Re: Modified Stag has Vibration Problems with Ford V6 Engine

[<PGAHOWELLS@domain.elided>]

Hi  Mike. Interesting one this. Very annoying.
It sounds from your desciption you are getting heterodyne vibration. Two
connected rotating masses both out of balance and vibrating at different
frequencies, giving a pulse or drone effect. 
Lets look at what is perhaps out of balance. For sure it will be something
with mass, ie heavy.
You have an Auto, so you have the original propshaft. In the Auto propshaft a
short way in front of the diff there is a rubber elastomer coupling. You can
see the rear most very short tube entering the long tube. The rubber ring is
in there. If this is slightly perished, then the weight of the propshaft will
slightly crush the rubber while the car is parked.  Then the propshaft is not
quite straight, and you get a vibration. The  severity may well vary from day
to day, because the amount of crushability may be different around the shaft,
and the parking period longer or shorter etc. Solution, take it to Feltham
Propshaft services and get a solid one made up, or to GKN in Kingsbury nr
Rugby and get a new piece of tube, complete with new elastomer joint  put in.
Quite costly these jobs. 
You might also have a worn out front sliding splined yoke. Get a new one from
Feltham
As a result of the Ford conversion you might not have a long enough length of
the splined yoke home into the back of the box. I think it may be possible to
pack out the rear propshaft mounting with a purpose made packing drilled
packing ring to shove that yoke further into that box. As at Feltham. 
You might have an early diff nose extension. On page 4-32 of the parts
catalogue you will find part number 211474 up to car LD 3325, and part number
217984 after. One of these has the input shaft too high in relation to the
subframes, and the later one gives a better drive line. I think the early one
is too high. If your car is before LD3325 let me know I will dig out the exact
data. 
Right, that should sort the propshaft.
I don't think its likely your BW auto box is a problem but sometimes torque
converters are out of balance. Lets leave that for the moment and look at the
engine.
I don't know exact data about Ford engines, but it is supposed to be a smooth
engine unlike the V4 which needed a counter balance shaft. So, with engine
warmed up, carbs balanced, and ignition right,and at rest, gradually raise the
revs until you get to whatever revs the vibration starts at, and carry on
raising up to about 4000. Can you feel a vibration, or roughness as you pass
through certain ranges.
If so you have an out of balance engine. It may be within lmits, but when
associated with the propshaft vibration it becomes noticeable. That means
sorting the propshaft may cure it. If not then the engine needs balancing. If
you are really lucky this is a missing fan blade or two. If not then its an
out of balance crank and/or piston rod weights.
If the engine is silky smooth as you rev it, and curing the propshaft hasn't
worked then my guess is it is the torque converter.
By the way to check if the propshaft is vibrating here is a rather difficult
and potentially dangerous procedure you may wish to avoid.
Find a very long gentle hill which has little traffic. Ensure the road is
completely traffic free. 
Drive down the hill at the vibration speed.
At vibration speed, select neutral, and let engine revs die. Do you still have
a vibration. Note yes or no.
Brake gently to slow car right down to 40 and reselect Drive. Don't reselect
2nd because this gives engine braking. Resume normal driving. Go home and
start propshaft balance checks above.
(I tell you this from personal experience but my vibration was at 50, rather
easier to deal with).
You thought your letter was long!!!
I hope however you find something in this lot, even though I cannot promise to
have the solution to your problem, except to say, for certain, things are out
of balance.
As for the previous late owner, you would be amazed what people put up with.
My car must have vibrated nicely for at least four previous owners, none of
them, nor their mechanics, knowing how to solve the problem!
 Peter Howells