Hey guys, I wanna replace the stock rear end in my 91 Trans Am (posi drum 2.73) with a 3.42 posi disc. I tried a search but it wouldn't answer my questions specifically. Now here are my questions:

1. Is it true that all disc rear ends on thirdgens were posi?

2. What will I need for the swap? (Including the drum-to-disc conversion, sorry if this should be in the Brake forum)

3. Is there a difference in the way that the 9 bolts and 10 bolts mount to the car?

4. Any tips/tricks that I should know before I commence?

5. How much should I expect to spend on the rear end I'm looking for in reasonable condition? Maybe something just a tad better than this:




6. Will my launches improve significantly with the 3.42?

7. Will highway fuel mileage suffer a lot?

8. What is this thing hanging below my brake cylinder?



9. And with the rear end up in the air, is there still any load on the springs/shocks that I should be careful with?

Thank you!

 

1. No.
2. Most of the brake questions and more will be answered in the following link: https://www.thirdgen.org/forums/tran...-10-bolts.html
3. No.
4. Assemble your tools and repeatedly drench every nut and bolt with PB Blaster or its like.
5. $200-300. Prices may vary according to location.
6. Depends on the driver .
7. See #7.
8. Combination valve.
9. With the rear drooping, no. Unbolt the shocks and the springs will most likely fall out--or very nearly.

JamesC

 

For #6 I meant pretty much between flooring the gas at 0 mph and how much faster I'd get to 60 or other desired speed lol.
For #7 I meant just cruising at a constant speed down the highway, like 70 mph. I know that mileage will go down due to the increased RPMs but I'm just wondering how much.
If anybody with a 305, 3.42 rear end, and 700r4 transmission could tell me what mileage they get, that would be great!

I followed your link for the proportioning valve under the "If I Swap From a Drum to a Disc Read End Do I Have to Change the Combination Valve*?" section and I guess this is what I need:
http://www.flynbye.com/catalog/i172.html
although a cheaper used one would be nice.
But the main page said that "Valves are no longer available." And that thing looks the same as the picture of the combo valve I put up that's already in my car. So what do I do?

But all in all, from what I understand the brake lines pretty much bolt right onto the discs from the drums, all I pretty much is the prop valve right (link above)?

And I assume I'd need a new speedometer gear to accommodate for the different rear end ratio.

 

Regardless of whether the combination valve is for a disc or a drum rear, they "look" the same. If you're installing a PBR rear end or converting your drums to PRB's in the 91, you need the correct valve 1LE valve.

PBR's require flex lines on both sides.

The change will require new drive and driven gears for the speedo to rear correctly.

JamesC

 

Oh I see what you mean. Looks like I gotta spend more money UGH. lol
But this is what I need right? http://www.flynbye.com/catalog/i172.html
I'm thinking of just pulling it from a parts car with a disc rear end to save money.

What? Please elaborate lol I don't know what you're talking about, I'm a newb sorry haha.

 

Note my EDIT above about the combination valve and your 91. Check the following link for pics of PBR's and their flex lines:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

JamesC

 

Oh I didn't notice the edit. So you're saying that my 91 has the correct valve and I don't need to replace it? I'm (pleasantly) surprised to hear that.

And thanks for the links to the tutorials, they'll be very helpful when I'll start this project.

 

My bad above. Revisit the EDIT. Here's a link that provides a bit more insight:

https://www.thirdgen.org/forums/brak...-question.html

JamesC