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Old 10-12-2017, 03:34 PM   #1
blazer2007
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truck 12 bolt pinion pre load

I have a 1980 chev truck with the 8.75 12 bolt rear diff. I can find the pinion pre load but can,t find the final pre load in inch pounds. I,m using a new outer bearing and used inner which is only 3 yrs. old and looks really good.I caught the outer one which is just starting to pit. Pre load says 13-15 new and 6-8 old bearings so where should I set my pre load
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Old 10-12-2017, 06:55 PM   #2
homemade87
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Re: truck 12 bolt pinion pre load

Pre load should be 10 to 15 used and 20 to 25 new . I would shoot between 15 to 20 and you should be good . 6 to 8 is pretty low for a pre load . I would never set a pre load that low .
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Old 10-12-2017, 08:49 PM   #3
blazer2007
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Re: truck 12 bolt pinion pre load

thanks, this the site I was looking at http://www.crawlpedia.com/ring_pinion_setup.htm
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Old 10-13-2017, 06:49 AM   #4
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Re: truck 12 bolt pinion pre load

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Originally Posted by blazer2007 View Post
thanks, this the site I was looking at http://www.crawlpedia.com/ring_pinion_setup.htm
In my opinion to low of a pre load could cause the pinion to move after several miles of wear or break in . Especially under performance use and towing and deceleration . Remember the pre load becomes less and less as bearing wear . Starting to low after some wear could put it at 1 or 2 in time . You need some tension to keep the bearings seated so the pinion gears mesh proper .

On new bearings I shoot for 25 to 28 . They usually settle out between 10 to 12 . If you shoot between 15 to 20 with one new bearing , after it settles it should put you at about the 10 to 12 mark as well .
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Old 10-13-2017, 03:23 PM   #5
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Re: truck 12 bolt pinion pre load

Just to make sure we are on the right page, pre load bearing,check my pattern on ring gear,tear apart and install crush sleeve and seal and crush bearing to what inch pounds now , the same 15-20
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Old 10-13-2017, 05:19 PM   #6
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Re: truck 12 bolt pinion pre load

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Originally Posted by blazer2007 View Post
Just to make sure we are on the right page, pre load bearing,check my pattern on ring gear,tear apart and install crush sleeve and seal and crush bearing to what inch pounds now , the same 15-20
Set pre load the same as when checking pattern . This will make your pattern the same as well . You want to duplicate what you were doing during pattern checks .
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Old 10-13-2017, 08:34 PM   #7
blazer2007
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Re: truck 12 bolt pinion pre load

I know is going to be hard to crush the sleeve, but that is all I need for inch pounds 15-20 or do I need more more on final assembly to compensate for ring gear and pinion bearing seal. Bear with me ,got ripped off on someone installing a new yolk and it wrecked the bearing. I,m not paying no more so I,ll try it myself. Too much info on I-net ,what,s right whats wrong. I have all winter to do this
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Old 10-14-2017, 08:42 AM   #8
homemade87
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Re: truck 12 bolt pinion pre load

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Originally Posted by blazer2007 View Post
I know is going to be hard to crush the sleeve, but that is all I need for inch pounds 15-20 or do I need more more on final assembly to compensate for ring gear and pinion bearing seal. Bear with me ,got ripped off on someone installing a new yolk and it wrecked the bearing. I,m not paying no more so I,ll try it myself. Too much info on I-net ,what,s right whats wrong. I have all winter to do this
The seal will be minimal . So just set it like you did in the pattern checks ( 15 to 20) and you will still be with in the specs and be fine .

Also go real slow when you get the slack out of the bearings . It takes very little to go over crushing the sleeve .

Sounds like you are doing fine .

Last edited by homemade87; 10-14-2017 at 08:52 AM.
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Old 10-15-2017, 08:35 PM   #9
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Re: truck 12 bolt pinion pre load

getting there but backlash is a little loose but pattern not bad, if I shim the carrier in, what will it do to my pattern, move it in or out. If you know of a good web site for this let me know. I can,t find any but my wording is probably wrong
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Old 10-16-2017, 07:10 AM   #10
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Re: truck 12 bolt pinion pre load

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getting there but backlash is a little loose but pattern not bad, if I shim the carrier in, what will it do to my pattern, move it in or out. If you know of a good web site for this let me know. I can,t find any but my wording is probably wrong
Moving the ring closer will make the pattern a little deeper . Could also move the pattern a little closer to the toe . Just set it to where it is in the middle of the spec of the gear set and see what it does .

I am a little confused . Is this a new gear set . No need to change anything on a existing gear set that is installed and run . Use the same pinion shim and set back lash with in spec .

Heres a write up and should give you all the info you need . There is things in there that you will not need to do .http://www.pirate4x4.com/tech/billavista/Gear_Setup/
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Old 10-16-2017, 08:51 AM   #11
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Re: truck 12 bolt pinion pre load

It was a new motive gear set about 4 yrs ago.
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Old 10-16-2017, 03:46 PM   #12
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Re: truck 12 bolt pinion pre load

I think I best leave it alone,it worked before. JUst watching too much u tube videos on the subject, thanks for the help Homemade
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Old 10-16-2017, 08:31 PM   #13
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Re: truck 12 bolt pinion pre load

This is out of the Yukon Gear & Axle Installation Manual that came with my Eaton Posi and gear set; Order of adjustments are; 1)Pinon Depth
2)Pinon Bearing Pre-Load
3)Backlash
4) Carrier Bearing Preload
Since the GM 12-bolt uses an outside shim design, (shims between carrier bearing races and the housing) Initially set the backlash, add equal amounts of shims to both sides of the carrier to set the carrier bearing preload as tight as possible without damaging the shims. Just get them good and snug because to adjust backlash you will transfer shims from one side to the other moving the carrier w/ring gear left or right, left to open or increase the backlash, right to close or decrease the backlash. Left side is always the drivers side...
If preload is close and backlash is loose, add shims to the left side of the carrier. This will tighten carrier bearing preload and decrease the backlash. Since your not in a hurry I would suggest getting this manual, they're on sale here for less than Amazon.com sells them and free shipping to boot... https://www.themotorbookstore.com/di...ir-manual.html Here's the specs for the GM 12T; OEM Pinion Shim Depth 0.030"
Pinion Bearing Preload 13-15 in lbs (new) 6-7 in lbs (used)
Backlash is 0.006" - 0.010" Since your running a four year old Motive gear set with only one new bearing and race on the pinion, if you land anywhere within the above specs you should be good to go. I don't know what you consider loose on your backlash but I would use a dial indicator to measure it and close it up to spec if you want the gear set to live.
Once your satisfied with your backlash and your pattern checks and your sure the new pinion bearing race is fully seated, then install your crush sleeve and bearing, then assemble the yoke washer and new nut. Pinion bearing preload does not exist until both bearings have contacted the races, that's the point where zero end play occurs and pinion preload begins. I don't know how your holding the yoke while you turn the nut but it takes something like 300 ft lbs of torque on that nut to collapse the crush sleeve. There is no final ft lb reading or spec once zero end play is reached so like HOMEADE87 indicated, go easy after that point with 1/2 hex turns and then take an inch pound reading on the nut. You will have to go slow taking several readings as you go until the desired reading is reached.
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Last edited by Ironangel; 10-16-2017 at 09:26 PM.
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