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Old 06-22-2006, 03:39 PM   #1
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Join Date: Apr 2001
Location: Euless, TX,USA
Posts: 48
Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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9 bolt problem diagnosis

I have searched long and far on here to try to find out what’s going on with my rear. I have been rebuilding this thing for about a month now, and I have run into problems. First off let me tell you what all I have done. I have two of these rear ends, the original, which was a 2.77 geared pbr and one I bought at a junk yard (3.27 out of an 88'). I bought a bunch of shims from larry burd and completely disassembled the carrier and had the cones milled down so they would not bottom out, and installed shims like stated in the article, in addition I put a set of 3.70 gears in and all new bearings (except wheel), setting up the pinion depth and backlash accurately.
When all back together the gears seemed to run fine and quiet, in a straight line. When I go around corners slowly a grinding noise starts and then kind of a clunk proceeds like something is getting binded until I straighten out and cruise for a bit. My first instinct was the brakes locking up, I removed the calipers to test my instincts and that didn't solve the problem. I then put the car back up on jack stands and found that the pinion was loose, I tightened it back up, and put a new nut on, and went back out. The problem was not fixed. It seems that it happens around corners gets caught when backing up. I took it all apart for the third time and found no metal shavings or damage to anything, further when taking the carrier apart found no shavings or damage there. I have not taken the pinion out, but I don’t think that is the problem because it is just fine while going forward.
My thoughts are now, either the wheel bearings are shot, or my Frankenstein rear end has some mismatched parts which are not working together. The carrier was put together with a combination of both carriers using the best parts of each so possibly that is where the problem exists. What do you think? Please help because this thing has been down so long that I have forgotten why I have it.
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1989 Iroc-Z camaro
XFI 280 HR, Vortec heads, Beehives, Stealthram
custom programming with Ostrich, All MSD
T-56 Spec Stage 3 Pro 5.0 shifter
9 inch; mostly Currie, 3.70 gears,
All Sphon rear suspension
Very equipped Nitrous System.
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Old 06-22-2006, 04:56 PM   #2
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Location: OKLAHOMA CITY
Posts: 580
Car: 89 FORMULA 350
Engine: 5.7 L98
Transmission: 700R4
Axle/Gears: 9 BOLT/ 3.27 GEARS

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I had the same problem in my 98 z28. It turned out that it was the limited slip that needed to be replaced. It would only make a shuddering noise around corners because the clutches werent opening and closing properly like they should around turns. Im no mechanic, but hopefully this helps.
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Old 06-22-2006, 10:57 PM   #3
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Location: Euless, TX,USA
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Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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Thats what I am afraid it may be, the 9 bolt has cones which are a little different than the clutch pack design, but it seems like that is where my problem is originating from, anybody else have something to chime in?



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Old 06-23-2006, 11:17 AM   #4
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Join Date: Jun 2002
Location: Ottawa, Ontario
Posts: 654
Car: 86 IROC
Engine: LQ4 6.0L
Transmission: T56
Axle/Gears: 4.11 9-Bolt

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How is the posi, does it funtion normally?

If your posi is 'clunking' around slowspeed corners it is just the cones sticking in the carrier. It is not a bad thing if it does this, it will not hurt the posi and just means that it is working normally.

If it bothers you, get a bottle of GM posi diff additive and add about 1oz at a time until the noise goes away. Don't add the whole bottle. This stuff reduces the friction between the cones and carrier and will reudce the effectiveness of the posi and will make it 'burn' out much faster by allowing the cones to spin in the carrier wearing them out again on you.

I'd just live with the noise and a tight posi unit!
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Old 06-23-2006, 11:45 AM   #5
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Location: Euless, TX,USA
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Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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Like when I pull in the driveway, it catches, and makes a clunking noise where I have to give it more gas to go, do you think it is possible that it just needs additive? It seems like its a lot more damaging than that. I looked at the axel races today, the passenger side has a rust spot on it, could this be causing the catch?
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Old 06-23-2006, 12:08 PM   #6
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unless you pulled the bearing off, you can't see the bearing races on the inside, so you are looking at the outside of the race, and that shouldn't be a problem. If the bearing was rusted on the inside of the race, this would be bad.

you probably is likely what someone else said, the posi lubrication, causing the cones to act jerky, as they release and catch. basically, at slow speed, you car will shudder, and get like a creaky noise. This can be dealt with by using the posi additive.

