I have a severe drive line vibration. Vibration starts at about 60 mph
and becomes severe at 65+. I have tried to drive thru the vibration,
speed wise I got up into the low 70s but the vibration kept on getting
more intense and I was concerned that I might be heading to a
catastrophic failure if I continued to increase speed to drive thru the
vibration.
Background: I blew apart my GT-6 diff last Fall and installed one from
a Spit parts car. While I had the diff out I also replaced the u-joints
in the driveshaft. While replacing the u-joints I noticed that the
driveshaft was one spline out of phase at the yoke. I had had a very
minor, subtle driveline vibration and I expected the phase correction
would improve my car. The severe driveline vibration manifested itself
after the reassembly.
I have removed the driveshaft from the car and checked the u-joints for
binding or play and there is none (I put about 500 miles on the new
u-joints last Fall). I rechecked the driveshaft for phase - u-joint
alignment - using a straight edge to make certain that the yoke end was
aligned with the shaft. I also compared the phase alignment with the
shafts of two other cars to make certain that my memory of u-joint
alignment was correct. I have checked the shaft for missing weights
and any sign of handling damage when I had it out of the car - none
observed. Finally I put an angle indicator on the two driveshaft mating
flanges on the trans and the diff. THe axis of both are pointed
downward (approx. 4 deg) when looking at the car in side view. From
memory are not the two mating flanges required to be parallel (in other
word if one is down 4 deg then the opposite surface would have to be up
4 deg)? Unless the Spit diff uses a different front mounting bracket,
there is no way that I could shim either the trans mount or the front
diff mounts to get the two driveshaft mating surfaces
parallel. One final observation, I had installed the driveshaft
backwards with respect the the yoke end (when compared to the
illustration in my Bentley's manual) but it had been installed backwards
for the previous 6 or 7 years (ever since I converted over to an OD
trans) without a problem.
Last thought, I previously had a 3.27:1 diff and now I am running a
4.11:1 ratio. The driveline now has to spin approximately 25% faster to
achieve the same road speed - could it be that the vibration was there
all along but I never got up into that rotational speed? Fastest that I
have ever driven the car (with the 3.27 diff) was in the low 80s mph.
HELP (please).
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