Heavy clutch pedal

[ctc62925l]

Felow TR owners.

 

On my TR4A i have been troubled with very heavy clutch pedal pressure. To the extent that the wear on push rod, clevis pin and other mec. parts are extensive. Also the clutchpedal action travel is also very small.

PS: the slave push rod is connected to the middle hole in the clutch arm.

 

This winter i reconditioned the pedal mechanics, gearbox and replaced the clutch at the same time with a Borg&Becker type. All mechanical parts move freely and smooth.

Things did not improve so the hydraulics is the next target.

 

Simple hydraulic laws indicate that small diameter pump and/or larger diameter slave cyl. will reduce pressure and reduce slave pushrod travel thus increasing the action travel on the pedal.

 

The pump i have installed is stamped 3/4 and control measurment confirmn a .75" pump diameter.

The slave i have installed is unmarked but is measurd to 7/8" (.875"/22.3mm) this is in accordance to Moss correct. None of my books on TR's mention slave cyl. diameter.

 

So i reconditioned the pump and the slave cyl.

When reconditioning the slave. the replacement kit(moss no. 505704) did not fit, it is to big (or i have a to small diameter slave) if this is true this also confirm my suspicion above on wrong diameter on either pump or slave.

 

So i need your advice on:

 

Is a 0.75" clutch pump correct?

Can i fit a 0.7" pump? (same diameter as brakes) (any part no.?)

Is my 7/8 slave cyl. correct?

Is there a larger bore replacement available ( any part no.)?

 

Regards

Eivin

Norway

[marvmul]

I believe the diameters are correct, and although noticeble, 0.70 or 0.75 cannot make that difference.

The pedal travel should alway be complete to the floor. Does it return to the stop?

I think it's not the hydraulics., rather the forc acting on the bearing carrier : probalbly the pin has sheared,

and then the forc has turned on the transverse shaft : the arm and/or fork is working at a wrong angle then.

[Andrew Smith]

Hi Eivin

 

Had a similar problem with my 3A - had only 2" of clutch travel after fitting a diaphragm clutch conversion.

 

My problem was air in the slave cylinder, as the bleed nipple is lower on the slave cylinder than the hydraulic pipe so air gets trapped in the upper portion of the slave.

 

So try this simple solution, it worked for me:

 

1. Remove the pushrod from the slave cylinder and connect a bleed tube to the bleed nipple, then undo it, by say half a turn.

 

2. Using a blunt screwdriver (so as not to damage the cylinder wall) place it in on the piston and gently push the cylinder back to its stop point and watch all the air that comes out - you'll be surprised!!

 

3. Make sure you connect the pushrod to the hole as detailed in your workshop manual.

 

After carrying out the above steps (which I got from the Technicalities Cd) I then had full clutch pedal travel.

 

Hope this works

 

Regards

Andrew

[stuart]

You may also need to check the flexible pipe to slave cylinder because they can collapse internally and give all sorts of problems including heavy pedal pressure and lack of travel even though they look ok externally.

Regards

Stuart.

Felow TR owners.

 

On my TR4A i have been troubled with very heavy clutch pedal pressure. To the extent that the wear on push rod, clevis pin and other mec. parts are extensive. Also the clutchpedal action travel is also very small.

PS: the slave push rod is connected to the middle hole in the clutch arm.

 

This winter i reconditioned the pedal mechanics, gearbox and replaced the clutch at the same time with a Borg&Becker type. All mechanical parts move freely and smooth.

Things did not improve so the hydraulics is the next target.

 

Simple hydraulic laws indicate that small diameter pump and/or larger diameter slave cyl. will reduce pressure and reduce slave pushrod travel thus increasing the action travel on the pedal.

 

The pump i have installed is stamped 3/4 and control measurment confirmn a .75" pump diameter.

The slave i have installed is unmarked but is measurd to 7/8" (.875"/22.3mm) this is in accordance to Moss correct. None of my books on TR's mention slave cyl. diameter.

 

So i reconditioned the pump and the slave cyl.

When reconditioning the slave. the replacement kit(moss no. 505704) did not fit, it is to big (or i have a to small diameter slave) if this is true this also confirm my suspicion above on wrong diameter on either pump or slave.

 

So i need your advice on:

 

Is a 0.75" clutch pump correct?

Can i fit a 0.7" pump? (same diameter as brakes) (any part no.?)

Is my 7/8 slave cyl. correct?

Is there a larger bore replacement available ( any part no.)?

 

Regards

Eivin

Norway

[ST TR5]

Hi,

 

I had the same problem after a gearbox change to my TR4A, a very heavy clutch pedal, I checked hydraulics etc, then failure, the clutch forc bent and I lost everything. To cut a long storey short, the new gearbox came from a TR4 which uses a different clutch bearing carrier!

 

Cheers Sean

[ctc62925l]

I got this answer from Tec. support.

New 1" slave cyl. is ordered and and i expect my left leg to be the same size as my right within reasonable time.

 

Thanks anyway for many good sugestions.

 

Eivin

 

"""""""""""""""""""2

Eivin Hansen writes from Norway about an excessively heavy clutch on his TR4A. However, he gives his master cylinder diameter as ¾ inch (which is correct) and his slave cylinder diameter as 7/8 inch which is wrong. The TR3, 4, and 4A were all fitted with 1.0 inch diameter slave cylinders as original equipment. The area of the piston in the 7/8 inch cylinder is only 49/64 of the area of the correct 1.0 inch cylinder so the effect will be considerable. Increased pedal pressure will be inevitable and failure of the infamous clutch fork pin can result from excessive travel of the clutch.

