"THUNK" in the left rear end

[jniolon]

2008 Suburban (same one discussed in the towing stuff thread) has developed a "thunk" when you accelerate from a dead stop. Feels and sounds like on the left side. If you pull off slowly, no thunk, but if you press it a little hard...thunk. We put it on a rack and looked all over and see nothing loose, all bushings look good, everything we shook or pried was tight even whether rear end was unloaded or loaded.

We removed the left rear wheel and rotor looking for problems there and found nothing OTHER THAN the caliper seems to freeze to the rotor when the brakes are applied and released.. pads are good.
We removed the caliper and rotor and tried it again and the thunk was there but very light. There is about 1/8" end play in the axle and maybe a 1/16" of play up and down. which is more than spec but I don't think it's excessive.

I read a thread on the information cul-de-sac that said it might be the slip joint on the driveshaft. we removed shaft and greased the slipjoint well...still thunks. My next try will be to have a friend with a scanner hook it up in run mode and check the ABS and such for a problem. Suggestions, comments, SWAGS and experienced fixes are accepted.

thanks
john

 

[Joseph Garcia]

Did you check the motor mounts?

Did you check the front differential mount bushings?

 

[jniolon]

hmmmm, didn't check motor mounts, that IS an old chevy problem...I'll check that today, the front mount bushings seem good

j

 

[iamdub]

2008 Suburban (same one discussed in the towing stuff thread) has developed a "thunk" when you accelerate from a dead stop. Feels and sounds like on the left side. If you pull off slowly, no thunk, but if you press it a little hard...thunk. We put it on a rack and looked all over and see nothing loose, all bushings look good, everything we shook or pried was tight even whether rear end was unloaded or loaded.

We removed the left rear wheel and rotor looking for problems there and found nothing OTHER THAN the caliper seems to freeze to the rotor when the brakes are applied and released.. pads are good.
We removed the caliper and rotor and tried it again and the thunk was there but very light. There is about 1/8" end play in the axle and maybe a 1/16" of play up and down. which is more than spec but I don't think it's excessive.

I read a thread on the information cul-de-sac that said it might be the slip joint on the driveshaft. we removed shaft and greased the slipjoint well...still thunks. My next try will be to have a friend with a scanner hook it up in run mode and check the ABS and such for a problem. Suggestions, comments, SWAGS and experienced fixes are accepted.

thanks
john

I agree with @Joseph Garcia- check the motor mount(s). My bet is the driver side has failed. If you see rust-colored stains around it (or both of them), it/they've ruptured and leaked. Just hold the brake hard and sharply goose the throttle with trans in D while someone watches the engine. If it jumps and clunks, I, and many others would strongly suggest you replace it with an OEM Hummer H3 mount: GM part no. 25847739. You can replace your LH and RH mounts with this if you want to replace both.

 

[Just Fishing]

Did you check the motor mounts?

Did you check the front differential mount bushings?

^ this

I got a clunk in the rear when taking off, but only sometimes.
i thought it was something in the rear, and got put in my "to do list"

Right now I'm building a new engine, and when pulling it i found my driver side mount was toast!

 

[Walchit]

Sway bar bushings? I have a broken bracket and get the thunk when my foot is feeling heavy

 

[OR VietVet]

Check the rear control arms for looseness and loose mounting bolts.

 

[exp500]

U Joints maybe?

 

[Dustin Jackson]

2008 Suburban (same one discussed in the towing stuff thread) has developed a "thunk" when you accelerate from a dead stop. Feels and sounds like on the left side. If you pull off slowly, no thunk, but if you press it a little hard...thunk. We put it on a rack and looked all over and see nothing loose, all bushings look good, everything we shook or pried was tight even whether rear end was unloaded or loaded.

We removed the left rear wheel and rotor looking for problems there and found nothing OTHER THAN the caliper seems to freeze to the rotor when the brakes are applied and released.. pads are good.
We removed the caliper and rotor and tried it again and the thunk was there but very light. There is about 1/8" end play in the axle and maybe a 1/16" of play up and down. which is more than spec but I don't think it's excessive.

I read a thread on the information cul-de-sac that said it might be the slip joint on the driveshaft. we removed shaft and greased the slipjoint well...still thunks. My next try will be to have a friend with a scanner hook it up in run mode and check the ABS and such for a problem. Suggestions, comments, SWAGS and experienced fixes are accepted.

thanks
john

@jniolon Pop your hood, put it in Drive, hold your foot on the brake and give it throttle till about 3000 RPM, if you motor moves around you'll have found your problem. I had the same problem and it was the driver motor mount.