4speedfunk
Well-Known Member
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So for the past month or so, I've been noticing a strange "thud" when I come to a complete stop...and a similar "thud" when I hit the throttle to take off. At first it felt like something was loose (similar to the dreaded cross-member bushing), but since the SAS...I don't have a crossmember anymore. Clearly it was something rotational and heavy, and it felt like it was coming from the rear half of the truck. Something was rocking back & forth based on my braking and throttling...obviously induced by axle wrap. Immediately I thought of a sticking caliper, a bad motor mount, loose U-bolts, broken leaf spring, smoked spring bushing, etc. So I crawled underneath and despite numerous double and triple checks...I found nothing. Then I spoke to a buddy that told me about the same exact problem he had on his bone stock 2004 GMC-2500HD:
The issue is that the rear driveshaft slip-yoke is sticking on the splined output shaft of the t-case (it happens on 2WD trucks too). When you take off...the yoke suddenly releases and slips forward. Then when you come to a stop...it suddenly releases again and the yoke slips rearward. This creates a soft and heavy "thud" that doesn't really hurt anything...but it is annoying. All trucks will have a certain amount of movement at the slip-yoke but, mine is probably more prone to sticking due to the increased angle of the driveshaft (6" of lift). There is a GM service bulletin for this problem and it can happen on many post 90's GM trucks...lifted or not. Apparently the problem has to do with the type of metal the yoke & and output shaft is made from...its more prone to galling and sticking than the pre-90s materials. Perhaps this explains why the issue is more common on newer trucks.
The fix? Pull the shaft out...pour an ounce of ATF into the yoke...roll it around and get the splines coated...then re-install it back into the T-case. Give it a few good ole "in-out / in-out" strokes to make sure the splines are completely coated, then bolt the shaft back into place. The slip yoke should be nice and slick...so it is free to move back & forth without sticking. That's all there is to it! Wish every weird noise on the H3 was such an easy fix!
The issue is that the rear driveshaft slip-yoke is sticking on the splined output shaft of the t-case (it happens on 2WD trucks too). When you take off...the yoke suddenly releases and slips forward. Then when you come to a stop...it suddenly releases again and the yoke slips rearward. This creates a soft and heavy "thud" that doesn't really hurt anything...but it is annoying. All trucks will have a certain amount of movement at the slip-yoke but, mine is probably more prone to sticking due to the increased angle of the driveshaft (6" of lift). There is a GM service bulletin for this problem and it can happen on many post 90's GM trucks...lifted or not. Apparently the problem has to do with the type of metal the yoke & and output shaft is made from...its more prone to galling and sticking than the pre-90s materials. Perhaps this explains why the issue is more common on newer trucks.
The fix? Pull the shaft out...pour an ounce of ATF into the yoke...roll it around and get the splines coated...then re-install it back into the T-case. Give it a few good ole "in-out / in-out" strokes to make sure the splines are completely coated, then bolt the shaft back into place. The slip yoke should be nice and slick...so it is free to move back & forth without sticking. That's all there is to it! Wish every weird noise on the H3 was such an easy fix!
