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Old 09-22-2018, 02:14 PM   #1
71threequarterton
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Master Cylinder how bad does this look? w/ pics

I pulled my master cylinder lid off this morning. You can see the diaphragm that covers the front part of the reservoir was partially collapsed and you can also see that front reservoir has an angled side rather than just vertical.

I'm assuming the collapsed diaphragm is a result of the slanted inside of the reservoir. Does that sound like a fair assessment and is that normal?

From the looks of this, is it possible to flush and bleed until I get all my new parts for a rebuild or how bad does this look?
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Old 09-22-2018, 02:27 PM   #2
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Re: Master Cylinder how bad does this look? w/ pics

Sounds like a fair assessment to me.

If your brakes have been working, I'd probably leave the fluid alone until your rebuild, if it's gonna happen soon. That is kinda ugly.
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Old 09-22-2018, 02:45 PM   #3
HO455
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Re: Master Cylinder how bad does this look? w/ pics

Your diaphragms look fine. Before you put the lid back on compress the diaphragms so they are flat.
The fluid is very dirty as I am sure the inside of the reservoirs are too. If it was me I would suck the old fluid from the reservoirs and as much of the crud with it. Then carefully blot the inside of the reservoirs a dust free rag to get more crud. Then rinse the reservoirs with clean fluid until you can't get any more crud. Doing all of this before bleeding the system means none of the crud you remove will end up inside of your system. It will add about 45 minutes to the job. I've used a hand vacuum pump, a shop vac, and even big syringe clean the bad fluid and crud out. It is a good idea to protect things below with plastic and rag to absorb the drips.

Stocker makes a valid point about waiting. Sometimes if nothings broke don't fix it. When you say rebuild are you talking all new components and tubing?
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Old 09-22-2018, 03:57 PM   #4
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Re: Master Cylinder how bad does this look? w/ pics

Thanks, guys. The brakes are sketchy at this point - they work most of the time but the pedal will often go all the way to the floor and I'll need to release and pump again to get full braking power. I'd call the situation urgent, based on that alone.

I was going to flush and bleed for starters, just to see if that helped but I tried hooking up a power bleeding system and couldn't even get it to seal up properly. It's the Motive black label system with rigid aluminum MC lid and I'm using an Irwin one handed clamp(which should be plenty of pressure) to hold the lid down on the reservoir. When I pump the system up to between 5 - 10 lbs I can immediately hear the air leaking out - it sounds like it's coming from the lid/MC connection but I'm going to test it on something else to see if I have a bad fitting or something on the bleeder system.

Ultimately, I am planning to rebuild the whole system: power booster, MC, prop valve, hard lines, flex hoses and wheel cylinders. I want to have a completely new system in there so at least I know what I'm working with. I wasn't sure if I would do it all at once though...

Thanks for any advice!
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Old 09-22-2018, 04:41 PM   #5
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Re: Master Cylinder how bad does this look? w/ pics

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Originally Posted by 71threequarterton View Post
I tried hooking up a power bleeding system and couldn't even get it to seal up properly. It's the Motive black label system with rigid aluminum MC lid and I'm using an Irwin one handed clamp(which should be plenty of pressure) to hold the lid down on the reservoir. When I pump the system up to between 5 - 10 lbs I can immediately hear the air leaking out - it sounds like it's coming from the lid/MC connection but I'm going to test it on something else to see if I have a bad fitting or something on the bleeder system.
The top of the MC is so crusty & cruddy that I would be surprised if it didn't leak.....
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Old 09-22-2018, 05:12 PM   #6
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Re: Master Cylinder how bad does this look? w/ pics

The symptoms you describe are classic for a failed master cylinder. Some of that crud has made its way to the lip seals in the bore it is causing them to allow fluid past. In addition I would bet the bore has rusted and there are pitted areas that will never allow the lip seals to seal. Time to tear the master cylinder down and inspect. If it has a flawless bore then rebuild with new seals and a complete cleaning. If the bore is pitted then get a new one. I would avoid rebuilt ones due to the lack of quality control by rebuilders these days.
The up side is that if you install a new master cylinder now you can still use it later as it is the first component in the system and won't be contaminated by other old components. You can work your way to the ends later.
Good luck.
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Old 09-22-2018, 05:36 PM   #7
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Re: Master Cylinder how bad does this look? w/ pics

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Originally Posted by Stocker View Post
The top of the MC is so crusty & cruddy that I would be surprised if it didn't leak.....
Good point and a test of the power bleeder system tells me that it is OK so what you're saying makes sense.

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The up side is that if you install a new master cylinder now you can still use it later as it is the first component in the system and won't be contaminated by other old components. You can work your way to the ends later.
That sounds logical to me and I was hoping that was the case so thanks for that.

