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Pumping For Clutch


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I've recently replaced both master cylinders and clutch slave cylinder on my TR3A because the previous ones were leaking. I refilled with silicone hydraulic fluid and bled both systems. The brakes work fine but I have to pump the clutch pedal a couple of times to get the pedal where it belongs. I know that there is no air in the line and it is not leaking. I've adjusted the slave cylinder rod according to the manual to no avail. I've bled the system at the slave and at the master cylinder and there is no evidence of air in the line. I can't figure out what might be causing the problem since it worked before replacing the older parts with the new ones. Any ideas would be appreciated.

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Hi Frank,

               welcome to the forum.

Is the slave cylinder positioned with the bleed screw uppermost?

Have you got the return spring fitted?

Was the everything adjusted with the spring fitted.

Is the master cylinder rod adjusted so there is minimal slack in the system.?

Roger

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Yes the bleed stew is positioned uppermost and the spring is fitted. I adjusted the rod without the spring being fitted so there was no slack in the system and then fitted the spring. The spring has a lot of tension so I don't know how one could adjust the rod properly with the spring fitted. I've done this procedure multiple times with the same result even changing the slave cylinder with another new one and getting the same result. Thank you for the reply.

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It's just that if the master had a smaller bore then original, or the slave had bigger, then you may well need to "pump" to get enough fluid into the slave to release the clutch.

However it is more likely to be something silly, like air in system, arm in the wrong hole on the clutch lever, too much free play between pedal & master cylinder,

broken taper pin :o. etc.

Bob.

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2 hours ago, Lebro said:

It's just that if the master had a smaller bore then original, or the slave had bigger, then you may well need to "pump" to get enough fluid into the slave to release the clutch.

However it is more likely to be something silly, like air in system, arm in the wrong hole on the clutch lever, too much free play between pedal & master cylinder,

broken taper pin :o. etc.

Bob.

I know it's not the taper pin because I took the gearbox out last week knowing that was a weak link. The pin was intact. The slave cylinder was an exact replacement of the original. Same part number so the bores were the same. The only thing that I did different was replacing the original hydraulic fluid with silicone hydraulic fluid.

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33 minutes ago, frankfast said:

The only thing that I did different was replacing the original hydraulic fluid with silicone hydraulic fluid.

Unfortunately that maybe your answer, When bleeding it you have to do it very slowly or it`ll froth and you`ll never get rid of the air.

Stuart.

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Hello Frank,  welcome and well done for raising this.... I have exactly same issue (only difference - ref Stuart above - I stuck with old DOT 4 fluid) but, have kept stumm up to now ... Only thing I could think, in isolation, was that replacement parts are not quite compatible with original (possibly worn) components?

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I consulted with the proprietor of an imported car service garage and he told me he had the same problem with a Jaguar he was working on. He corrected the problem by eliminating the spring that returns the piston in the slave cylinder. I did the same and the clutch responded perfectly. It seems the spring, having a lot of tension, returns the piston in the cylinder to the bottom of the bore. When depressing the clutch pedal the piston has to travel further to disengage the clutch and will not unless depressed twice. Obviously, this is not the way the system was engineered and there must be other factors at work here. But the clutch works fine without the spring since the piston doesn't have to travel as far. I've heard others say that a spring with less tension will also work. The one supplied by Moss has a lot of tension.

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Then you had the adjustment wrong !  the spring should pull the piston all the way back, & then you lengthen the adjustable push rod to get the required free movement.

That way as soon as you press the pedal the release bearing starts to move.

Bob.

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26 minutes ago, Lebro said:

Then you had the adjustment wrong !  the spring should pull the piston all the way back, & then you lengthen the adjustable push rod to get the required free movement.

That way as soon as you press the pedal the release bearing starts to move.

Bob.

The rod is adjusted with the spring off. Correct? Otherwise you wouldn't be able to see the free play on the lever. Yes, I agree the adjustment is made with the piston all the way back in the bore and the rod is turned to eliminate all free play on the lever. That is the way it is adjusted.

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This might not be the solution to  your problem but it is a possibility. If the spring in the master cyl. is weak or broken, the amount of fluid pushing the slave cyl. will be greatly reduced. A symptom of the problem will be a lot of free play in the  master cyl. rod and pumping the clutch pedal will help (temporarily) . This was the first problem I encountered with my TR3A in 1962, but not the last. 

Berry

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I had exactly the same problem. Eventually traced to the slave cylinder it was not returning fully, although it appeared to be. Replaced the cylinder, adjusted as per the workshop manual and problem solved. 