I would be more concerned about the loose pinion, if the preload is not right, you will quickly ruin the inner and outer bearings, and seal, and these could lead to other problems. It being loose after driving on it means that either the nut was bad, the races weren't fully seated, or it wasn't set right in the beginning and the crush sleeve wasn't drawn down completely.

if you've never set up a ring and pinion before, it is worth a couple hundred buck for someone who knows what they are doing to check it for you. Especially with used gears(were they new?). It might just take the guy to do a preload check and another run with the paint to check the pattern, but its worth it.
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Old 06-23-2006, 12:45 PM   #7
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Car: 86 IROC
Engine: LQ4 6.0L
Transmission: T56
Axle/Gears: 4.11 9-Bolt

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Don't know,
If something is binding you have some bigger issues in there.
Cones sticking would not stop a car from moving.

You should bring it to a professional to check out.
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Old 06-23-2006, 01:17 PM   #8
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Join Date: Apr 2001
Location: Euless, TX,USA
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Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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This is my second rear I have done, it is the first 9 bolt though. My first 10 bolt went well and I used used gears. The patteren on this 9 bolt looks great, so that was not the problem. The pinion nut was loose because after crushing the crush sleeve with the old nut I took it off and put the new nut on with my impact, and it didn't go down all the way allowing it to come back out. I have since then retightened it with a new nut, so it is tight once again.

Here is some pics of the axel race and the gear pattern,

Click the image to open in full size.

Click the image to open in full size.
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Old 06-23-2006, 01:57 PM   #9
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Location: huntsville, al
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Car: 89 iroc
Engine: 5.7 HSR N2O
Transmission: TKO 600
Axle/Gears: 3.27 9 bolt posi

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Posi-tive

I agree with most of what's stated above. I too am sticking with the 9 bolt for whatever reason and have had simular problems.
The clunking you hear is probably the clutches grabing and releasing as you go around corners. That's what differentials do- they allow the outside wheel to turn faster (and therefore farther) than the inside wheel. A posi simply resists this action. It seem to me there may be a bit too much prelaod on the cone clutches. You can certianly try some posi additive if you didn't to begin with, but I have only noticed a bit of chattering without the oil- not clunking or poping. If the additive doesn't help you need to go back into the differential. I'd take 0.005 shim out of the pack and see if your problem go away. Just don't go too far. Since you modified your cones, you may have to do a little trial and error. That's what I do...

Happiness is...a tight posi!
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Old 06-23-2006, 07:39 PM   #10
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as for it attemting to "stop" the car while cornering, ever tried to push a drag car with a spool around a corner? - If the posi is trying to stay locked(you clunking sound), then it will take more power to corner, as you have to force the inside tire to spin.
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Old 06-24-2006, 03:08 AM   #11
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Join Date: Apr 2001
Location: Euless, TX,USA
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Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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Thank you guys for your responses. I pulled my carrier back apart to check the preload, it had a little play still. Let me run my proceedure by you guys to make sure I am doing it right. First I have the carrier all apart and then place the cone, shims, sidegear then the crosshaft with the spiders on top of that. Then I check the preload by pushing from underneath on the bottom of the cone to see if there is still play. I kept adding shims untill there was no play, and then took one out. I appriciate your help and hopefully I will get this figured out.

Additionaly, should I still consider the axel race a possible cause of the problem?

Again thank you for all your help.

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Old 06-25-2006, 11:57 PM   #12
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Join Date: Apr 2001
Location: Euless, TX,USA
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Car: 89' Sunset Metallic Orange Iroc-Z
Engine: L98 Shortblock
Transmission: T56
Axle/Gears: 3.70 9 inch

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GOT IT!!!
I reshimmed the posi cones once more, using my new micrometer. Put it all back together and my backlash changed for some reason, so I reset it down to .007 and bolted her up. Took her for a ride today around some slow corners and some circle 8's, the most I could get was a small whimper around left turns. So it was the posi cones that were the problem.

Thank you all for your advice and consul. Now I can finally get some proper break in miles. BTW what would you guys recommend for break in time for a set of Motive gears.


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Old 06-25-2006, 11:57 PM
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