I have two jeeps. One is 1994 XJ 4.0 auto. The other is an 89 XJ 4.0 4x4 auto. They are both stock. Planning on 2" lift for the 89 later.

I've had the 94 for years and about one year ago it developed a horrible shake and I just drove it and didn't look into how to fix it because it's a best up work jeep and I was going to throw money at it.

It would shake exactly at 35 mph and sorta stop at 45mph and above. If I let off gas it would stop and coast smooth. As soon as I gave it gas it started right back. It did this for a month+ One day I left and no shake it ran smooth as silk. It turned out that I accidentally put too much oil in it and once it burned the excess off it stopped.

Now I got this 89 from an older man and it's in superb shape and low and be hold it does exactly the same thing as the 94.

The 89 has 195/65 tires on front and 225/70 on back. I am going to be putting 235/75's with balance all the way around.

I haven't changed the oil yet and while it is not over full it clearly needs changing. Could this old oil be the cause, same as too much oil in my 94? And has anybody heard of this?

 

I have never heard of a car shaking violently because of extra oil, may want to look for another cause.

 

Put all proper size matching tires on the '89. Change the oil so you know where it is. Drive it and see if the shaking stops.

 

I had never heard of that either but it is 100% what caused the 94 to shake. I didn't do anything to fix it it just stopped and I later discovered it was because the oil was too full.

I'm hoping changing the oil today in the 89 will fix it but I'm highly doubtful. I will be changing the tires probably next week.

 

Changed the oil last night and it stopped shaking at 35mph so on two separate jeeps now oil, whether it be old or too full, has caused shaking/vibration problems.

But I found/have a new problem. Because the shaking was so bad at 35 I dint notice until today it shakes at 45 mph. So, I unplugged my transmission control until and drove it down the road and shifted manually and it ran smooth as silk.

That let me know it's not my tires or my driveline or a mechanical issue but my TPS. Does this sound correct?