QuestionQUESTION: I have a 1965 Austin Healy Sprite that has an inoperative clutch. The clutch pedal when pushed the first time, disengages the clutch, but the clutch remains disengaged when the peddle is released.You can watch this at the slave cylinder. After a period of time the slave cylinder will bleed down and apply the clutch. Opening the bleed value on the slave quickly releases the slave and applies the clutch. This happens on the first push of the clutch peddle. Pushing the clutch peddle a second or third time gives a solid peddle that will no longer travel downward and feels more like the brake peddle then a clutch. The master and slave cylinders are new and there is a solid steal line between the master and clutch cylinders.
ANSWER: Hi Alberti
You have replaced the master cylinder.
If my memory serves me correctly, the 1965 Sprite has a dual unit master cylinder, serving both the clutch and the brake. When you replace this unit it is essential that you adjust the two push-rods that operate the mechanism. Their length must be set so that there is at least 0.8mm of free play before they start to operate.
My guess is that the clutch operating rod has been set too long, so the internal piston cannot return fully to its rest position. Therefore, when you press the pedal, it pressurises the system, but when you release the pedal it stays pressurised and if you press it again it merely increases the pressure.
If this is not the case, then I would suspect that the master cylinder unit has been built wrongly. The two bores have exactly the same internals, except that the clutch cylinder does not have a one-way valve in it. If the clutch cylinder has been built wrongly with a one-way valve, that would produce the same symptoms.
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QUESTION: Thanks for your quick reply. I did not have enough room to tell more of the story on my first post. After installing the master cylinder I did adjust the operating rods and do have free play. One master cylinder contains bores for both the clutch and brake. After installing the master and slave cylinders having the problem stated before I was able to bleed the clutch and it worked as it should. For two months, about twice a week, I drove the car from the driveway to the garage to work on it. The clutch worked fine. I even went around the block a time or to. Yesterday after not moving it for about three weeks I tried to move it into the garage. It worked ok once in reverse and once in first gear. Then the clutch started working like it did after I first installed the master and slave cylinders. No fluid leaks, master was full. The only bleed method that worked last time was to push down the peddle as fast as you can with the slave bleed open,close the bleed, release the peddle,and repeat many times. Then all worked for two months. I did not try this method yet this time because it takes a second person.
ANSWER: It seems to me that your clutch mechanism may be a bit stiff. Possibly some corrosion in the bushes of the operating lever pivot.
Imagine the following scenario:
1) The clutch pedal is depressed and the cluth has released correctly.
2) You take your foot off the clutch pedal, and the master cylinder retracts because there is a spring inside the master cylinder.
3) However, the clutch operating lever sticks slightly, so the slave cylinder is slow to return. That creates a partial vacuum inside the hydraulic line.
4) With low pressure in the pipe, the cup in the master cylinder allows more fluid to flow round the cup and into the hydraulic pipe.
5) The clutch is still slipping, so you press the pedal a second time, and now you are building pressure in the pipe, making the situation worse. You remove your foot a second time, but now there is residual pressure in the system and the clutch wil not bite.
You can release the clutch by bleeding off the excess pressure, but the next time you use it, it will happen all over again.
If I am right, you need to spray some thin oil such as WD40 on to the outside of the operating shaft (both sides) in the hope that you can lubricate those bushes. Remove the slave cylinder and operate the lever manually as far as you can, over and over again.
I might be looking in the wrong place, but it is worth a try.
Another possibility is that the metal pipe has been kinked causing a restriction. This would produce the same effect.
The reason I think it is those bushes, is because the problem gets worse after the car has been left unused for a while.
One final thought, have you got the right master cylinder? The Mk 2 Sprite (Chassis prefix HAN2) had a 7/8 bore, but the later HAN3 and HAN4 Sprites used a 3/4 bore. These later units are very hard to find, so replacements tend to be 7/8, which causes all sorts of trouble, including a heavy brake pedal.
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Between the metal pipe and the slave cylinder there should be a flexible rubber hose. If this hose has collapsed internally, then you would be able to pump fluid into the slave cylinder, but it would be unable to return. I have seen this with brake hoses, but never on a clutch.
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QUESTION: Hi Barrie,once again thanks for your time and input. The metal line from the master to the slave has no kinks and looks to be in good shape.There is no rubber hose in the run just steel from master to slave. Before I replaced the slave I checked the movement of the operating lever with the slave removed. It moved freely by hand forward and aft without roughness or binding. Of course I was not able to move it by hand far enough to release the clutch. I will give it a shot of WD-40 for luck when I get back on it. I bought the car back in 1965 off the show room floor. I rebuilt the master cylinder once in the early 80's bleed the brakes and not the clutch. The clutch worked ok when I tried it so I let it be. I 1986 I let the car plates expire and I parked it in my garage until now. I would run it in and out of the garage occasionally until in the mid 1990's the slave gave up all it's fluid. You are right about the master cylinder. I replaced the 3/4 bore with the 7/8 bore because the 3/4 is no longer available.The brakes do take a lot move leg force to apply. But the clutch worked for some time after replacement and the same slave cylinder is used on both master cylinders according to the parts stores. Do you think the new slave cylinder could have some internal problem?
Al
AnswerGiven that extra information, either the problem lies within the master cylinder, or the metal pipe has a restriction inside it, such as a piece of rubber that shouldn't be there.
The slave cylinder is so simple that it should not be a problem. I can picture the piston going rusty and sticking in the bore, but if that happened, the line would not remain pressurised, so bleeding off excess pressure would not release it.
There is a company that will re-bush your master cylinder to the correct size and rebuild it correctly. Look at:
http://www.brakecylinder.com/spridgetbrakes.htm
My latest thought is that the rubber cup inside the master cylinder may have swelled with age and/or lack of use. I believe there is a small vertical drilling that should just be revealed when the cup is fully retracted. If the rubber cup has swollen by as little as 2mm then the drilling will always be covered, so there is no way that any excess pressure in the system can be vented.
By the way, are you using regular DOT3 brake fluid, or have you used DOT5 silicone fluid? I have seen several cases of swollen cups with DOT5.
I hope this helps.
