Overdrive

[Brian]

My overdrive stops working when it gets to running temperature is this because it's low oil if so is it the same as the gear box oil and how do I check it any advice

[oldengineer]

Hi, Yes the overdrive uses the gearbox oil. There is no seperate filler it takes its supply from the gearbox. You just have to top up the gearbox via the very nicely positioned square plug by the clutch slave cylinder. You just top up until it starts to run back out of the hole.
The easiest way I have found is to use the oil container with plastic tube extension (most gearbox oil containers have them already fitted) or use a pump action oil can. As the oil is quite thick warming it first helps.
Then give it a go and see what happens
regards
Chris

[Galileo]

Certainly one possible cause and a cheap and easy one to check and if needed fix. Sprint oil fill is a square head on the left hand side just under the clutch slave cylinder, fill to it just dribbles out. If you have no idea when the oil was changed, would not hurt to drain and refill, there's a handy drain plug at the bottom. EP90 GL4 oil, or if you're feeling adventurous and wish to use a modern oil then I use Millers TRX 75w90 in gearbox and diff.

edit: Whoops, took a call before clicking submit and I've doubled up with the good advice already given!

[Richard the old one]

I had the same problem a long time ago and it turned out to be the overdrive switch on the gearbox, PART BAU1074A. When switched in initially it would make contact but when the gearbox /O/D warmed up it would open with the result that O/D would drop out. When I took it in to be looked at the experts fitted a replacement O/D but transferred the original gearbox switch to the replacement overdrive. The outcome was as before, for a short drive the O/D would work but when it warmed up it dropped out. I believe that the switch may have some spacers fitted to adjust its height and you may get it to work all the time by taking one or more out.