Driveline challenge of the year...

[makakio]

Brought to you by ... me. Okay tech guys and sorta-tech-guys - let's diagnose this problem (which a tranny/gears specialist and my Toyo tech has not been able to figure out):

The truck: 2001 Sr5 4x4 auto

The problem: downshift clunk when coming out of OD - and *only* OD at 10-5mph. This is NOT a slip/yoke lube issue. It is a drivetrain binding issue and one that caused my tranny to literally blow itself into pieces about five months ago.

Had it completely rebuilt, all clutches, solenoids, valve body, new TC (etc). Driveline is straight. No accident or hard wheeling on this truck (my wife's grocery getter). All fluids - rear diff, trans of course and transfer case are beautiful and have been serviced by the book since mile one. Rebuilt trans works beautifully BUT FOR that one OD downshift bind/release clunk when coming to a stop (or at least <10mph where the locked-up OD drivetrain would stall the truck completely if not for the pressure-induced shift out of OD it goes through). Had the trans/gears guy tear it back down, try another valve body, go back through all the gears, clutches, solenoids, TC/lockup, we put the scanner on it, drove it for hours shifting it by computer (etc) - it's operating perfectly as far as anyone can tell.

SO, we move on to driveshaft (straight, lubed). u-joints and support brackets (clean, straight, lubed). And the only thing we haven't torn into that we think might possibly be the issue is the rear diff.

The one really interesting thing - it doesn't suffer the OD downshift clunk when in 4wd.

So what are theories? Rear diff somehow locking up and staying locked? Some weirdness in the transfer case?

One last word: this is something that just started occurring about 6mos prior to the tranny originally blowing itself to bits. No incident worthy of mention that caused it -- just noticed it one day and though "slip/yoke - get it lubed" (which I did), but alas - not the solution here.

Please opine folks, I'm out of ideas and while we want to keep the truck to 225k because my wife loves it (and it's otherwise in p-e-r-f-e-c-t shape), I will (very sadly) dump it if we can't get this resolved. Don't want another $2k rebuild potential looming at all times, warranty or not (I did get two more years out of the gears guy).

Thanks

 

[Nelsonmd]

Hmmm, I don't know much about the inner workings of the tranny and TC, but have you tried replacing the tranny and TC with ones from salvage vehicles? You don't have your location in your profile, so I don't know where you are, but these seem to be pretty abundant in alot of salvage markets.

I would think that you could pick up salvaged TC and tranny for much less than the $2k you spent on the tranny rebuild. I would start with picking up a used TC since you have rebuilt the tranny already.

You could even troll the classifieds here and on yotatech and probably find one for very cheap within a few months. Look for part outs.

 

[NachoPitt]

Does it have the factory elocker?

Worn pinion bearing? Any audible hums or vibrations when driving?

No clunk in 4wd? How fast have you driven it in 4wd when you don't experience the clunk?

Does it to this only when cold or when warm?

 

[makakio]

@ Nelson: brand new factory OD unit *and* TC plus all new solenoids and clutches. Rebuilt valve body (pressure/performance tested)

@ Nacho: no e-locker on 2001. No audible hums or vibrations. Pinon is ? Happens cold and warm. It seems to me (and this is not empirical by any means), that the clunk gets markedly louder and more severe on stops after being in OD for long periods of time (think 30 minutes on a highway). No clunk in 4WD on the same cycle, which is simply 'get it into OD (4th), then come to a stop'. At somewhere b/t 10mph and 5mph it clunks, which can be felt in seat, pedals and both gear selectors, as well as obviously heard.

MORE: here's a link to the drivetrain video my tech created when we were trying to diagnose. On his YouTube page, go to "the gret noise mystery". The best example is at 1:11 in.

bingerboy's Channel - YouTube

 

[makakio]

Gears guy just handed it back (have a road trip to do over Xmas) and said he's ordering a rear u-joint or whatever connector goes into the rear diff. Said its moving fine in one direction but feels really tight in the other. Easy to throw it in and see if it helps.

He's also eyeing the rear end and wondering if there's play in the differential that's hanging it up as it comes down from speed and causing the clunk as it pops back together on the downshift from freewheel into locked state.

I don't know anything about either of those theories, but getting the rear end apart is a process and I don't know if it's worth the $$ to go there...

Please keep ideas and questions coming - I am appreciative and have to think there's a solution somewhere in our community!

 

[One]

It may sound stupid, but have you checked if the e-brake is sticking? Possibly putting uneeded stress on the driveline.

 

[the great him]

have you replaced the torque converter?

 

[makakio]

@ One: no stupid ideas. But no - not the e-brake.

@ Kid: yep. TC and OD units were shredded. Exploded. Think chunks and shards of metal. And it happened on a power-off, coasting to a stop on an offramp downshift out of OD just as I've described. But it shifted suuuuuuper-hard. So hard I *knew* that **** broke.

So of course my only logical conclusion is that it's just going to happen AGAIN at some point.