Shaking during uphill acceleration. If not a front-end problem, what is it?

Dear Car Talk

Dear Car Talk | Dec 01, 1996

Dear Tom and Ray:

I have a 1992 Suburban with approximately 50,000 miles on it. When we
accelerate up hills, usually going between 60 and 65 mph, the front end of
the vehicle shakes violently. We have taken the vehicle to our authorized
dealer and they can't find anything wrong with it. Since it began shaking
this way, we have changed the tires and have had the front end inspected
and aligned twice. Nothing is wrong, according to the dealer.

A friend of ours also had the same problem with his Suburban. He eventually
traded his in for another make of car. Since the problem occurs
haphazardly, we have had a hard time identifying it. Do you have any
suggestions for us? -- Charles

RAY: I don't know exactly what the problem is, Charles, but I'm going to
suggest it's not a front-end problem at all. Your dealer has checked the
front end twice, and I'm going to take his word for it that the wheel
bearings, steering components and structural elements are all fine. In
which case, I think it's an engine problem.

TOM: If you had a severe high-speed miss -- something that caused the
engine to skip and chatter at high speed -- you could certainly experience
that as a shaking front end. After all, the engine is where? In the front

RAY: And if you simply reported a "front-end" problem to your dealer, he
would interpret that as meaning the front suspension and steering
components, which is what "front-end" means in mechanic-ese.

TOM: Rear end, on the other hand, is the rear suspension and differential,
or, in my brother's case, where the mechanic's brains are found.

RAY: Anyway, if the problem never occurs when you're going DOWNhill at 60-
65 mph, that also points to the engine. And it's certainly conceivable that
a miss would occur when the engine was working the hardest, which it would
be pulling this tank up a hill at 60 mph.

TOM: Go back to your dealer and ask him to check for a "high speed miss
under load." That should send him in the right direction. Good luck,

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