Re: Performance Chip for 2000 Suburban


"Healeyman" <timoran@xxxxxxxxxxx> wrote in message
news:3B7cg.4813$Ar6.3700@xxxxxxxxxxx
Max & Jerry,

Thanks for the comeback. Yes, I have had both front (4-WD) and rear
driveshafts removed and balanced, had the tires rotated and balanced many
times and, the front end aligned at least twice.

The vibration starts about 50 MPH and cycles repeatedly from front to
back, back to front, front to back, front to back, back to front, and on
and on. It takes about 15 seconds to make the trip back and forth. The
cycle does NOT change frequency with increased speed, at least up to 90.

Superimposed on this "traveling" vibration, there appears to be about a 30
Hz vibration, like a wheel is out of balance, but at 60 MPH, the 29 inch
wheels only revolve 11 times per second.. NO change, either in or out of
4-WD.

I'm not talking about a LITTLE cyclic vibration here. When the vib is in
the front, it will actually displace the dash up and down about 3/4 inch.
Cups almost bounce out of the cupholders. 7 seconds later, it is in the
back and makes the spare tire cover bounce like a bass drum while the dash
is dead still.

One tech. diagnosed it as a bad LF shock and when I replaced them all it
was 1/10 of what it was. It is always there, but 3-4 X worse when towing
the trailer.

I love the car and have just learned to live with it. It's the nature of
the beast.....

Tim


One thing that you haven't mentioned checking is driveshaft ujoint angle -
the axle pinion shaft should be parallel to the transfer case output shaft,
so that the ujoints on both ends of the shaft are operating at the same
angle. Not uncommon for leaf springs to sag a little with age and load, and
this will change the angle - usually corrected with tapered shims between
the spring and the axle. Not saying that's what your problem is, but I once
went through much the same thing with a dodge dart and that was what finally
cured it - turned out later that the rear end had been replaced by the
previous owner with one from a different year, and the angle was 4 degrees
off...

Alan


.

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