Ok, so I seriously thought I had an open rear end. Everyone always told me when i did a burn out, it would only spin one tire. I couldn't believe them, so I took it on my self to test it to really see.

1. My first test involved lifting up the rear of the car. I stood at one side, spun the tire, and watched as the other spun in the opposite direction. It took some force to spin it. This is usually a sign of having an open rear, not a posi. However, I've read posts were worn out posi's have spun tires in opposite directions, with a lesser force being applied to the tire. I didn't get any info from this test.

2. The second test involved me still lifting the car in the back. I got into the car, started her up and put her in drive. Both wheels started to spin! I thought maybe it was because of the idle, however when I made an attempt to stop one, it created a great friction in my hand like it was being forced to move, not by vibrations. This was the same way for the other wheel. I than had another person stand on the other side, and we both tried to stop them, but we both encountered exceptional force. This test seems to pass for having a limited slip rear.

3. This test STILL has the car in the air. I got into the car, put it in drive, and put the brakes to the floor. I than began to press on the gas, and just as I thought, my bud tells me both wheels were spinning, just from the start, no lag for one wheel to kick in. Seems to me like its a pass for a posi.

4. My fourth test was doing a stand still burn out. I took the car to an empty lot, slammed on the brakes, and floored it. It stood still but I could feel the car moving with great force. My bud said both wheels were spinning. I could see the smoke from my rear view mirror coming from both tires. I don't think an open rear end is able to do this. I'm pretty sure judging from past experience that an open rear will only have one wheel spin.

5. The fifth and final test, GUN IT from a stand still point. I gunned it down the street, skidding for a good 5 seconds. Guess what? Equal track marks leading down the street from the point were I had left. My friend said that both tires spun from the beginning however, the left one took about 1/2 second to kick in, but he said it was such a slight difference, that if you weren't paying attention, you wouldn't have noticed it. I definitely think that this passes for a posi rear!

4 out of the 5 tests I made passed for having a positive rear end. I don't get why the first test didn't make the tires spin in the same direction, but others have said that their posi units made the tires spin opposite, and they were positive that they have a posi unit in their car.

What do you guys think? I know my rear is a 9-bolt rear, and according to this site, all 85 trans ams came with 3.08 gears. Do you guys think that its a "posi"-"limited slip" rear or an open thats just not operating correctly. I'd like to get some bigger gears, maybe 3.73, and I think that since they came with 3.08, that its a 3 series, and all I'll need to do is just swap the gears, and perhaps do a tune up while I'm back there.

If there is anything you don't agree with, or can provide me with some correct information, please let me know. I'd like to get started on this project soon, however I don't want to swap in bigger gears if my rear is not a limited slip. Thanks for reading this and I'll be looking forward to hearing your input.

 

You have a 9 bolt? If so, you can't get 3.73's for that. I don't know what the aftermarket is like but for stock gears I think they came with 2.xx, 3.27 and 3.45's. Also, clutch type posi's will wear out hence 1 wheel spinning first before the other kicks in. My rear is like that now.

 

The rear looks weird, but I counted and counted again, scooped away the dirt and grime, and even took a 2000 candle power light to it, but could only see 9 bolts, it looks like this

http://media.allrefer.com/s1/l/d0066100-decagon.jpg

except take the right side, and remove the tip point, and make that a straight line so that the figure becomes an irregular nonagon. That sucks that I can't get 3.73's, I really couldn't find many gears for a 9 bolt rear, and I've been searching around. How are the 3.45's, I though they were 3.42's? I don't know that much about them, but how well will they work?

I see this, a little expensive, but will that perform close to a 3.73?
http://store.summitracing.com/partde...5&autoview=sku

 

Why not forget all that testing nonsense and just take the cover off and look?

 

I'm doing this by myself, and I'm not that experienced. My old man said he'd help me swap out the gears, but I have to get the info and stuff first. I don't feel right enough yet to take the rear apart, I'm afraid that somethings going to fall apart or break. I'd rather let my dad check, and god knows when he'd be able to get around to doing something like that. So let me get this straight, the bolts going around the cover, determine the bolt size of the rear, I only counted nine bolts holding on the cover. Should I be looking inside the thing to determine the bolts?

 

The number of bolts on the cover identify the rear.

You don't have to take anything apart to find out if it's a posi. Just take the cover bolts out, drain the fluid and look inside. It's about as complicated as changing your oil. Chances are it's never been off before and it's long over due for a fluid change.

 

Well I bought the car from a mechanic in early april, so I really don't know much about it before that. I have no professional guidance on how rear's work, hell, I don't even know If I would be able to figure out how to refill the case. But I'd rather do all this in one shot instead of having to take it apart, look at it, fix it up, put it back together, than when i get the new gears, have to repeat the process. Since I'm 99% sure that its a 9 bolt rear, what are my choices for gears in the rear, summit only has 1 item that shows up when searched for 9 bolt rear gears, and thats the $400 one I posted before.

