What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[cfmistry]

hmm, I would check your motor mounts and front diff mounts also

So the front diff mounts look solid - not sure how to test them. The motor mount on the other hand, seems like my driver's side is gone. Could that be the source of this strange clunking on acceleration?

 

[Doubeleive]

So the front diff mounts look solid - not sure how to test them. The motor mount on the other hand, seems like my driver's side is gone. Could that be the source of this strange clunking on acceleration?

Yep, to check the front diff mounts I would jack it up so the front wheels are off the ground and then stick a crow bar or pry bar up in there and try to move the diff up & down, the rubber mounts should give a little but be firm. the motor mounts you can check with the hood open (so you can see the engine) and get in with your foot on the brake and put it in drive and give it some gas with the brake applied firmly and the same with it in reverse, the motor will move but you should be able to see if it just slams or has some tension, bad motor mounts are pretty common on the gmt900's the fix is to replace them with the hummer motor mounts which are solid rubber instead of a liquid filled. there is a couple of lengthy threads on here about it.

 

[iamdub]

Ok, I'll bite.... why the two stroke oil???

Two-stroke oil, particularly TC-W3 rated, has been known to clean the fuel system and protect against corrosion from the elevated alcohol content in modern gasolines. It's also a protectant for the hard parts and is used in rotaries for the apex seals, which would be equivalent to our piston rings. Yes, mine is a FlexFuel so the fuel system is designed for alcohol. But running it still satisfies my mind and it's cheap and harmless, especially at the one ounce per five gallon ratio it is used at. I had been running it for a few months before I modded the motor and I might have noticed smoother idling. But I didn't run it long enough nor do I drive it enough to really be able to tell. Surely can't tell anything now with the cam's idle. My cruising MPG on 93 now is better than before I disabled AFM, so I can't compare anything there, either.

 

[cfmistry]

Yep, to check the front diff mounts I would jack it up so the front wheels are off the ground and then stick a crow bar or pry bar up in there and try to move the diff up & down, the rubber mounts should give a little but be firm. the motor mounts you can check with the hood open (so you can see the engine) and get in with your foot on the brake and put it in drive and give it some gas with the brake applied firmly and the same with it in reverse, the motor will move but you should be able to see if it just slams or has some tension, bad motor mounts are pretty common on the gmt900's the fix is to replace them with the hummer motor mounts which are solid rubber instead of a liquid filled. there is a couple of lengthy threads on here about it.

So paying real close attention, the clunk is when I let off the brakes after moderate-hard braking. Before I even touch the accelerator. Makes the engine mounts a less likely source right?

 

[Doubeleive]

So paying real close attention, the clunk is when I let off the brakes after moderate-hard braking. Before I even touch the accelerator. Makes the engine mounts a less likely source right?

Not sure on that one, mine was clunking on acceleration and it turned out to be the front differential mounts

 

[Tonyrodz]

So paying real close attention, the clunk is when I let off the brakes after moderate-hard braking. Before I even touch the accelerator. Makes the engine mounts a less likely source right?

Have you checked your caliper sliding pins? Sounds brake/caliper related to me.

 

[wjburken]

WTF???

x2!

 

[wjburken]

So paying real close attention, the clunk is when I let off the brakes after moderate-hard braking. Before I even touch the accelerator. Makes the engine mounts a less likely source right?

How are your CV joints?

 

[Tonyrodz]

How are your CV joints?

Would that be more like a clicking noise?

 

[wjburken]

Would that be more like a clicking noise?

Usually, but worth checking. Something is going slack and then taking up slack when slowing and going. If the front differential mounts are good, motor mounts are good, and calipers seem to be sliding, I’d be looking at all other parts of the drive train just to be sure.