iv got a 84 trans am, im dropping a 350 with near 300hp at the wheels. I was told by my sisters BF that my rearend wont last more than a month with the new engine. i belive its a 10 bolt 3.23 gears. the trasnmissions is a th700-r4, been rbuild and added a shift kit. i hope she can handle it!! what are these rear ends good up to HP wise. i know the rear end is considedred GM's "weakest link" but how bad can it be?? plese help a fellow thirdgen owner out here, the engine is going in in 3 days!!

 

lay off the burnouts and neutral slams and you should be fine. they are weak but if you take care of them they can last.

My car came with an L69, someone replaced it with a 355 at some point in it's life and now it has the original L69 back in it making about 300 horsepower. It just now broke after all these years of abuse behind a T5 tranny and my youthful, stupid, rough shifting and launches. The rearend was never replaced after nearly 20 years of service (damn it's getting old!)

 

Hard launches with sticky tires are rear-ends' worst nightmares. It aught to last a while, if you don't abuse it. If you plan on throwing a set of slicks or drag radials on the back and going out to the track, beware...

 

Downshifting, I think I screwed mine up again...after only a year on new gears. My recommendation: look into a rear end girdle ASAP. My engine's a stock 5.7TPI. Also, you might look in the Tech Articles and read the one's about beefing up the rear. They've got some good info. I agree. Babying it will make it last longer, but where's the fun in that...then again, where's the fun in having it rebuilt yearly.

 

well i did plan on turning it into posi with better gears EVENTUALY, but with my engine swap project, i cant do it all at once. i love doing burnouts,, but it sucks that only 1 tire spins ...but at least i can get that to spin. i did plan on also getting some BF goodwrench drag radials for the strip, if not some cheater slicks. Can someone explain to me what a "rear end girdle" is?? thanks! ohhhhh also,,, does changing the rear end oil do anything at all? another off the topic questoin... i was told that changing transmission fluid can kill your trany instread of helping it.. this fact or fiction?....

Thanks!

 

A rear end girdle is a replacement cover. It has about 1/2 in thick mounting flange, made of aluminum, and has two studs with feet on them that tighten down onto the bearing caps. It's suppose to really strengthen the rear end housing--housing flex is one of the biggest weaknesses of these rears. Check out www.summitracing.com and look up part number SUM-730755. This is the one I'm looking at.

 

damn 130 bucks for that....aight well i guess ill do some more research on this. how weak would a rear end from a junk yard be? i was gonna look for one with either 3.73 gears, or posi... but the posi is probly gonna be shot.....then just rebuild that while i take it easy on mine.......

PS...anyone got an aswer to the trans fluid question i asked?

 

i forgot to add....i thought when you blow your rearend,, you bust the gears and all that stuff... how would the coever do that?? or is it the flex that casuses the gears to go out like that?

 

You do and it is the flex. The casing flexes which allows the pinion to "walk" up on the ring gear, causing premature wear. The girdle reinforces the casing preventing flex and the studs that tighten onto the bearing caps prevent the differential from moving. From what I've read, it's simply a design flaw. I agree it sucks that the rears are so weak, but like I said, man, if I have to rebuild mine again, it'll be the third time within the last 50K. Also according to what I've read, these rears won't even withstand 400hp, no matter what you do to them. (All this info from the tech articles--got to give credit where its deserved )

As for the tranny fluid, I don't know, but I've never heard anything like that. Seems like it'd be like any other fluid and need replaced periodically. There's a filter in there too which makes me think the fluid would be getting contaminated in some way.

 

She will if you get her drunk first

 

lol....