B y Robert B
I put this on my original website before I started the second iteration. There were problems with the first try, and I lay them out. I kept the original part because we learn from our failures as well as our successes. There are still issues with the second attempt, and there may be a third chapter to this saga.
Chapter 1 – Junkyard wars
The first step in converting my clutch to hydraulic was to locate a suitable donor vehicle. I chose an 84 Mazda B2000 pickup. Some things that I didn’t consider fully but should have, were the stroke length on the slave cylinder, and the size and shape of the master cylinder. The B2000 slave cylinder just barely has enough stroke length to operate the clutch, one of the things that I miscalculated in my conversion. I hope to find a cylinder with a longer stroke and put it in at a later date (I did, as witnessed in chapter 2.)
After finding donor parts at the local junkyard, I decided on the mounting location for the master cylinder. I located my clutch pedal inside and measured its location using a hole in the firewall as a reference. That hole went through, so I could locate it from the engine compartment side. My clutch pedal had a hole already in it for the push rod to connect to. I don’t know if this is common to all castings or if this was unique to mine. Make sure that where you mount your master cylinder will give the right amount of throw for the push rod. You can measure this by measuring from the firewall to your hole with the pedal fully up and fully down. If you have to much throw you will probably ruin the master cylinder by overextending the piston, and if you don’t have enough throw, you will not get the full travel from your slave cylinder, and the clutch may not operate correctly. In my case, I lucked out that the hole was giving me a good stroke length on the master cylinder. Unfortunately, the slave cylinder didn’t have the stroke needed to fully work the clutch.
Once I decided on the location for the master cylinder, I measured from the engine side of the firewall and marked the spot. I drilled through the firewall with a drill bit the size of the master cylinder. If I were to do this today, I would recommend using a step or “Christmas tree” bit. They work better on sheet metal and leave a cleaner hole. I had to do some filing and fitting to get the master to seat fully. I also drilled a hole above and below the main hole for the mounting studs, again if I were to do today, I would use my better tool choices to locate these. I would recommend investing in a set of transfer punches to locate the holes accurately. I had to do some fudging to get the studs through the firewall and the master cylinder flange. I originally recommended that if your master cylinder mounts in an area that is just sheet metal you may want to build a mounting plate to spread out the pressure that the cylinder is going to take from the pedal. Make the mounting plate. The pressures involved are very high, much higher that most people realize, and this will flex your firewall constantly. Eventually, it will crack from the strain. A little prevention now will save a lot of crying later. After drilling the holes, I mounted the master cylinder. Then, I measured the push-rod length using the rod from the Mazda pickup. I found that the original push-rod and end could be used if the push rod had some threads cut off. This is important because the end of the rod is shaped to match the master cylinder’s piston and it is typically hardened and polished. If you make your own, it may wear prematurely.
With the master cylinder mounted, I started work on the slave cylinder. I had several ideas on how to mount the slave cylinder, but due to time constraints I chose the quick and dirty method. I mounted the slave cylinder, so it operated the cross shaft. This mounting method leaves one short connecting cable in the mechanism, but I have never had to replace this cable anyway, so I felt confident it wouldn’t be a problem. I located the mounting point for the slave cylinder, and manufactured a spacer out of a thick piece of steel plate to hold the cylinder out from the frame so it would line up with the lever on the cross shaft. I mounted the spacer to the frame and bolted the slave cylinder to the spacer. Then I measured the length of the push rod I would need. I manufactured the push rod from oil hardening tool steel. I threaded one end to take the original clevis from the cable and put a radius on the other end to match the original push rod. I then hardened the rod and cleaned the burnt oil residue from the threads. I then used a buffing wheel and polished the radius to a high polish to limit friction. I assembled the clevis and push rod and connected them to the cross shaft.
The final item to connect was the hydraulic line between the master cylinder and the slave cylinder. My slave cylinder had a small length of flexible hose that allowed for movement in its original application. I left this attached, because if I took it out, I would have had to produce an adapter for the steel line to connect. I picked up a length of brake line from my local auto parts store. Make sure you get the right line, as there is metric and SAE sizes. Try and get the line as close to the correct length as possible because you do not want to cut it. If you have to cut it, you will have to re-flare the end. For brake and hydraulic lines like this, the line has to be double flared to seal well, and for safety. Single flares can split and cause failure. This will NOT happen at a convenient time. The last thing you want is your clutch engaging suddenly and unexpectedly. Most flaring tools you buy at the auto parts stores cannot put a double flare on the tube. There are kits available now for reasonable prices that will, so you can purchase one of those, or you can have your local brake shop re-flare the end for you.
