8.8 diff backlash

I recently purchased a 95 Mustang GT. I have a vibration from 90 MPH and up. I've pinpointed it to the diff. The gears were changed to 3.55's, but the
set up was not well done. I checked the backlash and I have .020 backlash, which I think is too much. I checked my shim thickness, LH 0.251, RH 0.388. I want to bring the backlash down .010. So, I need to reduce .020 on the left and add .020 on the right. I need 0.231 on the left and 0.408 on the right. Ford does not make the shims in these sizes. I'm assuming the pinion is set too far out. So my question is, Is there some kind of calculation, or does someone know how to set the pinion depth, with the info given, so I can adjust the backlash properly with the side shims available? So that I do not have to buy the tool to set pinion depth. Example, adding a .005 shim to the pinion to get less backlash. In other words, adjusting the backlash with pinion depth. I know, this one's a doozy. Thanks in advance, Steve
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Don't use pinion depth to adjust backlash.
Pinion depth is set long before backlash is adjusted, pinion depth is set where it is supposed to be and then left alone. To be done properly, it should be done with the proper measuring tools. The ProForm tool is $100 thru Summit racing. Aftermarket side shims for backlash can be had from any of the common vendors that deal with rear axle parts, Randy's Ring and Pinion is probably your best bet. the aftermarket shims can be combined to achieve what ever size you need. Backlash and bearing preload need to be considered all at once when selecting the correct shim size.
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On Fri, 09 Sep 2005 19:25:24 GMT, aarcuda69062

this would depend on gear pattern both pinion and ring may have to be shimmed to find suitable pattern i have pinion bearings which have been ground out a bot for ez removel and addand subtract shims to achieve a proper pattern
h u r c a s t
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snipped-for-privacy@hotmail.com wrote:

No point patterning a set up that is known to be assembled wrong and has way too much backlash.

Indeed, that is the procedure. The OP would be well advised to start from scratch, or have someone with the tools and knowledge to start from scratch.

Mine aren't "ground out", I had them honed on a Sunnen Rod hone.
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Would it not be simpler to use the correct tools (which your dealership should possess) to select the correct pinion shim in one simple operation? I would think that a Master tech would have passed Specialty 36 and learned how to use these tools.
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On Sat, 10 Sep 2005 00:48:29 GMT, "Jim Warman"

warman admitts to steeling tools
THIEF
hurc ast
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and the resident rectal orifice admits to being an idiot that has no idea what is going on in real life.

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Hi Jim, I'm not a Ford technician, so I don't know what specialty 36 is. I am however a GM tecnician and have been doing trannys, transfer cases, and diffs for years. Unfortunatly I don't have access to the tool required to set pinion depth, and don't really want to buy it for a one time use. That was the purpose of my question regarding backlash and pinion depth. You don't think setting my pinion in 5 or 10 thou will help me set my backlash properly with the shims available from Ford?

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Steve, just for your information, Jim was not flaming you with that spec 36 tidbit, but rather baiting the resident rectal orifice that this week is going by the name of fordman something or other, and signs off as hurc ast the rectal orifice. his sole reason for posting here is to give people bad, dangerous advice, and to start flaming wars.(hurc that is)

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wrote:

lmfao tell em how its done tom i need a laff
hurc ast
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duh........... I just did, dipstick

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wrote:

jim is no technician he is an oil boy
h u r c a s t
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"Steve" wrote:
I don't have the tool required to set pinion depth, and don't want to buy it for a one time use. That was the purpose of my question regarding backlash and pinion depth. You don't think setting my pinion in 5 or 10 thou will help me set my backlash properly with the shims available from Ford? __________________________________________________
The pinion depth shim is intended to align it with its matching ring gear for perfect mesh. The ring gear shim is used to establish the correct backlash.
Think of the pinion near the ring as a cone near a ramp. If the ramp angle is 30 degrees for example, the pinion could be moved .020 axially to bring it .010 closer to the ramp represented by the ring gear. However, if this were done, the movement would mismatch the meshing geometry, leading to higher shear loads, early wear, and ultimate failure.
Good luck.
Rodan. ____________________________________________
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Sorry to come back in so late, Steve... If worst comes to worst, using a frsh shim the same thickness as your old shim should put your pinion depth within about 2 or 3 thou of desired. While not the best situation, it is seviceable.... Tooth contact patterns can be ever so imprecise at the best of times.... one tech might say it looks a tad to the heel - another says it looks good and another may feel it's a bit toward the toe... As techs, one of the worst things we can do to ourselves is to get lost in that neverland of shim swapping.
I've been forced to work in some pretty primitive conditions in the past.... I've seen diffs that should have howled like a coyote in heat that were quiet... seen diffs start out with a noise and get quiet and seen diffs start out quiet and get noisey....
Now that I have access to the tools (why steal them when I can use them whenever I want..... though most big city shops refuse to give their techs keys...), I prefer to use the tools and remove interpretation from the equation. For your case, you have to start somewhere..... if you can't beg/borrow/rent the tools, subbing the original size shim should deliver a reliable repair most of the time.
HTH

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I had also considered what you're saying Jim but from the sounds of his first post, he bought the car this way and the original shims are long gone. Thus, he really really needs to do an actual measurement.
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You are trying to cure a high-speed vibration by adusting back-lash ? I think your barking up the wrong tree. Try balancing and rotating tires. If the rear-end isn't making any noise I wouldn't worry about it.....
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