Hello All!
I've got an '82 Trans Am, 305 Q-jet, 200 transmission, 10 bolt 2.73 open rear with drum brakes covered by the 14" Bowling Ball hubcap wheels. It is my daily driver from when the snow melts to when it comes back. I think that covers all the specs.

I want to put in a new rearend in, preferably a 4th gen, with posi and disc brakes. I've read the stickies and tech articles so I know it'll be 2" wider on either side and that I need to replace the proportioning valve, probably with the Wilwood one.

I'm going to buy it used, but I still have a few questions on specifics. I'll try and keep them concise. And help will be greatly appreciated!

1. Will the disc brakes fit inside the 14" wheel? I know they're on the small side, and most people have 15"s, but I'm stuck with the 14"s and I don't want to be stuck with wheels that don't fit over the brakes.

2. I definitely want positraction; that's the reason for this swap in the first place. What option should I look for to signify posi, and I've heard that an auburn posi is the less desirable one. I'm wondering why, and how can you tell the difference?

3. My 305 barely makes 150hp, but I plan on swapping to a crate motor 350 in the next year or so. I'll probably never get higher than 350hp, so what would be the best gear ratio?

4. Since I'm probably searching for the rear end from a junk yard, what should be the upper limit in terms of mileage and condition? I have a budget of about $300, and here of some people getting good ones for only $100. How many miles before things start to go bad? Is there a way to determine the condition on the gears? What should I be looking for? And what is a good price for a 4th gen rear?

5. I just installed a Founders adjustable phb, and I'm assuming it'll fit right into the 4th gen rear. Will it need to be re-adjusted to account for the extra 2" on either side, or is the bracket in the same place relative to the center of the car?

6. I've got a car from the very beginning of the Thirdgens, and I've noticed that somethings may be different from the later years. Is there any differences that will cause me problems with doing this swap?

Forgive me if what I'm asking is covered in stickies or other prevalent posts. I've tried to do as much searching as I could before I started asking questions.

Thank you so much for any information you can give me!

 

1. Don't think so. USE YOUR LOGIC: you've got a rotor that's DAMN NEAR 12"; that's 6" from center to edge. Put a caliper around that; call it, another ½", MINIMUM. You've got 14" wheels; that's 7" from center to bead surface. They're alloy, so they're kinda thick. Meaning their INNER radius is 7" MINUS some amount of thickness MINUS whatever curvature and shaping the wheels have on their inner face. And you're proposing to put THAT over something that's 6½" MINIMUM. I'd rate your chances of success as somewhere between Slim and None, except Slim just got up off the bench and left.

2. You should TAKE OFF THE COVER AND LOOK. If you see posi, then ... the option is present. If not, .... ,,,, ... you do the math.

3. Certainly NOT 2.73. No need to worry about it until such time as you get there though. Most often though, 3.42 or 3.73 will be the way to go.

4. Whatever you see when you TAKE OFF THE COVER AND LOOK. Make sure you pull the axles out before you buy. There is NO SUBSTITUTE for the simple act of LOOKING.

5. The same

6. Not until you get to the transmission crossmember, drive shaft, and/or the front sway bar bushing brackets.

No there is NO SUBSTITUTE for TAKING OFF THE REAR END COVER AND LOOKING. No "codes", no "options", no "mileage", no NOTHING will tell you ANYWHERE NEAR as accurately, as physically placing your eyeball on the site of interest. Don't bother with anything except LOOK AT IT.

 

Thanks for your help! However, when I take the cover off, what do I look for that signifies damage or a bad posi unit?

 

Look inside the carrier for posi. If you see nothing but a cross shaft and 4 gears, it's not a posi. If you see some plates and some springs between them, it's an Auburn posi. If it has 2 little weights on little teeny tiny shfts, it's an Eaton Gov-Lock; you DON'T want one of those. If you see anything else, or aren't sure, take a good clear pic of what's inside there and post it, and it'll be easy to identify.

The axle itself is the inner race of the axle bearing. I.e., the bearing runs directly on the axle. When you pull them, look at the place where the bearings run in them; should be the same as the rest of the machined area there that's about 2" long. If you see ANY signs of damage to the place the bearings go, which is to say if you can tell that there's AN difference between that particular spot and any other place along tat section of the axle, they're toast; and it needs new axles. They're about $230 a set. Either these http://www.summitracing.com/parts/sag-ev10-8/overview/ or these http://www.summitracing.com/parts/sag-ev10-5/overview/ depending on what year of rear it is.

