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Old 10-28-2004, 12:59 AM   #1
bimmerboi318
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Angry Toasted Diff

This is kind of a follow up on the last discussion I had where I assumed my rear u-joint was worn and I needed a driveshaft. Well...my assumption was wrong. The knocking noise that was coming from the rear of my car got significantly louder over the past few days and seemed to catch or bind up every now and then. I put it on a lift in 3rd gear running and I could easily hear that the sounds were coming from the diff. Rats...Today I pulled the cover and saw that the pin thingy (very technical I know) that the planetary gears turn on had slid out and was hitting the pinion gear every time the diff rotated. It has slid out about a total of 1/16" or so. Needless to say there is damage that would make rebuilding it too expensive to be practical. The pinion has some nice chunks out of it, that pin is ruined, the carrier is probably worn from the pin moving around, the bearings are all probably shot from having so much metal floating around, which leaves me with a very nice diff case and not much else. Back to driving the Nissan hardbody for now...

I plan on buying a diff off ebay or something used. I was thinking a 3.91 LSD. My big question is, will this throw off my speedo or anything, because I know there is a speed sensor on the diff itself with its own tone wheel. But I do not know if this is dedicated to the abs or if it also supplies the speedo signal. Thanks.
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Old 10-28-2004, 01:04 AM   #2
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Be sure to get the correct size diff. Not all diffs will fit.
You need one made for a 4 cylinder.

I don't think changing the diff will throw the speedo off but your speed will be different at the same RPM as previous. I never remember f it will be higher or lower.
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Old 10-28-2004, 01:10 AM   #3
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A good place to get a diff is here... http://www.cherry-auto.com/
I've bought from them before, and got exactly what I wanted.

Buying another diff and putting it in will NOT screw up your speedometer, even though the speedo does in fact use that sensor in your diff.
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Old 10-28-2004, 01:11 AM   #4
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Oh, and if your current diff is lower than 3.91, adding a 3.91 will make each gear shorter, meaning at highway speeds the engine will be turning faster to go 70 than it used to.
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Old 10-28-2004, 01:17 AM   #5
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RPM Calculator

http://www.368s.com/tools_rpm.phtml?...f620dfc2944bf3
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Old 10-28-2004, 01:16 PM   #6
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The speedo reading is taken off the left rear wheel speed sensor not the diff
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Old 10-28-2004, 02:54 PM   #7
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Quote:
Originally Posted by Jeff Spooner
The speedo reading is taken off the left rear wheel speed sensor not the diff

Mine is a '95 and only has 3 channel abs. It doesnt have speed sensors on the rear wheels, only one on the diff. I believe later ones had sensors on all 4 wheels. I was just curious if it had a sensor on the trans output shaft as well, but I dont think it does. I guess as long as there are the same number off teeth on the tone ring, the speedo will be accurate.
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Old 10-28-2004, 03:11 PM   #8
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i found good aftermarket parts for cheep here www.thepartsbin.com
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Old 10-28-2004, 06:26 PM   #9
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Quote:
Originally Posted by bimmerboi318
Mine is a '95 and only has 3 channel abs. It doesnt have speed sensors on the rear wheels, only one on the diff.

Same here.
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Old 10-28-2004, 06:58 PM   #10
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Not on our cars. Unplug your differential sensor and see if your speedo is working?


Quote:
Originally Posted by Jeff Spooner
The speedo reading is taken off the left rear wheel speed sensor not the diff
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Old 10-28-2004, 08:39 PM   #11
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Actually, my 96 M3 w/ 4 channel abs got its speed reading from the diff as well! Jeff, what are you driving?
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Old 10-28-2004, 08:46 PM   #12
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OK, OK I have been working on to many 740 BMW's latley. it is in the diff. I do know where there is two brand new 4cyl lSD diffs if any one is intrested.
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Old 10-29-2004, 02:05 AM   #13
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That's ok Jeff, I appreciate the help and know you're a good source for info seeing as you're one of the few (if not ONLY) BMW techs on the board.

So, speedo should remain accurate.

BTW how much do one of those lsd's you weren mentioning cost? I'm kinda leaning towards a used one off of ebay in the range of 200-300 bucks...but maybe if the price is right it might be worth it. Thanks.
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Old 10-29-2004, 06:05 AM   #14
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I think they want $750 each. they sell for around $1200 new. call me if you want more info tomorrow 803-551-1070
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Old 10-30-2004, 01:58 AM   #15
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I have the original diff from from my ti. Let me know if you are interested.
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