zf5 sudden rpm rise

[arctic-20v]

I just finished a zf5 swap behind my 6.9l, well all finished besides for the rear drive shaft. I got impatience waiting for the rear shaft and dove it around on the front shaft in 4H with a keg cup tapped over the tail shaft of the Bw1356 to keep the dust out of it. Anyways the tranny shifted smoothly and operated well except for two times when it acted like it popped out of gear. What I mean by acted, is that the RPM increased and as if it popped out. But as soon as I let off the throttle it would "re-engage" and it would operate normally. I didn't push in the clutch, just let off the throttle. It didn't make a loud clunk or grinding noise, just the sound of rpms raising. It even happened while holding the shift cane in fourth, so I know it didn't pop out.

Tranny specs:
Zf Sr-42
Luk/napa smf flywheel and 12.25 clutch
New slave and master
Tranny filled with atf

Any body have any ideas on what it could be? History on the zf5 is that it sat outside for the last two years after a buddy bought a f350 for full length axles for his jeep.

 

[93f250idi]

sounds like the clutch slipped.

 

[arctic-20v]

Very well could've. I just wouldn't have thought a brand new clutch and pressure plate on a new fly wheel would slip. Unless its just part of the breaking in.

 

[93f250idi]

well i wouldnt of thought that either but that sure is what it sounds like. did you smell anything burnt when, or right after it happened?

 

[oldblue05]

I'd leave it alone till the rear comes in, the t-case might not have liked being treated like a prius in front wheel drive.

 

[jam0o0]

did you clean everything when you put it together? is there a leak somewhere that is letting fluid onto your clutch or flywheel? did grease from somewhere get thrown or drip onto clutch?

 

[jam0o0]

I'd leave it alone till the rear comes in, the t-case might not have liked being treated like a prius in front wheel drive.

unless he;s running a full time case (clutched front output) the transfer is either in or out. and it doesn't shift from one to the other under load without a LOT of noise. i drove my bronco around on the front axle for a wile when i did the oneton axle swap.

 

[Silver Burner]

Did you replace the rear main when you did this? Could be getting oil on the clutch assembly.. Just a thought.

 

[hesutton]

I agree with what was said above. The clutch certainly seems to be slippling.

Heath

 

[typ4]

Its the tcase. engagement dogs are worn and dont like the full front load.

 

[arctic-20v]

I did replace the rear main seal while I had the chance. I also cleaned off the fly wheel after bolting it on to get rid of any oil residue. I also wiped down the pressure plate to remove any anti corrosive oils it may have shipped with.

Again, this was happening with minimal load on the motor mostly at cruise situations with maybe minor acceleration.

Drive shaft just got dropped off at driveline shop so it'll be a few days till I can test to see if it continues in 2H.

Thanks for all the replies

 

[sle2115]

I vote Tcase as well, clutch slipping intermittantly would be most likely when loaded, hard pull, etc. Doing it at cruise is most likely transfer case.

 

[flareside_thun]

x3 on tcase...had this problem in my truck...except I was in 2 wheel drive. Kicked in and out of gear without any noise whatsoever. The dogs are worn or,like mine, one of the shift forks could be broken.

 

[jam0o0]

cool to know. i've never seen that happen. thanks for the info guys.

 

[flareside_thun]

You're welcome, I guess your thanks is worth the hour and a half I spent driving home in 4 lo...that's the only range my t-case would select...15MPH anyone?