drive line noise

[74X4Burb]

I got a '74 1/2 ton suburban, and its got a viberating (cant spell) grinding noise that starts when ya hit about 65, sounds like its coming from the transfer case/rear end. we have had it in a couple times, had the u joints done,last time we had it in the transfer case bearing was hashed.none of this has seemed to help though.This beast has been converted to part time 4x4 (it made the same noise before)it has less then 5000 miles on rebuilt 350, less then 6000 miles on tranny it has an np203 tranfer case, the only thing I can think that it might be is a wheel bearing,or some thing in the rear axle.any one got any ideas on this one. thanks.Karl

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Vaporizers

 

[eugene68]

I would suggest connecting a tachometer to it, run it up to 65 m.p.h. or whenever it starts to vibrate, write it down, then drop to another gear,(slow down first!) go up to the same rpm that it was running when you were driving 65 mph,, if the vibration is there, then it probably is in driveline somewhere,,, if the vibration is not there, then it is probably in the wheel balance/bearings.... the theory behind this test is the fact that the engine runnning the same rpm in different gears will be spinning the driveline at different rpm(speed). If the vibration is not there check to see that u-bolts are good, and the driveline is straight... if it is there,, then check your wheel balance,wheelbearings, rearend,,tranny..etc....something to do with the harmonics of the crankshaft,tranny,driveline..etc...
I read this in old GM SERVICE REPAIR MANUAL..
hope this helps you.
anyone else have any suggestions???
let us know if this helps.
eugene

 

[74X4Burb]

Thanks.I'll have to go buy a tach.Karl

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Buy extreme vaporizer

 

[75_stepside]

i had the same prob on my 2wd and the drive shaft had lost the balance weight off of it and it was slightly warped. went a bought a new one and solved my prob , hope it does the same for you.

 

[87_silverado]

here is a suggestion, remove the drain plug on your transfer case and look for links off the chain.if you do see some links in the bottom of the tranfercase the chain may have started seperating and is mostlikely riding on the viscus hub.(been there and bought that t-shirt)if this is the case you will have to pull the tranfer case and seperate it, replace the chain and viscus hub.(new chain is about $75 dollars and you may be able to find a used viscus hub at a 4-wheel shop for about $100.)