Hey guys, I'm attempting to bench bleed my new master cylinder and can only get fluid to come out one of the brake line openings (the larger one). Is it possible I have a faulty new master cylinder or is there a solution? Thanks for your help.

 

Is it new or remanufactured? Are you sure that you are pushing the piston enough? I would not try to diagnose it too much or repair it on your own. Doing that with a new master will more than likely void the warranty, and of course brakes are a system that need to be effective 100 percent of the time. If you suspect it to be defective, better safe than sorry. I would return it for another one.

 

A big old plus one on ... ARE YOU PUSHING THE PISTON HARD ENOUGH???

One way to know is ... is fluid just coming out of the rear hole? If so ... you probably ain't pushing hard enough.

Let me ask ... how are you bench bleeding this master? What specific procedure are you following?

Have you ever done this before?

 

I may not be pushing it in far enough because fluid is only coming from the rear hole. How much travel is there? I had it in a vice and was pushing in the piston and planning on placing my fingers over the holes as the piston is released. Continue until there's no air bubbles. Since starting this and having a problem, I did some research and I see there are kits w/ fittings and tubing to run the fluid back into the resovior. It appears that some master cyclinders come with this kit. Mine didn't. Anyways, before proceeding I've got to figure out why no fluid from the front hole? Its a reman cyclinder.

 

Okay, now I have fluid coming from both holes. I'm headed out to get a bleeding kit for the master cylinder. Do you recommend one of the pressurized kits for bleeding the system? Everything in the brake system has been dry.

 

Went to Advance where I bought the master cylinder. They had no bleed kit for the master cylinder or the system! The two plugs they give you with the master cylinder is the bleed kit, they say. How can that work?

 

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AND … its an MGB Master Cylinder!!! No matter really, Both the Ford and the MGB Master Cyl. work exactly the same:
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YouTube - Dual Brake Master Cylinder - How to Bench Bleed (Moss Motors Tech)
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The “adapters” or “bleeding kit” that they keep talking about are a pair of fittings … one screws into the front hole … the other into the rear hole. These fittings each have a nipple on them … that you fit a length of tubing onto. Fill the Master Cylinder’s resiviors with brake fluid … put the ends of the tubing into the fluid … and pump the brakes. Do this until you get no more Bubbles … just fluid under pressure.
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BUT!!!! If you cannot get one of these fitting kits …
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YOU CAN DO IT WITH THE MASTER INSTALLED IN THE TRUCK!!!
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You are gonna need another person … to sit behind the wheel and follow your instructions.
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Install the Master Cylinder into the truck … DO NOT install the brake lines into the master.
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Fill the Master Cylinder with brake fluid.
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... then, cover the holes the brake lines get fitted into with your finger tips.
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Now tell your partner ... seated behind the steering wheel ... to press down AND HOLD PRESSURE on the brake pedal.
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YOU now lift your fingers slightly from the holes.
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This should allow a brake fluid/air mixture out of the master cylinder.
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Even is nothing comes out … YOU tighten your fingers on the holes ... and tell your assistant to "LIFT SLOWLY".
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As long as you have your fingers tightly over the holes ... This will cause the pistons in the master cylinder to suck fluid from the reservoir into the master.
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Repeat the above procedure until you get a good, strong jet of fluid from BOTH holes in the master.
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Install the brake lines into the Master Cylinder.
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MAKE CERTAIN THAT YOU DO NOT LET THE LEVEL OF THE BRAKE FLUID DROP TO ABOUT ¼ FULL … or you will suck AIR into the Master … and will have to start all over again.
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Then bleed the brakes at each wheel, starting at the wheel (right rear) furthest from the Master.


Sorry I didn't answer sooner ... I was out Deer Hunting this afternoon.

Or perhaps I should say ... I was peering anxiously into the woods ... hoping to annoy gentle woodlands creatures with firearms!

No Luck ... oh well.

There's always tomorrow.

 

You need a bigger gun! Around here, folks just use their cars. Works pretty well.

 

Wow, thanks for your help and the video. Good luck with your deer hunting. My sons has killed a 9 and 10 pointer with his bow in the last 2 weeks! He's the luckiest hunter I've ever seen.

Anyhow, I've got the master cylinder off. I was afraid of spewing brake fluid on the new engine and newly painted firewall! You make it sound pretty simple. We'll give it a try and see what happens.

 

Quick question after thinking about your procedure. When pushing the piston in , will it allow me to keep my fingers over the holes?

 

At first ... possibly yes ... Because you will be only pushing air.

But as the Master starts building up fluid to compress in them bores ... and starts pushing more fluid ... and less air ... No.

And THAT'S GOOD!!!

When their bled out correctly ... Masters Cylinders create a LOT of pressure.

 

Bled the master cylinder just like you said......I appreciate the tips. Repainted it and put it back on the truck. Bled the system and have good pedal. I was a little worried since I converted from manual to power during the rebuild but, it all seems good. I won't be able to test it out until I get the front clip back on, but I think it's good to go. Thanks again.

 

Personally, I have never, ever had the need to bench bleed a master cylinder and I probably never will. No system that I have put back together (and there have been a few) has ever needed it. I can't see the point to it really as you have to disconnect the bench bleed lines to put it back in the car which lets air into the system which means you have to bleed the whole system again when its in the car anyway.

Each to his/her own however, so if you feel like doing it then go right ahead...

 

Ozstang, I started out not bench bleeding the master. I put it on the truck but it would not build pressure. After bench bleeding and reinstallation, a few pedal pumps and the system had pressure. It was so simple to do, I wish I had started out doing it.

 

It is hit and miss. I have done it both ways, with successful and unsuccessful bleeding when it is on the truck. For the time possibly saved and lack of frustration chasing it down, I would rather bench bleed it first to save future headaches of taking it off and having to bench bleed anyway.