I have an '88 IROC 350 with the posi blues. At the drag strip
one wheel hooked up in the water box and seems to have
smoked the posi. I have searched third gen for answers but I'm now really confused about options I have.
My rear is plain cover w/ 10 cover bolts. axle code reads (I think)
6 H Q CO85 2. Iwas going to buy a posi but I don't know what
my axles are. They are probably weaker than 28 spline?
Would a good plan be to buy a 28 spline posi + axles to fit?
I wish there was some lo hassle fix for what seems to me to be pretty marginal differentials in these cars.

You have 2 options for beefing up your rear:

1) https://www.thirdgen.org/newdesign/t...nguprear.shtml or http://www.ws6transam.org/10bolt.html .

2) buy a moser or strange rear.

A 4th gen rear is basically the same as the 3rd gen 10-bolts.

buy the video "Five minute Buns"

i vote moser rear. some say its too expensive but i think two grand is a great deal for what they are

You have 26 spline axles.

Buy a posi/locker etc for 7.5/7.625 10 bolt for 28 spline axles. If you can find them you can use 28 spline axles from a 1990 - 1992 third gen only although they are still weak factory axles. You can buy better aftermarket 28 spline axles for around $125 each.

You can pull a posi from a 1990+ third or fourth gen or an S10 but finding a used posi may not be in much better shape than yours.

Buying a complete aftermarket 9" or 12 bolt for a third gen will be over $2000.

A fourth gen diff is a direct bolt in however the axles are 2" wider on each side so your wheels will stick out unless you use fourth gen rims or buy aftermarket rims with the proper backspace.

With delivery the Moser 12-bolt with the proper 3rd gen brackets, a posi, your choice of gears, bolt-in axels (no more c-clips), and no brakes will set you back just a bit more than $2,000. A 9" bolt in is going to run you closer to $2,500 or more depending on a variety of factors.

A fully built 7.5" 10-bolt is still fairly wimpy, and will set you back about $1,200 if you do all the work yourself. New gears, bearings, posi, axels, and a cover girdle willa ll improve strength,but the ring gear size to a large extend determines strength, and there just isn't anything you can do about that short of a rear swap. You are also limited to 28-spline axels, whereas a 12-bolt has 30-splines standard, and a 9" ccan be had with 31, 35, or 40 spline shafts (way overkill for most applications).

It all depends onwhat you want to do. For serious track use with sicks a 12-bolt or 9" are the only way to go. For street tires and occassional track use you can beef up the 7.5" 10-bolt.

Great info.
The comments are very helpful. I was all worked up
to buy a posi but for right now I think I'll hold off and
fix the whole problem at once. The car is an automatic ,
with normal street tires, and runs a little over 102 on a
good day. I'm mostly concerned with MPH right now so if
I run hi 13's- 14.0 (no "burnouts"), I imagine the rear will last a
trip or 2 more to drags before I fix it.

I am completely with TKO on this one. I am doing my own rear rebuild right now, but it is really not that cheap when you add up all the parts and pieces.

This is what I have so far (I did this list more for myself because till now I didn't even know how much I spent). This doesn't include an aftermarket pozi (at some point I will probably put Auburn (sp?) unit in there, but I don't think they are cheap).

220 - gears with warranty
100 - master rebuild kit
225 - moser axles
180 - support cover
50 - setup bearings
50 - solid spacers(2) with axle bearings and seals
200 - used 4th gen rear with posi
------
1025 + tax(in some cases) + shipping

60 - in-lbs torque wrench
170 - press
50 - bearing splitters (2" and 4.5")
-----
280 + tax(in some cases) + shipping

I don't count tools as part of the cost because 1) I like tools and I'll keep them. 2) most of them will be used to rebuild my tranny 3) I like tools.

But if you add up the labor to do all this work (including cleaning up and painting the outside and welding axle tubes), fully ready 12 bolt or 9" that just need to be bolted up don't look like a bad option.

I hear ya TKO. After breaking a stock 7 5/8 F-Body rear, thats exactly what I did. New gears, and I upgraded to an Auburn. After all was said and done, I broke that rear too.

From the sound of your post, Airflow, sounds like you enjoy racing. Running 13s with the automatic probably will be a little more forgiving than a stick would, but you have to decide.

Ive decided I did not want to spend any more $$ on somthing that was definatley going to break again, as we are always increasing the output of our engines.

I called Currie, had a rear built to "my specs" and that was it. Besides a gear change, my rear problems became a thing of the past. Got tired of saving pennies to spend dollars, if you know what I mean?

[QUOTE]Originally posted by VILeninDM
[B]I am completely with TKO on this one. I am doing my own rear rebuild right now, but it is really not that cheap when you add up all the parts and pieces.

