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Discussion Starter #1 (Edited)
In setting up my 8.875 12 bolt with a Richmond 3.73, I've now got a good repeatable .008 backlash. Pinion preload is around 22 inch pounds. About 30 with the carrier in. All I can say is thank god for "Super shims". How would you get a stack of thin shims in otherwise?

My pattern now shows a very noticable high bias toward the crown and slightly toe on both Drive and coast. Pattern shows no marking compound visible at the crown whatsover. I Feel the pinion is too shallow, and needs to be moved out towards the carrier.

Following BGH's "Forget pinion depth measurement" and for right or wrong, a recomendation I saw on line on a Hot Rod magazine tech tip. It recomended a starting point of a .025-.027 pinion shim with a 3.73 gear. I realize I have to go bigger on the shim, but how far should I initially go? .002, 005 or more?

How much would you add? And was .027 a reasonable starting point, or was I way off?

Any thoughts?

Cheers, Mark.
 

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I start at around .037 on a 12 bolt. Can you post a picture of what you have now? If not, can you send it by email? Most of the time if I think I am pretty close then I make moves of .003 until I get real close, then move .001. If you think you are off pretty far then make moves of .005 to .007 and see what happens.
 

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pictures say a thousand words. either me or big gear head or somebody will try to help you but got to see the marks on front and back of gear.
 

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hard to tell somewhat but when you look at the pinion on the gear there is a line where they put the 2 together you want to be at that line look at bottom of a gear you will see it. it will be a different color than rest of gear. than you got good depth on gear.
 

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Discussion Starter #7
Thanks guys,

Ok, way shallow as suspected. So it's up to about .036 I go. Sounds good.

jaguareats, the line your talking about, do you mean the slight machining line you see near the root of the pinion gear faces, running toe to heel?

Cheers and thanks, Mark.
 

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The drive and coast look very centered - are you checking the backlash correctly?
 

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Discussion Starter #9
Mike, I suppose I am. I'm using a dial guage with a magnetic base. Keeping the shaft of the dial indicator as low as possible to the tooth being read (without the indicator touching the tooth below), and parrallel to the ring gear itself. Checking in 4 spots around the ring.

Well, here's todays results. Backlash of .008 spot on all round. Pinion preload of about 20, rising to 30 with the carrier shimmed in. Solid spacer kit instead of crush sleeve. Using .038 worth of shims on the sleeve. Pinion nut to 140ft/lbs. Carrier side shims in tight.

Now with .035 worth of shims on the pinion. The first result had .027.

Drive



Coast



Cheers, Mark.
 

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That is much better. Are you using an axle to turn the differential when checking the pattern? The coast pattern looks like it wasn't wiping the compound off completely. It is hard to tell exactly what the coast pattern is. The drive pattern looks great. I think I would try .034 and see if the coast pattern looks a little better.
 

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Can I break in and ask Freddie a question? What is the right way when marking? I usually turn the pinion while putting a little load on the axle. But I'm not sure if that's right or not.
 

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yes then you look at pinion gear on bottom of gear it is darker than rest of gear.that is where the line should be at. if it is closer need a shim to bring it out. if closer than that bring it out means lesser shim. but go little like .002 it goes a long way lol. i always go with original (if a old gear set was in there take old shim under pinion bearing and put in there)gms like original but doing a dodge or ford different story tho.
 

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guess my last posting go through at 1040 those pics look alot better looks like you got it right remember when you look at pinion gear on bottom it is darker than other part of gear when your line of chalk is there you got it. when up and back stroke of pinion hold pinion and do complete spins of yolk dont stop it screws up pattern
 

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Discussion Starter #14
Yes Freddie, I'm using an axle to turn the gearset.
I'll shim down and try .034 next. But I'm tempted to go .033 or even .032!
But I'll stick with the advice given. Thank you all.

Cheers, Mark.

BTW, I found a great old local automotive machine shop (in a Carquest store) that can press off my bearing without touching the race. A great oldschool guy runs it. Ten bucks off and on, not bad since he even likes to drop everything and chat cars for a while! Just around the corner, and I never even knew that parts store had such a little treasure out in back. So in this case, it's no hassle to change shims at all. LOL!

Later.
 

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Mark,

It looks much better now. You basically want the contact point centered on both sides, and as wide and long as possible.

PS - I hold the carrier and turn the pinion to run a pattern
 

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go2fast, I always turn the ring gear against the pinion. If the pinion bearing preload is set correctly then it will have enough resistance to mark the ring gear well. Don't turn the pinion, you won't get as good of a mark as you do the other way. You can use a wrench on a ring gear bolt to turn it. If I'm building a rear end with a posi (and most of the time I am) I use an axle to turn it. This makes it easier to turn without stoping. Any time that you have to stop with the gears in contact where the marking compound is then it will make lines in the pattern. It is best if you can turn it without having to stop.
 

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go2fast, I always turn the ring gear against the pinion. If the pinion bearing preload is set correctly then it will have enough resistance to mark the ring gear well. Don't turn the pinion, you won't get as good of a mark as you do the other way. You can use a wrench on a ring gear bolt to turn it. If I'm building a rear end with a posi (and most of the time I am) I use an axle to turn it. This makes it easier to turn without stoping. Any time that you have to stop with the gears in contact where the marking compound is then it will make lined in the pattern. It is best if you can turn it without having to stop.
Thanks for the tip!
 

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Discussion Starter #19
I'm turning it with an axle, but I've gone one better. I've bolted up a brake rotor to the flange. Makes it easier to turn, as well as to steadily slide the axle in and out of the carrier, without clanging the splines around inside the tube. It really helps!
 

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Discussion Starter #20
Ok, heres the latest.

Now using a .033 shim in place of a .035. Backlash a little looser at .009.
Same preload.

Drive with .033 and .035 to the right



Coast with .033 and .035 to the right



Cheers, Mark.
 
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