dbtk2

I have a '86 Trans Am, and I'm trying to figure out what it has for a differential (whether is posi or not, I don't think it is), and what spline axles it has. I believe its a non-posi 26 spline but want to make sure before spending the $ on a posi unit only to find out it already has posi or is 28 spline, and I don't want to pull the diff cover. What are the RPO codes and whatnot to figure out what it has. I know it has had a gear change in the past (it has 3.42's in it now) so its possible they changed out the diff as well, but I'm just wondering what it had originally anyways.

I'm thinking of going to 4.10's or 4.56's but I'm just trying to figure out what it has for axles/diff first.

Thanks,

Shawn

CrazyHawaiian

The only way to know for sure whats in there is to take the cover off and look. The RPO tells you what it came with from the factory, but dosnt guarantee what you'll find in there today. Our cars have been in use for quite some time, there is the posibility someone else has already done something to the rearend before you got it and changed the gears. G92 was the "upgraded" option from the factory for a better ratio. I believe G80 means posi but not completely sure. I wouldnt gamble on RPO's.

fitbmxseries1

well i can tell you one way to tell you if its a posi... and we all know how to do this lol.
other wise id definatly say pull the cover

dbtk2

I'll probably just end up pulling the cover to see what it does have, just wondering how to see what it did have stock. It smokes both tires off with a clutch dump and really pretty much every time the tires break loose, but in the snow and stuff sometimes it feels to me like it only spins one.

I appreciate the help anyways,

Shawn

Pat Hall

iTrader: (31)

If you're wondering what it had originally, all you have to do is look at your service parts identification sticker if you still have it in the car. All rear end codes start with the letter G. If you find G80, that denotes a posi rearend. The GU code will tell you what ratio, for example GU2=2.73, GU6=3.42. The service parts label is usually located inside the console glove box, or the locking storage box in the driver's side of the hatch panels. As far as what's in there presently, just do what everyone else said and pull the cover. It's the only way to know for sure. It's not like it's all that hard to reseal it and dump a couple of quarts of gear lube back in.

coolram62

iTrader: (2)

Pulling the cover is the best way to know what gear is in there now and if there's a posi/limted slip there.The RPO list will tell you what she originally had(make sure the VIN on the sticker matches the car - the console lid or console could have been changed also).If you look on the front of the axle tube to the right of the center carrier,this is looking from the front of the car,you'll see some numbers and letters.For example mine looks like this 5 PZ C153 2.The 5PZ is the axle code for 3.23 w/limited slip.Also my '83 has 4 wheel disc brakes(did the 10 bolt come in disc brake form on the early '82 to '84 cars or was it just the 9bolt?).

Pat Hall

iTrader: (31)

I could be wrong, but I don't think the nine bolt was even offered until like somewhere between 85-87 and was discontinued after 89. So if there was any rear disc cars, which I'm pretty sure there was, between the 82-84 years, they'd have to be ten bolts. In fact, a friend of mine pulled a 3.73 geared disc brake ten bolt from an 84 Z/28 in the junkyard not too long ago.

Randy82WS7

pull the cover

as it is anyone guess as to what is in it nowadays

good luck

dbtk2

I have to find my RPO sticker, since the interior has all been changed its not inside the car anymore. I have it in an envelope somewhere but can't find it right now...when I do I'll look at it and see what it originally had. I am planning on just putting a gear in it anyways, and if it originally had a posi then I figure chances are someone wouldn't have taken it out (you never know though). But it would just be nice to know what it had originally anyways. I know the original gear was a 3.23 (thats what the previous owner told me anyways), just not sure about the diff.

Being a college student tight on cash, it doesn't make sense to me to pull the cover this week to check the diff, and buy the new gear oil (although I could re-use it I guess), if I'm just gonna pull it again in two weeks to put the gear in it. Plus its a lot easier to look at the numbers on a paper to figure it out then it is to pull the cover. (and it doesn't smell as bad either)

Thanks for the help, I appreciate it.

Shawn

Zepher

iTrader: (1)

I am not sure how many posi's are like the Zexel Torsen, when both wheels are in the air the wheels turn opposite like an open diff.
I would either do a nice burnout or jack up the rear and see if both wheels turn in the same direction.

For reference, my 86 Trans Am LG4 5 Speed car came with 4wheel Disc Posi 9 bolt with 3.27 gears.
It had a worn out posi after I had it for a couple of years and would sometimes only spin 1 wheel when burning out, most of the time it would burn both.

dbtk2

Like I said, everytime I've done a burnout in the car it has definately turned over both tires, so that doesn't help. I know on a hoist the wheels spin opposite but thats because its not a locker, being a limited slip it should do that. Also, I have drums in the back and definately a 10 bolt. Its pretty much a stripped car, for options all it has is power windows and rear defrost from what I know anyways. (unless power steering was an option?)

Shawn

Pat Hall

iTrader: (31)

Actually, a limited slip carrier that's in working condition will turn both tires the same direction when the car is in the air. The zexel-torsen is the only limited slip diff I know of that they turn in opposite directions, just like an open diff. Your car being an 86, it's extremely doubtful you have a zexel unit in it anyways, considering they weren't available until 98, unless the previous owner went to the trouble to round one up and install it, which means he also would've had to round up 28 spline axles too, since the 86 rear has 26 spline axles originally. It's also hard to imagine that even a college student is on too tight of a budget to buy 5 bucks worth of gear lube and a tube of RTV. But if you're really that strapped for cash, just use a clean container and recover as much of the old gear lube as possible. If you're going to be doing a gear change soon anyways, you're going to be replacing all the bearings anyways, so old gear lube won't really hurt anything. I guess the bottom line is, it's easier to check rpo codes and stuff like that, but if anyone's ever changed anything in the rearend, those codes are completely useless. Besides that, it'd be good to know if you really have a posi carrier or not, so that you'll know if you need to get one when you go to purchase the new gears. Good luck whatever you decide!

CrazyHawaiian

So you want to buy parts without verifying what you have versus taking the time to check and make sure its the right parts? I dont understand the reasoning, but have fun I guess. Hopefully you end up with the right parts and the install goes smoothly.