Car Talk

March 1999

Dear Tom and Ray:

I have a '95 Jeep Cherokee 4 by 4 with 51,000 miles. It has the 4.0 liter engine. The three motor mount bolts that go into the block sheared off on the passenger side. They had to drill out the bolts. They put in a new motor mount, too. The bolts on the driver's side were OK and tight. Six days and 900 miles later, I went slowly over a railroad crossing and the same three bolts sheared off again. What's going on? I don't drive hard, and I don't go off-road. I've never hit a curb, stump or rock. This time, it took a chunk out of the block, so it will need some welding. Why did it take 50,000 miles for the first set of bolts to go and only a week for the second set? What's going on? -- Neal

Tom: Neal, you poor schlemiel. [redtruck.gif]

Ray: Here's what I think happened. For some reason, during that first 50,000 miles, those bolts started to come loose. Why? I don't know. Perhaps they weren't tightened properly at the factory. Or maybe the holes were never drilled and tapped correctly. The bolts should not have come loose on your car, but they did.

Tom: The three bolts go through a bracket, and with one or more of the bolts loose, that bracket slides up and down and has a shearing action -- acting like a knife against those bolts. Eventually, a bolt got sheared off. That weakened the mount even further, making the shearing action even more intense, and eventually the second and third bolts gave way, too. And when the third one broke, the motor fell down and you noticed it.

Ray: And the reason it broke again a week later is because the repair was not as good as the original. When you drill out broken bolts, you can't always drill as deep as you'd like (especially when you're drilling into somebody's engine block). So you often end up using shorter bolts, which, in this case, weren't up to the job. Or maybe they neglected to use "hardened" bolts. In any case, as you discovered, it didn't take much to shear off those inferior bolts the second time.

Tom: It's possible that they can weld it all back together and make it work. But it's also possible that the whole thing is going to be even weaker still after another repair attempt. So if the next repair fails, the next step would be a new engine block.

Ray: And in my opinion, DaimlerChrysler Corp. ought to pay for it. This shouldn't happen on a 1995 car with only 50,000 miles on it, and they'll probably agree with that. I'm not aware of any preventative maintenance that Chrysler requires on the motor mount bolts. So it would seem as though you're absolved of all responsibility. It seems to us clearly a manufacturing error.

Tom: I'd make a case to your dealer and, if necessary, the company's zone representative. Make a deal with them. Let them take a crack (no pun intended) at welding it, but if it doesn't work, get them to agree to buy you an engine block. Good luck, Neal.

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