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8.8 pinion bearing fit question


French-connection

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Hi everyone.

I'm currently rebuilding my rear axle and was checking the pinion bearing fit.
The lower one needs to be pressed in, that was clear to me, but what about the upper one?
When I handfit the bearing, it doesn't slide down on the seat.
It seems that it'll have to be pressed in too.
Not sure how much pressure this will require.
My question now is, is it supposed to be that way?
I had the impression the the upper bearing is a slip fit on the pinion shaft.

My parts are all from FRP.

Thanks for your help.
Olivier
 


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ericbphoto

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I don't recall hand fitting my new bearing. But I do remember that during disassembly, after removing the nut, I needed a dead-blow hammer to get the pinion to push into the housing, free of the outer bearing. So the outer bearing must have been a snug fit. When re-assembling, I was able to get the nut started and use it to draw the assembly together. That was a tricky operation. It takes a lot of torque. But you still have to be sensitive enough to feel what's going on and know when to start checking for the pre-load with your beam torque wrench. I don't like that crush sleeve assembly design.

I've only done it once so far. But it seems to be ok.

Eric B
 

French-connection

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Thanks for your input Eric.

I finally installed the pinion shaft last night and that was a job.
I did clean up the pinion shaft from small burrs and the coating and the bearing slipped on it no problem.
Towards the end of the installation the torque wrench was set at 200 lb-ft to it wouldn't click. Crazy.

Got it all set up and it has the exact preload it should have.
Now it's the differential's turn and I have another question for you out there.
The original shims are one solid piece vs the ones in the kit are thinner ones that needs to be stacked.
Can / should I use the solid ones to start with and add on new ones as required, or should I only use the new ones?

Thanks.
 

adsm08

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Install the carrier with the original shims, in their original spots, and take the backlash. Then, if you need to, use your build-a-shims to make ones of the correct size to adjust as needed. DO NOT attempt to stack shims.
 

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Adsm08,

Thanks a lot for the advice.
I'll do what you're suggesting.
Hopefully I'll get the diff in tomorrow or Sunday.
I'll keep everyone posted.
 

French-connection

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Hi. Working on the differential carrier installation today.
Currently shimming it for backlash and I have to add a .017 shim to the original one on the left to get correct backlash. I added it between the large shim and bearing. Can it just stay that way?
The right side one is too big now and I had to mock-up shim with a stack to get the value.
I'll grind down the larger one to match the thickness.
I'm following the Ford Performance Part installation instructions and there's one thing that confuses me.
Step 9 requires to add .006" shims left and right for bearing preload after setting the backlash to .008-.012". That would effectively reduce the final backlash to .004-.008". Is that the correct intent? I thought backlash should be the first set of numbers. How do you guys preload the bearings?

Thanks
Olivier
 
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1. Unless you have access to a very expensive machinist's surface grinder, don't even try to grind a shim thinner. It must be made perfectly parallel and flat on both faces, and you can't control that well enough by grinding with any hand-controlled methods.

2. Yes, it's perfectly acceptable to use a main shim and a spacer shim in your final assembly.

3. When you add shim width for preload, you ADD thickness to BOTH sides, which forces the bearings tighter together but does not move the carrier and gear, and therefore does not change the backlash.

Backlash only changes when you ADD thickness to one side and REMOVE thickness from the other, which shifts the carrier sideways.
 

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Spott.

1. Yes, I have access to a surface grinder at work. :headbang:

2. and 3. Thanks for the info and clarification.

I hope to get everything set today. Cross fingers.

Update:
I ground the shim and installed everything.
.009" backlash. I had to already had to slightly 'convince' the right shim in place and there's no way to insert any more on either side. How is this supposed to work to be able to get the bearing preload? Am I supposed to pound the large shim in? It seems to cock at an angle with the race and hang up on the edge of the seat in the housing.
Thanks.

Olivier
 
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ericbphoto

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That's a tricky job. Pro shops have jigs to stretch the carrier slightly to make it at least a little bit easier to install the carrier and shims.

When I did mine, I measured the original shims left and right and added the numbers together for a total. Then I added to one side and subtracted from the other to set backlash, making sure that the total always remained the same.

My assumption, whether right or wrong, was that that method should keep the preload where it needed to be. Time will tell. I only have about 1500 miles on it so far.

Eric B
 

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I just did the math and with the two .006" shims I'll be within .001" of the original width.
I'll try tomorrow with the help of a friend to put the carrier and shims in as a unit. Hopefully that will be easier and more effective.

I did a pattern check today and it doesn't look bad.
My paint seems way more liquid than in other pictures and it doesn't print well.
How can I upload pics for someone to check if it's ok? Where do you guys host your pictures to link them?
Thanks.
 

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Somehow my marking compound gets wiped off a lot.
Maybe anyone can see the pattern.
Setup is .027" pinion (original thickness) and .008-.009" backlash.
Thanks for any input


 
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French-connection

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Ok, I've been looking at this a bit more tonight.

And the more I look at the pattern, the more I think I'll have to change something.
Here are some other pictures I took tonight.



The drive side seems to be close to the toe as if it needs a thinner pinion shim.
The coast side looks something in between of needing a thicker pinion shim, or reducing backlash.
Both really don't make sense to me since I'm at .027 pinion shim and .008 backlash.

Am I interpreting this wrong?
Thanks.
 

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Usually cutting the gear marking compound with a little bit of gear oil improves readability. Another trick is to rotate the assembly using a wrench on a ring gear bolt (while putting a small bit of resistance on the pinion flange) rather than rotating things by the pinion.

A case spreader will make the extra .006" shims go in much easier. Be very careful with a spreader though, it is not difficult to permanently distort a housing with one (spread it just barely enough so you can tap the shims in, no more).
 

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You can rig up a quick-and-dirty case spreader with a couple of pieces of heavy angle iron (drilled appropriately) and a couple of pieces of all-thread.
 


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