I know that there is reference in the archives about this, but I thought it worthy of reviving it for the upcoming driving season. After doing some ‘heavy maintenance’ to my E-type over the past few months (new frame rails, installing the engine block heater, new clutch release bearing/pressure plate and wiring harness) I felt obligated to share one easy upgrade others should consider. It is an easy and relatively cheap upgrade, and is really a single day project. The original slave cylinder with the cup seal and internal spring is really pretty crazy in how it operates. The cup/seal gets cocked and fails easily.The 1991 Isuzu Trooper uses a clutch slave cyl with the same internal bore diameter and a ‘modern’ single piston with a lip seal. I ended up needing to change my clutch release bearing because of premature wear due to the combination of the Jaguar design of internal slave and slight constant pressure of the release bearing on the pressure plate. By going with the Isuzu internal piston and the original E-type SI external slave return spring, I am now able to get the 1/16" free play at the pressure plate face and a slave cylinder that doesn’t need any internal parts other than the piston/seal single unit. The slave cylinder is about 15 dollars at Autozone (part #12413). All you will need to do the change is the external clutch return spring for a SI car with the tab where it hooks at one of the slave mounting bolts, and possibly a new threaded pushrod (I made mine from a long bolt) and some brake/clutch fluid. It works with either type (long or short) slave cyl housing.
My clutch slave failed me last fall and left me stranded, fortunately not too far from home. Second time it happened, the first 25 years ago. This sounds like a great solution. Bookmarked! Thanks.
OK Nick – that got my attention!
Just how, exactly, does one bookmark a thread? can’t find the button . . .
Craig
click on the three dots to the right and below the text of the message, the 4th icon from the left is the book mark.
I did basically the same thing to mine years ago, after several almost immediate failures of stock seals, even in two brand new Lockheed cylinders, which both failed catastrophically within 24 hours of installation. I found a good, generic, off-the-shelf EPDM lip seal, machined a new piston for it, to fit the stock slave cylinder. It’s been working great ever since.
Regards,
Ray L.
Hi Are you just useing the internals in your original S1 Slave or useing the whole cylinder…I looked up the Autozone part…cant see this cylinder fitting the fixing lugs are wrong. https://www.autozone.com/drivetrain/clutch-slave-cylinder/duralast-clutch-slave-cylinder-12413/69754_0_0_104257
Some graphics on this modification would really be helpful.
Looks like he’s using the internals of the Isuzu cylinder and also fitting a S1 return spring.
I am using a Jaguar E-type clutch slave cylinder (sorry, I can’t remember whether it is a SI or SII slave). I took out all the original Jaguar internal parts (internal spring, cup seal and piston stuff). The ONLY thing I used from the Isuzu slave is the internal piston with its attached seal. You can throw away all the other parts from the Isuzu slave (body, internal spring, boot and rod). I used a Jaguar SI slave cylinder external return spring and the ‘tab’ washer that goes on one of the two mounting bolts for the Jag slave. The tab is where the external Jag return spring mounts, and the other end of the spring goes to the fork pin.
During my period of house arrest , like many others, I’m keeping busy by doing a few projects on the E-Type including the Kassaq slave cylinder mod - thanks Kassaq. 
Instead of buying the whole Isuzu slave cylinder I bought the Isuzu slave cylinder repair kit consisting of only the internal parts plus rubber boot. As Kassaq mentions only the Isuzu piston with integral seal is used in this mod. The repair kit I used is Wagner WK124280 for 1988-1991 Isuzu Trooper 2.6L.
Here’s a pic showing the E-Type Lockheed slave cylinder (3.75") with the original piston and seal (top) and the Isuzu piston with integral seal (bottom):
Once the new piston was popped into the cylinder I was able to bench test the piston movement in the cylinder bore using a small squeeze bottle on the supply port - nice and smooth as it should be!
FYI, you may also have read complaints from forum members about the trouble gaining access to the upper mounting bolt when removing the slave cylinder due to lack of room between the cylinder body and the tranny tunnel and the bolt being blocked by the cylinder body. Common tools, other than maybe a swan neck or gooseneck wrench, won’t do the job but I’m sure others have bent up a wrench to get the job done. Instead of that approach, and with time on my hands, I was able to use a 3/8" drive socket (5/8" socket shortened by 1/8") mounted on a short piece of 3/8" square bar stock and a 3/8" open-end wrench on the bar stock in order to turn the socket - nice to have the “right” tools. Here’s a pic:
Fantastic. Thanks Gary. This is one of those cases where pictures are worth a thousand words.
awesome write up! thanks for the pix and part numbers.
Bob F
Gary, I think your socket solution is absolutely clever, not sure I would have thought of it. I use a ‘flex head’ wrench to get to that bolt. I’m glad you were able to post a good picture of the Isuzu slave piston comparison. It makes much more sense to people not familiar with my initial description. 
I found the rebuild kit on Rockauto and had it shipped for a ridiculously low price!
The design is very nice, I do like the concept a lot better than the original. the design reminds me of the piston inside the brake master. It seems to me the seal would outlast the original version, except…
My only concern is that the wagner piston is steel. the original is aluminum.
I dont know if this is a real issue, but it seems to me the slave is suspect to moisture and rust. at least the three I have replaced all had pitting in the bore from moisture getting in. I worry that the steel piston in the steel sleeve could rust in place quicker. The positive is, rather than the seal failing when you are at the furthest point from you home is that you may come out after a long park and find the slave wont work.
I could be wrong. I will still try it the next time I replace a slave cylinder.
Bob F
My S1 is steel IIRC. But I just went ahead and ordered from Rockauto as well. Closeout price couldn’t be beat even with the $3 shipping. Cheap insurance for down the road
The original Lockheed cylinder on my car had an iron piston so when the slave cylinder let go and dumped all the fluid I replaced it with a stainless steel unit from Hyd-dra-cyl (see pic in my previous post) - SS cylinder body and piston … but it also used the simple OEM cup seal so theoretically it still had the possibilty of cocking in the bore! With the SS cylinder & iron piston rusting will not be a concern and, hopefully, the new piston/seal combo (Isuzu) is the fix! 
The chances of a slave cylinder piston rusting solid inside a bore is almost nil with anything less than a multi-year slumber.
If you’re getting that much moisture accumulation in your system, I would suggest more frequent flushing.
By the time the piston is sticking in the bore, there would likely be so much corrosion that your seals would be getting destroyed.
I have the kit also…seems correct…not much to go wrong…
Be sure to take the spring off the Isuzu piston and throw it away. You DON’T NEED the internal spring anymore once you have a one-piece piston. It will only cause you grief. The external return spring is supposed to bring the piston back down to the bottom of the bore and hold it there. Once it is down at the bottom, you then adjust the release bearing to be about 1/16" off of the back of the clutch pressure plate. That way you have ZERO contact between the carbon release bearing and the clutch when everything is at rest. You might need to fabricate a new pushrod as the length of the new set-up might be different than what you had before the change.