Loss of Power - GKN Overdrive Issue...?

1995 Defender 300 Tdi / R380 / GKN Overdrive
Newish to me.
Unless the engine’s warm, I can’t change down gears unless the engine’s idling. This is making progress uphill a nightmare as it's anyone's guess whether the engine slows to idle before I lose too much momentum.
Also, if the engine is warm, I can’t reverse - the engine just revs albeit with some progress backwards sometimes.
I've just changed all her oils from grey/brown goop to MTF94 (gearbox), EP90 (transfer box), ATF DII (overdrive) to no avail.
I had an issue a few weeks ago with the clutch pedal not springing back but filled the pot back up with DOT4 and the pedal returned to normal.
What might be the problem? Clutch? Gearbox? GKN overdrive? Transfer box...?!
Thanks.

Clutch I reckon.

Col

Thanks - engine clutch or overdrive clutch?

I'd start by making sure the engine clutch is working properly

Col

Might be time to fit the new clutch slave/master which I have delayed because topping up the reservoir seemed to fix the issue I had with the clutch pedal not springing back!

Can you get an assistant to operate the clutch pedal whilst you watch the actuating arm to see how much it moves. If you needed to top up the reservoir, it must be leaking somewhere. Is there any sign of escaping fluid?

Col

Oddly, there was nothing in the cab floor under the clutch pedal.

Would a lack of movement cause the symptoms? I'm confused as the problem I have shifting forward gears is only there when the engine's cold, and the problem with reversing is only there when the engine's warm?!?!?!

It could be leaking at the slave or the pipe work. A dodgy clutch that still partly works can cause odd problems with gear changes and it is the easiest place to check for problems before worrying about the gearbox.

Col

I really appreciate your help - thanks so much. Best crack on with changing that master and slave cylinder and hope that solves the problem...

benjaminpalma said:

I really appreciate your help - thanks so much. Best crack on with changing that master and slave cylinder and hope that solves the problem...

Click to expand...

Good luck.

Col

could be a few issues over drive wont effect gear selection but likely is the reverse issue

Two problems for the price of one?! That might explain a lot...

benjaminpalma said:

I really appreciate your help - thanks so much. Best crack on with changing that master and slave cylinder and hope that solves the problem...

Click to expand...

Well, it turns out that both the 'plungers' (actual name?) in both master and slave cylinder were heavily corroded. It seems that they were just getting stuck in their bores causing a delay in the release of the clutch, with the delay disappearing once the engine got up to temperature. While changing the cylinders for brand new ones, I took the opportunity to clean up and grease all the other components meaning that my once squeaky clutch is now smooth and silent.

I still have the issue with her not engaging properly and only reversing very slowly if at all. Next stop will be the handbrake, followed by removing the overdrive to see what difference that makes - which will necessitate buying a PTO cover plate and input gear