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Old 10-25-2007, 12:11 AM
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Tooth Pattern

Wassup gang,


I'm still somewhat of a noob to this board as well as the in's and out's of a car's rear end. I'm currently working on my ford 9" an got it complete. But I'm a bit leery of the gear mesh. I asked a couple of friends and they think it's fine, but i'd like to get some of your reactions to the photo's. I'll be posting them in a bit because I need to get to my other computer but so far here's the info. The bearing pre-load was set at .011" and the backlash was set at .008". I'm running motive gears, in a 4.57 ratio on a Detroit tru-trac with a Strange Nodular Iron center section. Any help or suggestions, or comments would be greatly appreciated!

Ron

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Old 10-25-2007, 02:43 AM
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This is the coast side



Drive side


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Old 10-25-2007, 07:38 AM
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From the pattern shown, your setup is going to give problems.
The preload is measured in foot-pounds. It is the amount of torque applied to the pinion nut to crush the collar and load the pinion bearings. Each diff is different in its specs. After this is set, you measure the turning torque of the pinion with an inch-pound wrench.

The pattern you show is off center. A good rule for mesh patterns is the centering rule. All contact must be centered in the teeth, and the contact must not extend to the edge of any tooth. Also, the shape of the contact pattern must be oval in shape. Backlash is also speced by specific diff. I think the coast side is too deep into the tooth, and there is not enough contact between the two teeth that are meshing. The drive side is too far towards the inside of the gear, and it almost touches the edge.

When I set up a diff, I've got about 200 shims to choose from, and I don't "let it slide" with alittle too much or too little here or there. When you take your measurements, take them 3 times. If they aren't all the same, take a deep breath, relax and measure again. This work takes a lot of patience, and you have to be very picky. The hardest part is setting up the pinion properly, becasue the crush collar is not reuseable. One collar for each try. I use the crushed ones for decoration on a shelf. Sometimes it takes a couple of tries even for the pros. Here is a little trick. When you have loaded a bearing, rotate the work back and forth a bunch of times, like 20 times, to let the bearing find its seat, then measure again, then make any adjustments. Remember, be picky here, it will pay off. After you have a good pattern on both sides, and your preload and backlash are in spec, coat the entire ring gear with litho, and do a full pattern check all the way around. This will tell you if the ring gear is centered on the diff carrier. Yeah you heard that right, sometimes they make the diff or the gear off center then you get a real wierd wowowowowow sound and a slight pulsation under load. Have fun, I admire your guts for taking on a diff project.
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Old 10-25-2007, 01:06 PM
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Thanks for the help TechnTool! The bearing pre-load i mentioned about was for the diff, I think they some times call it the case spread. I'm not using a crush collar on the pinion but rather a 2-piece solid set-up that has removable shims to set the running torque of the pinion in the support.

Now to center the drive side better, I'd have to add to the thickness of shims on the pinion depth correct, i.e. between the thirdmember and the pinion support correct. Or could I reset the backlash and add a couple of thousandths, like take it to .011-.012"? The manufacturer suggests .008-.012" for street gears. I have it set on the tighter side I guess, with a .008" reading.
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Old 10-26-2007, 06:26 PM
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ARRRGGGGHHHHHHHHHHHHHHHHHHHHHHHh




This is so frustrating! I've added shims to move the pinion off the toe, at least twice, going from my original .008" shim to .001" and now .014" and re did the backlash back to .008" and nothing. I've also decreased the backlash from .008" to .005" and nothing as well. It doesn't look like the thing is moving at all. It all looks like it's in the same place. Am I doing something wrong? When I *** shims or take away I reset the backlash by moving the diff either closer or away from the ring gear, but keeping the preload on the diff bearing the same. Any other suggestions gang?
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Old 11-09-2007, 08:53 AM
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You ever get that diff figured out?
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Old 11-13-2007, 09:36 AM
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Actually I'm still in the process of figuring this damn thing out. I've been going both in and out from my base readings, and have'nt really seen any major differences. Right now I got about .017" worth of shims inside there right now and am going to check it out. I've been keeping the backlash to .008-.009" as well. So hopefully things go well. I'll keep ya posted.
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Old 11-13-2007, 11:35 AM
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Keep at it you will get it, took me about 6 tries to get mine close to where it should be. I don't think many people achieve the "perfect pattern" either. I have surfed several sites to find pictures of other people's real world experiences. Here is a site that shows a pretty nice picture of his pattern. His isn't perfect either but I bet it's as good as it will get with that set up.

http://www.macamar.com/sitefiles/for...gear/index.htm

His gears are yukons and they may have a different "acceptable pattern" than what a motive is suppose to have. It still doesn't hurt to look and read about the experience though.

Have you tried taking a pattern with no shims on the pinion?
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Old 11-13-2007, 12:46 PM
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You know, I never thought of doing that. Taking it with no shims, like a base line to see where it ends up and go from there. If it doesn't come in or close enough on this one, .018" then I'll go and do that. Thanks for the suggestion

Ya it is hard, cause you get so many different suggestions and stuff, but I'm pluggin away at it, and the most fun is cleaning off that damn grease, I usually go thru 2 cans of brakekleen for it thank God for Wal-mart's brand.
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Old 11-13-2007, 05:13 PM
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Hey Javelin69, do you have the original pinon support shim?
This shim is for the case assembly and would be your starting point + or - what the original gears needed. The original shim will usually be within .005" of what you need and will give a reading that in most cases will be close enough to make one change and be there.
All cases are made to run with a fairly heavy shim and never without one.
In conclusion, if you have all the original parts, simply take the original shim, look at the original pinon gear's markings, It will tell you how much was added or taken from the case shim for that gear set, (generally very little). This value is the case shim amount and your starting point.
Regardless, start with the original shim if you have it, unless the new gear is off an unusual amount it will be close.
If the pic looks as i think it does, the pinion shim is too thin.
Keep the backlash at .010" during setup.
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Old 11-13-2007, 05:32 PM
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Hey boss68,
Well the bad good news is all the parts are brand new, the bad news the parts are all brand new
I have the original set-up, but right now I'm running a brand new one. I have a Strange Engineering nodular iron case, motive gears, and a Detroit tru-trac diff, and all new Timken bearing. But at least I know now I'm heading in the right directions with going bigger on the shims. Thanks guys for all the help!

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Old 11-13-2007, 05:38 PM
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Nice stuff!
Did the case and pinion support come with a shim? If not, how about starting with a .025".
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Old 11-13-2007, 05:42 PM
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Nah, I bought a shim kit for it and right now I got in .018", but if .025" is a good starting point then I'll try that after wards, if it doesn't work.

But I totally had a brain fart and forgot to ask, but how do I and does it make a major difference on putting pressure or a load on the ring gear? If so how can I go about doing this? I hear things like using wood or a brass bar, but where would I place the load while trying to rotate the ring gear to get the pattern?
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Old 11-13-2007, 05:54 PM
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I always just use the palm of one hand leaning on the outside of the ring gear and turning the pinion yoke with the other. It only takes a little drag to make the pattern and you can turn it slow and easy, no need to hurry.
Bet ya a lug nut she falls in between .025" and .035"

Last edited by boss68; 11-13-2007 at 06:12 PM.
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Old 11-13-2007, 08:30 PM
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It's a bet

Just let me know if ya want it in a standard or metric lug nut
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