Engine revs drop on clutch depression.

[TomLS]

As above really. The car idles really nicely when sitting in neutral, but when I push in the clutch the revs drop right off and it makes the whole car vibrate. Not a massive inconvenience, and it doesn't stall, but I was just wondering why!?
In all other vehicles the opposite has happened due to the removal of the load of the clutch plate and input shaft from the engine.
It always returns to normal immediately and without fail if I put the engine in neutral and lift the clutch.

I had considered the possibility of the clutch vacuum assistance putting extra load on the engine - until I remembered it's a cable operated clutch .

Any suggestions from the collective mega mind?
Cheers,
Tom.

[mogbob]

Tom
First of all ...have you checked the clutch adjustment as per the manual ? After that, a "look see " at the lickage, under the car, it might throw up some worn parts.
Otherwise , if all apparently OK,it might be end float on the crankshaft.DO NOT put hands anywhere near the front pulley to check whilst the engine is running.Merely observe, engine not running, someone pushing the cluch in and out.
Hopefully it will be the adjustment problem.

Bob

[chrisryder]

it could just be perfectly normal. clutch depression always slows the engine down in minors. that's why when you're setting the tickover speed when in neutral, you set it a bit fast so it still ticks over ok with the clutch depressed.

modern cars tend to have roller release bearings which make very little friction, whereas the minor uses a carbon thrust so there is physical, albeit 'self lubricating' contact when the clutch is depressed, which slows the engine slightly.

with your vibration problem, you could try speeding up the tick over slightly, so that when the clutch is depressed the engine slowing isn't so slow as to cause the horrid vibration.

[MarkyB]

I'm afraid the chances are that the thrust washers are quite worn.
Riding the clutch will make it worse, this means sitting with the car in gear and the clutch depressed when you are waiting at traffic lights or a junction.

If you avoid doing these things it will take a long time to get worse, very worthwhile as it's a fair sized job to sort them out.

[bmcecosse]

Could be the carbon thrust is worn out - and you are now running steel on steel - you can take the rubber bungs out the bellhousing - shine a bright light in one, and look in the other to inspect the carbon. As others have suggested - if the adjustment is too tight - you will be over-pressing the clutch, causing excessive drag. Don't worry about thrust washers just yet..... But yes - it is v important with the Minor to NOT sit with foot on clutch EVER. Not even at traffic lights! And - it's not a cable operated clutch, and certainly not a 'vacuum' clutch - in fact I don't think I know of ANY cars with vacuum clutches!

[TomLS]

Hmmm, all valuable knowlege, cheers chaps!

I need to get under and check the linkage any way - just read up on how to adjust the clutch in the maunal and it seems pretty straight forward.
I hope it's not the crank end-float, I wasn't looking at replacing the engine this year Although I do have an engine oil leak (based on the smell of the oil) which collects where the engine mates with the bellhousing at the bottom...

Chris - nice to know its fairly normal - I'll stick the idle up a smidge and see if it goes away!
Mind you, from what MarkyB says, that might just help to accelerate the wearing of the bush...

When you say its a fair sized job, I take it you mean an engine-out job? Or is it more complex than that?

Not riding the clutch for at least a few seconds is not an option - it takes a few seconds from depressing the clutch, to being able to select first without a fairly almighty CRUNCH!

My mistake about the cable clutch - from what I can see it's a rod-actuated assembly? As for vacuum clutches, how else do they go about assisting the clutch pedal in modern cars? It's the only way I was aware of. I got out of my minor the other day and into our work's box Luton, at which point I nearly put my foot through the floor as the clutch was so light! And that's on a 3.0l Diesel, so I can't imagine the clutch plate is easy to move.

Hopefully, if tomorrows second house viewing and subsequent structural survey goes well, I'll soon be living in a place with a double garage, so a junked 1098cc will be my first purchase for a rebuild and 'tweak' any way. As long as the thrust washer lasts long enough for the rebuild, the engine will be coming out any way

[bmcecosse]

Clutch down - select second gear - then forward into 1st gear.

[kennatt]

never heard of a vacuum assisted clutch

[bmcecosse]

It is done I believe for disabled cars - with a hand lever for the clutch. Seems much easier to just use an autobox!

[katy]

How does the clutch feel if you push the pedal without the engine running? Does it operate w/the same pressure as when it's running?

[daveyl]

I've had this problem a couple of times and in both cases it was clutch related.
The thrust bearing fork doesn't always align perfectly with the pressure plate. So when you apply pressure, it does so, in a 'wonky' fashion (tech term.)
Over time the pressure plate can drop one of the 'locating springs' that hold the 'pressure plate' actuator thingybob (the circular ring that the thrust bearing makes contact with) in place.

The other problem was similar but in this case the clutch fork travel was so extreme that in the end,the thrust bearing inner diameter was rubbing on the shaft. Both cases caused the engine to slall.