by Karl Bermann
Recently I rebuilt the clutch master cylinder on my ’92 NA. Since I didn’t have any helpers handy to pump the clutch pedal or refill the reservoir, I had to devise a method for doing it alone. The method, described below, worked well.
A piece of wood 26 3/4 ” long. This can be a 1 x 2, a length of thick dowel, a piece of broom handle or molding, anything stiff enough to hold down the clutch pedal. (The length may have to be adjusted for later models.)
A length of clear plastic tubing about 24” long and sized to fit over the bleed nipple on the slave cylinder. The piece I used had an inside diameter of ¼ inch, but something a little smaller would make for a snugger fit.
A quart-size glass or plastic jar or similar container for the tube to drain into.
It helps to have a closed end 8mm box wrench. You can put the wrench on the slave cylinder bleed nipple and leave it there to use like a valve handle because you’ll need to open and close the nipple quite a few times.
Since I wasn't planning to remove the slave cylinder, I found it easier to use a set of ramps under the front wheels and work under the car rather than jacking the car up and taking off the right front wheel. Put one end of the plastic tubing on the end of the nipple, the other in the empty jar.
When you have reassembled the clutch hydraulics, refill the clutch fluid reservoir, make sure the bleed nipple on the slave cylinder is tightly closed. Now, with the piece of wood within reach, slowly depress the clutch pedal with your hand and hold it down while you prop the wood against it, wedging the other end against the bolt that holds down the left front of the driver’s seat. Next, open the bleed nipple on the slave cylinder. You may see some fluid, or just a puff of air, or perhaps some of both in the form of bubbles. In any event, close the nipple tightly again. On your way back to the clutch pedal, check the fluid reservoir and top off as necessary. Hold the clutch pedal down with your hand as you remove the wood brace, then slowly release the pedal. When it is all the way up, press it down again slowly and reinsert the wood. Open and close the bleed nipple again. Repeat the entire process as many times as needed until you see a solid stream of clear brake fluid coming from the nipple with no air bubbles. Be sure to close the nipple tightly each time to avoid sucking air back into the system when you release the clutch pedal. And don’t forget to check the fluid reservoir each time.
Check the clutch pedal with your foot to see if you have normal pressure. If it seems okay start the car and put it in gear (reverse if you’ve got it up on ramps). Now take it around the block and road test it. If all is not right, you’ve still got air in the system and will have to bleed it some more. Re-check the fluid reservoir again after a few hours—you may find that you need to top off the reservoir one last time.
Note: When I did mine, I had let the system drain so I could flush out dirty fluid. The first couple of times I opened the bleed nipple, therefore, I pumped the clutch pedal three times in order to make the process go a little faster, because I knew that the first couple of times all I’d be doing was compressing air.
I have replaced both my master and slave cylinders on my car and have found through this experience that you do not need to open and close the bleed nipple. Because of the location of the slave cylinder gravity does the job. Just loosen the slave nipple and let the fluid run out until there is no more air. You might have to pump once or twice but once the fluid starts to move it works on its own. Tighten, nipple and you're done.
I recently purchased the second Miata (2000, my first a 1990) I've owned and it soon needed the dreaded clutch slave cylinder/master cylinder replaced. I wasn't sure which was the problem so I just replaced both and I'd recommend that to anyone rather than replacing one and then having to go back and maybe replace the other later. My only reservation on doing this repair myself was the bleeding. But, after watching a youtube video someone did I found a great and easy way to effectively bleed the system after installation of the slave cylinder, master cylinder or both. In fact, it was simple. So, here is my description of how to do this one person bleeding that is fast, simple and effective.
First, bench bleed whatever cylinders (slave and or master cylinder or both) you intend to install. There are a number of ways to do this and these methods can be found easily in an online search for how to do the bench bleeding for both the master and slave cylinders. So I won't explain that part here. Main objective is to get some of the air out and some fluid in both parts prior to installation since it will make the final bleeding much easier.
The next part is the most effective way I've found to bleeding the system once the parts are installed. It only takes a few minutes and works like a charm. You will need the following
a small "oiler pump" like you can buy at most auto parts stores for oiling things. One with either a thumb pump trigger or a squeeze type trigger is fine. While they have fairly small reservoirs they will be sufficiently large enough to hold enough brake fluid to fill your system with fluid to spare. And you'll need some clear tubing and of course a new bottle of brake fluid.
Once the parts are bench bled and installed fill the pump oiler with new brake fluid. Attach a piece of the clear tubing to the oiler long enough to go from the engine compartment down to the bleed screw on the slave cylinder (about two feet). Pump the oiler until the fluid is solid in the plastic tubing and coming out the other end. Then temporarily pinch off or plug the end to keep it full of fluid and without any air coming back into the tubing or minimal air from coming back in. Then, fill the master cylinder reservoir about halfway to the full mark with new fluid and leave the top cap off. Now drop the tubing down through the engine bay so it is at the bleeder valve on the slave cylinder and prop the oiler can up somewhere in the engine compartment. Then get down where the slave cylinder is from the wheel well and unplug the end of the plastic tubing and get it on the bleeder valve securely. Make sure to loosen the bleeder valve enough so fluid can easily go through it. Now you are ready to start the bleeding process.
You are now going to pump fluid down into the slave cylinder and up through the line into the master cylinder with any air escaping up through the fluid in the master cylinder reservoir. This works easily because air wants to rise up from the system not down as most people usually try to pump it. It?s just the reverse using this method and the air will come out far more easily. You just lean over the fender into the engine compartment and pump the oiler watching the fluid as it goes down into the slave cylinder and also being able to look over at the master cylinder reservoir for air escaping as fluid and air bubbles come up into the reservoir.
While it may seem like the small oiler doesn't pump a lot of fluid it will if you just keep pumping it. You will eventually begin to see air bubbles come up through the reservoir (make sure cap is off of reservoir) and escape the system. The level of fluid in the reservoir will begin to rise as you are pumping especially as air escapes the system. Once fluid rises above the full mark stop pumping and remove fluid from the master cylinder reservoir (suction or whatever method to get it out) but leave enough fluid in the reservoir (again about halfway to the full mark) to keep air from getting back in the system. Also make sure you still have plenty of fluid in the oiler can
or add some if it?s low. Continue the pumping procedure. You may need to do this about 2 or 3 times until you no longer see any air bubbles rise up through the fluid in the reservoir and only the level of fluid rising. On the final pumping go ahead and pump enough fluid up into the reservoir that it
aligns with the max mark. Now, close off the bleed screw at the slave cylinder making sure it is tightened sufficiently. Get into the car and you should have a nice firm clutch pedal! It really does work like a charm. Remove the tubing from the bleeder valve, lift the oiler pump with the tubing from the engine bay without dripping fluid on fender or engine parts
and you're done! This whole process should only take you about 30 minutes. It is the most effective bleeding procedure I've ever used and it only takes one person to do it
with no other assistance!
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23 December, 2016