[Lumps!] vibration

Lumps
1

I’ve had a chance to do some checking on my vibration problem.
The drive shaft was balanced when built for me. If I’m doing 60-70 and put
it in neutral and coast it almost goes away. Seems to be tied into the
engine, under any load or acceleration it gets worst. The engine was new,(
crate 350/330hp with harmonic balancer and flex plate) anything specific to
check for on it. Is it possible for a new torque converter to be out of
balance. It doesn’t seem to be any exhaust pipes as I can’t get a clunk just
reving it at a stand still, however the vibration will come on the higher
the revs. Could incorrect timimg cause any of this. The motor does have a
mild cam, but I would think that would smooth out as revs went up

Jeff

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2

This is a normal symptom of many of the converted
cars. The culprit is usually the trans mount., While
the engine is actually double rubber mounted (engine
mounts plus the subframe mounts), the trans on the
converted cars usually has only just the rubber
isolator, and some replacement crossmember bolted to
the unibody. There are wide variations in the type of
rubber used in typical Chevy trans mounts, which
translates into varying degrees of vibration
transmission (sorry about that). Some people go back
to the Jaguar spring design. I also had a customer who
put rubber bushings on each of the 4 mounting points
of the new crossmember to kill the vibration. That
seemed to work well.

You might want to get a different (new) trans mount
and try it- might make a difference. I’m assuming
you’re not running polyurethane mounts- they vibrate
like hell…> I’ve had a chance to do some checking on my

vibration problem.
The drive shaft was balanced when built for me. If
I’m doing 60-70 and put
it in neutral and coast it almost goes away. Seems
to be tied into the
engine, under any load or acceleration it gets
worst.

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3

Andrew and Lumps Folks:
In reading this post on vibrations, it coincidently was posted right as
I started to deal with my own type of vibration. I would first like to
address the trans mount issue to see if I don’t have a similar problem.
I used the JTR boilerplate for the trans mount. A nice heavy sucker
that I had fabricated locally. I don’t recall any rubber in that
construction at all. I am steel to steel at all 5 points, i.e.: 4
mounting bolts to the uni-body (along the tunnel) and the one bolt from
the trans through the trans cross member. I have always felt a little
tug that came apparent at the shift lever when I goose the Kat. And I
can feel a vibration in the shift lever itself as I motor along. Should
I be considering putting rubber bushings at all 5 points? And where
would one get such bushings?

Now on to my vibrations …

About 2 months ago, I started to get a vibration (feels like the front
end) that was reminiscent of a tire starting to separate tread. I have
been using “take offs” on my car, experimenting with tire size to get a
good feel (to me). Long story short, I went from 215X70, to 225X70,
back to 205X70 and felt the 205X70s gave me the best feel, sans a little
weak feeling on cornering. The latter tire size was on my car up until
yesterday. The vibration in question was only there around 55-70 miles
per hour.

Yesterday, after having a new set of 225X60s put on the car all around,
I noticed that the vibration was still there. It was not so radical,
only slight, but had moved up the scale more towards the 65-80 mph
range. I am guessing that the difference in tire size height, has
changed my speedo readings a little and that it is the same problem that
is causing the vibration.

The front end is a relatively new rebuild. The car does need an
alignment but this vibration has only been there twice now, once when I
did have a tire tread separation issue and now with the new 225X60s.

And as additional information, I have always had a coming and going
issue of vibration when I brake. Sometimes there, sometimes not. Could
this be tied to this issue as well. I have replace front end disks,
rotors and calibers -and- brake master, but the cavitations in the pedal
seems to be still there. I have tested this back and forth and there is
not a steady pattern to the vibration on this issue, i.e.: braking from
different speeds, conditions, etc.

Any ideas folks? Where should I start looking.

Smitty
The Arizona Leaper (76XJ12L - L82 build/700R4)
Phoenix, Arizona

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4

In reply to a message from The Lumped Leaper of Phoenix sent Tue 20 Jan 2004:

Smitty;

Here is an ‘‘Idea’’ as to your vibration… You might have a
set of tires that have ‘‘flatspots’’ in them, (from locking up the
brakes & skidding-hence flatspots) I have that problem on Cindy’s
Durango right now. I bought a set of BF goodrich Comp T/A’s @ a
yard sale for $10.00 (2 tires) Tires still has casting nubby’s on
them…put them on the Durango & @ 75mph I get a vibration in the
truck. Only cure I know of involves pouring bleach in a parking lot
switching front tires to the rear & doing some smokey burnouts to
reround the tires out,…I have done this quite a few times with
very good success.

Anyways my .02 cents :slight_smile:

Gary B. & Ms. Kitty–
J Gary Bodnar 1987 XJ6 V8, 1981 XJ6 Parts car
Phoenix, Az, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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