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The pinion is too deep. Use a thinner shim and try again. Remove about .005 and see what happens.

That pattern was with a .026in shim and .009in backlash. I will try a .020in shim and reset the backlash and get pics up in about 1 hour. Thanks.

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This is with a .020in shim and .007in backlash

I always set the pinion a little towards the toe because when you put the power on it the pattern will migrate towards the heel. .005-006 backlash is a good starting point on new gears, if you using worn in gerras go for 7-8. I would move the pattern a bit further to the heel, see if you get a larger contact area then.

So I should tighten up the backlash and pull out about .004 from the shim?

Are these new gears? Coated or not coated? Toms gears for instance are coated.

Try and get it like this:

Drive Side


Coast Side


Also, when pulling the pattern, try to keep some drag on the pinion while turning the ring gear. This will give a better pattern to read than if you just turn the ring gear alone.

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They are new gears and are not coated. It is in a 9 bolt rear. The above pics are with .005 backlash ans .016 shim under the pinion.

Contact areas are real small, did you try to put some drag on the pinion while pulling the pattern?

Yes I held the carrier while I spun the pinion?? What would cause that?

Oops, I meant to say spin the ring gear while holding the pinion. Looks like you have the diff in the car. If so, bolt up the driveshaft and put a leather strap around it and pull on it to create drag. Then either use a wheel or something else to turn the axle (like a modified hand crank), you need this drag to pull a proper pattern.

A helper would be useful/handy here.

How many times do you spin the pinion? Coat a couple of teeth (or all of them if you feel like it), and spin it a few times, not just once. It will take a couple of spins to wear off the yellow paste to get a good readable pattern.

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This is back to .020in pinion shim. I attached the drive shaft and spun with the axle. I was very hard to turn. Which way do I go with the pinion shim?

How are you setting the pinion bearing preload? It needs about 20 inch pounds of drag on the bearings if the bearings are new. If the bearings are not new then I recommend that you replace them before going any farther. With the bearing preload set correctly you won't need to add any more drag to it. Be sure that you set the bearing preload the same each time you assemble it. If you don't then your pattern on the final assembly might not match what you get with the trial assemblies. Always turn the ring gear against the pinion. Don't turn the pinion. Use an axle to turn it and be sure that you make at least 3 or 4 full rotations in both directions. This will give you an accurate pattern.

Try this with the set up that you have now and see what the pattern looks like.

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20in/lbs preload on pinion, .020in pinion shim, .006 backlash Turned by the axle.

The pinion is close to the right position. Try about .009 backlash and see what happens.

ok be right back with pics

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.020 shim under pinion, .009 backlash (huge PITA to get), 20in/lbs preload, spinning ring gear. Does it look too deep now?

That didn't help. Try about .004 backlash and see what it looks like. I know this is a pain, but this is how you find the right pattern. Try something and if it doesn't work then try something else. I think the pinion is close, but the pattern just doesn't look right.

I'm starting to wonder if these are 2 step gears. Most gears are cut in 5 steps, but some new ones are cut in 2 steps and require a different set up.

The gears are from Motive Gear. The install sheet says they are lapped and should be installed with .008 to .012in backlash. It also gives a pinion install height. I will try a tighter backlash......that carrier sure is getting heavy...

OK, then if tighter doesn't work go for about .011 and see what happens. I know that it's no fun doing this over and over, but the pattern just doesn't look like it should. It's too small and I don't understand why.

I will try again in the morning. I pulled the rear end out I was getting tired of rolling around on the ground all day. It was pissing me off that everytime I moved I got a face full of rust and then I have to reclean everything before it goes back in to be sure no rust was on anything. I believe the stock pinion shim was .026in if this helps? New bearings were installed on the carrier and new bearings and races were installed on the pinion.

Hey Slow... did you ever get back to the rear gears and get it all sorted out? I am currently shopping for rear gears and these Motive's gears are on the top of my list right now... would be interested to see if you got these to work with your 9 bolt....

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.020 pinion shim, .005in backlash, 20in/lbs preload on pinion.

That's the best looking pattern that you have had so far. I would go to a .018 pinion shim and keep the backlash at .005.

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.016 shim .004 backlash 20in/lbs preload.
I only have a .010, .016, .017 pinion shim.

I think you got it. I don't think it's going to get any better than that. I'll worn you up front, these gears will probably make some noise. There is something about the 9 bolt 3.70 gears that are just a little noisy.

Do you think .004in BL is too tight? If not then thats what Ill go with. Also how much carrier bearing preload is required? The smallest shim I have is .010in and I dont think I can squeeze 1 on each side as it sits?

Got a question about the axle bearing races. When I removed the axles I notices that they were not pressed in but could be removed by hand? Rear only has 65K on it??? Is it time for new bearings?

If you have some .010 shims in it now that can be replaced with .015 shims that would be an option, or some .025 shims that could be replaced with .030 shims. Sometning like that is usualy the way to go. .004 backlash is tight. I'd try to get .005 if possible.

The axle bearings aren't always a tight fit. I've seen them loose like that before. I don't think it's a problem.

Hey Slo.... did you ever get those gears straightened out afterwards? Are they noisy? Do you recommend these gears for our cars as I am looking at getting these as well