Taking apart brake master cylinder, and how I spent my weekend
#1
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Taking apart brake master cylinder, and how I spent my weekend
Hi guys -
First, I'm looking for any insight on taking apart the FD stock brake master cylinder. More after the story.
So, been working on my buddy Jon's FD for about a year now - basically building a chassis up from nothing. Got it running last weekend, and did the brakes this weekend.
Put the calipers, freshly turned discs, and new pads on the car. Used my Motive power bleeder and a vacuum bleeder at each caliper (and Speedbleeders, overkill). I was able to bleed the whole system but I noticed -
- the front calipers didn't move at all. Stomp the brakes and you could spin the rotor by hand.
- Rear brakes did fine
- The brake pedal would go down about halfway then feel like it hit a SOLID WALL. You could NOT push past it.
With a rear bleed nipple open, you COULD push past the "wall" but you could still feel it and going past took some effort.
We tried a few things - bench bled the master cylinder, opened lines and checked for pressure at different parts of the system, etc. The master cylinder was on his old car when it was wrecked (long story) about 2 years ago and has sat since then.
Finally we swapped another master cylinder in from the rolling shell that we built up and BINGO - brakes bled like normal, all calipers working, and the pedal feels totally normal. You push down about an inch or something and get firm resistance - not a wall, but firm pushback.
So, I'd like to see what's wrong with the bad master cylinder. Doing some reading I found that people have stated that a valve inside will stick if it sits, and if you open it up and get the valve moving again you're fine. Thing is I can't figure out how to take the damn thing apart!
There's a snap ring at the back where the rod from the booster goes in - removed that, and removed the washer under that. There's another flat surface under that with 3 very shallow round indentations. It looks like that needs to come out and then the rest of the assembly slides out. But it won't go anywhere, even pumping the piston of the master in and out.
I also removed the lock pin on the side of the master.
Any ideas? If it's simply a stuck piston I'd like to open it up, fix it, and have a good master (it's clean and has no external leaks).
Thanks,
Dale
First, I'm looking for any insight on taking apart the FD stock brake master cylinder. More after the story.
So, been working on my buddy Jon's FD for about a year now - basically building a chassis up from nothing. Got it running last weekend, and did the brakes this weekend.
Put the calipers, freshly turned discs, and new pads on the car. Used my Motive power bleeder and a vacuum bleeder at each caliper (and Speedbleeders, overkill). I was able to bleed the whole system but I noticed -
- the front calipers didn't move at all. Stomp the brakes and you could spin the rotor by hand.
- Rear brakes did fine
- The brake pedal would go down about halfway then feel like it hit a SOLID WALL. You could NOT push past it.
With a rear bleed nipple open, you COULD push past the "wall" but you could still feel it and going past took some effort.
We tried a few things - bench bled the master cylinder, opened lines and checked for pressure at different parts of the system, etc. The master cylinder was on his old car when it was wrecked (long story) about 2 years ago and has sat since then.
Finally we swapped another master cylinder in from the rolling shell that we built up and BINGO - brakes bled like normal, all calipers working, and the pedal feels totally normal. You push down about an inch or something and get firm resistance - not a wall, but firm pushback.
So, I'd like to see what's wrong with the bad master cylinder. Doing some reading I found that people have stated that a valve inside will stick if it sits, and if you open it up and get the valve moving again you're fine. Thing is I can't figure out how to take the damn thing apart!
There's a snap ring at the back where the rod from the booster goes in - removed that, and removed the washer under that. There's another flat surface under that with 3 very shallow round indentations. It looks like that needs to come out and then the rest of the assembly slides out. But it won't go anywhere, even pumping the piston of the master in and out.
I also removed the lock pin on the side of the master.
Any ideas? If it's simply a stuck piston I'd like to open it up, fix it, and have a good master (it's clean and has no external leaks).
Thanks,
Dale
#2
Rotary Freak
Pulled 2 or 3 of them apart a year or so ago, 1 was reluctant.
