HELP....1990 jeep comanche shake

[slimslover]

I bought a 1990 jeep comanche 4.0l i6. Auto 4 speed tranny.. I love the truck and want to restore it but I'm at wits end trying to deal with this shake I get.

I don't feel any shake with it until it hit's 45mph in 4th gear.. and only when I'm on the throttlw.. it shakes up until about 52 as long as u stay at low rpms... if I run it in third gear at high rpms all the way through 45 to 50 i get no shake.

About 6 months ago I had a buddy put a new engine in it.. with the engine he did the intake manifold and the injectors and 02 sensor. I didn't feel the shake before I had the new engine put in.

Since I got it back and felt the shake I have replace the maps sensor, tps, exhaust manifold, egr, ball joints, tie rods, steering stabilizer. All the vacuum lines.. lately I've been thinking it was something with the suspension.. but if I'm going 45 in 4th and it's shaking and I take my foot off the petal it stops shaking... so that's telling me it's not something with the steering or suspension..

My mind is now thinking ita something with the tranny.. could it be tranny mount or the tranny itself?? I'm at a loss and am ready to give up on it...thanks for any help u have

[ftpiercecracker1]

 

I am thinking there is something wrong with the torque converter when it goes into overdrive. I definitely think you're on the right track looking at the transmission though.

[Jeep Driver]

What's the cost of a trans mount???? $12 or so?

 

I'd start there.

[HOrnbrod]

Agree with the tranny mount possibility. Also, did he reuse the old motor mounts? Did you check all the mount bolts to make sure they are tight and torqued?

[slimslover]

He put new motor mounts on.. I checked them and the bolts felt tight.. although they looked a little uneven.. maybe just look. Not sure where the tranny mount are.. but that's my next step I guess. The torque converter sounds like it could be suspicoous. Cause the overdrive seems like it's whata causing the shake... also when he pulled the old engine out we did have to reef on the motor to get it off the tranny..

[gogmorgo]

The tranny mount sits between the transmission crossmember and the transmission. Or rather, the transmission sits on it. It bolts to both.

 

Care to describe the steps you took when separating the motor and transmission? The two may kinda hang up on each other a bit and take some wiggling to get out (the XJ/MJ engine bay was initially designed to not fit an inline six, but then they shoehorned one in there anyhow) but as long as you've unbolted the bellhousing to motor bolts and the torque converter to flexplate bolts, the two should come apart pretty easily. The torque converter stays on the transmission. If you leave the torque converter bolted to the flexplate, you can very easily damage it by reefing the motor and tranny apart — if you can even get them apart at all.

[Eagle]

I once bought a used 1968 AMX that had that sort of vibration. Turns out a previous owner had replaced the factory 390 engine (externally balanced flywheel) with a 343 (internally balanced, zero/neutral balanced flywheel). Swapping the flywheel for a 343 wheel solved the problem. So my guess would be that the torque converter is eitrher out of balance or installed wrong.

[Strokermjcomanche]

I have seen where on the torque converter where the front nose goes in the crank it breaks off when beaten on . If it was Hard to come apart , and could not be centered when put back together that would give a vibration .

[big66440]

If it helps any I got rid of a shaking/humming vibration by replacing the extension housing bushing and tranny mount recently. I was going to take my drive shaft in to get balanced but turns out it was both those items now its nice and steady on the freeway. FYI most of the time you can hear a loud knocking noise where the exhausts goes over the cross member when your cranking the engine to start it when the tranny mount is busted.