Clutch stop technique

Julian West · Joined: 27 Aug 2012 Posts: 29 Location: Bayern, Germany

Can anyone advise on the technique for using the clutch stop to enhance upward and downward gear changes?

There is a video in which the late Stanley Mann advised depressing the clutch pedal fully before engaging first gear and only depressing it halfway for gear changes, thereby avoiding active use of the clutch stop altogether.

Paul Spencer · Posted: Wed May 04, 2016 5:25 pm Post subject:

I think you just have to experiment and see what works for you. It also depends on which gearbox you have. The owners' manuals give advice, although I think this is just for the A box. If you don't have one, they are available at http://www.vintagebentleys.org/. The main thing is only to depress the clutch halfway for down changes.

I have a BS box, which has wide ratios, especially between 2nd and 3rd. I use the clutch stop without double-declutching for 1st to 2nd (usually) and 3rd to 4th, but double-declutch for 2nd to 3rd. I don't use the clutch stop usually for this change, but do if I am going uphill. 1st to 2nd is actually impossible going uphill with this box unless you use the clutch stop - the car is slowing faster than the engine.

This probably doesn't help!

John Murch · Posted: Thu May 05, 2016 5:03 am Post subject:

My car has an A box, in the past I have had the clutch stop set up so that it only really caused an effect with the pedal depressed over half way, It is now set so that it comes in much quicker. My car has a 4 1/2 type clutch stop rather than the 3ltr type.
Upward gear changes are done without double declutching, 1st to 2nd with the pedal almost fully depressed and the lever moved quite quickly. (Previously a circa 1/2 second delay), 2nd to 3rd dont depress the pedal as far, and move lever as quickly as possible, (previously move lever slightly slower) 3rd to 4th as 1st to 2nd.
With the new clutch stop setting, I am finding it more difficult to achieve the silent "knife through soft butter" change, but you can get some very fast changes! With more practice I will improve.
Of course the speed of change will depend on the rpm used.
The above is based on 250miles of driving last weekend, much of it in torrential rain, when my windscreen wipers performed very well for the first time in decades. (Following a linkage rebuild a few months ago).

Paul Spencer · Posted: Thu May 05, 2016 8:09 am Post subject:

The 4 1/2 clutch stop is said to be far more effective than the 3 Litre type (which I have). They are interchangeable. I can set mine to be more fierce than I like it. I seem to remember that the general guidance is to start by setting the stop to stop the shaft from idle in 1 second, then adjust to taste. I have mine a little tighter than that, but not as tight as it was set by a racing man after he did some work on my clutch. Cleaning it every now and then isn't a bad idea.

Julian West · Joined: 27 Aug 2012 Posts: 29 Location: Bayern, Germany

Paul & John,

Thank you for the helpful advice, as up to know I have only been using the pause technique at the change up speeds generally recommended for the A box.

Like Paul's car mine has a BS box which, like the C box, also has a finer mesh than the A, B, or D boxes. According to the literature, this finer mesh demands rather more precision when changing gear.

Another problem I have is getting out of gear into neutral. Sometimes a gear just will not release. Presumably, there is an accelerator pedal technique that I need to learn as well.

John Murch · Posted: Thu May 05, 2016 1:20 pm Post subject:

Julian, could your clutch be dragging slightly? (Not quite fully disengaging). This might give the sympton you describe.
John

Paul Spencer · Posted: Thu May 05, 2016 10:11 pm Post subject:

If you have a BS box, let me know if you find the technique for changing from 1st to 2nd! I have had my car for 13 years and not mastered it yet. I mentioned that I do it on the clutch stop. I didn't mention that I do it at very low speed. The alternative is to drop to idle and 6mph, when it just slots in. But this can mean about 5 seconds in neutral and doesn't work going uphill. You are right that this is the hardest gearbox because of the finer mesh. I have only once changed from 2nd to 1st on the move (I have a 4.23:1 back axle so can get up almost anything in 2nd), and that went in without a sound. Very satisfying!

Robert Craven · Posted: Thu May 05, 2016 11:09 pm Post subject:

When I'd only had my 3 Litre (an A box) a few weeks I had a breakdown on the road and a helpful and obviously mechanically knowledgable stranger stopped to help me. We got the car going again but it wasn't very encouraging when he said he'd had a 3 Litre for a while but in the end sold it because he got thoroughly fed up with the difficulty of changing gear. He said one minute it worked and then next time you used exactly the same technique and it didn't. I've stuck at it though.
PS I agree with John about the possibility of a dragging clutch. Very occasionally I find disengaging a gear needs quite some force as though I haven't pressed the clutch enough and I think it may be an intermittently sticking clutch.

John Murch · Posted: Fri May 06, 2016 4:11 am Post subject:

Julian, If there is a bit of drag on the clutch you would find putting the car into gear when stationary all but impossible. However if the drag is only small the clutch stop may well be able to deal with it. You could try adjusting the clutch stop a bit tighter and see if matters improve.
Get some one to watch what is happening when you depress the pedal.
Do you have a cone clutch? They can sometimes 'stick'.
John

Julian West · Joined: 27 Aug 2012 Posts: 29 Location: Bayern, Germany

John,

Yes I do have a cone clutch, which might well be sticking sometimes. At first I thought the problem was my failure to depress the clutch fully. After fitting a back support, full depression of the clutch then made it impossible to change gear, as I was unaware that a clutch stop was fitted. Is it possible to tell when the clutch stop begins to engage while driving?

If clutchless changes, as recommended by some, are possible surely it shouldn't matter if the clutch does stick? Perhaps the accelerator needs to be set so that there is no torque acting on the gears when deselecting a gear. Hence the question about accelerator technique when slipping, or snatching, into neutral. Perhaps I could achieve this by applying some hand throttle, as suggested by Paul in another thread.

Paul Spencer · Posted: Sat May 07, 2016 1:44 pm Post subject:

I found that the hardest thing with clutchless changes was getting out of gear. It's easy to try - just do the first part of the change without the clutch and see how different it is.

I don't think you will feel the operation of the stop while driving. Best to do it in the garage with someone else looking under the car to tell you what is happening.

Chris Card · Guest

Julian - if you are having difficulty in coming out of gear, it is possible that you have the clutch stop too tight. On my C box, if the stop is too tight the gearbox becomes locked and you cannot move the gear lever until the car is at rest.

I set my clutch stop to stop the clutch in about 1.5 revolutions at tickover (450 rpm).

Chris

Julian West · Joined: 27 Aug 2012 Posts: 29 Location: Bayern, Germany

Chris,

Thanks for your advice, I'll check this when I've next got someone with me.