1991 Sierra K2500 automatic trans "clunking"

[sr17]

My truck is "clunking" (for lack of a better word) when switching between forward and reverse.

My uneducated guess is that it is not a worn u-joint issue since the drivetrain is otherwise nice and tight when driving.

The transmission shifts very smoothly when driving.

Fluid is clean.

Any ideas what might be going on here?

 

[SteveSRT8]

Typically we would look at the transmission mount on the crossmember, check the motor mounts, too.

FWIW it's sounds like you are describing bad u-joints...

 

[bubbatime]

Safely climb under it while transmission is in neutral and twist the drive shaft. If you feel a lot of play, then the u-joints need replaced. If not, then look at the transmission cross member, and then the motor mounts.

 

[ARCOgraphite]

Thinking this is normal for a truck - most of mine did it when new. Most play is in the 3rd member - ring and pinion play. Did the truck get a rear diff lubricant change after break in? That about all it needs unless you submerge it.

 

[Bgallagher]

Originally Posted By: bubbatime
Safely climb under it while transmission is in neutral and twist the drive shaft. If you feel a lot of play, then the u-joints need replaced. If not, then look at the transmission cross member, and then the motor mounts.


+1 Can't stress safely but this is how I would go about it

 

[Rob_Roy]

May also be the transfer case...common to have some play, especially on plow trucks.

 

[Lyman]

Xfer case and third member is where I would start looking. I like what was said above about getting under it and you should be able to see where the slop is. But do it in a SAFE manner.