There's no additional bits beyond the circlip to undo. It turned out it was just drag from the two O rings around the piece surrounding the push rod iirc - and surprisingly strong! The hard pedal sounds a bit like the pin was inserted in the front piston groove improperly at one stage maybe? I wouldn't take outside condition as too indicative of the bore shape either.
There's no additional bits beyond the circlip to undo. It turned out it was just drag from the two O rings around the piece surrounding the push rod iirc - and surprisingly strong! The hard pedal sounds a bit like the pin was inserted in the front piston groove improperly at one stage maybe? I wouldn't take outside condition as too indicative of the bore shape either.
#3
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Thanks for the input! The master has never been taken apart, he bought it with low mileage back in '02 or so and I've been the only one working on the car.
I messed with it last night, still can't get the damn thing to come apart. The seal around the shaft that goes in and out came out, but that didn't get me any closer to anything. Beat on it some with a hammer, that didn't do anything .
Any other suggestions are appreciated!
Dale
I messed with it last night, still can't get the damn thing to come apart. The seal around the shaft that goes in and out came out, but that didn't get me any closer to anything. Beat on it some with a hammer, that didn't do anything .
Any other suggestions are appreciated!
Dale
#5
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Not yet, but that's a good idea. I have a feeling it will make a BIG mess if it does pop out .
I'll try that out tonight.
Dale
I'll try that out tonight.
Dale
#6
Racecar - Formula 2000
I'm guessing that somehow something got in there that swelled the (front) seals and locked them to the wall. I've seen that in race masters, clutch slaves and calipers that were not cleaned and lubed with "brake grease" after manufacture or rebuild.
#7
Racecar - Formula 2000
If you have some brake fluid and a hydraulic pump or empty grease gun, you could use that to force it apart. Since the fluid is almost incompressible, you wouldn't have the energy that would be stored in air if you used that. So it would be less dangerous /messy.
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#9
Racecar - Formula 2000
If you didn't change pads, and they've been on there for a while, you may have some pad taper wear which will make the pedal lower.
#10
RX-7 Bad Ass
Thread Starter
iTrader: (55)
So, tried compressed air - no dice. It was getting 110psi of compressed air, put it on full blast, pumped it, nothing.
I imagine using a hydraulic force could help but the reservoir is part of the circuit, you would have to fill the reservoir or remove the reservoir and block off the ports for it.
Any other ideas? Anyone actually done this?
Dale
I imagine using a hydraulic force could help but the reservoir is part of the circuit, you would have to fill the reservoir or remove the reservoir and block off the ports for it.
Any other ideas? Anyone actually done this?
Dale
#11
I did this a couple of weeks ago, I had some trouble, but not nearly as much as you appear to be having. I used some channel locks with rubber over the jaws, and a small block of wood against the flange for leverage.. All while the master was in a vise of course.
#12
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Thanks! I'll try that tonight. Not wanting to get super medieval if I'm just missing something dumb, like a tab that has to be pressed or something.
Dale
Dale
#13
Rotary Freak
Here's what is inside. Notched soft jaws in a vice might be best to avoid damaging the hard anodised finish, seals do ride inside the large piece with the O rings on the outside.
#14
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Cool, that picture is a big help!
I think that rear seal (the 3rd item in the picture from the left) is just stuck big time. I'll try a vice and see if I can pull it out.
Dale
I think that rear seal (the 3rd item in the picture from the left) is just stuck big time. I'll try a vice and see if I can pull it out.
Dale
#15
RX-7 Bad Ass
Thread Starter
iTrader: (55)
THANK YOU! It's apart!
First off, I put some of these in my vice -
Clamped the hollow rod coming out of the back of the master cylinder in there - firmly but not crazy tight. Got my hammer and tapped on the back flange of the master cylinder, it came out SO easy. I'm embarrassed it took me this long!
The front assembly seemed to have been the culprit, it was sticky in there. After removing the side bolt/retaining pin I had to fiddle with it a bit to get it out.
Cleaned out the bore with a shop rag and brake fluid, lubed everything up with brake fluid, put back together.
