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Twini Clutch Problem
https://www.ausmini.com/forums/viewtopic.php?f=2&t=80816		 Page 1 of 3
Author:  IndigoBlueCooperS [ Sat Mar 23, 2013 11:03 am ]
Post subject:  Twini Clutch Problem
The Twini clutch has been giving me problems for ages – not enough travel for a smooth disengagement.

The clutch uses standard Mini hydraulic components and pedal box. All hydraulic components and mechanical wear points are new including the arm, plunger and all pins.
The only difference being the use of tin cans, not plastic, on the clubman GT pedal box. Not sure if the pedals are the same between the old and new Australian Minis. And for some reason the clutch pedal sits lower than the brake pedal.

Measured up some old master cylinders and found that the push rod on the tin can is about 3mm longer than the one on the plastic style cylinder.

This will result in 3mm more travel in the clutch master cylinder, which equates to about 0.4mm travel at the clutch thrust bearing. Referring to the following link you only need about 0.82mm travel to release the clutch.

http://www.minimania.com/classic-mini-c ... cfm?id=153

Image

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So I will extend the push rods by 3 mm, and give it a go. Need to get the rear engine back in first.
Author:  Mick [ Sat Mar 23, 2013 11:16 am ]
Post subject: 
I don't believe the piston rod length is the issue. Both pistons are pushed up the same distance by the pedal. One may start lower than the other, but it will still go up the same distance in stroke.

If both pistons are the same bore, then both cylinders will displace the same amount of fluid. All a longer push rod "might" do is take up any slack which can be cured by replacing the worn pushrod or clevis pin, or soft/broken pedal spring.

If it is simply two standard mini systems working in parallel, then the solution will be with the same answers we use on our own single clutch minis which have problems of disengagement.

ie. throwout adjustment, clevis pin condition, worn clutch arm ball or bearing carrier, bleeding or master cylinder bore diameter. I would not expect it to be any of the obvious of course given the amount of care you have put into the car. Sometimes its easier to set the clutch cylinder up with the larger 0.75" bore instead of 0.70" to push a little extra fluid through.
Author:  Kennomini [ Sat Mar 23, 2013 11:20 am ]
Post subject: 
Try to make up some threaded pushrods so adjusting them is eaiser in the future.
Image
Author:  IndigoBlueCooperS [ Sat Mar 23, 2013 12:51 pm ]
Post subject: 
Thanks for the comments so far.

I believe it is the piston rod retaining ring that stops the pedal coming up further from the floor. The ring hits the circlip inside the cylinder when you take your foot off, which stops the pedal coming up further.

Thus, the longer rod in the tin can will allow the pedal to come up a little further when you take your foot off. The 3mm longer rod will bring the pedal up about 12mm when you look at the ratio. Thus, with the pedal up higher to start with, the stroke is longer as you push it down and hit the floor.

I am also checking the diaphragms are flat, but I can’t see how that can affect the amount of disengagement – just makes the pedal heavier, or lets the clutch slip if it’s not correct.

Both cylinders are ¾ inch, which makes it a bit heavy with two orange springs.
I like the idea of the adjustable rods, but not sure I will go that far.
Author:  kiwiinwgtn [ Sat Mar 23, 2013 6:55 pm ]
Post subject: 
3mm will make a big difference in disengaging the clutch

what you need to remember 50 odd years on the clutch is probably sitting further down on the crank.

Replaced every thing clutch related in my car and still had problems with the clutch welded in 3mm in the clutch as you are planning rod and the clutch has worked good ever since

you are on the right track
Author:  Mick [ Sat Mar 23, 2013 7:06 pm ]
Post subject: 
IndigoBlueCooperS wrote:
Thanks for the comments so far.

I believe it is the piston rod retaining ring that stops the pedal coming up further from the floor. The ring hits the circlip inside the cylinder when you take your foot off, which stops the pedal coming up further.



Ah yep, now I understand.
Author:  peterb [ Sun Mar 24, 2013 7:03 am ]
Post subject: 
I was reading about your twini project, very interesting. I may be overseeing something and be wrong but why do you need two master cylinders? Why not just one to work 2 slaves? You don't have 4 m/c's to work brakes.
Author:  Mick [ Sun Mar 24, 2013 8:05 am ]
Post subject: 
Brakes are about pressure. They don't need to move the pistons very far at all before they take up thereafter needing simply foot pressure to do their job. Clutches are more about volume. A clutch uses a lot of fluid to move a piston through a longer distance.
It barely manages this one slave cylinder as it is, let alone two pistons.
Author:  IndigoBlueCooperS [ Sun Mar 24, 2013 8:27 am ]
Post subject: 
Two separate circuits were necessary to have both clutch’s disengaging simultaneously at the same rate. If you have one master cylinder feeding two slaves, the one with the least resistance operates first, then the other. I also considered using a cylinder from a duel brake system, but the one I checked had different sized bores for the front and rear.
I think it is like Mick's comment - volume compared to pressure.
Author:  kiwiinwgtn [ Sun Mar 24, 2013 6:39 pm ]
Post subject: 
I just read thru my notes I increased my clutch rod by 6mm
Author:  IndigoBlueCooperS [ Sun Mar 24, 2013 7:28 pm ]
Post subject: 
I was looking at extending the rods by 5mm. If it is too long (rod hits the cross member on the inside) I will put a shim under the cylinder to lift it.
Author:  dalmeny [ Sun Mar 24, 2013 8:29 pm ]
Post subject: 
I believe you are on the right track. I recently spoke to a owner of a clubman LS and he was complaining of the position of the clutch pedal in relation to the brake. You guessed it, someone had fitted a tin clutch master.
Author:  IndigoBlueCooperS [ Sun Mar 24, 2013 8:36 pm ]
Post subject: 
The tin cans work on the "BMC" minis, why do some of us have difficulties fitting them to the late ones?
Author:  Harley [ Sun Mar 24, 2013 8:41 pm ]
Post subject: 
Are the holes or pins worn at all where the pushrods connect?
Author:  dalmeny [ Sun Mar 24, 2013 8:42 pm ]
Post subject: 
I would have thought that with the shaft shorter you would have to push the pedal down to get the clevis hole to lie up with the M/C rod hole :?
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