Clutch Master Cylinder Rebuild - Exedy vs Mazda internal Parts
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Clutch Master Cylinder Rebuild - Exedy vs Mazda internal Parts
For anybody that is interested in things like this and was wondering. Exedy and Mazda clutch master parts are interchangeable. Now before I go through the details, this wasn't planned and full disclosure, the price between a brand new Exedy Master and the Mazda rebuild kit is probably around $10-$20 depending on where you source them. So if you aren't the type that likes to take things apart or rebuild things or your Master has a lot of miles on it, a brand new master is probably the better option and you don't have to worry about a worn bore and such. I had replaced my clutch master with a new Exedy unit about a year and a half ago. Less than a 1000 miles later, it was leaking internally causing the pressure to bleed down and engage the clutch if you held it in long enough. I had plans to rebuild the factory one and stash it as a hot spare as I do with a lot of my parts that I am able to. Long story short, I could not find the original master cylinder I had pulled out of the car, so I decided to just rebuild the newish Exedy unit with the Mazda rebuild kit for ***** and giggles and as an experiment to see if it was even compatible. Now on Mazdatrix's website, they state "The old Mazda part number FD01-41-990B has been updated to this item." when you are in the Exedy master page. I didn't look too hard but when I was trying to find a Mazda master, everything showed NLA with no part number update. So I'm guessing Mazda just doesn't make them any longer. I was still able to get a new slave cylinder from Mazda.
If you don't want to watch the whole video, the Mazda rebuild kit works in the Exedy master. About half of the parts are definitely different. If you have never rebuilt one, they aren't hard at all and can be done in under 5 minutes depending on how much cleaning you need to do and if you need to try to hone the bore at all (which if you have some serious bore scratching, just scrap it, the rebuild probably won't last long.)
Different parts
- Plunger - Exedy is a steel plunger with 4 vent/bleeder holes vs the Mazda plunger is a plastic type material with 6 vent/bleeder holes. The plungers are dimensionally the same but the seals are in slightly different locations on the plunger as you can see from the video. This doesn't affect the operation since this isn't the main pressure area. This seal is what keeps the fluid from leaking out the back of the master on the inside of the car where the pedal rod enters the master and what was leaking on my original one that caused me to replace it.
- Plunger Washer - Exedy is a copper or brass material while the Mazda is again made of plastic.
- The main spring looks and feels identical between the two.
- The umbrella seal looks identical. This is the seal that I would expect to be bad when you have an internally leaking master cylinder with my symptoms. If you don't find this seal to be bad, then it can be a worn bore (which usually wears the seals as well.) In my case, I could not identify a bad seal nor a worn/damaged bore. Since the master was nearly new mileage wise, the bore still had a very fresh crosshatch and no scoring that I could see. The seal looked to be in perfect shape, no nicks or cuts. The only difference I could find between the seals was the "feel" of them. The Exedy one I pulled out of the master was really soft, while the one in the Mazda rebuild felt pretty firm for rubber, almost on the plastic side of firmness. Now this could be because the one I pulled out had been in Brake fluid for the past year and a half and totally normal. Or it could have been a bad batch of seals that maybe had the wrong compound making it susceptible to break down in the brake fluid. Who knows.
- C-Clips were identical
So not being able to identify an obvious fault with the master, I decided to throw it back together with half new parts and replace the parts that could cause my issue with new ones. I like the idea of having the steal plunger in there rather than the plastic one from Mazda, not to mention, if there was a slight discrepancy in plunger seal diameter that I couldn't find with my caliper, I would rather use the part that was meant to be used with that Exedy body and bore. Mine was not leaking externally so I knew the back seal was fine. I used the new main spring (nothing felt wrong with the old one, I just used the new one) and I installed the new umbrella seal which was my main suspect. The umbrella seal rests on the spring so I matched those two Mazda parts together. I re-used the copper washer as well since there is probably a reason why they used metal with metal and plastic with plastic with the plunger/washer combo, and again, nothing was found damaged with it.
After throwing it together, problem is fixed. So there had to have been something wrong with that umbrella seal. Maybe it was too soft and part of it was rolling back causing it to leak? Maybe being too soft just allowed the pressure to compress it a little too much and bleed by? I will never know, but the new parts fixed the issue so the issue had to have been with that seal one way or another.
If you don't want to watch the whole video, the Mazda rebuild kit works in the Exedy master. About half of the parts are definitely different. If you have never rebuilt one, they aren't hard at all and can be done in under 5 minutes depending on how much cleaning you need to do and if you need to try to hone the bore at all (which if you have some serious bore scratching, just scrap it, the rebuild probably won't last long.)
Different parts
- Plunger - Exedy is a steel plunger with 4 vent/bleeder holes vs the Mazda plunger is a plastic type material with 6 vent/bleeder holes. The plungers are dimensionally the same but the seals are in slightly different locations on the plunger as you can see from the video. This doesn't affect the operation since this isn't the main pressure area. This seal is what keeps the fluid from leaking out the back of the master on the inside of the car where the pedal rod enters the master and what was leaking on my original one that caused me to replace it.
- Plunger Washer - Exedy is a copper or brass material while the Mazda is again made of plastic.
- The main spring looks and feels identical between the two.
- The umbrella seal looks identical. This is the seal that I would expect to be bad when you have an internally leaking master cylinder with my symptoms. If you don't find this seal to be bad, then it can be a worn bore (which usually wears the seals as well.) In my case, I could not identify a bad seal nor a worn/damaged bore. Since the master was nearly new mileage wise, the bore still had a very fresh crosshatch and no scoring that I could see. The seal looked to be in perfect shape, no nicks or cuts. The only difference I could find between the seals was the "feel" of them. The Exedy one I pulled out of the master was really soft, while the one in the Mazda rebuild felt pretty firm for rubber, almost on the plastic side of firmness. Now this could be because the one I pulled out had been in Brake fluid for the past year and a half and totally normal. Or it could have been a bad batch of seals that maybe had the wrong compound making it susceptible to break down in the brake fluid. Who knows.
- C-Clips were identical
So not being able to identify an obvious fault with the master, I decided to throw it back together with half new parts and replace the parts that could cause my issue with new ones. I like the idea of having the steal plunger in there rather than the plastic one from Mazda, not to mention, if there was a slight discrepancy in plunger seal diameter that I couldn't find with my caliper, I would rather use the part that was meant to be used with that Exedy body and bore. Mine was not leaking externally so I knew the back seal was fine. I used the new main spring (nothing felt wrong with the old one, I just used the new one) and I installed the new umbrella seal which was my main suspect. The umbrella seal rests on the spring so I matched those two Mazda parts together. I re-used the copper washer as well since there is probably a reason why they used metal with metal and plastic with plastic with the plunger/washer combo, and again, nothing was found damaged with it.
After throwing it together, problem is fixed. So there had to have been something wrong with that umbrella seal. Maybe it was too soft and part of it was rolling back causing it to leak? Maybe being too soft just allowed the pressure to compress it a little too much and bleed by? I will never know, but the new parts fixed the issue so the issue had to have been with that seal one way or another.
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