New LS1 Owners - Newbie Tech - Formula rear end

Ok so admittedly I really should have known this, having owned my car for over a year now, but apparently the rear end in my '99 Formula is a V6 rear? At least according to a buddy of mine it is. We had it on his lift to install my SFC's and he said it was a V6 rear end. I always assumed that the Formula would have the same rear end that was offered on the Trans Am's in a given gear ratio, in my case 2.73's, but I remembered my dad will sometime's say "You know what they say about making assumptions" so I figured I should ask my fellow tech members to clear this up. If I do indeed have a V6 rear end then I'll probably try to find a local M6 rear that has TCS/ABS equipped...but I'd be nervous about them being beat. Pinion seal is leaking too on my rear end, I was quoted between $50-$125 to fix that.

hmm i dont think theres much difference between the two still a shitty 10 bolt rear end. What led your friend to believe that it came from a v6 car? definitely need to do something about those 2.73 gears tho

I don't think v6 cars come with 2.73's.

Does it have a steel or aluminum Drive shaft ?

3.08's I think were the base gears for v6 cars.

hmm i dont think theres much difference between the two still a shitty 10 bolt rear end. What led your friend to believe that it came from a v6 car? definitely need to do something about those 2.73 gears tho

I'm not sure. Both wheels spin and it'll leave 2 nice big lines of rubber if I brake stand it. And yeah I know but I'm going to enjoy the fuel economy a little while longer. I'll replace them with 3.50ish gears when I get a beefier rear.

Does it have a steel or aluminum Drive shaft ?

Pretty sure it's steel, I think they were all steel for the 99 Formula A4's.

Steel drive shaft means 2:73's and aluminum is 3:23's & 3:42's but the v8 and v6 have the same rear in them.

V6s' came with 3.08s' or 3.42s'.
2.73s' came with steel driveshaft,3.23s' came with aluminum driveshaft.
Externally,a V6 rearend looks the same as a V8 rearend.

I don't believe V6es came with the Torsen. 2 stripes means
you have some sort of limited-slip chunk if you can do it
at all consistently.

I've only done it once from a standstill, lines should still be there. I suppose I can try it again. I'll definitely find out after my FTI converter goes in next week.

He may have thought it was a V6 because the rear is so small visually (the other F-body he has worked on has a Moser 9"), but it had me concerned when he said that.

He may have thought it was a V6 because the rear is so small visually (the other F-body he has worked on has a Moser 9"), but it had me concerned when he said that.[/QUOTE]

no they're just small stock. odds are you have 2.73s in your rear since only ws6's, ss' and some z28s had them. look inside the drivers door for the code gu2 or gu5.

no they're just small stock. odds are you have 2.73s in your rear since only ws6's, ss' and some z28s had them. look inside the drivers door for the code gu2 or gu5.

Hate to do this to ya Mark but...:read: lol

I always assumed that the Formula would have the same rear end that was offered on the Trans Am's in a given gear ratio, in my case 2.73's

He may have thought it was a V6 because the rear is so small visually (the other F-body he has worked on has a Moser 9"), but it had me concerned when he said that.

That was referring to the fact that the stock 10 bolt is so small compared to aftermarket unit like the 9" he is used to seeing, which could have made him say that mine was a V6 rear.

Sounds to me like you have a stock V8 rear. 2.73s + a steel shaft and limited slip would be the base combo for a Formula/Trans Am/Z28 (RPOs GU2 = 2.73 and G80 = limited slip).

SS and WS6 cars required the manditory 3.23 option (GU5) when ordered with the auto trans (MX0 & M30), which came with an aluminum shaft and also limited slip (G80). This "performance axle ratio" was also optional on Z28/Formula/Trans Am.

All M6 cars of any V8 trim level came with 3.42s (GU6) and an aluminum shaft, plus limited slip (G80).

The 7.5" 10-bolt is a small looking rear. They are tiny compared to the 8.5" 10-bolts and the 12-bolt/9" versions. But, behind an A4, that tiny 10-bolt has been known to hold up to some pretty serious 60-foots and tons of street miles/hard launches. If you can keep wheel hop away, then this rear can last a long time with an A4, even with a big stall.

I knew I had the GU2 but thanks for the limited slip RPO of G80. I have a build site for my car and it has all the pics the dealer took before I bought it and they had a pic of the RPO sticker so I just checked it on my site and it has the G80 RPO. So I do indeed have a stock V8 rear then.

I'm hoping it will last a good while (I need to replace the damn pinion seal, I don't know how much fluid I have lost, no whining consistently, once in a while I hear a very faint whine but it doesn't happen a lot). I have street tires on it, UMI 2 point SFC's, UMI PHB, and BMR LCA's plus a Founders STB which really doesn't do much. It will have the custom FTI stall but shouldn't kill my rear.

I don't believe V6es came with the Torsen. 2 stripes means
you have some sort of limited-slip chunk if you can do it
at all consistently.

Some A-4 auto V-6's did indeed come with Torsen rear ends as part of the V-6 Performance package. My 2001 V-6 had this, 3:42 gears, Limited SlipTorsen Rear, code GU6.

My 1997 V-6 had the 3:08 rear, code GU4. I still have both window labels here in front of me.

The OP should run his VIN through Compnine site and see what he has. You only get to run 2 VINs per day for free. I already used my 2 free searches today but here is the old VIN for the 2001 if you'd like to see; 2G2FS22KX12139670

http://www.compnine.com/vid.php

You sir, just made my day. Found out my car is pretty darn rare for what it is.
1 of 10 with package option 2, gray cloth interior, bright red exterior, t-top, 2.73 limited slip/posi with tcs.

You sir, just made my day. Found out my car is pretty darn rare for what it is.
1 of 10 with package option 2, gray cloth interior, bright red exterior, t-top, 2.73 limited slip/posi with tcs.

Now don't get carried away by that '1 of 10' stuff. There are a lot of individual combinations of the options. A lot of people get real excited about the rareity of their car when they first run the VIN through these decoding sites.

It just means that a thousand others may have come with black cloth interior, or an ash tray. Or maybe don't have a power antenna. Little things that don't make the car any more valuable.

Calm down.

True, it was a good ego boost though. 1 of 1,427 total Formula coupe's in 1999 is still pretty good in my book.