Takedown

First off im new here. I have an 89 jeep grand cherokee pioneer with a 4.0 engine and trans swap from a 91 cherokee. Ive had the vehicle for awhile and just recently I started getting an engine vibration at around 2,250-2800rpms when not under heavy load.

At first I thought it was the driveshaft u-joints but I later tried slowly climbing the rpm range in neutral and I still get the vibration so I ruled that out. Plugs are good, wires are new, cap and rotor is brand new.

My next guess is going to be the harmonic balancer. Has anyone else had to replace one before and is it common for them to go bad?

XJRed96

i dont know how common but it is a known problem with the harmonic balancer. if you crawl under the jeep and look up at the crank you will be able to see the rubber sandwiched in between the outer edge of the pulley and the center part of the pulley, if it looks chewed up it's time to replace. also take a look at motor mounts. have a buddy slightly brake torque the motor over in drive and then in reverse and see if the motor leans more one way or the other or see if you can visually see separation of the mounts.

Takedown

Sounds good! Thanks!

Takedown

Well I did change the spark plugs and gap them accordingly, put a new transmission mount in due to it being rotted to hell and I was going to install new engine mounts since I ordered those aswell but those appear to be in great shape and theres no engine sway that I noticed. I also changed out the u-joint closest to the rear diff because it had alot of slop in it.

The engine vibration has subsided quite a bit but is still strong in reverse during mild acceleration and faintly in drive at about cruising speed. Could it be the diff or the transfer case????

cruiser54

Harmonic balancer takes out vibrations that a human couldn't feel that causes metal to fatigue. Yes, they fail, but not in the "vibe department".

Here's a photo of a failed balancer:

Takedown

But a harmonic balancer confuses me as being the problem. How come the vibrations are much stronger in reverse?

cruiser54

Because the issue you describe is NOT the balancer. I wish that had never been thrown out there.

Someone, you or a trusted mechanic, needs to give your Jeep a good dose of "noggin pokin'".

That's where someone crawls under the Jeep, either while it's on the ground or on a lift, and uses 4 of their 5 God given senses to look for the problem.


Suggestions:

Engine and trans mounts, Loose motor mount brackets, loose bolts from the engine to trans, exhaust pipe hitting on the crossmember.....yada yada.

Takedown

Engine & trans mounts are gold. Motor mount brackets are tight. Ill have to check engine to trans bolts and its more of a binding kind of vibrantion if that makes any sense at all.

cruiser54

Exhaust pipe on the crossmember? Can you fit your thumb between the pipe and crossmember?

Takedown

IIRC yes it does. Ill post up pics today.

straxcla

Did you ever fix this issue? I have a similar problem with my 98. It's not a metal on metal vibration but more of what a drive line vibe feels like. I know it isn't my drive line though because it does it in park.