Master Cylinder Rebuild - DIY

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I had MC bolted to a bracket in a vice and with clevis back on and a screwdriver through it as a handle to pull with, so think I used a good bit of force. Have you done something similar?
 

ClassyJalopy

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@Beto Cruiser are you trying to pull the master cylinder piston from the cylinder without removing the whole assembly? I am having a hard time visualizing it, could you post a pic of what you are dealing with here?
 

Beto Cruiser

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Here's where I'm at. I removed the entire assembly, removed the snap ring, reattached the clevis and put a screw driver through it as Skidoo originally suggested. It came out a little, but not much and not without a ton of force.
PXL_20210130_223120688.jpg
 

flintknapper

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Here's where I'm at. I removed the entire assembly, removed the snap ring, reattached the clevis and put a screw driver through it as Skidoo originally suggested. It came out a little, but not much and not without a ton of force. View attachment 2570715

Used a slide hammer to pull mine. You need to find a way to give it a good jerk (where you are now). You won't be able to pull it out with just smooth pressure. I tried.
 
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HI! Did another road test before pulling out the whole MC for inspection and troubleshooting (MC cleaned before road test). No leaks appeared whatsoever in the areas suspected. But this happened..... 😫

Despite the ABS VSC lights on brakes are functioning. No alarms or beeps. Weird thing is it goes away then comes back. The time I brake tested on gravel to know if ABS works it disappears then comes back on when at full stop and brake pressed (ex. waiting on a stop light). Any clues? I'm losing more hair figuring this out....😩

View attachment 2515563
Did you find the leak?
 

Beto Cruiser

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We able to get the piston out. Leaving overnight seemed to loosen it for some reason. Didn't take much to pull it out.

Now I'm struggling with the reservoir cap... Won't seat anymore. The o ring seems to have swelled. Anyone experience this? Wondering if I can buy a generic o ring for it.
 
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We able to get the piston out. Leaving overnight seemed to loosen it for some reason. Didn't take much to pull it out.

Now I'm struggling with the reservoir cap... Won't seat anymore. The o ring seems to have swelled. Anyone experience this? Wondering if I can buy a generic o ring for it.
I'd go with a generic one

I do have a reservoir for sale if you want to replace the whole thing :)

For Sale - 100 Series Brake Fluid Reservoir - Almost new - So Cal - $70 - https://forum.ih8mud.com/threads/100-series-brake-fluid-reservoir-almost-new-so-cal-70.1225485/#post-13570424 - I'm in SoCal
 

flintknapper

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Beto Cruiser

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Good time to replace the grommets too if he goes this route.

View attachment 2572200
My grommets seemed fine, but when I screwed the reservoir back on it wasn't very right. I could easily rock it around. Couldn't recall if it was always like that tho...

Ill try to match the o ring with something from the store. I'll post the size if I get it right.
 

flintknapper

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My grommets seemed fine, but when I screwed the reservoir back on it wasn't very right. I could easily rock it around. Couldn't recall if it was always like that tho...

Ill try to match the o ring with something from the store. I'll post the size if I get it right.

Grommets have probably gotten soft then.
 
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Was not able to pinpoint exactly where the leak was. But my suspect is where the abs box is.

Update:
After 3 weeks of and changing the MC piston from my previous MC so far so good no leaks. But still have the ABS VSC/TRAC lights on. It comes and goes when I press the pedal long enough. So still not a 100% but ill take it.... a new MC is on my mind but not pulling the trigger just yet....
 
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What is the booster motor run time?
This is after IG key OFF and pumping brake pedal at least 40 times, set level to max mark and no higher. Than IG key to ON and time booster motor run time. Repeat 5 times.
 
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My grommets seemed fine, but when I screwed the reservoir back on it wasn't very right. I could easily rock it around. Couldn't recall if it was always like that tho...

Ill try to match the o ring with something from the store. I'll post the size if I get it right.

My brand new master cylinder’s reservoir rocks around as well. My initial thought is that it’s normal, but I can’t verify.

I’ll add the fact that they when you receive the new master cylinder assembly, you’ll see that they partially fill the reservoir with brake fluid. No signs of leakage when I received it.
 
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abuck99

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The reservoirs seem pretty loose (you can wiggle them around easily). Always wondered about that-but guess its normal.
 
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What is the booster motor run time?
This is after IG key OFF and pumping brake pedal at least 40 times, set level to max mark and no higher. Than IG key to ON and time booster motor run time. Repeat 5 times.
Run times:

32.9 secs
33.0 secs
32.8 secs
32.9 secs
32.8 secs
 
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Was not able to pinpoint exactly where the leak was. But my suspect is where the abs box is.

Update:
After 3 weeks of and changing the MC piston from my previous MC so far so good no leaks. But still have the ABS VSC/TRAC lights on. It comes and goes when I press the pedal long enough. So still not a 100% but ill take it.... a new MC is on my mind but not pulling the trigger just yet....
Did you actually clear the codes after repair and they came back? Just disconnecting battery may not be enough to clear abs codes could require tech stream in your case
 
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Was not able to pinpoint exactly where the leak was. But my suspect is where the abs box is.

Update:
After 3 weeks of and changing the MC piston from my previous MC so far so good no leaks. But still have the ABS VSC/TRAC lights on. It comes and goes when I press the pedal long enough. So still not a 100% but ill take it.... a new MC is on my mind but not pulling the trigger just yet....
A bad MC piston seal, leaks to inside of cabin in foot well. I suppose some could flow to engine bay past firewall to bottom of master, but nor common
Run times:

32.9 secs
33.0 secs
32.8 secs
32.9 secs
32.8 secs
Those times are good Indication no leak or air in system.

Make sure level set to full mark, after pumping pedal 40 times, before IG key turned on.

With these good booster motor run times and level set properly. I'd be diligently listening for booster motor to running, when it should ever time. A motor with a deal spot on commutator can run intermittently. So be mindful of when it should run. Typically after vehicle sat idle for a few hours or after pressing brake pedal 3 times, even 1 press in many cases. If pressure in system drops to point motor is commanded to run and build pressure, but does not. You will then get alarms/lights.

Also be mindful, if most any drive-train DTC (code) is activated, ABS shuts down setting of lights.
 
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Hey guys, I am still chasing a leak to this damn day... its been a long time, and I have incorrectly thought I have fixed it a couple times.

I have replaced the MC, bought a rebuilt pump, and replaced the reservoir grommets.

I do not have leaks in the cabin, so I do not think its the MC seal. The brake lines themselves do not seem to be leaking. It appears that it drips from bottom of the pump to the chassis. Can the pump itself leak? I don't believe the pump is meant to actually communicate with brake fluid, but I could be wrong.

Any ideas? I am at my wits end. Obviously I dont want to buy a new unit, as its over 2k, but I dont know what else to do.
 
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