My 1999 Cherokee sport 4.0L maunal 5 speed has a vibration problem. It is almost like a rumble, but not violent. No shaking. It is low pitched, and when it happens it can be felt in the stick and the metal of the hood visibly vibrates. It might be described as something like the sound when you hit those grooves on the side of the highway that wake tired drivers, but not as loud and at a lower frequency. I notice that it does not do it at all in first gear, very little in second gear, and is worst in third and fourth, and in overdrive very little. I notice that it seems to be the worst in 3rd and 4th at about 30-40 mph (pain in the back side on back roads) at 1500RPM. In overdrive or 5th gear it will do it at a lower RPM but once up to highway speed it stops. If it is vibrating and I depress the clutch or shift into neutral it immediately stops completely but comes back when I put it back in gear. It does not seem to do it at 1500 RPM if I am going down hill with the gears holding the jeep back. It will do it uphill. Due to issues unrelated to this it has been tuned up (dist, rotor, plug wires, plugs, TPS, CTS, MAT sensor, both o2 sensors, air filter all replaced, throttle body and IAC cleaned, air filter, etc) so I think the engine is running well. Also new tires. Since it does not do this the same in all gears at the same engine speed I suspected the driveshaft. But I am new to this and I don't know (please bear with me) if the drive shaft is even turning while the vehicle is moving in neutral. The problem is consistent and does not "come and go". I can make this vibration happen at will so if anyone has suggestions about something to check while driving or if there is anything I could check in the garage underneath I would appreciate any input. Have been doing most of my own repairs for a couple of years but I am no mechanic so any ideas would be appreciated. THANKS! Neven

 

At what RPM do you shift? Sounds like you have drive line slack! Usually the culprit is U joints in the rear drive shaft.

Park the Jeep in 1st with the parking brake and crawl underneath. Grab ahold of your rear drive shaft and start shaking and twisting and yanking on it. You're looking for play at the joints at the transfer case end and the rear axle pinion end. With such a slight rumble it may be hard to spot. Another common occurence is the slip yoke drying out: on 97+, the tail shaft from the transmission or transfer case needs to be greased. To do this you must remove the drive shaft and pop off that rubber dust boot.

Welcome to the forum!

 

Yes, I crawled under there and could see that the u joint is bad: seal on cap broken, strap loose, lot of play, a mess. Will change it and see if it cures it. I bet u are right! BTW it is the rear one like u said. Thanks for the education! Neven

 

Per the (correct) advice I got here I changed the rear u joint and it cured the vibration/rumble immediately. But before the day was out a bolt on the u joint strap broke off, leaving the shaft of the bolt in the yoke. I don't know why (wish I did). I brought it home and tried to get the broken bolt out of the pinion shaft yoke with a bolt extractor but broke the extractor off in the broken bolt. GRRRRR!!!! Extractor is case hardened so trying to drill more did no good. So can the pinion shaft yoke be changed without pulling the whole rear end apart? Is there another way to get that bolt shaft out? I can see the large nut in front of the yoke but do not know how the yoke is attached behind the nut. If I take the nut off the yoke can the yoke be taken off and replaced without pulling anything out of the rear end? Any info will be appreciated. HELP!!! (educate me please) and thanks! Neven
1999 jeep cherokee sport 4.0l

 

If you can get the U joint out, you can remove the yoke.

Bot sure if the strap bolts are hardened, but one workaround is to drill out the bolt and use U bolts in place of the straps.

 

I decided to let my mechanic handle the yoke, since I dont' want to break anything else. He can't get the part till Monday. Jeep is my only ride. I have my rear drive shaft in the back seat and the slip yoke from the transfer case on it. the mechanic says I can drive the jeep with just the front shaft (like a front wheel drive) on short trips, low speed (like a mile or two to get groceries, etc). Will this damage the transfer case? I drove it 2 miles today and don't see any fluid leaking. Is the case sealed with the slip yoke off? Can it be driven like this on short, slow trips till I can get it fixed? Asking to be schooled again,
thanks,
Neven.

 

No, knock yourself out. Just don't pop it out of 4H lol

 

A FWD XJ, say it isn't so!? lol

I would only drive it like this to the mechanic to get fixed, I would not continue to drive it like that. Whatever you do don't go fast, turn sharp or take it out of 4HI and use your e-brake when you put it into park.

 

Aww too bad you already took it to the mechanic. I did the same thing, broke off the strap bolt. So I drilled out the broken bolt with a titanium bit, widened the hole and installed new straps.

https://www.cherokeeforum.com/f51/re...version-28141/

You didn't need a new yoke.

 

there it is! Exactly what I was thinking of

 

My son-in-law had to help me with the drive shaft due to my physical condition so I kinda threw it in and went to the shop. But he has changed a hundred u-joints, and all 4 on the Chevy truck he has now. Does anyone have an idea why that bolt broke? The strap had been loose and the u-joint shot for a while. With the new one in and the strap tight, why would that bolt have broke in the first place?

 

Well I'm not a physicist or an engineer, but as I understand it, it's because of the shock to the fastener. Normally, with a good U joint and secure strap, the tightness of everything allows a lot of the force to be transferred via the yoke. This is why there are only 8 tiny bolts holding those straps down. With them loose, when you hit the gas it's going to be yanking on that bolt and transferring a lot of force through it, instead. The extra torque and constant shock loading will trash a rusty small bolt in no time.

 

Poor design really. The bolts are thin. In my case, it was rusted in so as soon as I put some torque on it it sheared off. That's why the U bolt is a much more robust upgrade. It's a nut and bolt solution instead of threaded. Much smarter design and much easier to remove next time.

 

Never even thought of this, I'll be putting that on my to-do list.