I saw a couple of videos showing the 8.5 rebuild. one video said that you set pinion preload without the carrier in place and you want about 20 in/lb of force to keep the pinion moving (not starting rotation). Then after the carrier is in place and shimmed the preload will increase maybe 5-8 in/lb higher. The side bearing preload is the difference of preloads (5) x the gear ratio (3.73) = 18.65. It said you want this to be from 5-35. This is all with the old crush sleeve. Then after getting the proper gear patterns you put the new crush sleeve and seal in place and tighten the pinion nut to force the crush sleeve.

If preload is different depending on the amount of shims on either side of the carrier, what would be the preload at the point of final assembly? I think the Yukon spec is 16-19 in/lb. Is that with or without the carrier and shims?

thanks
Rob

That is without the carrier installed.

 

Again, youtube as failed. You can't measure the preload on the differential bearings, and you do not set the pinion bearing preload with the old crush spacer in place. You do not use a crush spacer at all when doing the trial assemblies. Save that for the final assembly. You also can not set the pinion bearing preload if the differential is in the housing. Differential preload is correct when the differential is tight enough that you can not pull it out by hand, no matter how hard you try, but not so tight that you damage the shims or the housing when driving them in. You should need a pry bar to get the differential out when the preload is correct.

 

I love this site, get so much solid advice. especially thanks Big Gear Head..thanks for helping me along. I have all my tools and parts, now I'm just trying to get my facts straight and will start this weekend. I think it all makes sense now.

 

Be sure to put gear lube on all of the bearings during assembly. You want to feel a nice smooth rotation. If you put the carrier without the pinion as big gear head described you can get a feel for the rotation and preload once it’s all assembled and the backlash is correct.

 

Making progress on the rebuild. I set the pinion preload to about 20 in/lb once it’s turning using the shim that came out of the rearend. I was then able to get the backlash from .007-.009” depending on which tooth I tested. Having the indicator in the middle of the gear tooth approximately.

Here are my patterns I didn’t get great contact with the paint so it’s hard for me to tell but I think maybe the pinion is too close.

how does this look? Pinion too close?

 

The pinion might be a little too deep, but it's hard to tell anything about that coast pattern. Stick an axle in it and turn it at least 6 full turns in both directions.

 

Does deep mean more shim or less shim on the pinion?

 

Too deep means that you have too much shim. More shim will make it deeper.

 

I noticed i can barely turn the carrier by hand without spinning the yoke. I took it back apart and with no preload and no carrier shims, just caps (not fully torqued) I still could not really turn the carrier. After reassembly to the proper preload and backlash it really doesn't turn without using the pinion. i flipped it over and the preload with the carrier is 25-30 in/lb. Is this normal?

When putting the carrier shims in I had to tap them pretty good to get them in. To remove the carrier i have to pry it out, but it doesn't require a ton of prying to get it out. When i tried the 2 factory carrier shims i had to hammer those in and wrestle the carrier back out so i thought that was too tight.

I wont' be able to get back in the shop until Saturday and Sunday.

 

20 inch pounds of pinion bearing preload is going to feel really tight when you try to turn everything using the differential. If you stick an axle in it and turn it with the axle it might take both hands to turn it. The shims should go in tight. If you can easily pry it out then it might take just a little more shim to get it tight enough. Just remember that these bearings are going to loosen up quite a bit. If you don't get enough preload when you put it together then you will loose all preload after it runs a while.

 

If you stick an axle in it and turn it with the axle it might take both hands to turn it.

When I was checking my gear pattern by turning the axle, I used a 2 foot length of 1x2 and placed it between a couple axle studs and used the 1x2 as a handle to turn the axle. As the axle turned, I reposition the 1x2 on another pair of axle studs and continued to turn.