9 replies to this topic

[mk=john]

Hi
From the title of this post, I am experiencing clutch drag yet again. The clutch on my mini is a pre-verto diaphram type. I first thought I got rid of it by replacing the following items:

Release Bearing, Plunger, clutch arm, allthe clevis pins right up to the clutch pedal.
Basically, now, there is no play in the clutch mechanical systam, and I have also made sure to bleed the clutch hydraulic system. I have checked the seals in both the slave and master cylinders, and everything is as new.

Has anyone had a problem like this, considering I have done a complete overhaul? because my gearbox is 3-synchro, its difficult to change to 1st and reverse without grinding. The clutch pedal has to be right to the floor to change gear.

So, I want to try the following: I want to add a little extra length to the end of the slave cylinder push rod, by putting an M10 size cap (acorn) nut on the end of it (loose fit), so the dome end of acorn nut will sit on the piston in the slave cylinder. I would then need to adjust the clutch, as the arm would be in a slightly different position at rest.

Can anyone give advie on this, and if this is a viable method to prevent clutch drag?
Thanks

Edited by mk=john, 12 September 2007 - 04:11 PM.

[Udo]

I had the same syptoms on the same 3 sync gearbox, even double clutching to first didnt really help, and I added about 1/4 inch to the the end of the slave pushrod with a welder and filed to shape now works perfectly.

Think I read it some where on the IME

[Big_Adam]

Rather than faff about with a m10 bolt. Just set the clutch rest stop out a bit more.

[dklawson]

John, I'm sorry the problem is back. With all you've replaced I'm at a loss as to why you're still having problems.

The adjustable pushrod you're talking about is available from MiniMania. Surprisingly I could NOT find it on the MiniSpares site. Visit www.minimania.com and look up part number C-13H396. Perhaps Simon at MiniSpares could get one for you... perhaps it's available in the U.K. but isn't shown as a catalog item.

I don't think you'll find the acorn nut will fit in the slave cylinder but it certainly won't hurt to try. If you've got all the adjustments done and the wear taken out of the system... the adjustable rod won't do anything for you. Whether you try the threaded rod approach or weld like Udo did, the travel of the throw-out arm is a function of the clutch pedal (master cyl) and slave cylinder travel, neither of which changes by changing the rod length. However, if you have a slave cylinder with a damaged (pitted) bore, using a longer rod can move the piston back in deeper in the slave to extend its life.

Have you tried narrowing the gap between the stop bolt on the clutch cover and the throw-out arm? I know the factory spec is something like 0.020" [1/2mm] with the spring removed. However, that's really a flexible number. If you haven't already tried setting that clearance tighter, I would give that a go. Drop it down to about 0.005" clearance and see how that (hopefully) improves things.

[mk=john]

Hi Guys

The clutch arm is a function of pedal travel, yes, but I am thinking that if the length of the pushrod is increased, the position of the clutch arm at reast is shifted slightly toward the outside of the car. The piston can't be moved deeper in the cylinder as the fluid can't compress.

This all means that when the clutch is disengaged, the pressure late willy be slighylu further away than before eliminating the drag.

Is this a correct theory?

Thanks

[dklawson]

The clutch arm is a function of pedal travel, yes, but I am thinking that if the length of the pushrod is increased, the position of the clutch arm at reast is shifted slightly toward the outside of the car. The piston can't be moved deeper in the cylinder as the fluid can't compress.

This all means that when the clutch is disengaged, the pressure late willy be slighylu further away than before eliminating the drag.

John, once all the wear clearances are taken out, the throw-out arm/clutch travel is strictly a function of the master and slave cylinders. Yes, putting a longer connecting rod in the slave can move the arm further toward the inner wing... but it's not going to do what you think. It will not increase the motion of the components pushing on the pressure plate.

Remove the arm return spring and push the arm toward the inner wing using your hand. This will bring the throw-out bearing into contact with the pressure plate. This is the absolute maximum position towards the wing that you'd ever dare set the arm. It's not really a good practice since there's no allowance for the effects of thermal expansion and you don't really want the throw-out bearing running all the time. Bring the stop bolt out close to the arm in this position and leave at least 0.005" clearance, then refit the spring. That's the most you can hope for. The longer rod won't change this... all it will set the "rest position" of the piston in the slave cylinder "deeper" in the slave.

EDIT:
After setting the stop bolt in this maximum (tight) setting, don't forget to set the other stop nut... the big one on the clutch cover. It's important not to set that one too tight as it controls the force applied on the crank's thrust bearings. However, remove the spring from the clutch arm. Loosen the big nut on the end of the clutch cover. Have an assistant press the clutch pedal and hold it to the floor. Turn the big nut IN until it contact the clutch cover. Have your assistant release the clutch and turn the nut in ONE flat more, then tighten the jam nut. That controls the travel of the clutch and at the same time prevents too much load being placed on the thrust bearings.

Edited by dklawson, 12 September 2007 - 07:38 PM.

[mk=john]

Hi Doug
Yes, shortly after I posted that, I realised that of course the clearance between the clutch arm and its stop bolt is to allow the release bearing to have the clearance (so it doesn't spin) when the clutch is engaged. And so with the spring removed, pulling the clutch arm toward the outside of the car will move the release bearing to touch the diaphram assy.

So, tomorrow I will make the stop clearance smaller on the clutch arm housing bolt. Its currently set to 0.02", and I will make it 0.005"

How much effect does this have on clutch drag, realistically?

Thanks

[mk=john]

Hi Doug, Guys
Today, I checked the clearance between the clutch cover bolt and clutch arm, and I would asy it was somewehere between 1.5 and 2mm!! I didnt check this yesterday, as only recently I set the gap to 0.5mm and didnt expect a shift of this much. I dont know why there was such a shift in gap.

Anyway, I have set the gap to 0.006", and clutch is now operating perfectly. I took it out for a drive, and it shifts easily into all gears. I guess the gap is something I should be checking regularly, perhaps once a month os so, even though I cover a maximum of 3000 miles a year!

Anyway, the clucth now seems fine, but any clues as to the big change in gap which I noticed yesterday will be welcomed.

Thanks

[dklawson]

Hi John, I'm glad you got it sorted with a minor adjustment. I don't really know how to explain the rapid change in setting that you experienced. I know all the components you installed have very little "run time" on them.

Like you, I found during the past few months that I had to put my clutch pedal nearly to the floor for all shifts if I wanted the clutch to completely disengage. On the suggestion of an acquaintance of mine I narrowed the stop bolt gap to 0.005" as you did and found it made a significant difference in pedal height. Based on your experience, I'll check this more often in the future.

[mk=john]

Hi Doug

Yes. its all sorted out now. Perhaps the gap increase was due to all the new components having to "seat in" properly, but thats only a guess. The clutch plate is a new one with no wear, and by now very little wear since it was installed.

I know I also used thick enamel paint to paint the clutch arm after it was installed, and this possibly went over the bolt. Its possible this paint could have worn away where the arm contacts the bolt head, but this wouldn't amount to aver 1mm of paint thickness.

But anyway, it works fine now. The clutch travel/pedal movement I think had a fundamental design flaw as this is a common problem for a lot of people. Where there are fine margins for clearance like this do point to bad design practice on this area of the pre-verto system originating in the 1950's and 60's!!

But that's my view