Clutch Slave Cylinder Piston Replacement

Michael, assuming the piston was bottomed out in the cylinder, it seems it is not traveling that far. But remove the boot and check just how far it is moving and be sure. Then again, would it really matter if it does hit as long as the boot stays on? Use a tie strap?
Tom

Agreed: no matter if it hits the end cap boot, so long as it doesnā€™t push it off. The accordion boot would be OK, too.

Why would the piston bottom in the cylinder? This has been mentioned, but I think itā€™s a gross error. The piston is located midpoint by the internal spring, thatā€™s itā€™s natural resting place. That leaves half the cylinder for travelā€¦about an inch. If it was bottomed, it would be impossible to achieve any free play in the actuator, even the meager 1/16" required by the FSM, because the spring would always hold it taught. Not only that, but the strength of the internal spring would be sufficient to keep the release bearing always engaged, and wearing away.

I canā€™t photograph the boot at the moment, but the problem is that it goes down a way into the cylinder. If the piston bears on it directly, it will eventually pop off. Remember that it wonā€™t always be new. OTH, if itā€™s being lifted by friction from the central rod, that can be relieved with a dab of silicone grease. Itā€™s a lot of fidgeting for something so simple. Jaguar, go figure.

I think the boot is being lifted by the air that is being displaced by the moving piston. Every time the clutch is actuated air must exit the boot and re-enter. If there is water in the area then the slave cylinder will be contaminated. A large bellows type boot might alleviate this problem. I put silicone grease on my clutch rod so that it slides easily in the boot.

The new stainless clutch slave I installed has a rubber boot that grips the actuating rod tightly and the boot will move, even with silicone grease applied. Itā€™s something I plan to keep an eye on once the carā€™s on the road.

The slave I removed had the boot safety wired to the slave housing. I may do that if it becomes a problem. Worked pretty well - the clutch slave was in bad shape, but the boot was firmly attached!

Michael, I see you have the external spring, thus you are setting it up in the non-hydrostatic version. The external spring is stronger than the internal spring. Thus the external spring will pull the rod and the rod will push the piston until it hits bottom, collapsing the internal spring completely. With the piston bottomed out, you then are adjusting the rod for the 1/16inch free play. The external spring will always bring the rod and piston back to this at rest position.
In your case, the internal spring is not really doing too much, which is why some leave it out when using the external spring. Some even say the internal spring my bind up. We have had discussions on this before, and I personally believe it is probably good to keep it in, but not a necessity. (In the previous discussions, I was strongly advocating it be left in for the hydrostatic setup.)
Tom

Much as I dislike playing with the slave cylinder, I think Iā€™ll go back in tonight and install the bellows. The Lockheed seal is 100% dependent on friction to stay in place, and itā€™s resisting force from the actuator rod, air pressure and may impinge the Isuzu piston. Add a little water and a drop or two of clutch fluid, and the friction goes. Thatā€™s a lot of reasons to switch to the bellows seal. The bellows naturally expands and contracts, and it canā€™t impinge on the piston. Thereā€™s no relative movement between seal and rod. Once thatā€™s installed, Iā€™ll do a final adjustment and not think about it again for a long while. Fifteen minutes to install: three days to get it right. I suspect that if I had just used the stock cup seal, Iā€™d be sitting in Barnes and Noble, reading a magazine. Who knew that being an old man could offer so many enticing diversions?

Rob: did you use a Hydracyl slave? If I have to do it again, Iā€™d look at that product. BTW, I notice you have a clutch pin that secures with a cotter pin or maybe thatā€™s a spring pin. Is that stock? Mine secures with a stainless clip, which mates to a notch in the top of the pin. The clip is a real test of eye hand coordination, although I must say itā€™s satisfying when if finally snaps home. I should probably post some photos of this stuff after tonightā€™s do over.

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Yes - a ā€œHye-Dra-Cylā€ stainless slave I purchased from Moss last year. I believe my clutch pin is OEM, but it does have a groove for the clip, and also a hole for a pin. I suspect maybe the hole for a pin was a PO mod? I liked the clip solution, although mine was installed with a cotter pin. I purchased a 10mm clip online and filed it a bit - fits well and I agree with you on the satisfying snap!!

Pin with visible hole and groove, before I cleaned it up:
image

Installed in the car, but only with a paperclip to hold it in place for now. Iā€™ll put the new clip in once I fill and bleed the system, and I have more assurance I wonā€™t need to remove the assembly:
image

If you refer to this photo from Angus McRaeā€™s post, youā€™ll see the problem with that statement:

The Isuzu system isnā€™t the Lockheed system. The spring is much beefier.Itā€™s designed to maintain the piston halfway down the cylinder, although it may not seem that way from the photo. If you try to compress the piston all the way to the back, you end up with a lot of spring force pushing the release arm forward, much more than the external spring can counter. So if you retain the spring, you need a shorter actuating rod and the piston will sit forward in the bore, not compressed back. Having said that, I may go all the way and remove the spring. Or just throw my arms up and install a standard setup and be done with it.

