Hi all,

First of all, I apologize if this topic was covered on previous thread(s), but I couldn't find out the exact answer to my question. My car is a 92 RS with 305tbi and currently the rear end has 2.73 gears, non-posi, and drum brakes (stock).

This weekend I found an '86 305 Trans Am at the local self-service junkyard with the rear end that I want: 3.23 gears (I believe), posi, and disc brakes. They want $250 for the whole rear end assembly.

My questions:
1. In general, it looks like a pretty straight forward swap. But how involved it really is?
2. Will my current driveshaft will bolt on to the other rear end (same length, etc)?
3. What do I do about the brake lines? What will be different on it btw drum and disc? Do I need a new proportioning valves?

Any help is greatly appreciated!
Thanks guys!

 

It's a direct swap as long as its out of a 3rd or even 4th gen. I got a rear out of a berlinetta in my 89 RS. All you have to do is take some pics of what all the suspension looks like before you do anything and then you can start ripping the old one off. Unbolt the brake lines from the rear end and the drums while still in the car.(It is a lot easier to put the new one on this way. The driveshaft will work.
Just make sure you bolt everything up tight and check it after about a week to make sure its all solid.
As for the brakes, if you plan on using the disc brakes, you will need a new master cylinder. I would get it out of the car you are getting the rear end out of.
Another thing is make sure the springs are seated properly with the rubber mount above them to assure alignment. I think you can use the old brake lines on the discs.
What you need to unbolt is the torque arm that has 2 large bolts, the shocks, the panhard bar (unbolt only from rear end leave it in car), Lower control arms and than the springs will drop out when the rear end is lowered from the car.
Something i would reccomend doing is upgrading suspension parts while you have everything out. It would be a lot easier to do than. I replaced the shocks with Monroe Sensa-Tracs and got a UMI Panhard bar. I would have gotten new lower control arms and a torque arm but ran out of money.
I hope this helps you out and you can get what you want for your car.
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Oh yeah another thing is the e-brake will need to be disconnected from inside the drums and re-used

 

1. Straightforward.

2. Drive shaft will bolt up.

3. The new rear end will have the lines you need. Nothing. Yes.

JamesC

 

I swapped in a 4th gen LS1 disc brake rear on my 84 3.73 non posi, alluminum drum brake rear, and did not have to change the proportioning valve. I did several hard breaking stops to make sure everyting was working correctly and the braking was still balanced. Major difference in stopping power and the 3.42 posi gear are alot better on the gas.

 

So your 84 originally had drums on the rear, right?
If so, good to hear! Less trouble and less parts to buy

Thanks!

 

you didn't have to switch the master cylinder?

 

Thanks for all the replies!

I finally got a chance to take everything apart from that rear end I picked up at the junkyard. So it's a 9-bolt, posi, with 2.77 ratio. Can I get different ratio gears (3.xx) into the stock carrier or do I need a different carrier? If I can, who sells those gears? All the places I called don't have the 3.xx ratio that'll fit my carrier.


Thanks again.....

 

The stock rear disc brakes suck so alot of people mod the prop valve. By that I mean they basically get rid of it- just plug the hole with an allen head plug. I remember seeing alot of people do it, I did myself and noticed a slight difference. May be worth "upgrading" to the plug rather than pulling a different prop valve.

 

i am pretty sure you can get a 3.08 gear on that carrier but i dont think any higher than that
i may be totally wrong

 

So here's the latest: My friend who owns a '99 Z-28 replaced his posi unit with an aftermarket one, so he gave me the stock carrier from that '99 Z-28.
Do you guys know if this carrier will fit into the 9-bolt rear end I have?
If it is, great! I can pretty much get any 3.xx gears from anywhere.

Thanks again!

 

Okay, I found out that the carrier from the '99 Z-28 won't fit into my 9 bolt (Duh!).

For the 9 bolt:
I heard that in order to mount 3.27 or numerically higher ratio gears on the 2 series carrier, there are shims available to position the ring gear closer to the pinion gear. Do you guys know if such shim exists? If you do, can you let me know where to get one? I'm just trying to get away from buying a new 3-series carrier (as they're kinda costly for the 9 bolt).



Thanks!!

 

I hate to be your black raincloud, but you're getting into a whole new game with a nine bolt rearend. The parts are a major PITA to find, especially for a good price, the posi units burn out in them left and right, and the 88 and older rear disc brakes were defective in operation from the day they left the factory. This is just one member's suggestion, so take for what you will, but you'd be far better off getting a 3 series 10 bolt posi rear from an 89 or newer camaro with the pbr aluminum caliper disc brakes. Another plus to running the pbr rearend is that you don't even have to change the proportioning valve, the drum one operates them just fine. I ditched my stock 89 2.73 drum rear for a 3.23 posi/disc rear from a 91 GTA, and I couldn't be happier. I have three buddies with nine bolt "posi" rears, and every one of them is burned out. Ten bolt parts are cheap in comparison, and the sky's the limit on ratio choices. The only aftermarket gears I've seen for nine bolts are 3.70 ratio, and they're damn expensive. Just my .02.

 

just get a 4th gen rear end out of a z28. youll have a posi, disc brakes, most likely 3.23 or 3.42 gears, and a lot better rear end

 

I know..... The 9 bolts seems like a non-practical solution, but at the same time this is what I have to work with and I hate to waste the $$ I already paid for it. I'll look around to see if I can find some used 9-bolt 3-series carrier, but if I can't find one, I may have to resort to other solution

Thanks for all the input guys! Greatly appreciated!

 

Yeah, I can totally understand the position you're in right now, and I don't blame you for working with what you got. I just figured I'd give you some straight up facts I've learned about the nine bolts since I got into thirdgens. Hope I didn't put ya in a major funk over it!

 

Not at all!
I'm glad that people tell me all these things, I rather be informed ahead than be sorry later. And I kinda figure out that the 9 bolt parts can be expensive after talking to some drivetrain shops. I'll give it couple more days to do some search in used 9 bolt 3-series carrier, if no luck, then time for 'PLan B'....

 

I see 3 series nine bolt carriers pop up on ebay quite often, and they usually sell fairly cheap. Ebay's definitely your best bet for an affordable one.

 

Having been been through several 3rdGen rears, I can assure you having someone rebuild them is more expensive than the "salvage yard" option, which buys enough time to save up and buy a new 12-bolt or 9-inch instead of fooling around with parts 20 years old.

 

Yeah, I have to agree with the salvage yard option, especially when you have connections! We just picked up a complete 3.23 fourth gen disc brake posi out of a 94 T/A for my buddy's car for a lousy $80!