BW 35 Automatic Gearbox problem

[Mike Wattam <MikeWattam@domain.elided>]

Hi Peter

First a pair of checks;
.  make sure you have enough oil in the gearbox
.  stall test the torque converter to make sure it is working properly. 
This is a dangerous procedure and MUST be done by an auto gearbox expert
who knows exactly what he is doing.  As a rough-and-ready check, you can
get some idea of how well the torque converter is working by trying a fast
start on a very steep hill - it should still pull away very smartly.  Then
see if the car has good acceleration (and engine speed rising in response
to accelerator movement) in 3rd speed without kickdown.

If it doesn't pass your road test or an expert stall test, you've got a
torque converter problem.

Now, If the gearbox is still involuntarily changing down from 3-2 and the
oil is overheating, I believe your problem lies in the rear clutch which is
obviously slipping and heating up the oil in the first place.  Take half an
eye off the oil and temperature guages and check the rev-counter against
the speedo at speed - if you are getting more than about 3% slip under
load, your rear clutch is slipping.  This is a specialist repair if it is
due to the clutch itself being worn out and you might as well have the
whole 'box sorted out.  

Also suspect a broken/loose hydraulic pipe connection on the valve block. 
The latter can be checked when you whip the sump off.  There is also a
slight possibility that these pipes have been incorrectly connected by DPO
at some point - look for evidence of the sump having been off before, and
of kinks/unusual shaping of the pipes.  However, this is unlikely to be the
cause as you say the problem is heat-related and this fault should show
itself also when the oil is cold.

If as you imply your gearbox oil has been well and truly 'cooked', you will
need to drain it thoroughly, clean out the sump (any evidence here?) and
refill with good clean oil.  personally I would do this twice, to purge the
'box as well as possible. 

I expect you already know that scrupulous cleanliness is essential when
working on an auto 'box, dust off a garage floor is not well received.

Mike Wattam
Chairman - Triumph Stag Register