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Gm 8.5 gear pattern problems

Old 03-27-2017, 08:09 AM
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Default Gm 8.5 gear pattern problems

Hey the rear end in my 96 k1500 blew up the other weekend so I got a rebuild kit with new carrier and ring/pinion. I put it all together with the original .032 pinion shim, backlash set to .005 and my pattern showed the pinion depth was way off (marking on very bottom and heel of drive and bottom toe of coast) so I tried with a .025 shim under pinion, and then a .010 and then with no shim at all. The pattern now is starting to center up on the drive side but the coast still shows its way off to the toe.. any ideas what I could possibly be doing wrong? Here's the pic with no pinion shim, .005 backlash and 15 in/lbs rolling torque on pinion. Any help would be great. Thanks.
With the .032 origional shim the pattern was just touching the toe on coast but it was a much harsher line. It looks like im going the right direction but theres no more shims under the pinion to remove.
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Old 03-27-2017, 11:59 AM
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maybe double check your pinion races are hammered all the way down. you can also compare your old parts to see if anything is larger in size than the oe parts.
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Old 03-28-2017, 10:20 AM
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You are way off . Put the .032 shim back in . Most likley you are to deep with the backlash . Put it at .007 to .008 with the .032 and send us a picture . No way you need to make those extreme moves .

Also what make gears are these . Look at the gear set to see what the manf suggested B/L is . Also slack off the gear marking compound . All you need is a even thin coat .

Was the pinion bearings and race changed?

Last edited by homemade87; 03-28-2017 at 10:30 AM.
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Old 03-28-2017, 09:20 PM
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Something is definitely off. Here's a pic with the origional .032 shim in at .009 backlash. The gears are Pro King 3.73s, it says .006-.010 is recommended backlash. All bearings and races were replaced with a new carrier and gears, everything is new. Its marking the bottom of the tooth on the toe on coast side
Its marking the top of the tooth on the heel on drive side
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Old 03-29-2017, 12:38 AM
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I'd pull the pinion back out and inspect the races carefully, you may have something trapped behind the race and the case on the inner race. Something has the pinion way far back in the case.
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Old 03-29-2017, 07:34 AM
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As said , Something is definetly wrong . Check your bearings with the old ones and be sure they were the same number . Also check the numbers on the race as well . Could be you have a miss match between the bearing and race . As Rockin said , Take a good look at the races to be sure they are seated . You need to fine the problem before you proceed .
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Old 03-29-2017, 09:09 AM
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Yeah thats whack. Take everything apart and inspect.
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Old 03-30-2017, 08:26 AM
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OK so last night I removed both pinion races and reinstalled then. Double checked to make sure there was nothing behind them. Removed the pinion bearing and lightly scuffed where the shim would go to make sure everything was sitting flat. Put it all back together with the .032 shim and my pattern still looks the same as above. Is it possible my housing is bent or something? This is driving me crazy.
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Old 03-30-2017, 08:40 AM
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Or you have a bad set of gears? How did the ones look that came out?
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Old 03-30-2017, 09:00 AM
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Originally Posted by Stitch1717 View Post
OK so last night I removed both pinion races and reinstalled then. Double checked to make sure there was nothing behind them. Removed the pinion bearing and lightly scuffed where the shim would go to make sure everything was sitting flat. Put it all back together with the .032 shim and my pattern still looks the same as above. Is it possible my housing is bent or something? This is driving me crazy.
Did you check the bearing numbers and race numbers while you had them out against the old ones that came out .

There is only a couple things come to mind what could be wrong . The bearing or race is wrong or the gear is of the wrong series . My guess is the large pinion bearing or race .
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Old 03-30-2017, 05:41 PM
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I couldn't find any numbers on the bottom of the bearing. The old ring gear was missing probably 80% of the teeth and pinion was VERY marked up/ruined. The bearings all came in a kit with both carrier bearings and pinion bearings. I'm gonna pick up another ring and pinion and swap it out to try and eliminate if it's a bad gearset or not. I'm also going to pick up a new GM pinion bearing for it tomorrow so then at least i'l know for sure it's not the bearing. I'l post pics of the new markings this weekend after i get it back together. Thanks for all the input!
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Old 03-30-2017, 06:31 PM
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AND DON'T put on such a thick coating of marking compound. Apply very thin as to the point you can almost see thru it. When it's too thick,the wiping/meshing of the gears causes a re-coverup of the true pattern. I've seen seemingly bad patterns become good patterns just by reducing the amount of compound.
Also as you're rotating the 'compounded' ring gear,some of the compound with be applied/transferred on gear nd as you rotate to/into an 'un-compounded' area of ring gear teeth,the compound on the pinion gear will transfer to the uncoated teeth of the ring gear and you will see an 'opposite' pattern of yellow on bare tooth instead of clear area on a yellowed tooth. I find that 'opposite' a true picture of pattern.
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Old 03-30-2017, 07:08 PM
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Originally Posted by Stitch1717 View Post
I couldn't find any numbers on the bottom of the bearing. The old ring gear was missing probably 80% of the teeth and pinion was VERY marked up/ruined. The bearings all came in a kit with both carrier bearings and pinion bearings. I'm gonna pick up another ring and pinion and swap it out to try and eliminate if it's a bad gearset or not. I'm also going to pick up a new GM pinion bearing for it tomorrow so then at least i'l know for sure it's not the bearing. I'l post pics of the new markings this weekend after i get it back together. Thanks for all the input!
This is troubling , no part number on the pinion bearing . With out this there is no way to know if you have the proper bearing . Was there a number on the race . Never seen a bearing that did not have the proper number for the application . Not sounding good .

As stated in a early post and what firstlyr1z is saying . Only put a thin coat of marking compound . You are using to much .

Last edited by homemade87; 03-30-2017 at 07:16 PM.
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Old 04-07-2017, 05:13 PM
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the bottom of the old pinion bearing was all worn down as if it were wearing into the pinion. Good news though i put another ring and pinion in with a gm bearing and the .32 shim and my pattern looked much different, although i still had to go down to a .010 pinion shim to make it where i wanted it the pattern looks much flatter and it's perfectly centered on the tooth both heel/toe, and root/face. No pics sadly i was just trying to get it finished. Thanks for the help, i'm marking that one up to shitty/cheap gearset.
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Old 04-09-2017, 09:39 AM
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Glad you got it sorted out
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