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I have a later model LSD diff in my '69. After blasting around a couple of days with a fresh motor I am noticing an odd thumping up front (under the driver's feet) as I pull out of a dead stop up to about 3,000 rpm and again shifting into 2nd. In the process of troubleshooting this, I raised the rearend and noticed that I've got a fair amount of play when I turn the tire before the driveshaft reacts. Does this indicate that the LSD plates need adjusting or is there bearing/gear failure ahead? Also, does it seem possible that the thumping noise/vibration is from the diff?

I have checked the dougnut, the driveshaft intermediate bearing and the exhaust pipe but none seem to be in play.

Thanks,
 

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The play sounds like the pinion to ring gear depth is out of adjustment.

The lsd would make the other tire move. I don't know of a way to test it other than feel. Try an on ramp with a tight curve. When the inside rear is light if you stomp on the gas the lsd should help the car drive forward, if it is slipping the inside tire will spin with little or no drive to the rear.

Regarding the thunking in front...check your bell housing for cracks and tightness of all mounting bolts. Sometimes a few loose fasteners allow just enough movement to start a crack in the bell.
 

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well, how do you test if you have an LSD, can you more a tire with the car jacked up, then if the other tire moves one way it means something, but if it moves the same way as the tire you are spinning it has posi... I don't remember. I think is you spin one wheel clockwise and the other spins counterclockwise then it is an open diff, but if they spin the same way it is posi, but how can you tell if its LSD?
 

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....spiders!.:eek:.spiders!..:eek:. i see too many spiders!... it's freeking me out.....:D
 

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The 2L posi (LSD) doesn't typically lock up until a load is put on it. So you really can't tell if it is working just by jacking up the car and spinning a wheel. One way to know, however, is to put it in first gear, rev it to about 4000 rpm and drop the clutch. If both rear wheels spin, your posi is working. If only one spins, it isn't!:)

Erik
 

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Erik is right about the LSD. only if the LSD is built with an internal preload will the wheels spin together when jacked up in the air. but then, the friction plates would quickly wear down and remove the preload, anyway.

about the thumping, i would triple check over all three joints in the driveshaft, since that is by far the most common source for that condition and kind and of sound. exhaust is doubtful, since that would most likely cause a buzz, not a thump - unless you were seriously bogging the engine, causing it to shake violently, and the exhaust was banging against something. speaking of shaking violently : check the engine & transmission mounts ?

ps. i like Erik's LSD test ! fun, and maybe that will help to explode the worn out giubo that you couldn't diagnose :)
 
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