Stick Shift Puzzle

First thing I would do is remove the rear drive shaft and try the truck in

Don't fully follow the problem from the description... but for some reason I bet it turns out to be a busted motor mount/s problem after all.

Will it 'do it' at low enough speeds where you could (very carefully, safe and legally) drive it with the hood open, and watch and see if the engine is dancing around?

Also, stopped with the hood open, put it in 1st, give it just a little gas, and gently 'slip' the clutch for a second while holding the brake. Watch the engine, it should move, but only just a little. (Compare to another car without the prob). Repeat the same test in reverse too.

Good Luck! Let us know what you find...

Erik

First, ensure the bolts from engine to bellhousing have not worked themselves loose. Since the problem seems to disappear when the rear differential is held by the emergency brakes, sounds like you've narrowed the problem. Check the rear differential when it is exhibiting the symptoms to see if the posi-traction is trying to bind up. If so, changing the grease and adding Jeep's recommended additive for their posi-trac'n (if such exists--service or parts manager at Jeep dealership can guide you) may solve your problem. Good luck, s

Erik, Thank you for your reply. One question - when I went to get the mounts checked for the second time, the mechanic asked 'If it's the mounts, why wouldn't they act up when the car is cold as well as when its warmed up?' I'll do as you suggest and check to see what things look like myself to see if I can spot something. Thanks again for the reply.

- Vin

Sdlomi2, Thanks for your idea - and a good one it is. I did have the rear differential fluid changed about 10K ago, and the wrong fluid could be a problem. I'm going back to the shop where the change was done to see what they used. On the receipt, it just shows that the diff. was serviced, but doesn't say with what. The shop manual only calls for regular "SAE 80W-90" but I'll check to see what was used. Thanks again for the idea - no one else came up with that one.

Shep,

Good idea. The oil change shops never even think of the slip-yoke lube. I've been doing it myself every 5K, but your question made me look in the manual and I see that I haven't been putting in nearly enough, so it could be binding. I'll get under there tomorrow and pump it full to see if it helps.

- Vin

If both rear tires are going at the same speed then the posi plates should not be sliding against each other and there should be no problem from there even if it did have the wrong fluid or was otherwise messed up. Messed up posi should really only show up during turns or other times when the rear tires are not going the same speed from side to side.

If I'm following this, it only does this shake while you are starting up from a stop and only does it when it's warmed up. To me that sounds like a clutch/pressure plate problem, perhaps they are contaminated with oil or brake fluid (if you have a hydraulic clutch) and it only gets "grabby" after it warms up. Lots of "good" clutches have a slight shudder on start up so a contaminated one might have a lot. It could also be that the clutch is binding on the transmission shaft but again, only when hot.

If it were a mount, I really couldn't see it being temperature sensitive by itself either. But who knows... always check the simple stuff first, mounts are simple, quick and free to check.

Question, does this vehicle have a linkage, cable or hydraulically operated clutch? If it's linkage, the mounts are even more suspect... a vicious cycle can sometime be created by the engine moving enough to engage and release the clutch on it's own.

I've seen busted mounts take a toll on plastic air intake ducts of fuel injected engines too (the big duct between the air cleaner assembly and throttle valve.) Cracks/leaks opening and closing as the engine 'slops' around can raise all sorts of hell if the engine is equipped with an air flow meter. These ducts are a good thing to look at close on a regular basis anyway, and sometime leak unprovoked.

Again, good luck, can't wait to hear the outcome!

Erik

I would open the hood and have someone hold the brake hard while letting up on the clutch in both 1st and reverse to watch the engine.

My guess is the tail will shift side to side when warmed up while doing this.

I have had the exact same thing happen and ours was a oil soaked spongy tranny mount. When cold it is hard, once warmed up it went sponge so the tail could wag causing a wicked judder when starting out under load.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

V>

Mike, You're the first person who has reported the same problem. Even though I had the mounts checked when I had the clutch work done, after your comments, I'm going to take it to another place to have the mount checked again. If this turns out to be the solution, I owe you one.

- Vin