There are three different propshafts for MGA, and you didn't say
which model car. See here: http://mgaguru.com/mgtech/propshaft/ps101.htm
1.) Don't assume anything. Always check the facts. It there is any
perceptible freeplay in a U-joint replace it. See here:
http://mgaguru.com/mgtech/propshaft/ps202.htm
2.) If it is a late 1500 or 1600 type with 2-piece propshaft (fange
at front), there might be wear and freeplay in the sliding spline
just aft of the front U-joint.
3.) The spline joint may also be assembled wrong. Axis of the two
U-joints have to be aligned in same plane to avoid vibration, See
here: http://chicagolandmgclub.com/driveline00/0404/drshafts.html
4.) It is possible to install an early 1500 propshaft with a mid
1500 gearbox. In that case the coupling spline is a mismatched size
and wil not be engaged far enough, which can cause very odd wear on
the spline. That itself should not caue vibration, as the front yoke
is carried in a sleeve bearing that is same diameter for either
propshaft. However, the short engagement length can lead to
premature wear on the sleeve bearing.
5.) The sleeve bearing is very commonly worn. I suppose every early
or mid 1500 type gearbox needs to have the sleeve bearing repalced if
it has not been done before. Running clearance is originally like a
crankshaft bearing, 0.002" on the diameter, or 0.001" clearance on
the radius for oil film. When the sleeve bearing is worn the front
yoke of the propshaft can wobble around with exactly same results as
a loose U-joint (vibration). The radial motion will also make oil
seals fail prematurely. When the sleeve bearing is badly worn it can
make the propshaft yoke and gearbox tail housing catastrophically
self destuct (same as having very loose crankshaft bearings). If the
front U-joint is tight but the yoke moves, then the sleeve bearing
needs to be replaced. See here: http://mgaguru.com/mgtech/gearbox/gt104.htm
Barney
At 11:01 PM 9/8/2012 +0200, Hans Duinhoven wrote:
>....
>After some tests at several revs of the engine and speed I finally
>found, that some vibrations between the speed of 50 and 70 m/h are
>caused by I think an unbalanced driveshaft between the gearbox and
>the differential gear.
>What is the cause of this?
>Can this be rebalanced and if so - how?
>Is it easier to replace the driveshaft with a used one instead of
>rebalancing the one, which is on the car?
>....
At 09:17 AM 9/9/2012 +0200, Hans Duinhoven wrote:
>.... the vibration is in for many years ....
>....
>Play in the UJ's is always verified as part this safety test, so I
>assume the joints are ok.
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