I purchased a lightly used 3.27 carrier & gears to upgrade my 1988 IROC's 2.77 posi. I used what is considered one of the very best rear end shops in North Cali; (The Rear-End Shop). I had them evaluate the parts I purchased to be sure they were appropriate. The shop accnowledged their quality and light use and rebuilt my Borg Warner 9-bolt with all new bearings, seals, cap bolts, etc. Everything seemed fine. This was approximately 6-months ago. The only time's the car has been driven is back & forth a few times to a transmission shop, and a few other shops. My old L98 block has knocking rods and the new engine isn't ready yet, so I've only done a small handful of burnouts while testing new parts.

Last week I finally took the car out for a three hour freeway cruise and then stripped the undercarriage down for all new end to end suspension (Moog, UMI, Spohn). After bolting up the Torque Arm, I ran the car while it was on the lift and noticed the rear end was so sloppy that it was loudly banging when put into gear and when pressing down on the brake. When I turned one of the rear wheels by hand, the opposite wheen didn't turn. The rear yoke moved about 3 inches before engaging.

I took it back to the rear end shop yesterday and when they pulled the rear cover off , there was a load of shrapnel in the bottom gear lube. The posi was completely eaten up. Allegedly, the technician stated; the only way for this to have happened was for someone to have hammed on the rear, which caused the two rear wheels to spin at different speeds.

Since I'm the only one who drove the car, other than the tranny shop who's had to fix their initial 700R4 build a couple times so far; and that I have to baby the engine so it dosn't throw one of the loose rods- how could this have happened???

I spoke today with the owner of the shop, and he didn't make any excuses or try to blame me for driving it hard; but he did suggest that the 9-bolts are prone to posi cone failure and I might want to rethink what I'm doing. I'm going to be using the IROC for regular commuting and weekly runs at my local dragstrip. I'm only going to be running approx. 360hp/400tq max; plus with the automatic trans, there should be less of a shock hit off the christmas tree.

I thought the Borg Warner unit was way-way better than the usual Camaro rear end and would stand up to 600 hp off the line???? Did I do something wrong or can the shop be wrong or is there a better set up that won't cost me an arm and a leg??? I just dumped in $3 grand in the suspension and I still have to pay for half of my new engine and get it installed. Now I am Soooooooooo dang Frustrated!!!!!!!!!
Nitro

 

the rear would be rated in torque. not horsepower. Its stronger than the 10 bolt, but not by a lot. From the sound of things i would say something was not assembled correctly, but i am not master in this subject

 

That's part of what I'm questioning. At least the shop is not making excuses or blaming me. The owner knows his stuff inside and out & seems as mystified as me. What could have been assembled incorrectly to do this??? Nitro-Nicky

 

I am thinking that the clearances on the bearings were not right. Too tight- burned up bearings. Too loose- bearing chatter. Both will cause premature failure.

 

could have been a bad install, or something wrong with the torque arm? possibly the pinion angle was off and caused some stress on the posi?

 

What actually broke in the posi? Knowing what actually broke could help to figure out what could have been wrong with the posi before.

If I had to toss a guess I would say one of two things happened. Either the housing is bent and is putting stress on the posi or that the posi had some cracks that were not easy to spot.

When they did their inspection of the parts, did that include disassembling the posi and carefully checking each piece? My guess is a loud "NO". They probably just quickly looked at a few things to get a feel for how much wear the unit had.

If the unit had some kind of a crack then they could have done a fine job of rebuilding the axle and still had problems. For such a short life it is hard to see pinion preload or carrier bearing preload being a factor. Those would only be likely to cause gear damage in that time. The only way I could see for all top-quality parts to fail that quickly would be, as suggested, you simply put more torque through the axle than it was designed to handle.

The 9 bolt axle is a decent axle, and it is a bit stronger than the tiny 10-bolt axles used during the same years. A good condition axle with a modest gear ratio (3.45/3.27/3.08) should have no problems handling the power levels you are talking about. I would say the same of the 10-bolt, especially the later units with 28 spline axles and the slightly larger ring gear. This is around the power range that GM offered full warranties on during the last years of the F-Bodies' life. In other words, you should not have to buy an aftermarket axle to have a reliable axle behind your stated engine.

You won't ever catch me saying a 9-bolt can take a 600HP full throttle launch. They just don't have enough meat most anywhere in the axle to handle that kind of abuse with any kind of reliability.

