97 4x4: anyone know how to resolve coast clunk?

[drdoom]

Hello everyone, my 97 4x4 started the coast/downshift clunk after the transmission being overhauled and installation of the Superior Shift Kit. As with other members, VERY FIRM braking between 30-40mph is the only thing that will prevent it. So, somehow, it is capable of smooth operation, there is just something wrong that prevents it. I have searched on and off for a couple years now, never finding a firm resolution. Unit is high mileage 218K, gets severe duty service schedule or better, including slip yoke service every 7K. The driveshafts check out good. there is a substantial amount of rotational play when hand turning both shafts, I'd say thirty degrees or more. TPS is good, pretty sure the BOO is good also. Also there seems to be a wee bit of vibration, that phases in & out. It is getting worse, and now coast-clunks even when not downshifting. It's really starting to bang hard, and I am afraid it won't hold up much longer. Sometimes I wonder if a sprag has failed, or the front diff is worn out.
Many Thanks,
Doc

 

[JK080]

Down shift clunks can be caused by a faulty EPC solenoid or one that has been adjusted (turning the screw in). Installing a line pressure gauge may help with determining if this is caused by high line pressure. Obviously the shift kit can play a role in this, I don't use shift kits on these so I am not that familiar with what they change, but you may want to look through the instructions to see what changes they are making.

"Coast - clunks even when not downshifting" makes me think of something other than the tranny, maybe be more descriptive on what you mean here.

 

[drdoom]

James, the Superior kit includes a pressure riser for the EPC. I have considered unplugging it, to see if it helps. I replaced the EPC recently, as I had put 40K miles on it, and it came to me on a salvaged VB.

Well I'm posting late because I lost high range today, and had to creep back to the shop in 4low with the fuse pulled. I'll open the case up in a day or so because I need to rebuild and sleeve that. Maybe that is the problem.

And to describe the clunk, its like when you are coasting, you have raised your foot from the accelerator, and it's not cyclic, but random, like you are slamming someone from one side of a narrow corridor to the other. You can feel it, like there is a physical distance between them, and the right clunk has a slight different tone than the left.

Other wise it runs fabulous, t case checks out electronically and funtionally, well, before today! Lol The ControlTrac works perfectly, this rig has been totally stomping in deep wet snow. Its really cryptic to me, been a thorn in my side for a while. I appreciate your input and experise, James. Thank you.

 

[drdoom]

Draining the case now, so far I have a bad bearing at rear output...

And the front output bearing, by hand, it vibrates a good bit. The rear case, now that is ovalling pretty good, and there is some pump lug wear, a good 3/8". The front case is not ovalled near as much. And of course the range collar is stripped.

 

[drdoom]

To update, I rebuilt the transfer case (ovaling of shift rail bores repaired by machinist, a rebuild kit, a range cam, and of course the range hub) and the random clunking is completely resolved, with just the usual downshift clunk remaining. It is a firm clunk, and is really ganking on the t case. I am going to drop the pan and unplug the pressure riser, then report back in a week or so.

 

[drdoom]

Sorry I was waiting for the service interval, so I finally got around to dropping the pan for a filter change, and I removed the pressure riser. That didn't make any difference, it still clunks when downshifting, unless you use firm braking. Just wanted to update.