Ok I'm stumped. Rear end help please!

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KevinB

KevinB

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Ford 8.8 that I'm trying to setup. I'm having trouble setting the pinion depth. Every time I try a new shim, I then put in the carrier and shim it correctly for .008 to .0012 of backlash measured with a dial indicator.

The pinion is stamped Ford. Started with .033 of pinion shim, then went to .027, now I just tried .011 of shim. Each shim gives me a gear pattern showing contact on the inner side of the ring gear on the drive side of the teeth, and contact toward the outside of the teeth on the coast side. The .011 shim was an improvement, but the edge of the pinion teeth only make contact on the inner half edge of the drive side teeth. What should my next step be?

Also, I'm tightening the pinion nut until there is no play in it, leaving the crush sleeve out until I'm ready to use it. I will double check the inner bearing race is all the way seated, but I would think the force of tightening everything down would have sucked it up in there.
 
You may have already seen this.... It is a balancing act sometimes.

drive_axle_gear_tooth_pattern.JPG
 
Actually that is more helpful than what I've been going by
 
So comparing that to what I've been going by, they say the exact opposite things! My pattern looks like the second drawing in that image, that says it indicates more shim needed. As far as I can tell in the attached image my pattern is the second photo, which is labeled as "thinner shim needed"

I'm at a loss
 

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Don't confuse 'drive' side to 'coast' side. I think the image you posted is showing drive side. Guner's above shows both.
 
The image I posted shows both, just look at the curve of the teeth. Looks exactly the same to me
 
Shim correct increase backlash? See how it looks with 0.020. Drive side is the vertical part of the tooth and coast is sloped.
 
My tooth pattern definitely matches "backlash correct, change shim", and my backlash measurements have been spot on before I roll the gears every time. I guess I'll go on the assumption my go-by has been wrong and use the new one posted, which would indicate more shim is needed. Since I started at .030 shim, I'll try .045 next just to make sure it moves in the right direction, then back it off as needed.

In other words, I'm not having trouble reading the pattern, and I understand which side of the tooth is which...its more of a question of: If I'm doing what I'm supposed to be doing, why isn't this working. and incorrect reference is a reasonable explanation, if that's what's happening

One thing that helps is marking compound...if you don't buy a ring and gear kit it's a ***** to find! Of course auto parts stores have no idea what it is, I had to dig until I found out prussian blue works, which is something the locals DO sell. It is helping more than the white lithium was.
 
Ok so maybe this is a clue:

The website linked to below (dana) explains that there are two ways gears are made, face milled and face hobbed. In my gear pattern marks you would add shim for one style and reduce for another. So both go-bys are correct, I just have to figure out which I need to use

[ame]http://www2.dana.com/pdf/5717.PDF[/ame]
 
If the gearset is used;
it is often impossible to get a perfect pattern.
Concentrate on the driveside, cuz you will be putting power into that side; and let the coast side be what it will be.
The depth shim sets where the pattern sits on the tooth from end to end, the long way, while the backlash moves the pattern up and down, the short way. This is an oversimplification, cuz,there is quite a bit of interplay between them.
I spent several years building those and found that sometimes/manytimes, I had to sacrifice a little backlash to get a good drive pattern.
If the coast side gets too crossed up, with a very nice drive side, the rearend will be noisy when decelerating,especially with a manual transmission. It never gets better than the day you put it in. So sometimes you,again, have to compromise.
With new,quality gears, the pattern usually dials in nice.
Try not to let the pattern creep up too far towards the heel or the top, Big power tends to break them off,out there.
 
Ok so I see now I have face milled gears which require thicker shims when my gear contact pattern is seen. That adds up. Now back to the lab to experiment with thicker shims
 
Good call, Kim
Grab the yoke stump and squeeze. The load will distribute the checking fluid, and make reading it much easier and more accurate. I have big hands, so I grab it with my left hand. I place the stump down at the rooy where my thumb meets the pointer finger.Then I wrap the other 3 fingers around the nose of the case, and squeeze it to my palm, to anchor it. Then I can vary the load by squeezing my thumb and pointer.
I have also used a leather belt wrapped around that same stump, but it's harder to control.
 
Ok guys I made a dumbass mistake...I've been using a dummy pinion bearing during this process...when I pulled it off this morning I realized there was a shim that had aloof let affixed itself to the bottom of the dummy bearing, a pretty thick one too! So every test I did was pointless and that's why even going down to .011 of shim showed a high pinion still. Doh!!!! Just tried out .024 of shim and it's much closer. Now that it's behaving like it should, I should be able to get it dialed in. Thanks for all the help, I'll be back after starting back at square 1! Gaahhhhh!
 
AJ/FormS said:
That's learning 101, no biggie, just time lost for you. Thanks for coming clean, cuz we could have been racking our brains for ideas, soon.
May the Force be with you.
Click to expand...

LOL it just wasn't adding up…but I've got to wait to do any more work on it because I realized one of the pinion teeth has a small chip at the end of the tooth. These are used gears and I don't want to take any chances, I'll have new gears tomorrow.
 
zinc oxide (nose-coat or diaper rash ointment) makes a good marking compound too, thick white goo. gear set up is relaxing.....Then you tighten the crush washer and the thing pulls out of spec again, yeah!
 
Ok I think I'm there, but if someone could eyeball my pattern that'd be great. These are brand new gears with .012 of backlash and .0325 of shim. To me the drive side is spot on, the coast side looks good but it didn't mark as clearly
 

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Coast side photo 2
 

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Ok so here's a new question. I set the pinion preload without the carrier installed to 28lb (I overshot a little but I figured it was ok). Then once I put the carrier in and snugged up the caps, now the preload is at 10lbs. What gives? I don't want to tighten it further unless I have to. I know the spec for new gears is 16-28 in-lbs, and used gears is 8-14in-lbs.

I do know the pinion was still cold from the freezer when I put it in, I suppose it's possible once it warmed up it lengthened a bit. Any other ideas?
 
I almost like that pattern, but it's really hard to see from here. The pattern is real close. I think I would try a little less backlash, and see if the pattern walks down the face. It seems too high for me. .012 is too much.Maybe try .002 less,at a time.
I try to run my pattern closer to .006 to .008

The pattern, with the tighter bl, might want a bit more spacer
 
AJ/FormS said:
I almost like that pattern, but it's really hard to see from here. The pattern is real close. I think I would try a little less backlash, and see if the pattern walks down the face. It seems too high for me. .012 is too much.Maybe try .002 less,at a time.
I try to run my pattern closer to .006 to .008

The pattern, with the tighter bl, might want a bit more spacer
Click to expand...


Once I put the real pinion gear on with the crush sleeve, etc, the backlash ended up at .0105-.011", and I think the pattern centered up just a little bit more. I ran the gears a few times and the marks became more clear. The coast side looks good too. I went ahead and tightened the pinion nut just a tad more and got the preload to 20lb
 
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