Not to mention the hard work of yanking that big old rear out evertime.

My stock rear broke. The pinion lost four teeth, which ruined the bearings. It started as an open rear with 26-spline axels. I didn't want to spend the money to rebuild it, but at the time I couldn't really afford the cost of a bolt-in 9" or 12-bolt. I changed gears to a 3.73 ratio, installed new bearings, upgraded the axels to 28-spline Moser units, put studs in the carrier caps, installed a TA girdle, and added a Lock Right to the stock open differential, which I cleaned up with a die grinder to remove stress risers. I wish I'd ponied up the extra $50 for an Auburn posi, because the locker isn't that great on the street. I've had zero trouble with the rear thus far, but the engine is mostly stock & I don't run slicks, so for now it's a decent rear. Eventually when I swap the motor for something more brutal the rear will get pulled and sold, allowing me to recoupe maybe half my investment. Then that money will offset the cost of doing the 9" swap slightly. It isn't the way I wanted to do it, but sometimes that little thing called life backs you into a corner with these things. At least I was able to swap in the T56. That part of the car is 100% the way I want it. You've got to be happy about something!

Yeah, without having the tools you need up front the cost of rebuilding a rear yourself can start to mount. Especially if you're only going to do one or two in your lifetime.

The first rear I rebuilt I didn't have a press or bearing pullers. I bought a dial indicator with a mag base, and an inch/pounds torque wrench. I knocked the bearings off with punches and a hammer. The ones I couldn't do that with I cut them apart and then cut the inner race to within 1/16" of the part the bearing mounted to. Then I'd stick a chisel in the cut and smack it with a hammer causing the race to crack, opening up the ID, and allowing me to slide it off. Reinstallation came courtesy of a set of brass punches on the bearing's inner race. This method also gave me a pleasant surprise when a small piece of one bearing's race flew off the chisel point and imbedded itself in my hand. I removed the part I could find, but it always felt like there was something else in there. About two months later the shrapnel worked it's way to the surface and I pulled another small piece of steel out of my palm. The moral of the story is that this method will work, but I wouldn't recommend it! Plus the time saved using a press is considerable.

OUCH!

Because of the high cost of getting a stronger diff the best thing to do is like mentioned above. Drive it until it breaks. Then you'll know what needs to be upgraded. Even a stock diff can be broken driving on the street but it's usually from some sort of abuse.

Even doing all the 10 bolt buildup stuff, you'll still have a weak link with the tiny ring and pinion teeth.

There is no real cheap way to upgrade the diff. You spend what you need to buy the parts that you need.

I go to the speed shops now and don't even question the cost if it's a part I need. I know the cost of high performance parts and don't question it any more. If I need it, I buy it no matter what the cost. If an old part doesn't break, I don't upgrade to something better until it does break or I feel it won't survive the abuse I put it through. I admit to having some parts as overkill but at least I know they won't fail.

Here's another resource for you:
www.reiderracing.com

I've rebuilt my 10 bolt twice already and its gonna break again. You'd think Id learn after 3 times. well, I am learning and my piggy bank is slowly getting filled up. Im gonna go with a moser 12 bolt since it will work with my $500 torque arm. anyone ever explode there 10 bolt while running the 1/4? Its not funny or amusing at all. I hit the 1100 ft mark (doing about 100mph) and I heard a loud tick tick tick noise. 4 or 5 ticks later and it happened. the rear locked up on me, the back of the car bounced up and down, the tires locked up a bit and then BOOM. BANG SMASH. What I found when I pulled the cover was a massive amount of ground up metal parts. The ring and pinion gear was dimarlished. my posi unit was dead forever and the cover had dents in it. I dont ever want to go through that ever again.

you think my 11" wide nittos drags are gonna kill the 10 bolt again?

Ive grenaded one of my "wimpy" rears in the 60 ft. I tore 5 teeth off the ring gear. I pulled on the side of the track and "clackity clacked" it back to the pits. I did drive the car home, (approx. 45 miles), and made it within 1 block from my house. Then I called my brother with the rollback. It finally gave up the ghost.

A griddle LOLOLOL

just kidding look at the axels that drag racers use there is steel brackets welded to them to hel avoid flex and deflexion

later and

GB

rick

Yeah, wow BOTTLEDZr28...
when they break at the big end WHOA! I've broken them at both ends and I prefer near the start failures myself. Had my IRS (c'vette) break and lost a wheel and brakes at the big end and
it was thrilling.
It sure seems that rears would break at the start as Trans multiplication is in play there, but does'nt always work that way..
Now that you've made me remember back I think I'll get more serious about a good fix. ....and this was supposed to be my daily driver putt putt $$$

wow wish i couldve seen that!! If mine goes I hope it happens that way!!