po0dingles

Hi Guys,

So many issues with this Jeep.

So I noticed the other day that while driving on the highway, if I let off the gas around 70mph - 80mph and gently get back on it, the transmission seems to hesitate and shift around before finally staying in a gear. It happens really quick and then there's a vibration felt through the floor, as if I partially neutral dropped the damn thing.

Interestingly, this doesn't happen going up the gears, so I'm thinking it's only a downward or hesitation issue.

I tried searching about this issue but the threads I find are about transmissions that aren't shift UP or holding a gear too long. I don't have these symptoms.

It's exclusively when I let off the gas for a moment and then get back on. It seems to happen at a variety of speeds but is most noticable around 70mph-80mph.

Any clues/tips/tricks?

Edit: Not sure if this provides any additional support, but my ABS light has been permanently on since purchasing this vehicle.

dave1123

Sounds like the O/D clutch. Try locking the O/D out and see if it still does it.

po0dingles

Thanks, Dave. I appreciate your response.

How do I achieve this? Just by putting the transmission into 3rd gear?

dnuccio

Hit the O/D off button on the dash

po0dingles

thanks

So if that stops the issue, is this a mechanical problem concerning the internals of the transmission or something more simple such as a sensor?

po0dingles

So I was able to test this last night. With the overdrive off it does not produce the same effect, which probably indicates I have a problem engaging/disengaging overdrive?

What would be the fix for this? Do I need a transmission rebuild? I have a leaking rear main seal and some light rubbing noises coming from the rear axle/rear diff.

I may have to overhaul the entire drivetrain: transfer case, axles, rear end, transmission.

Gee oh Dee

Most likely mechanical.

dave1123

I don't have any experience with Mopar transmissions, but I have rebuilt several GM THM 350's and one 700R4. In the 700R4, there is a sprag clutch (a gear unit) in the transmission that only drives in one direction and is in the O/D section. If it's bad, it will create noise during coast. Actually, O/D is the top gear (4th) in most transmissions, while lock-up is sort of a 5th.

Unfortunately, this clutch is one of the first things put into the case when assembling a trans, so replacement is usually done on a total rebuild. If you're going to take it apart that far, it's normal to replace all the "soft" parts anyway. I've had "shop" estimates of from $900 to $3000 for a rebuild. Some shops, with the more "popular" transmissions, used to put in a rebuilt trans and then rebuild yours for the next customer. I don't think this is done anymore.

If you're going to go "all the way", your transfer case could probably use a new chain. Get the rear diff checked out for worn pinion bearings or spalded gear faces.

My first THM 350 was done by my brother with me looking over his shoulder. My next one was me and the telephone to him. The third was a piece of cake. These are only 3 speed trannys and rather simple. My 700R4 was me and a tech manual, a lot of sweat, and more than a few mistakes. This one was a 4 speed with lock up convertor very similar to Jeep's but without the electronics. The THM 350 was used for drag racing a lot, so they got a lot of abuse.

That's about all I've got. Good luck.

po0dingles

Thanks, Dave.