 

Eiven asks about part numbers for the various hydraulic components. The correct clutch slave cylinder was originally Stanpart 114531 but this was changed several times ending up as 516788 and the Girling part number was 3010320W (later became 64068867) with Service Kit SP 2036 (later became SP2487).

 

Unfortunately the incorrect 7/8 inch cylinders were much more widely used (on dozens of different vehicle models) whereas the 1.0 inch was comparatively rare (but it was fitted to the GT6, if that helps!).

 

Eiven also asks about substituting the correct 0.75 inch clutch master cylinder for a 0.70 inch one as fitted to the brakes on the 4A (this was a factory change from the 0.75 inch brake master cylinder used on the TR3 & 4). The equivalent master cylinder for the clutch, but 0.7 inch rather than the factory-fitted 0.75 inch, was Girling 64067616 fitted to a number of 1960’s cars including Riley 4/72, Morris Oxford, MG Magnette, Humber Hawk etc.

 

There is nothing to prevent this being done, and it slightly lightens the clutch action at the expense of some lost travel. Whether the lost travel will be a problem varies between individual vehicles and as it is a departure from the original specification Eiven will need to exercise his own judgement..

 

The best advice would be to get the correct 1.0 inch slave cylinder fitted first and then contemplate a master cylinder change as a later possibility.

 

#################

[adriantr4]

Hello

 

I dont think this is your problem - but elderly clutch hoses can contract thus dramatically restricting flow.

This happened to me, I practically had to stand on the clutch when I first got the car. Plus it wouldnt return very fast, giving a "clutch-slip" effect.

 

hope this helps

Adrian + TR4

[jerrytr5]

My problem was air in the slave cylinder, as the bleed nipple is lower on the slave cylinder than the hydraulic pipe so air gets trapped in the upper portion of the slave.

 

I'd suggest yours is fitted upside down. I thought that the slave cylinder was positioned so that the bleed screw is the upper one and the fluid pipe was lower...or am I missing something?

[rudi]

The bleed nipple should be up indeed.

regards, Rudi

[ctc62925l]

I have tried it all, and still the same result.

 

Odered a new slave cyl. from moss. Part no.516788 as recommended from tec. support. Well it is the same 7/8 in. inner diameter and thus exactly the same as the one on the car.

The hydr. hose is replaced. ( no fault with the old one)

The slave cyl. position is corect. with bleed niple upwards.

 

Gearbox is original just renovaqted (profesionally). clutch and bearing is new.

 

This is driving me mad.

 

Regards

Eivin

[marvmul]

Perhaps the problem is a sheared fork or forkpin : if this is the case, the forc will have moved on the transverse axis, and then the clutch arm is working at a wrong angle. This arm should be nearly vertical when the clutch pedal is half way of the travel.

[Bill Wirz]

Eivin,

 

I'm having the same problem. When I changed to a new clutch I started having the problems.

When I compared the old clutch with the new, I found they were not the same size. The old one was aprox. 2" from the face of the flywheel to the top of the clutch housing. The new one was aprox. 1 5/8" from the face of the flywheel to the top of the clutch housing. The fingers on the diaphram spring are about the same height on both. My new clutch works fine, but my wife can't drive the car with this clutch. I'm thinking about replacing the new clutch.

 

Hope this helps,

Bill

[Bill Wirz]

Hi Eivin,

 

Did you ever resolve your problem?

[ctc62925l]

No, did not resolve it.

 

Still very heavty clutch.

The return of the pedal is OK, so no colapsing hose. New steel braided hose.

 

The returnspring is in place ( missing the small piece at the GB end but make no difference.

The action span is short ( eg. the clutch is very "digital" , ON/OFF) very difficult to controll start from standstill)

So i dont know. it seems like a hydraulic problem , so a larger slave or a smaller pump is the answer. But th slave from moss is 7/8" and not 1" as tec. support indicates.

 

The clutch is brand new ( B&, the gearbox is newly renovated.

The only thing i can think of that is not as in the book is that the rod going trough the gearbox where the fork and lever is attached do not have a greasing niple..... but it was lubricated when the gearbox went inn. New trow-out bearin as well. Yes, the fork pinns are in the groove in the bearing.

So i will leave it over the summer and return the car to the shop that did the gearbox. ( i am not happy with the job , 3.gear syncro is not good and there are whining noises when retarding.

 

Another thing... i have been kicking myself hard today.

The engine have had veeery bad power since installing new exhaust, and stalling when pushed hard on high revs.

I hav tried ignition components switch. needles. renovated carbs ,,, you name it. Then i notice some leakage between manifoil and first exhaust pipe, making a little noise. I tried to tighten, but no response. So i dismantlled that joint and removed the gasket..... gues what.... i had placed the gasket 90 deg wrong so that the exhaust was almost blocked. No wonder the car was not performing... after remounting the right way the car was totally transformed and i got the power back. Silly me. But the clutch is still just as hard.

Eivin

[Bill Wirz]

Perhaps the problem is a sheared fork or forkpin : if this is the case, the forc will have moved on the transverse axis, and then the clutch arm is working at a wrong angle. This arm should be nearly vertical when the clutch pedal is half way of the travel.

 

 

Eivin,

Have you checked the position of the clutch shaft as Marvmul has stated above? It should be angled toward the front of the car when the clutch pedal is not depressed and angled toward the back after its fully depressed.

 

Bill