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Bleeding MC on car?

  • Tutti57
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09 Mar 2019 19:23 #27700 by Tutti57
Bleeding MC on car? was created by Tutti57
My wife's uncle just bought a total roach, thinking it was a deal, and ask me to look it over for him. Well, he drove it over with the brake pedal going to the floor and the thing is all rust.

It needs a lot. I told him it's not worth keeping but he thinks it is, so I started a list and have been working through the problems. The brakes look like that haven't worked in a while. After I flushed the swamp water out, the pedal was still bad bit the brakes for grabby. I figured something was getting hung up, so I put in new calipers and wheel cylinders. That fixed the grabby feel but the pedal is still sinks. I'm not seeing any leaks anywhere and spent a bunch of time bleeding with no changes. I'm think the master is ready for replacement.

I'm wondering if using a vacuum bleeder you can just fill the master and suck out any air through the brake bleeders on each corner or do you HAVE to bench bleed them?

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10 Mar 2019 09:25 #27709 by Matts Auto
Replied by Matts Auto on topic Bleeding MC on car?
You need to bench bleed master, install on car, bleed lines on master then each corner
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10 Mar 2019 09:27 #27710 by Matts Auto
Replied by Matts Auto on topic Bleeding MC on car?
I assume you meant when installing new master?

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10 Mar 2019 09:53 #27712 by Noah
Replied by Noah on topic Bleeding MC on car?
I've had this conversation with other guys at my shop. One of them simply cannot make a brake system repair without changing the master cylinder.
I asked him what is difference between bleeding the MC in a vise versus bleeding it where it lives and only ended up making him mad at me...

I kept a couple little clear tubes with plastic fittings that push into the ports that came with a new master cylinder. I loop them into the full reservoir and slowly pump the pedal, then bleed the system as usual.

For a creeping pedal, I like to plug the MC ports and hold the pedal down. If it still creeps isolated from the plumbing, then the MC is at fault.
If not, then block one or the other port so you can identify which leg of the system is at fault.

"Learn, apply, repeat."
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10 Mar 2019 10:21 #27714 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Bleeding MC on car?
Years back there was a product recall on the master cylinders in a Chrysler UK model to change the master cylinders without bleeding the system. I primed and bench bled the master cylinder in the vise then single pump bled each circuit (slacken any union close to the mc, push pedal hold down close union , allow pedal to return, repeat a couple of times) doing it this way a master cylinder could be changed in 10minutes.

However on some master cylinders the seals seem to fail if you attempt to bleed them the conventional way for this reason I switched to using a pressure bleeder. The fluid resevoir is put under about 10psi pressure after which all you need to is open each bleed nipple in turn.

"Speak Softly but carry a Big Test Light"


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Yesterday 20:55 #27927 by Tutti57
Replied by Tutti57 on topic Bleeding MC on car?
What do you use to block the ports?

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Yesterday 06:22 - Yesterday 06:24 #27934 by Noah
Replied by Noah on topic Bleeding MC on car?

Tutti57 wrote: What do you use to block the ports?


I took a walk through the junk yard and snipped some lines about a quarter inch from various master cylinders and use those fittings. I pinched the cut ends in a vice and gave them each a good glob of brazing rod for good measure.

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Last edit: Yesterday 06:24 by Noah.
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Yesterday 07:26 #27940 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Bleeding MC on car?
Also on non-ABS system ypu can use a bleed nipple, on ABS system with the larger thread a bolt will do.

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