Originally Posted by big gear head

Do you have the GM 7.5 10 bolt or the Borg Warner 9 bolt? You must know which one you have before anything else can be done.

Originally Posted by articwhiteZ

dont waste any money on the 7.5.. if your not drag racing..nothing you can do will make it live with 4.10 gears and sticky tires. dont go under 3.42 and stay away from slicks... 7.5 is ok for driving.

Originally Posted by AlkyIROC

I'm guessing with an 87 and L98/700R4, there's a good chance you have a 3.27 geared 9 bolt.

Best suggestion is to run what you have until it breaks but until then, start saving up for a 9", or 12 bolt as there is no cheap and easy upgrade.

With a good 383 and a TH350 trans, I pushed a 3.27 9 bolt into the 11's before swapping it out for something that allowed me to get a deeper gear. A 10 bolt with 4.10 gear allowed be into the low 11's and I finally installed a 9" to survive behind a transbrake.

Originally Posted by big gear head

Do you have the GM 7.5 10 bolt or the Borg Warner 9 bolt? You must know which one you have before anything else can be done.

Originally Posted by sofakingdom

No. 5-speed ones came with 305s for sure.



EVERY small block Chevy in EVERY used car is ALWAYS a "vette motor". That's one of the first things any beginning hot-rodder knows. The fantasy comes crashing down when one realizes that there are now about 25 times as many "vette motors" in the world as there have ever been Vettes. However in this case, THE ONLY thing that makes a Vette L98 a Vette L98, is its heads; so whatever "Vette"ness it once had, is now gone.

Another thing you'll learn as you gain experience in this hobby is, that metal parts have ABSOLUTELY NO MEMORY WHATSOEVER of the sheet metal (or fiberglass) that they have been wrapped in at any given stage of their life. No matter what body the parts have ever been in for however long, no sublime magic wafts itself out of the body and imbues the castings with any superior attributes. A rebuilt 350 short block that was in a Vette for some portion of its life is indistinguishable in every manner way shape form and fashion from a rebuilt 350 short block that has been exposed to any other body. So, in the interest of not advertising your n00bity, I would counsel you to leave all the "Vette" crap behind, as it just shows that you are gullible and inexperienced with stars in your eyes over something that sounds cool but you have no clue what it even means.

Same thing goes for 350s in general. I cannot begin to count the number of times we see on this forum "PO told me it has a 350", "looks just like a 350", "runs too good to be a 305", "I heard {fill in the blank}s all came with 350s", and so on. Only way to know for sure is by the block casting number (NOT the stamping code) which is [sarcasm] conveniently located in a conspicuous and easily accessed place [/sarcasm], namely the top of the bell housing flange right behind the driver's side head. I'd STRONGLY urge you to get that casting number to verify what you've REALLY got before trying to mod it.



Look at your SPID sheet. The RPO code for the GTA appearance package is Y84 if memory serves. (some one of you Firebird people please correct me if I've got it wrong, I'm sure you will anyway without me asking for it) If it has that, it's a GTA; if not, it's not. Pretty straightforward.



2.29, 2.41, 2.73, 2.92, 3.08, 3.23, 3.42, 3.73, or 4.10.

While you're changing the fluid, as you mentioned you are about to do (being the common-sensical new owner of a car that you are, you are doing what any such person would do as part of catching up on unknown deferred maintenance by replacing all the fluids), whatever you see in there, is what it is.



Yes and no. Depends on year and transmission. 6-cyl 5-spd cars in the later years generally do have that gear, similar auto cars usually have 3.23. 90-92 will have the better axles (larger diameter) with 28 splines instead of the earlier 26. Unfortunately however about 99.999% of all 6-cyl cars came with drum brakes, which in those same years, disc brake rears would have the good PBR setup instead of the crappy Saginaw setup they used up through 88. And a similar proportion come with an open (non-posi) carrier. So I'd suggest, if you find that the gears aren't to your liking, that since the gear set is one of the cheeeeeeepest parts of a rear, that you not worry about trying to score the ratio you want in the junkyard, but instead, find a 90-92 core with disc brakes, and put a good posi and whatever gears you want in it, rather than the other way around.

Originally Posted by big gear head

There are many ways to go with the 7.5 rear end. If this is just a street car then I would probably go with the Eaton Posi or Yukon Dura Grip. There is a new differential out now that I have no experience with, but it looks good. It's the Power Trax Grip LS. That might be a good choice if your money it too tight for one of the others. The '87 will have the smaller 26 spline axles.


If you could find a good '90 to '92 rear end with a gear ratio that you like then that would be a better place to start. You would have the larger 28 spline axles and you wouldn't have to go through the set up process of installing another set of gears. You could install one of the differentials that I listed and be ready to go.

Originally Posted by Justin69

Depending where you are located, I'll have mine for sale soon. It's out of a 99 Z-28. Rebuilt about 13k miles ago. Aftermarket carrier ( Sorry not sure of the brand. Was in the car when I bought it. Richmond 4:10's. It will be complete drum to drum. Also have an aluminum driveshaft too.

Originally Posted by luvofjah

I was hustlin, as noted a 91 rear end, $60...
I got a smokin deal with coupons for Factory 10 28 spline axles from Advance (for 1,) but Jegs matched the price so I got 2... New Richmond gear off Ebay for $100 or less... I bought a "new TrueTrac" for a 10 bolt off ebay, $250, and later realized it was for a Ford 9", sold on ebay for $350 (made $100) and Summit / Eaton were having a $50 rebate, got the one I needed for $350 from Summit, normally $400.... I got the welding / powder coating done for $150, etc... again, ok for daily driver with street tires, but don't plan to put slicks on it...

Originally Posted by Ron U.S.M.C.

If your OK with your gear ratio this could work =


http://www.powertrax.com/index.php/p...ertrax-no-slip

Originally Posted by luvofjah

TPI?

3.42 OR 3.23... 3.73 is a small first gear, and also weaker physically.

Originally Posted by MoJoe

The 3.08 first gear in the 700r4 auto came factory with a 3.23:1 performance gear. You might be OK stepping up to 3.42, but 3.73 with the auto is usually considered to low of a rear gear.

Originally Posted by Ron U.S.M.C.

If your OK with your gear ratio this could work =


http://www.powertrax.com/index.php/p...ertrax-no-slip

Originally Posted by Ozz1967

3.73 came factory in the earlier L69 Trans Am's with the 700R4. I really like the 3.73 as a street gear.

Originally Posted by luvofjah

With 350 TPI, I would go 3.23 or 3.42... the 3.73, neeeds good traction and others say it changes the power band of where the TPI is happiest...

As for differential...

The clutch style ones...
Good straight line...
But give power to wheel with less traction when turning or slipping...

The gear ones.... True Trac, like I got...
Good straight line...
Give power to the wheel with traction...

Not sure about the powermax one above...