Tranny question

rdstoney · Aug 27, 2006

Puzzling one -
94 Grand - All standard 5.2 equipment (so far...hang on) Had tranny rebuilt due slippage. 249 started the coupling grind noise after being driven for any real distance, so removed front driveshaft (while getting a 242 replacement lined up)

Jeep has twice now 'drifted' after being put in park. ie...put in park...jeep continues to slowly drift if on any down hill direction. Engine on, engine off doesn't seem to matter.

Know there are some good tranny guys lurking the boards here (I am in Maryland so let me know if you are close) so welcome opinions here. Whilest you are at it - any recommendations of 'better' auto trannies to use behind a 5.2 ?

CSMDakota · Aug 27, 2006

I'm not very familiar with the 249 transfer case. It's possible that a bad coupler could allow slippage between the tranny and the driveshaft; how does it drive down the road? Do you get slippage when you take off from a dead start?

If it drives cherry, then sounds like the tranny rebuilders didn't get the park lever mechanism working correctly. PARK should initiate a mechanical stop to the transmission, in no way should your ZJ be rolling off on it's own like that!

My advice = take it back to the rebuilders, they should check it out for you.

Good Luck,
--CSMDakota--

AndyZJ · Aug 27, 2006

x2 The parking paw is suppose to lock the gears when engaged in park. It literally sits a rod onto the driving member to keep it from moving back or forth. There should be a linkage adjustment for it. Sounds like it may be not sitting fully in.

rdstoney · Aug 27, 2006

Driving - even with a utility trailer loaded with 10 railroad ties (figure 150 + lbs each) pulls strong, runs great. Only pulled the front shaft to make sure I wouldn't hurt anything with that bad vc.

I didn't *think* the tranny should let the vehicle move, but didn't know if the 249 might allow it after taking that front shaft off. I cannot get it to malfunction routinely.

Will take a look at the linkage, and make sure park is really putting that tranny in park tomorrow when there isn't a storm winding up. Thanks folks !

VirginiaZJ · Aug 28, 2006

when the t case is in neutral, putting the tranny in park is not effective. The TC must be slipping somehow.

RSL · Aug 28, 2006

It is the transfer case that is causing it to creep. With the 93-95 249 you have to have both driveshafts installed for park to work properly. If you have a 96 to 98 249 you can put it in lowrange and lock the viscous coupler and it won't creep when in park with the front shaft removed.

What you people fail to realize is the Viscous Coupler is a differential -it consists of 2 sets of plates, 1 set splined to the rear output shaft and 1 set splined to the front ouput shaft, these plates are in a housing surrounded by a silicone fluid that is heated by the shear between the 2 sets of plates - this allows the front and rear shafts to rotate at slightly different speeds if they have to when cornering etc, but when one axle loses traction the silicone fluid in the VC heats up and locks the VC.

Over time the silicone fluid in the VC gets contaminated and doesn't work as it should usually locking and staying locked till it cools down completely, causing binding in corners.

With the front shaft removed the VC senses this as a massive loss of traction and heats up and locks allowing all the power to be sent to the rear driveshaft thus causing the vehicle to move.

When you park the vehicle the VC cools down and unlocks and once again allows the plates in the VC to move again but with no front shaft there is nothing to stop the front yoke from turning and the vehicle slowly creeps if parked on an incline.

With the front shaft in place the yoke can not turn because it is stopped from rotating by the gears in the front differential.

Tranny question

rdstoney

CSMDakota

AndyZJ

rdstoney

VirginiaZJ

RSL

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