5" in my 69 Firebird, I had to shorten my driveshaft one inch, with the 12 bolt I did not have to shorten it, but had to change the rear U-Joint. You can also use the 8.2" rear from the same cars, but not sure if they are as strong as the BOP readend in our cars already, but with upgrades they can be made strong.
This from a Nova site I am on, the dimensions for the 68-79 are the same as for our 1st gens.It shows how to identify the different GM rearends except for the 12 bolt.

https://www.novaresource.org/axle.htm

.
Posted By: wovenweb

Re: Rear End Interchangeability Question - 08/02/19 05:09 PM

I’m curious why are you thinking of swapping?
Posted By: Bartbird

Re: Rear End Interchangeability Question - 08/03/19 01:35 PM

ANY rear later than 67 that you use to replace the 67 8" will require the drive shaft to be shortened about 1", so measure carefully, the nose sticks out more on the stronger rear ends.

good info here from this site

https://firstgenfirebird.org/f-a-q/rear-end-swap/
Posted By: thedad

Re: Rear End Interchangeability Question - 08/03/19 03:14 PM

congratulations on your retirement! I'm sure that, once retired, I'll wonder how I had time to work! Golf, shooting, FISHING, piano/guitar, and my cars. I cannot wait!
Posted By: thedad

Re: Rear End Interchangeability Question - 08/03/19 03:15 PM

thanks for the information! I appreciate the detail!
Posted By: thedad

Re: Rear End Interchangeability Question - 08/03/19 03:26 PM

because my current unit is the factory, open rear that came with the 326. Given that the 326 has been replaced by a 455, it would be nice to make better use of the power
Posted By: Firebob

Re: Rear End Interchangeability Question - 08/03/19 04:43 PM

What gears do you currently have?
Posted By: firebird69racer

Re: Rear End Interchangeability Question - 08/03/19 10:48 PM

Originally Posted by Bartbird
ANY rear later than 67 that you use to replace the 67 8" will require the drive shaft to be shortened about 1", so measure carefully, the nose sticks out more on the stronger rear ends.

good info here from this site

https://firstgenfirebird.org/f-a-q/rear-end-swap/



On my 69 when I changed to a 12 bolt I did not have to shorten my driveshaft, just change the U-Joint. When I changed the 12 bolt to the 8.5" 10 bolt I had to shorten the driveshaft by 1 inch
Posted By: wovenweb

Re: Rear End Interchangeability Question - 08/03/19 11:24 PM

Originally Posted by thedad
because my current unit is the factory, open rear that came with the 326. Given that the 326 has been replaced by a 455, it would be nice to make better use of the power


Understood. Depending upon the 455 you've built there are several ways to go. If you aren't talking hugely more than stock 455 and have something like a 3.08 already(Firebob's question), you may be able to just install an aftermarket posi unit. Obviously, swapping in a known rear end and making the necessary modifications to spring perches, driveshaft, u-joint, etc. is another viable direction. Lots of choices, that's why the questions.
Posted By: thedad

Re: Rear End Interchangeability Question - 08/04/19 12:30 PM

256
Posted By: Firebob

Re: Rear End Interchangeability Question - 08/04/19 03:51 PM

Wow, are you sure? I thought the lowest number gear set installed was in the 279 region? Something like that must've been used behind a two sp auto? Regardless, If you're now running a 4speed, gears like that will fry a clutch in short order. My 69 has m20 4speed and 3.23 gear set. I like them but even still I find myself searching for an extra gear when getting on the freeway. I run around 3100rpms at 70 mph.
Posted By: Hank350

Re: Rear End Interchangeability Question - 08/06/19 01:03 PM

The 2.56 was fairly common in lower h.p. birds. My '69 350 came with one behind a th350. It even came with posi from the factory.
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