I have the opportunity to buy a 83 trans am rear end. Owner says it's a borg warner 10 bolt 3.73 gears posi. Also has disc brakes. Would this have come stock on this car? Was in a 305 5 speed car. Is this a desirable rear end? Thanks for any help.

 

That is a desirable set up and was available on an 83’, probably a WS6 or L69. The early WS6/L69 cars had better gears than the later cars barring G92 IMO. 3.42 or 3.73 are nice gears in these cars and a good upgrade.

 

The Borg Warner is a 9 bolt. If it's a 10 bolt rear cover then it's just a standard GM 10 bolt. Nothing special. Even the 9 bolt isn't that special without upgrades.

GD

 

Thanks for the replies. So my current rear end in my 5.7 88 iroc is a 9 bolt 2.73 posi, disc brake. Would you consider this rear out of the trans am an upgrade or just keep what I have? Thanks, still learning about third gens.

 

If it’s a mostly stock car it would give you a good seat of the pants increase. You have highway gears in your car now which I assumed earlier and if you put those 3.73s in there it would pick up down low for sure and spin the tires much better lol. It would make it a nice street cruiser and liven it up.

Lot of guys on here say basic mods, increased stall converter and a gear swap like that can give a boost of performance for not a lot of money. It really depends on your plans for your car, ability and budget.

That being said If you plan on swapping to a different motor like LS and going for a real high performance build I wouldn’t bother with it IMO.

 

Thanks again for the help and advice, I'm supposed to pick it it up sometime this weekend. The guy I'm getting it off of is really nice and giving me a good deal on it.

 

Keep us posted on here, it will feel like a different car if you swap. Do you have any idea what kind of condition it is in?

 

Yeah depends on condition. The posi cones are probably shot on both yours and this 83. A Torsen upgrade could fix that. It would be a 3.70, not a 3.73, and your factory would be a 2.77 not a 2.73

GD

 

I'd rather have a 9 bolt but anything numerically lower than 3.23 gears in these cars just make them sluggish.. period. 3.23- 3.73s is where you wanna be.

 

I pulled a 10 bolt Posi 3.73 rear from a friend's wrecked 83 or 84 L69 5spd car and that is what I'm currently running. I didn't think the 9 bolt Borg Warners were out then but I may be wrong. They were much stronger rears I've ran them before when 10 bolts didn't hold up.

 

There is no difference in strength between the 9 bolt and 10 bolt...

 

The 9-bolt didn't appear until 85 in FIrebird and 87 in Camaro. No 9-bolt was factory-installed in a 83. Now, in the ensuing ... almost 40 years, who knows. It was somewhat of an upgrade over the 10-bolt in terms of "strength" but it comes with its own list of problems. (ahem: opportunities for solutions)

Assuming that this REALLY IS a 83 rear, it's a 10-bolt. It's got the weenie 26-spline axles, the crappy Auburn posi that is almost certainly dead, and the crappy Saginaw disc brakes that are usually less functional than drums. I would NOT classify it as "desirable" in any manner way shape form or fashion, except as something to put under a body that was missing a rear so that I could tow it.

A set of 3.73 gears NEW is right around $200. I would only pay LESS THAN ZERO for a 40-yr-old set. Which is to say, I would pay somebody to come haul them away. Same for the Auburn posi and the Saggy disc brakes and the pencil-d*** axles: I would pay somebody to keep them, if that was the only way to avoid them cluttering my property; or to come take them away, if they inadvertently found their way there against my will.

I would recommend NOT buying that POS.

 

I agree. I wouldn’t consider this rear an upgrade over what’s in the car now for the reasons listed. Also, 3.73 is probably too much gear for a stock 350TPI/auto.

 

3.73 is absolutely NOT too much gear. I had 3.70's on my 86 305 TPI and it was absolutely an excellent ratio for that application.

GD

 

Not quite the same, but I agree it was probably just right on an 86’ 305TPI. An 88’ 350TPI would be better with 3.42’s.

 

I pulled that 305 out and stuck a built 350 in it's place. I have over 300 HP at the rear wheels and that same 3.70 is a BLAST. I just don't agree.

GD

 

It probably is a blast with the 3.73’s, but does that built 350 have more RPM range than a stock 350TPI?

I’m talking more about optimizing for 1/4 mile trap speed when I say 3.73’s are too much gear for a stock 350TPI’s RPM range.

 

A little more. It's a FIRST TPI. Peak HP is 4700, but it does pull to 6500. I have the governor shifting at 5k though. The power delivery is pretty flat.

GD

 

Sounds like a fun ride!

 

Yes there is. While neither are the best for sure and we know aftermarket offerings are better.. Nine bolts held up better and that is not an opinion- its a known fact.

 

​​​​​​...... I just got off the phone with the Procharger sales rep. Yes it's very fun. But apparently I'm looking for stupid and fortunately for me..... they sell that.

GD