Grinding noise

[camper95GMC]

Hey,
New to the forum, I have a 1995 GMC ex-cab SLT 4x4 with 178,000 miles, no major motor work or transmission work. I have noticed a grinding noise right before it downshifts to first, sounds like the drive shaft u-joint checked it and seems to be ok. Has anyone else experienced this problem. Thanks!!

[stumpuller454]

do you have a manual or automatic trans? (:

[junior3382]

you say a grinding noise, but then mention the u-joint.... is more of a clunking then a grinding? I ask because actual grinding could lead me to think more of a tranny problem, whereas a clunking could be the u-joint, or even the center bearing in the rear axle. Is it only when you down shift? or is it also there when you take off, or use reverse?

[stumpuller454]

Originally Posted by leolkfrm

tranny fluid does not leak thru the slip joint on a driveshaft!

IT CAN cause it did on my darn 80 gmc... noting alot of silicon didn`t fix, there was a pressed in cap in the end of the joint, silly thing eventually started seaping enough to cover the botom of the truck with gear oil!

Although most slip joints are designed in one peice now to eliminate this...

So whats this tranny?

[camper95GMC]

Originally Posted by stumpuller454

do you have a manual or automatic trans? (:

4 speed auto .I Think its a 4L60E. 1Pc drive shaft. It seems like it does it while lugging right before it downshifts. Its not a clunking noise at all. It also does it when pulling out (more so on a hill ) and also backing up. I have changed the tranny fluid and filter and also changed the transfer case fluid and it made no difference whatsoever. I had a S-10 (4sp man) that sounded similar before I would have to downshift.

[stumpuller454]

hmmm have you checked your rear diff fluid? maybe your pinion brgs have gone out and the gears are interacting in an unatural way... would be most noticable during load changes...