 

this could possibly Limited slip but i have seen Differential do it too, i have owned total of 2 72 C/10 and first one i had was 10 bolt 3.73 differential, best set of gears you can put your hands on heh.. it was quite interesting.. it will spin both wheels every once in a while. 2nd one.. has 3.08 12 bolt limited slip.. doggy ... but so fast but it also spins 1 wheel every once in a while but most of time 2 but has quicker take off with the force of 2 wheels but yet requires more power.. running 312 CI in front of it.. its pretty hot. but yea, just take that cover off and check it out for yourself, only best way to find out.. doesnt cost much to do oil change. always best to change that oil at same time as transmission.. every 2 years at the most, every fluid breaks down and gets dirty..

 

Aren't you the guy planning to do a twin turbo setup? You should pick the gear based on what your setup is going to be otherwise you'll end up doing it all over again.

 

I always read all 9 bolts were POSI? I have the RPO code G80 (limited slip) and if I turn one tire, the other one spins in the opposite direction.

 

I am the guy doing the twin turbo setup, however Im having extreme difficulty locating gears for a 9-bolt rear. I'll take the cover off the rear today and check it out, what specifically will I be looking for, and also, is anything going to fall out/spill out if I take off the rear cover, I dont want to be drenched in the face with oil...or a twenty pound piece of metal ...

**UPDATE**

so i found some brands, here they are
motive rear and axle
yukon rear and axle
precision gear
and there is a motive rear for austrailian borg warner(is there a difference?)

im liking the precision one, good price, and they make it sound like it works pretty good.
I dont mind whine, as long as its decent, not to over powerful...what do you guys think... my only other question is, if its a 3.08 gear in the car now, shouldnt 3.70's not fit, or are they made specifically to go into the 3.08 and lower carrier. The site says when moving from a 3.08 or lower carrier to a 3.23 or higher gear, a thicker gear must be installed. Do the 3.23's and higher come thicker? such as the 3.70? IS there a universal spacer that i could put in to make the 2 series a 3 series carrier. Now I'm pretty sure that they are 3.08's, that what this site says....

 

so i opened it up, its a posi unit alright, wasnt as hard as i thought. I didnt know that the gears all fit properly, and no adjustments were necessary. I am gonna order a set of strange gears 3.70, says it fits 3.07 and numerically higher carriers, so I should be alright. Well this saves me a good 2500 bucks especially considering I really thought I had to get a new rear. I hope I'll notice a good difference...

 

There are no "adjustments", but the setup of the gears using shims and such to correctly position them relative to each other is still critical.

 

There is a master install kit, would that help with the install? I was just gonna order the basic install one, but the master one comes with everything, hell I could probably put a new tranny in with it.

 

what did you see to lead you to believe it's a limited slip?

 

Besides the fact that all my tests passes for a posi unit, when I had opened it, scooping away about 25 years worth of crap off the cover, the unit and hole rear was actually pretty clean, like what my engine looked like when I had it opened up for the first time... I spoke with Jim from Strange Eng. and he said to my question...

-----Original Message-----
From: James [mailto:gibsongod716@comcast.net]
Sent: Wednesday, September 19, 2007 3:17 PM
To: strangeeng1@ameritech.net
Subject: 9 bolt gm 7.75 strange pro street gear sets[/font]

Hi, I have a quick question. My 85 trans am has a 9 bolt rear. It currently uses 3.08 gears which is a 2 series gear. Your catalog states that your 9 bolt 3.70 gears state that they fit 3.07 and higher carriers. 3.07 to 3.23 is a 2 series carrier. 3.23 to 4.10+ is a 3 series carrier. The 2 and 3 series carrier ring and pinions are not interchangeable. How is it that the gears you advertised fit both a 2 and 3 series carrier. Do they come extra big so that they fit 2 series carriers as well as 3 series carriers?

Thanks a lot,

Jim

I am unsure where the carrier break is on this specific rear end. We have sold this gear to a number of customers and this issue has never come up before. We will have to do some checking around to see what we can come up with. Thanks

JIM BUSCHMAN

847-663-1701 EXT 4790
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**THIS IS MY RESEARCH**



From the little bit of research I did, it seems that 2 series and 3 series do not matter with a 9 bolt Borg Warner case. The gears from 3.07 and up are interchangeable. I don't know about the 2.73's, but that shouldnt matter for me, I've got 3.08's so I should be alright.

sorry if its hard to read this, im working off my laptop and I cant figure out how to re-edit the size of the font...