 

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I to bought a new slave cylinder and spring from Moss and I had nothing but trouble with the clutch afterwards. I agree with the originator of this thread that the Moss supplied spring is too strong, it has the affect of pulling the S/C piston too far back into the bore. In my case , the effect of this was to give barely enough clutch to change gear and reverse would often be difficult without crashing the mesh! I recently did away with the spring altogether, adjusted the rod as per W/M and I now have a transformed clutch that works as it should. Is a return spring really necessary? 

Rob

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18 hours ago, RobTR3 said:

I to bought a new slave cylinder and spring from Moss and I had nothing but trouble with the clutch afterwards. I agree with the originator of this thread that the Moss supplied spring is too strong, it has the affect of pulling the S/C piston too far back into the bore. In my case , the effect of this was to give barely enough clutch to change gear and reverse would often be difficult without crashing the mesh! I recently did away with the spring altogether, adjusted the rod as per W/M and I now have a transformed clutch that works as it should. Is a return spring really necessary? 

Rob

As stated above even if you have a stiff return spring if you adjust the clearance correctly by pushing the cylinder fully home and then setting the clearance then it will be fine. Its there to pull the thrust bearing off the clutch fingers to lessen the wear on them.

Stuart.

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When you adjust the free play with the spring removed you need to push the piston all the way back in the cylinder. You may need to do this several times because without the spring the piston will come forward on its own and you may think you have taken out all the free play but it could be way out. when you think you have it right push the clutch lever back as hard as you can and feel for any free play then make the adjustment.

 

  Graham

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18 hours ago, RobTR3 said:

I to bought a new slave cylinder and spring from Moss and I had nothing but trouble with the clutch afterwards. I agree with the originator of this thread that the Moss supplied spring is too strong, it has the affect of pulling the S/C piston too far back into the bore. In my case , the effect of this was to give barely enough clutch to change gear and reverse would often be difficult without crashing the mesh! I recently did away with the spring altogether, adjusted the rod as per W/M and I now have a transformed clutch that works as it should. Is a return spring really necessary? 

Rob

Absolutely it is. I had a too weak spring on my TR2 and it allowed the thrust race to lightly touch the pressure plate. After about 15-20,000 miles it had worn one of the pressure plate arms so much  the pressure plate failed with a bang spreading debris around the bellhousing. The correct spring MUST be installed.

I suspect the problem here is bleeding with silicone fluid. My restoration TR2 has silicone and bleeding is a whole new ball game. My other TR2 has Dot 4 and I have had no problems bleeding its clutch over 43 years ownership.

I spent ages bleeding the silicone fluid clutch and it still isn't right. I will have it done by my mechanic with a pressure bleeder. I understand there is a bit of frothing issue as noted above but for some reason it just can't clear all the air in the clutch line above the master cylinder. I don't know why, maybe somebody here can enlighten us.

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John,

Begs the question, why persist with trying to bleed silicon fluid, when the old DOT4

has never caused any problem?

I tried the silicon fluid years ago, against better advice and regretted it.The new hydraulic rubbers,

of whatever the project was at the time, were swelling up after contact with the silicon and causing mayhem.

New rubbers and a good flush thru with DOT3/4 and all was good.

Cheers

Roger M-E

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After reading this thread again I see you replaced the master cylinders, I did the same and found the same problem with the clutch I just could not get the air out. My fix was to get the original master cylinders sleeved and rebuilt and haven't had any issues since.

 

  Graham

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Stuart/Graham

Thanks for your comments and point taken. I will re-adjust as suggested.

I use Dot4 fluid and have no issues with it.

Rob

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On 5/1/2019 at 10:40 PM, roger murray-evans said:

John,

Begs the question, why persist with trying to bleed silicon fluid, when the old DOT4

has never caused any problem?

I tried the silicon fluid years ago, against better advice and regretted it.The new hydraulic rubbers,

of whatever the project was at the time, were swelling up after contact with the silicon and causing mayhem.

New rubbers and a good flush thru with DOT3/4 and all was good.

Cheers

Roger M-E

Hi Roger,

Dot 4 destroys the paint. No other reason.

The Lockheed master cylinder will leak. If it doesn't initially (highly unlikely as the pipe attachments on the back of the cylinder are a pain in the a...) it will during service when the seals wear. When it does leak it destroys the engine bay paint, many a restoration has started because of master cylinder leaks.

The slave cylinders also leak as it is very difficult to get the joint seating right first time. It took me a few weeks to finally eliminate all the leaks in the various joints. If I had used Dot 4 the new paint would have been severely damaged.

Silicone brake fluid can only be used on a new brake system. Some people will say you only need to replace the rubbers and hoses but you really need an entirely new system.

The car in question is intended to be an immaculate example of an original TR2. It has an all new brake system and all new paint. Silicone is the only answer.

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