when driving my truck around for the past few weeks I have been noticing what seems to be a knocking coming from the transmission mount/transfer case area, noise happens during accelleration from a dead stop (knocks 3 times then stops) when downshifting, when coming to a stop, and somtimes upshifting.

u-joints in both front driveshaft and rear driveshaft have been replaced, as well as the centering ball in the front driveshaft. the transmission and transfer case seem to work fine.


any input/ideas would be greatly appreciated, because this is really starting to get annoying.

 

Maybe the flex plate is loose.

 

now would be most likley to be loose at the crank or the convertor??? because it would suck if it's loose at the crank.

 

Check crankshaft end play also.. if thrust bearing is worn out will cause crankshaft to walk back and forth. Convertor bolts could then hit adapter plate on rear of engine block.

 

wow, that seems pretty serious, how likley is that to happen?? truck has a touch over 187,000 miles on it. (300,000 kms). would a wornout/ broken engine mount cause the same noise/effect??? either way I am checking the mounts once I get back from work. just hoping it somthing like that, rather than a loose flexplate etc...etc...

 

My truck is doing a similar thing in the same area and i found out my torsion bar was shot at the ball joint and the torque of up and down shift produces a loud clunk or some times a few of them. im at 177k maynot be your problem but i chased this one for a month and sounds similar

 

do you mean the track bar?? and where it attaches down by the balljoint, on the right hand side of the truck?

 

Since crankshaft is a very heavy mass of iron, it will move forward under hard braking condition. The thrust bearing is the only engine part preventing this from happening. If the thrust bearing surface is worn beyond spec's it will cause convertor bolts to rub on rear of engine. This will make a rapid tapping noise in rear of engine. I have seen this happen several times but only on high mileage engines. Moving the crankshaft by the front harmonic balancer you will hear and see the movement if excessive. Check with dial indicator.
CRANKSHAFT END PLAY SPECIFICATIONS
MIN 0.100 mm (0.004 in.)
MAX 0.430 mm (0.017 in.)
If the end play is good you should look elsewhere for noise. Possible broken flex plate can cause similar noises. Usually this noise will stop if engine is put under load but when in neutral or park can be heard, or when starting or shutting off the engine.

 

I am having a similar issue and just found that the support inbetween the tranny/transfer case and the crossmember is wasted. Two bolts sheared off in the trans or tcase I dont remember which but you cant miss it. It is a rubber vibration isolater/support. I have an 06 QCab with the six speed . I occasionally drive down my buddies extremly rutted out bouncy driveway if you can even call it a driveway. I think it must have happened there. Anyone else with this problem. Phil