LOUD thump when taking off!!!!! wtf?

[carfox]

it seems to be coming from the transfer case, front drive shaft.

the U joints seem fine, i can wiggle the drive-shaft with little play, i think its mostly gear play, not U-joint play...

any ideas on what more i could check? the transfer case and everything functions very smooth in all gears with no noise.. but you can feel this THUD in your seat when you take off from a stop....

anyone else have this problem? what was it?

 

[RonD]

Check torsion bars/bushings

 

[carfox]

Check torsion bars/bushings

no moving parts in a torsion bar... its a spring.

 

[carfox]

im pretty sure its the transfer case chain.... so.... ffffffffuuuuuuuuuuuuuuuuuuuuuuuuuuuuck.... thats not cheap...

this isnt even a good 4x4.... no front locker and no posi in the rear, and no skid plates anywhere on the whole truck.

 

[carfox]

i went to change out the transmission mount.... turns out i bought the wrong part and put the stock one back in
(which turned out to be fine anyway)
then the sound went away!.... for a few hundred yards...

any idea what this could be?

 

[carfox]

how could it be the torsion bar?
im curious
has NO ONE else seriously had this problem before?

 

[RonD]

torsion bar does use rotational torque to dampen up and down suspension movement but it also prevents axle roll because of it mounting location.
If torsion bar bushings/mounting under cab were worn/loose the axle roll could make a thumping sound felt in the cab.
And it would often be noticeable mostly when accelerating, or braking, when axle roll can happen, depending on how it is worn out.

 

[carfox]

thanks!

torsion bar does use rotational torque to dampen up and down suspension movement but it also prevents axle roll because of it mounting location.
If torsion bar bushings/mounting under cab were worn/loose the axle roll could make a thumping sound felt in the cab.
And it would often be noticeable mostly when accelerating, or braking, when axle roll can happen, depending on how it is worn out.

i have never heard of, or, experienced this with IFS suspension though....
what should i look for? how could i test this?

I had a full sized chevy before this, the suspension is very similar.
the A-arms are quite sturdy and the cross member is solid.

 

[Grey_04]

A broken bolt in the sway bar end links could make the noise described. the sway bar bolts run through a tube so examine them closely for damage.

 

[carfox]

Found it!

good suggestions.......... but we were both wrong...

i lifted up the truck so both front tires were off the ground, then i rocked the truck side to side so one tire would touch the concrete, then the other.... its the ball joints. lower ball joints.
you can see the tire touch, the ball joint move, then POP, when the tire went back up in the air... there is slop in the ball join in the lower A-arm.

and my heater hose vacuum actuator is leaking... Fix Or Repair Daily LOL

thanks everyone!

 

[RonD]

Good work finding the source of the noise

And thanks for posting the follow up