Once you have the line connected and tightened, fill the master cylinder with the fluid that is recommended for the donor vehicle. Have someone help you bleed the system. The correct procedure for bleeding is having one person in the cab and one under the vehicle (make sure to chock the wheels). Run a clear vinyl tube from the bleeder screw on the slave cylinder to a jar half full of clean fluid. Have the person in the cab depress the clutch pedal completely and hold it. After the pedal is depressed, open the bleeder screw until the pressure is gone from the line. Close the bleeder screw, and then have the person release the clutch pedal (they may have to manually pull the pedal up). Repeat this process until no more bubbles are seen coming through the vinyl tube. Check the fluid level about every 4th or 5th press to make sure you don’t run out. If you run out it will suck air into the system, and you will be starting over.
Caution: never reuse any fluid that you have bled out of the system. Dispose of the old fluid in an appropriate manner.
After this installation, my clutch worked MUCH better. However, there were still issues. The slave cylinder stroke was so short, and the sloppiness of the counter-shaft absorbed some of its motion, I had to adjust the clutch so the throw-out bearing was touching the fingers of the pressure plate, causing unnecessary wear on the bearing. Even with this tight adjustment, the disengagement of the clutch was never complete. If I sat in neutral with the clutch depressed, there was enough movement in the transmission that it was difficult to shift into gear and would cause grinding when going into reverse. I ran with this solution for a few years until the master cylinder failed, and I had to find a better solution.
CHAPTER 2 – Mail-order mayhem
After the clutch failed, I knew I had to find a better solution. The answer came to me in the form of a catalog with Wilwood parts. They are better known for their brake parts, but Wilwood has a good line of clutch and hydraulic parts as well. I found that they had just what I thought I needed. A slave cylinder that shortened under hydraulic pressure. By using this, I could eliminate the counter-shaft and have all of my energy go into the clutch itself.
I picked up the slave cylinder and a new master cylinder from the mail order catalog. When they arrived, I went to work on converting my conversion. First, I removed the line and pulled the master cylinder. Luckily, the new master fit with almost no adjustment. I was able to re-use the mounting holes with no problem. The push-rod also fit well and didn’t need any further tweaking.
The real work was down on the slave cylinder. I removed the counter-shaft, the old Mazda slave cylinder, the mounting bracket, and the short cable that ran from the counter-shaft to the clutch fork. I removed the jam nut, nut and pivot washer from the slave cylinder and inserted it into the clutch fork. You can’t slide it in the side like the cable because the stud is too large, and widening the slot would weaken the fork. You may have to drill out the center hole to allow the stud to slide freely through the center hole. I loosely installed the pivot washer, nut, and jam nut. I extended the slave cylinder out to its full length and made sure the clutch for was all the way forward to clear the bearing from the pressure plate. I used this position to figure out how and where to mount a bracket to hold the other end of the slave cylinder. You have a lot of adjustment of the ball end of the cylinder, so this doesn’t need to be exact. I fabricated a bracket to hold this end of the slave cylinder and mounted it. Make sure the body of the slave cylinder is fixed and not the part moving, or it will flex your line constantly and it will break. Make sure you orient the cylinder so the bleeder will face up, or you will not be able to bleed the system. I then installed a new brake line. The same notes apply to brake lines, flares, etc. I then bled the system, and this solution worked even better than the first one.
There are still issues, but most of them are minor and can be lived with. The stroke is plenty for the clutch provided you have the right master. There are several sizes to choose from. I have also had the jam nut come loose and cause my adjustment to change, and even one time it fell off and I nearly lost the pivot washer. All in all, this solution has been very successful. Much better than the original cable solution that would constantly break, pull through the floor, and find other creative ways to fail. I have found that there is a bracket available now that would allow for the use of a more traditional push type slave cylinder, I may try that in the future if I ever have a need to replace this solution.