[Saloon-lovers] 2-pcs Driveshaft Vibration

I’m trying, unsuccessfully so far, to cure a vibration on my 1955
MVIIM, 4-spd O/D. Briefly, the vibration is speed, not RPM
related. By my speedo, it vibrates noticably around 40-45 MPH.
This is felt in the seat, etc., not the steering wheel, and the
vibration stays even while coasting downhill with the engine
shutoff in neutral. The other day I disconnected the rear flange
from the diff, tied it out of the way, and coasted down a long hill
at highway speed. The car was smooth at 40-45. Then I put the
frame on blocks, disconnected the front flange from the O/D, and
ran the engine in 4th gear up to 60. No vibration. I have a 2
piece driveshaft. I’ve replaced and professionally installed 3 U-
joints, the center bearing, and have put new rubbers in the bearing
mounting. I needed a new rear flance due to wear, and part of my
shaft was replaced due to an out-of-round condition, I guess. I’ve
had the driveshaft balanced and rebalanced. In both cases, the
shop added weights where there were none before. In fact, I now
have 1 weight on the rear shaft and 2 weights on the front (short)
shaft. Their balancing machine is calibrated to spin at 600 RPM at
which speed my car is smooth anyway, so I asked them to spin it at
1200. My vibration occurs in 4th gear around 2000 RPM and can’t be
felt above 2500-2600. The tires are new Michelin MXV4 radials.
Tire pressure is at 36 PSI. I’ve spent over $500 on this issue and
can’t ask the driveline shop to do any more. I can either assume
they did a poor job and have the driveshaft checked elsewhere, or
appeal to Jag-Lovers for advice. Spinning my wheels!!

ASC, JANE–
asc
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In reply to a message from asc sent Wed 14 May 2014:

I once had a vibration on the overrun in my 3.8S at about 50
MPH. After much checking I found that during some earlier
repairs the transmission cradle mount had been removed and
the shims between it and the floor were not replaced
correctly. I refitted the shims and the vibration went
away. It appears that even 1/8 inch difference in position
of the rear of the transmission could set up a vibration
under certain conditions.–
The original message included these comments:

This is felt in the seat, etc., not the steering wheel, and the
vibration stays even while coasting downhill with the engine
shutoff in neutral. The other day I disconnected the rear flange
from the diff, tied it out of the way, and coasted down a long hill
at highway speed. The car was smooth at 40-45. Then I put the


John Quilter 1965 3.8S, 1951 MGTD, 1960 Morris ,1990 XJ6
Eugene, Oregon, United States
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In reply to a message from asc sent Wed 14 May 2014:

Hello,

I have a Mark 2 Auto which had very similar symptoms the
vibrations were road speed related very bad at around 55mph
and got worse.

I had the prop shaft balanced, the UJ’s aligned properly,
had the discs machined and spun at speed to check balance,
changed wheels, tyres, even changed the axle 1/2 shafts. All
to very minimal effect.

I gave up.

So I had a few other fixes to deal with including new front
springs which lead me also replacing rear springs to get the
car level. This ‘lifted’ the car off the ground a bit more
and also stiffened response on the road - a dramatic
improvment.

After that change the vibrations dropped dramatically. Then
after going through the propshaft alignment process - the
vibrations stopped completely.

The short version of my answer make sure you don’t have worn
out rear springs - I think the weak/sagging causes alignment
issues under acceleration and loading etc…–
GlennLogan
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In reply to a message from asc sent Wed 14 May 2014:

Hi,
Has the car always done this? It could be a number of
things.

Does the diff have enough of the correct oil? Low oil will
cause the diff to grumble, sometimes at a particular speed.
What about transmission oil?

Did you check the pinion angle and alignment of the D/S
while installing?

If the VIIm has a splined yoke(s) are the marks to get the
yoke/DS aligned? If the marks are anything other than 180
Degrees about the DS will ‘‘wallop’’ pretty severly.

What about the rear suspension mounts, have they (or the
sections of the body shell that they mount to) let loose?
If the rear end is free to move about it will not matter
how carefully you align the shaft, as all the angles will
change under load. I presume the VIIM has a Panhard rod, is
this adjusted? Check the ride height, are the springs
tired?

If the XIIM has a rear transmission mount, is it shimmed as
suggested above? Does it have a spring and peg, and if yes,
is the transport pin still in the peg?

What about the rear engine mount? Does the car have one,
and is it adjusted correctly?

I (perhaps naively) presume that a shop specializing in
driveshaft work can be trusted to get the rebuild right. If
you are still getting a vibration with the correct oil
levels and the DS properly aligned at installation, then it
probably means that either the engine or the rear
suspension (or both) are moving around with respect to each
other.

You mention replacing a rear flange due to wear, do you
mean the OP flange on the OD tail, or the input flange on
the diff? How was it worn? This might be a clue as to which
section of the driveline has been moving about (for a long
time).

Andrew–
The original message included these comments:

MVIIM, 4-spd O/D. Briefly, the vibration is speed, not RPM
related. By my speedo, it vibrates noticably around 40-45 MPH.
This is felt in the seat, etc., not the steering wheel, and the


1968 3.8S
Zurich, Switzerland
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