"MichaelT" <
[email protected]> wrote in message
news:
[email protected]...
> Running an auto at about 80kph (50mph) on unsealed roads. The gearbox
> seems to be changing to third, then bach to 4th all the time. If I run at
> about 85kph it seems to stay in 4th gear. Can the gearbox be 'fixed' to
> stay in 4th gear. (RR 300Tdi, ZF, standard wheels)
> Michael T, Aussie RR
Are you sure it's changing between 3rd and 4th, not 4th locked and unlocked?
There's a hydraulically controlled clutch within the torque convertor that
locks above a certain roadspeed - around 53mph! - to provide a direct drive
for "economy" reasons.
If it's hunting between 4th unlocked and locked and you wish to alter the
roadspeed that this occurs at, then the answer is to remove the sump pan
from the 'box, drop the hydromechanical control valve block assembly off and
invert it to gain access to the 'convertor lock valve' and either soften the
control spring to reduce lock-up speed or stiffen to increase. The effect of
altering the spring pressure is purely trial and error to reach something
you are happy with, but it doesn't need a lot of change, I'd imagine
grinding 2mm off the free length would do what you require.
Badger.
