thud when accelerating

[Teahead]

got urethane diff bushings (all three), yet still got this thud.

how to check if my driveshafts and/or u-joints are bad?

I went underneath and twisted the shafts by hand, but both were tight.

hoping it's not pinion lash/slop in one or both diffs.

or worse, transmission output shaft loose.

trans was built about 30k miles ago

 

[wpage]

Have you contacted the company that did the tranny?

Record the sound and play it for them.

 

[Happy Hummer]

Remove drive shafts and check each of them. Block the wheels.

 

[rascole]

Check the transmission mount. Bad bushing or loose bolts will appear normal when sitting still.

 

[4speedfunk]

Could be lots of stuff...

Motor mount.
Front shock bolts.
Skid plate bolts.
Front driveshaft.
Ball joints.
T-case chain.
Rear driveshaft.
Excessive lash in one or both diffs.

Can you describe the "thump" better?
Does it happen from a dead stop (or from a slow roll)?
Does it happen every time?
What percentage of throttle induces the thump?
Have you tried power-braking the vehicle, with the hood up? If its bad motor mount, you will see the entire motor raise up a couple inches, and sit back down when you relax the throttle.

For what its worth...I'm working on an 09 Alpha T right now. I discovered the tranny mount had no bolts whatsoever! Gravity was the only thing holding the mount in place (sandwiched between the crossmember and the tailshaft).

 

[Teahead]

Not sure if it's motor mounts as doesn't do it in P or N.

Doesn't happen all the time. Of course, if I feather the throttle, it won't do it.

It doesn't really make a sound; if it does, it's real faint; it's mainly felt.

I'd say, if I'm rolling/coasting at 15mph and I step on it say, 25%+ throttle, I'll feel it.

Front shocks are new, installed by pros. Ditto all bushings up front and new control arms.

Can I remove just the front driveshaft and drive around like that to further isolate things?

 

[Teahead]

Tranny mount LOOKs fine, but can't be 100% sure.

The transmission like I said, was rebuilt maybe 30k miles ago by the PO, so I doubt they'd (have the receipt so done by pros) put in a bad mount.

 

[Teahead]

Oh duh, ya, let me power brake it (or wife) and see what the motor is doing.

The motor was ALSO done (rebuilt) by the PO, so I doubt they'd put in a bad motor mount back on.

 

[BertaBumpkin]

i'm having a very similar same problem, i've started a mission to replace all the bushings but if it's anything else i'm not going to be a happy camper
edit: mine mostly happens if i'm driving at around 40mph , let off the gas, and as soon as i touch the gas again, clunk. lower speeds i don't notice it

 

[Teahead]

Here's a video of me turning by hand the driveshafts.

Not sure if that's a legit test or not to test for bad u-joints, diff play, etc.???

 

[4speedfunk]

Looks normal to me. These trucks have sloppy drivelines. At that mileage, you should probably replace the t-case chain…but I would not expect a huge improvement.

As for the ring & pinion lash…you can’t really judge that from grabbing the driveshafts. This is because some of the looseness you feel could be the spider gears. To check properly you must pull the driveshafts out, pull off the diff covers, and put a dial indicator on the ring gear teeth. I can tell from your video that your axles are probably okay. I look at lots of these and I don’t see anything alarming.

A heavy “thump” when transitioning from coast to drive is probably something else. Something big is rotating back & forth during the transition. I still suspect motor mounts or maybe rear leaf spring (shackle) bushings. At that mileage, the bushings (all of ‘em) are done.

 

[4speedfunk]

A sticking caliper can create a thump, but only when using the brakes. You might take a drive and put the AT in 2nd or 3rd gear. Then roll on/off the throttle using engine compression to twist the driveline back & forth. This will tell you if the thump occurs without using the brakes.

 

[Teahead]

Interesting is from a standing stop, and I accelerate rather briskly; no thump.

And if I'm going >40mph, and I accelerate, hardly if at all, noticeable.

It's most noticeable at 15-20 mph then hitting the gas.

Front driveshaft doesn't look OEM, but who knows? Could be a POS causing this issue.

 

[Teahead]

OK, so found the issue.



Removed the front driveshaft. twisted the cv joint and rest of the driveshaft in my hand. can definitely feel/hear a click.

Drove the rig without it. NO CLUNK!

Guess I'll be buying all the Spicer parts to build a double cardone driveshaft and have one made.

 

[rascole]

OK, so found the issue.



Removed the front driveshaft. twisted the cv joint and rest of the driveshaft in my hand. can definitely feel/hear a click.

Drove the rig without it. NO CLUNK!

Guess I'll be buying all the Spicer parts to build a double cardone driveshaft and have one made.

Or, buy the ready made unit from Outfitter Design. Turn key and no headaches and guessing.
https://www.outfitterdesign.com/h3-front-driveshaft.html

 

[Teahead]

Right, but I can't find anyone who has run that.

So for a bit more money, getting one exactly built like from this thread:

Everything you wanted to know about H3 Front Driveshafts (and more).

Okay...I stopped by the driveline shop today, and here is some additional info: In addition to the Cardan parts & u-joints listed above, you will also need some driveshaft tube, a 1310 slip yoke, and the slip stud. These are the items you have circled in my photo, and they go on the front end...

hummer4x4offroad.com

 

[Jeepwalker]

If the rest of the driveshaft is in good condition...I'd see how it goes with the Spicer. How do the trunions look on the front u-joint? Might consider replacing that. And perhaps, mark the driveshaft yoke and shaft and remove/degrease and put back together with grease. Maybe even add a zerk to the yoke. Then you're set.