 

Pics of open, Gov-Loc, and Auburn in the following link:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

 

Have to agree with the guys upstairs I put a 1998 10 bolt rear with ausi in 3.42 .everything bolts rite in except the e brake cables there is an e brake mtg plate spot welded in the tunnel of the forth gen , drill out the spots and take the plate with you It will make your life alot easier , be sure to take the cables too dont just hack them off . you will stil have to replace the cable that goes from the lever to the link with a longer one I had one custom made . neither the third or forth gen front cables work . keep in mind while searching ,in 1998 GM upgraded the rear breaks with the 1997 corvette stock set up much beefier so that size may be too big for your 14 " rims not sure . I havent changed my prop valve yet and it seems fine ,but I'm running c-5 vette wheels so you can put the rear in ......... no you should use the prop valve . another thing to look for when these 4th gens were shipped they liked to hook the rear axcel on the drivers side . the hard break line sits on top of the axcel and even though the breaks worked fine there is a spot that will be crushed to about 1/2 the inside diameter so look for that . after checking every 4th gen in 3 yards and finding they were all the same , I removed mine and tapped it with a rubber hammer to get it back in shape .. anyway good luck. nice sofa! must have taken some happy pills or something.

 

[quote=dads old blue 9;5460139in 1998 GM upgraded the rear breaks with the 1997 corvette stock set up much beefier so that size may be too big for your 14 " rims not sure .
[/quote]

So, a rear end from pre-98 should have small enough brakes? I've searched around at found that the 4thgen had 11" rear discs, which I think will fit, but these may only be for the pre-98.

My rims have an inner diameter of about 13.5"(at least that's what my tape measure read). I don't know how correct that is, because when I measure the rim itself, the same way you measure the diameter of any circle, I get about 15", but the tires say 14" rim. Maybe I'm not measuring from the right points? Shouldn't be difficult on a circle.

 

A good part of your measurements should be based on depth but my 1998 rotors measure 11" but if I put my stock 15 iroc wheel on there is only 1/2'' clearance between the inside of the rim and the caliper so no your wheels will not fit on the 1998 rear and probably not any 4th gen with discs min is 15" rim . sory

 

I did the 4th gen conversion on my 82 Trans Am with bowling ball turbo wheels.

As stated above, the wheels won't fit and if they did, they would stick out something crazy and look reall REALLY bad. I used a Willwood prop. valve and it works great. I love that i can adjust my brake bias.

As for e-brake cables there IS a simple solution. After trying different years, different models all with different lengths, I used 1992 1le brake cables at the wheels with the factory primary cable at the handle. They fit and work!!!

 

just get some 15s and 2'' spacers for the front you'll be good to go where do you live you can have my 15s for free. you only! please dont everybody ask me for free wheels thanks the tires are even good.

 

Because new wheels are not in my budget, and I'd like to get posi and discs before the winter thaw, would the discs from a thirdgen rear end work for my 14"s? Either the iron calipers or the PBR ones?

 

not sure of the third gen sizes. as far as the wheels i'll take pics tomorow the only other thing is shipping cost. you can have the rims -tires you'll just have to take care of shipping. my zip is 29483 sc

 

I could be wrong because it's been a long time but i don't remember any combination of disc working with those 14". It was a very hard desicion to get ridd of the ones that came on my car but because of this and, very limited tire choices, i did. I have seen some 15" with disc brake. It shouldn't be very difficult to find a 9 or 10 bolt 3rd gen rear with disc at your local junkyards.
Here is what mine 'looked' like before mods but fresh paint...

 

There has to be something that works, because the front has disk brakes. I don't know much about brakes, but would there be a problem with getting the size discs I have on my fronts, and putting them in the back, or is the design of the two completely different?

BTW- I really like the looks of your car. Black and red were an excellent combination for our cars.

 

One other issue I haven't seen pointed out yet is the threads on your brake lines. 1982 3rd gens used SAE threaded brake lines. Around 1984 or so, the brake lines were changed to metric threads. Not too big of a problem though, just get some metric to SAE adapters.