 

Now THIS is more of the type of information I needed; and I really-really appreciate your well thought out reply.

The current engine is still the factory 350 with approx 150k miles. It's run like total crap ever since I got it. Last time I checked, the torque was 90 ft lb down from the factory numbers. I finally got the last issue with the TPI system sorted out two weeks ago (the system was stuck in closed loop), but I doubt I was anywhere near the torque needed to destroy the cones.

What I saw, when the tech showed me the parts after the disasemble, was a round heavy bearing shaped object. The face was ground up with heavy grooves.

Now when they pulled off my aluminum heavy duty cover to do the initial check, the fluid was way lower than than it was supposed to be. They assumed I had changed the fluid and only put the amount of rear end fluid that went with the factory steel cover; thus, the gears must have 'burn't up'.
When they actually did the disassemble, it became more obvious (so they said) that the fluid was unburnt and they wanted to wait till the owner arrived to figure it out.

The trans shop got the IROC right after the rear end was first done and they built a stage 3 700R4. I know they test drove it, as they told me it would burn rubber shifting hard into 2nd. As I drove it home, it was shifting sledgehammer hard into each gear. When I went out to the car two days later, it was stuck in first gear and wouldn't upshift.

When the tranny shop returned the car, it shifted into gear firmly, but no longer sledgehammer hard. Then the new 2200 stall converter started acting up by shifting into the next gear earlier and earlier. Now it starts shifting up just above idle.

My engine builder told me that he thought I was making a mistake by using a 9-bolt. The rear end shop owner is telling me that if I fix it, it will probably fail within one season of Wed Night drags. I certainly don't have an extra $2000 to invest in a Ford 9 inch setup.

Whatever the shop did or didn't do, they did provide me with a one year warrenty and will fix mine or assist me in coming up with a different solution.
Did the 4th Generation have any better, more durable differentials than the 3rd's???
I am so frustrated and need to make a decision in the next couple days. Nitro

 

sounds too me like they didnt install it properly especially since you said they did your tranny and couldnt even do that right. if they cant do it right the first time i wouldnt trust them ever touching my car.

but if you decide to get a new rearend 4th gens are 10 bolts so youd need a new housing with it all. 4thgen had the zexel torsens which arent suppossed to wear like regular posi units since it has worm gears i think it was. but think stock ls1s break those rearends too.

 

Did the piece you saw have rollers on it or gear teeth?

I think you just added a very interesting piece to this puzzle. A 700R4 can smash 2nd gear like there is no tomorrow. The transmission can literally tear itself to pieces with a few simple changes to the valve body and a larger 2nd gear servo. That says nothing about what the shock wave is doing to the universal joints or rear axle. It sounds like it quickly shattered some internal parts and was toned down a bit when the shop had to fix the parts destroyed by a poorly set up transmission.

This might actually be the cause of your failure. If something were damaged through one (or more) of those super hard shifts then it could have failed shortly down the road. It is a hard game to really say if this is what happened, though it is completely plausible.

You won't find many axle people that will sign off on abusing an axle with a 7.x diameter ring gear. It is a fairly light duty axle that can't take tons of abuse. Something like an aftermarket 12-bolt probably could have taken an overkill 2nd gear shift without breaking. Now, what you want doesn't really fall in the category of "a ton of abuse". An automatic transmission with appropriate (crisp, sharp, firm) shifts and an engine with only 400-450 ft-lbs will not hurt a well rebuilt 9 bolt or 10 bolt. Again, this is really nothing over what GM was putting through the smaller 10 bolt axle in 2002.

You asked if the 4th gen axles are any stronger, and the answer is no if they are compared to the late '80s to early '90s 10 bolts in the 3rd gens. The 4th gen axle is easier to get in good condition with low miles. They also are more likely to have a posi and rear disc brakes. This can make them a real steal in some cases when the axle can be used in stock form without upgrades.

You can really go one of two directions here. Rebuild your 9-bolt again and you most likely will not have any more problems. If you want to swap back to a 10-bolt, then make sure you use a core with 28 spline axles. Replace the posi and gears, add a girdle, and use a solid pinion spacer in place of the crush sleeve. These changes should make certain the axle is reliable and ready to go for many miles to come.

When parts break it can be really frustrating trying to figure out why and what to do better or different the next time. It is a character building exercise.

 

my 700r4 with a corvette servo and m/t et streets raped my rearend on the 1-2 shift and after a good month or so of abuse it just let go.