I keep reading over and over about all the Chinese junk that's out there, otherwise I'd have bought a new MC already but at this point I don't trust anything that's out there unless I know it is made in USA and gets good reviews from guys on here.
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Old 09-22-2018, 07:27 PM   #8
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Re: Master Cylinder how bad does this look? w/ pics

Quote:
Originally Posted by HO455 View Post
The symptoms you describe are classic for a failed master cylinder. Some of that crud has made its way to the lip seals in the bore it is causing them to allow fluid past. In addition I would bet the bore has rusted and there are pitted areas that will never allow the lip seals to seal. Time to tear the master cylinder down and inspect. If it has a flawless bore then rebuild with new seals and a complete cleaning. If the bore is pitted then get a new one. I would avoid rebuilt ones due to the lack of quality control by rebuilders these days.
The up side is that if you install a new master cylinder now you can still use it later as it is the first component in the system and won't be contaminated by other old components. You can work your way to the ends later.
Good luck.
Yup, it is bypassing and is a clear and present danger for you and the people around you when you are driving it. If you replace the master with a Chinese product, it probably just means that it will possibly fail sooner than a US-made product, but there are no guarantees either way. Be sure to bench bleed the new master per the directions, and then try to gravity bleed the system before pumping the pedal. The nasty fluid at the outlet of the master can surge up into the master when you pump it. In fact, if it is that bad, I'd do like was mentioned and mop out the old fluid, but then flush the lines with brake fluid before putting the new master on. That's only a couple of bucks' worth of brake fluid. When you take the old master off, you will be able to assess the quality of the lines. If they have corrosion inside, you may as well chase the lines all the way out to the wheels with replacements.
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Old 09-22-2018, 07:39 PM   #9
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Re: Master Cylinder how bad does this look? w/ pics

No dont leave the fluid alone. protect all surfaces around the MC. then, using as many paper towels as needed. blot the fluid from each reservoir until the reservoirs are empty. then get more paper towels and soak them in Isopropyl alcohol 93%. then continuing to be carfull of the surfaces around the MC wipe out the interior of the reservoir until it is spotlessly clean. then get so Q tips and soak them in Isopropyl alcohol and then carefully clean out the several bleed and drain holes in the bottom of each reservoir.

now when you add new fresh fluid to the system it does not cary filth and rust to the rest of the system and you can be confortable knowing that that filth will not damage the rest of the system as you flush.
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Old 09-22-2018, 08:41 PM   #10
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Re: Master Cylinder how bad does this look? w/ pics

IMHO...that master cylinder needs to be swapped out ASAP....the top seal is being sucked down by internal pressure bypassing inside the old cylinder...

New units are available for around $50...

The brake pipes also look sketchy...lots of rust...should be swapped out ....

Pull some wheels off and the drums / calipers...check for leaks...

Biggest issue when it gets to this stage are the rubber hoses between chassis points to each wheel and chassis to rear axle...they swell internally and can either balloon or develop internal issues that prevent full release...

GOLDEN RULE ....never shortcut on Brake Systems
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Old 09-22-2018, 10:23 PM   #11
71threequarterton
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Re: Master Cylinder how bad does this look? w/ pics

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Originally Posted by AussieinNC View Post
GOLDEN RULE ....never shortcut on Brake Systems
Agree
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Old 09-22-2018, 11:14 PM   #12
Steeveedee
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Re: Master Cylinder how bad does this look? w/ pics

Quote:
Originally Posted by AussieinNC View Post
IMHO...that master cylinder needs to be swapped out ASAP....the top seal is being sucked down by internal pressure bypassing inside the old cylinder...

New units are available for around $50...

The brake pipes also look sketchy...lots of rust...should be swapped out ....

Pull some wheels off and the drums / calipers...check for leaks...

Biggest issue when it gets to this stage are the rubber hoses between chassis points to each wheel and chassis to rear axle...they swell internally and can either balloon or develop internal issues that prevent full release...

GOLDEN RULE ....never shortcut on Brake Systems
The top seal sinks into the master reservoirs when the fluid disappears, right? Such as into the calipers to take of the wear volume of the pads.
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Old Yesterday, 12:56 PM   #13
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Re: Master Cylinder how bad does this look? w/ pics

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The top seal sinks into the master reservoirs when the fluid disappears, right? Such as into the calipers to take of the wear volume of the pads.
That is correct. The seal has the accordion (?) pleats in it to do just that. The idea is to limit the fluid's exposure to air and the moisture it contains. The fluid will absorb moisture out of the air which leads to internal corrosion. (It is best to check your brake fluid on days with low humidity. Not that I ever remember that. You folks in the southwest once again have it better). When the fluid level drops the seal drops without pulling fresh air into contact with the fluid.
If you just put an air tight lid when the fluid dropped it would pull a vacuum and nature being abhorrent would end up pulling air into the reservoirs through the end of the master cylinder. Don't ask how I know that.
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Old Yesterday, 11:51 PM   #14
lil hoodlum
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Re: Master Cylinder how bad does this look? w/ pics

My master cylinder is about the same shape yours is in less the rust on the top. I have another MC waiting to go in.

Question, how do you go about flushing the brake system? I know my brake fluid is in about the same condition as 71 theequartertons.
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