I don't know if I'm going to re-install this master since the one in the car seems to be fine (the spare we put in) but may keep it on hand.
Thanks for everyone's input!
Dale
First off, I put some of these in my vice -
Clamped the hollow rod coming out of the back of the master cylinder in there - firmly but not crazy tight. Got my hammer and tapped on the back flange of the master cylinder, it came out SO easy. I'm embarrassed it took me this long!
The front assembly seemed to have been the culprit, it was sticky in there. After removing the side bolt/retaining pin I had to fiddle with it a bit to get it out.
Cleaned out the bore with a shop rag and brake fluid, lubed everything up with brake fluid, put back together.
I don't know if I'm going to re-install this master since the one in the car seems to be fine (the spare we put in) but may keep it on hand.
Thanks for everyone's input!
Dale
#17
Boost Addict
iTrader: (3)
Just cross referencing another post that I think will be handy for others coming across this:
https://www.rx7club.com/3rd-generati.../#post10424226
https://www.rx7club.com/3rd-generati.../#post10424226
Last edited by nashman69g; 05-06-18 at 10:21 PM. Reason: doh
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DaleClark (05-07-18)
#18
bow leggin'
iTrader: (25)
Dale,
we just had basically the same exact issue. We had the brake system apart to paint the engine bay and the car had been sitting for years.
When we reassembled and bled everything the the front calipers grabbed near the very bottom of the pedal stroke. Fluid would gush into the reservoir when depression the pedal and it was very soft. We swapped the master with a spare that had been sitting, bench bled it and pressure bled the system to no avail. The issue persisted. We took apart the master cylinder and found the stop valve/center pin was stuck and the oriface was clogged.
We blew out be valve, greased the orings and moving parts and reassembled... boom. Issue completely fixed. Hopefully this helps others. It was a fairly simple fix that saved us the cost of a new master cylinder. Here’s a pic of it disassembled and the clogged center pin.
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fc3s-ty (08-03-23)
#19
RX-7 Bad Ass
Thread Starter
iTrader: (55)
Nice! Were you able to take apart, fix, and re-assemble without any new seals or parts or did you have to replace some of the internal components?
Tracked down a NOS Mazda brake master cylinder for the hope chest for my car .
Dale
Tracked down a NOS Mazda brake master cylinder for the hope chest for my car .
Dale
#21
Boost Addict
iTrader: (3)
So just got off the phone with Ray and the master cylinder is currently unavailable. Looks like I have to check stock else where. I disassembled my master and the seals seem fine and pliable but my pedal still goes to the floor. I did notice some very fine scratches (can't feel them with my nails) near the opening of the bore. This could be the issue?? So I'll see if a new master cylinder solves the issue unless y'all think something else is wrong. I tested the ABS system with the car running and the back wheels stop and no leaks else where in the system.
#22
Rotary Freak
Fine scratches at the start of the bore from the metal washer seem common , I know one of these masters was in use and was fine - until an engine bay fire melted the reservoir a bit, but it was still operational even then.....your diagram seems to indicate, no seals bearing on that area in use anyhow. On one bad Alfa in the distant past, did have fluid bypassing the rear seal and filling the booster though!
You could throw a kit at it I guess, but the latest rebuild kit, which should be BCYA-43-41ZA from my scribbled notes from more than a year ago, was almost $Au100 iirc, so it was almost as cheap getting a non-oem master from Rockauto.
You could throw a kit at it I guess, but the latest rebuild kit, which should be BCYA-43-41ZA from my scribbled notes from more than a year ago, was almost $Au100 iirc, so it was almost as cheap getting a non-oem master from Rockauto.
#24
RX-7 Bad Ass
Thread Starter
iTrader: (55)
I've seen a few new master cylinders on Ebay recently. Keep an eye out. Some may be NOS, the one I bought recently was.
Dale
Dale
#25
FD brake master cylinder rebuild
What up guys, I’m rebuilding my master cylinder and I forgot to take pictures of the tear down. Assembled it all and I have 2 left over seals idk where TF they go.
Here are the seals
Here are the seals