Defender gearbox problem diagnosis please

with it in a high gear, level ground, all brakes off and clutch pedal depressed will the starter still turn the engine over without the vehicle moving?

I'd expect to be able to snick it out of gear on transition between drive and overrun but a disintegration clutch plate or seized needle roller bearing in flywheel would have these symptoms.

AJH

Clutch not releasing? If the clutch is releasing normally, then I think a gearbox overhaul may be on the cards :-(

Does the clutch pedal pressure feel the same?

If you've not got a hydraulic problem then it may be release bearing or carrier pivots on their way out, a cracked pressure (clutch cover) plate spring, clutch driven plate or lining material or spigot bearing breaking up. May even be oil contamination of the linings. Any of these would necessitate removal of the box, and while you're in there don't forget to renew the clutch fork, they don't last long and may be the main cause of your problem.

Martin

Forgot to mention also seized needle roller between first motion and output shaft.

AJH

Ok, latest symptoms as follows. First, as you suggested, I tried it in high gear, level ground, brakes off, clutch pedal to the floor, engine started normally, no sign of the car trying to move, and then, on easing the clutch up, it bit normally. Switched engine off, disengaged gear. Next, slight uphill gradient, brakes off, first gear engaged, clutch to floor. Starter motor starts engine easily but car then crawls forward very slowly for a few feet, then stops. Ease clutch up, and it bites normally and car moves off. Cannot then disengage gear without switching engine off. Then tried same thing using reverse, with similar result. However, gear would not disengage when I switched off the engine. I had to restart the engine with the clutch pedal depressed, then switch off again, before I could get it back into neutral. So it seems as if it intermittently remains locked into the selected gear even when the engine is switched off (on other occasions, reverse disengages easily once the engine is off). I managed to get it into reverse from neutral with the engine running, but it graunched going in and was reluctant to do so, then would not disengage. Needless to say, I did not try that again in case it made the problem worse! Does that information help to narrow the diagnosis? I think further investigation will have to wait for some daylight and, hopefully, better weather - it's now pitch black and sleeting here! Thanks to everyone for all their input. Simon

"AJH" wrote in message news: snipped-for-privacy@4ax.com...

Failure to disengage with the engine stopped sounds like the gear train being under load when you are not on the flat. I think that's a red herring.

Follow Martin's suggestion - clutch hydraulics should be your first point of call. Does it feel 'normal'? Have you still got the same amount of fluid? External fluid leaks? Pedal returning fully? Pedal return spring unbroken? If the pedal does not return fully, help it by putting your toe under the pedal to keep it up when not pushing it down - any different?

but the clutch behaves normally when a gear is engaged!

We agree there is some strain in the gear train and I think that is what is causing the syncro dog clutches to hold in. Reverse is a separate idler gear which is why that moves but graunches because it's the only gear that is not pre engaged. I think the wind up could be a seized needle roller in the first motion shaft to output shaft unless the lt77 is a lot different from other gearboxes I've seen.

AJH

But not to engage it first, there's definitely something binding.

Unlikely I would have thought, the bearing loading is usually on the layshaft, unless of course there's no oil in the box, and the centre bearing on the input shaft is usually the first to go. Could be a few red herrings in there. :-) If it's not the hydraulics then it's got to come out and you will find it then for sure but I would carefully check the clutch first before stripping the box as you can check that by hand.

Martin

Thanks Martin, that sounds like good advice! As soon as the rain stops I'll thoroughly check the clutch hydraulics, so fingers crossed they are the cause of the problem. Thanks again to everyone for the prompt input - it is all very much appreciated. Simon.