Okay.

okay

That I do not follow. Are you saying somehow the external spring and the internal spring are somehow perfectly matched to balance at some ā€œhalfway point?ā€
I do not know for a fact as I am not familiar with the particular Isuzu system, but I believe the Isuzu system is a hydrostatic system. Therefore, I believe the internal spring in the original Isuzu system will push the piston out to remove all free play from the system. The TOB is in constant contact and will constantly spin. If you call that maintaining a halfway position, I agree. But that is not what you are looking for, you are looking for 1/16 inch free play, thus you need the piston to retract fully each time.
Tom

Mike,

FWIW - You have the little arm fastening the external spring to the slave cylinder mounting bolt in the position that provides the least tension. Mine is about 135 degrees from where yours is - pointing 45 degrees towards the front of the car. And my spring is FAR beefier than the spring you have inside the cylinder. Rotate that arm to put more tension on the external spring, and Iā€™m sure youā€™ll find the external spring will easily push the piston all the way forward until it bottoms in the cylinder.

I would simply remove the internal spring. It serves no useful purpose when you have a carbon throw-out bearing. In the Isuzu cylinder, it is used to eliminate pushrod adjustment, but, as Jaguar learned the hard way, such a system does not work well with the carbon throwout.

I just installed my slave cylinder keeping the Isuzu spring. I used rubber grease as recommended. It will be months before I know how well it works. Iā€™ve not yet researched the external spring arm position. Is there a consensus?


Properly done and adjusted, thereā€™s not a damn thing wrong with that.

Thereā€™s too much JL overthink going on on this one.

The sensible move is to ditch the spring and go back to the longer rod. I canā€™t see increasing spring tension, the clutch system has a heavy enough feel as it is.

I came across the Lockheed service information for clutch slaves. Their description of operation and adjustment is subtly different. Most important, they describe the 1/16" free play as being between the release bearing and the clutch, not in the slave actuator. The question that raises is whether the lever arm ratio is 1:1. Definitely overthinking (See P 29:)

http://www.ttalk.info/Brake-Service-Manual.pdf

Angus: if you fiddle with that, youā€™re going to find that the actuator is being restrained by the release bearing, not by the external spring. This was what prompted me to make a shorter rod. With the stock rod and the Isuzu piston and spring, and especially with the external spring under only light tension, the release bearing riding is the clutch and will rapidly wear.

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The tension of those little springs is completely lost in the noise once you have to start moving the pressure plate. Probably 1%, if that.

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Okay, tomorrow Iā€™ll remove the Isuzu spring (which was @kassaq 's original recommendation) and rotate the external spring arm to increase tension. Iā€™m keeping the stock rod. I believe this is consistent with your recommendations. Thanks to everyone for their help on this topic.

I just spent half my Saturday night under the car, R&Rā€™ing the slave for the third or fourth time this week. I had bought an NOS Leyland-boxed slave, and planned to just drop it in. But no, I decided to read through here and there to see if there were new best practices. And lo and behold, I end up spending most of a week under the car. So here are the facts, no BS. Mind that this is on my '69, your experience may differ, but not really by that much.

  1. It takes just 1.5 lbs of force to compress the Lockheed internal spring. The Isuzu spring requires 8 lbs. Thatā€™s not inconsequential. IEven if the external spring provides over 1.5 lbs of counterforce, it may not have another 6.5lbs in reserve. If you use the Isuzu piston with the Isuzu spring and make no other changes, you are asking for a worn release bearing. I donā€™t care how many hands you wave around, 6.5 lbs is enough to be a problem.

  2. Thereā€™s no need to cock the spring retainer, unless you decided to ignore point 1. The force required to pull the lever back 1/16" is minuscule: free play means no resistance. The external spring is strong enough to do it, without any tricks. unless you insist on compressing the Isuzu spring all the way to the back of the cylinder.

  3. Two things matter with an external slave cylinder: First, the throw. The clutch lever barely moves an inch from rest to full release. If you wanted to move it further, you couldnā€™t do it with a 20 ton press.

The second thing that matters is free play. 1/16", but itā€™s not a critical number. A little looseness is all you need to lift the release bearing off the contact plate. If youā€™re concerned over whether it should be 1/16 or 3/32", your problem isnā€™t mechanical.

  1. The slave cylinder is 3" long. The piston, less than an inch. If you think about what I said in 3), the piston can be in any number of initial positions and offer an inch of throw and 1/16" of free play. So if you choose to use the strong Isuzu internal spring, you can shorten the actuator rod to about 3 3/8" and adjust it with the piston supported at half depth by the spring, with a bit of free play in the rod. It works, but better off without the spring and a long actuator.
  1. The Isuzu accordion seal is da bomb. It doesnā€™t move relative to the shaft, so thereā€™s not going to be any fretting or lifting. Itā€™s probably metric, but that only means the fit is tighterā€¦

  2. When all is said and done, Iā€™m not sure what Iā€™ve gained over the NOS piston and seal. The old slave was installed when I did the five speed, more than twenty years ago. I could have simply installed the NOS cylinder with the stock insides and it would have served for the duration.

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Michael, it does sound like the Isuzu spring is quite strong, and as much as I do think there should be an internal spring, that one should not be used. So I would agree, with the Isuzu piston, do not use the internal spring.

IMO, bottom line, just use what Jag used and worked.
Tom

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FWIW - Mine has run for many years with a piston and seal essentially identical to the Isuzu (except I machined the piston and sourced the seal myself), and NO internal spring. It has always worked perfectly. The internal spring is entirely unnecessary.

Oh, really? Howā€™s this then? Yes, itā€™s a double lip seal slave cylinder piston. It looks like designs have changed a bit in 60 years. I think Iā€™ll stick to the much simpler Isuzu single lip seal piston (with no internal spring BTW) - itā€™s working just fine for me. Thanks for the concept @RayLivingston and @Kassaq. :sunglasses:

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