93 Jeep slow trans & kicking/bucking between 40 and 50 MPH

I have a lot of issues with my 1993 Jeep Grand Cherokee Laredo. The ones that frighten me the most are the slow transmission: it is inconsistent, the transmission will stay in a lower gear and the engine will sound like it’s going to explode while I try to increase my speed. Sometimes braking, or taking my foot off the gas and then trying to accelerate again will cause it to shift, but frequently it doesn’t work and I end up driving in 2nd while trying to go 35 to 40 MPH.

The kicking/bucking is the most disturbing. I have been eliminating one issue after another in an effort to eliminate the shaking. First I thought it was a balance and alignment issue. I had it balanced and aligned. The mechanic told me the alignment had been WAY off, and that it wouldn’t be able to maintain what he had done because I had a bent rim. He also said that the intense shaking that occured when I turned on the jeep was because of the rim and because I had a bad motor mount. So I paid him , took the key and got in my car. When I turned the car on it shook VIOLENTLY, and then shut off. It did this a few times in a row, and then it stayed on - still shaking violently - and I drove to the end of the parking lot. The more gas I gave it the better it was. It kept this up every time I got in the car for the next few days and then it stopped happening. The car still shook while driving, especially from 40 to 50 MPH, but I thought that it was the rim and the motor mount. I fixed the motor mount, put a full size tire on my spare rim until I could get a replacement for my original and still the car shook.

I realized that neither of those was the problem after putting a brand new tire on the spare rim. I went to visit someone an hour and a half away, and the car drove really well the whole way there. I took the turn pike, so I was going 65 or so the whole time. When I got off the turnpike I was going through country and towns so the max speed was 55. The jeep again began to shake violently - but it would shake from 30 MPH to 55 MPH. It was difficult to go 55 MPH because it would continue to shake more intensly the faster I would go at this point. When it was time to go home I added a fuel and oil additive by STP thinking that the fuel injection system might need to be cleaned, and not sure if the 1 foot diameter oil stain under the jeep on my driveway might be a cause for concern. It seemed to help. The jeep was still shaking but it seemed to be shifting smoother the longer I drove with the additives, and it shook less the longer I drove as well.

It’s been two weeks and the jeep is right back to refusing to shift, and the shaking only occurs from 40 MPH to 50 MPH - aproximately. I don’t know what is going on. I got new spark plaugs, but I don’t want to do anything until I have some idea what might be wrong. And I am tired of spending money with the mechanic because he doesn’t know what’s going on, and is guessing as much as I am. Any ideas? Is this worth fixing or should I just get another used car that’s not so bad off?

Have you taken it to a tranny shop? All of the problems could possibly be traced to a bad tranny. I’d start by getting that checked out.

I’ll have to have my mechanic or the Jeep dealer look at the transmission specifically. At least it’s a direction to move in. My dad thinks I should keep pouring money into this Jeep instead of buying a new car with the current state of the economy. I’m just hoping it’s something that can be fixed. Thanks for the advice!

I don’t know if this will help but I had a similar problem with my Subaru Outback. When decelerating to about 40 mph it would start to buck violently. It was very bad at taking off from a stop as well. I took it into the Subaru service and of course it would not happen when they drove it. I had them look at the motor mounts to rule them out as well. They couldn’t find the problem. I had bought a code reader and had results saying “misfire”. Checking the manual, I saw I was way behind on changing the spark plugs (and someone from this forum suggested looking at them) so I bought a new set and installed them. The old ones were in good shape but the gap had widened and were obviously misfiring. The car is running much better. The bucking has ceased. If you have the spark plugs, I would put them in. It helped my problem.
Good luck!

I was thinking specfically of a torque converter not locking and unlocking properly, perhaps as the cause of the symptoms and perhaps even as a symptom itself of another tranny problem.

Which engine is in your Jeep???

Also, do you have a delay in the transmission when shifting to Reverse??