Brakes: Once More: Bench Bleed the Master Cylinder!

[BobPalma]

'Got a Co-Operator inquiry today from an SDCer who was at his wit's end about no "pedal" on the Avanti on which he was working. All new everything, including a Turner Brake disc kit up front, dual-piston master cylinder conversion; the whole nine yards.

But he couldn't get a "pedal" on the first stab no matter how many times they had bled the system.

I replied that it sounds like they hadn't bench-bled the Master Cylinder and there's "no way" they were going to get a pedal unless the master cylinder had been properly bench bled before being installed on the car.

'Got a reply later in the day saying they indeed had not bench bled it and they had just removed it and bench bled it and now the brakes work fine; a good pedal on the first stab.

This cannot be overemphasized. BP

[pbrown]

I'm about to pick up a running 59 Silver Hawk that has no brake pedal.

I was just going to fill it with fluid to see

1: if if works at all once there's fluid
and
2: where it might be leaking

Obviously I'm not planning on removing the master cylinder and bench bleeding it first - but do I take this to mean that I will never have a good system unless I eventually do?

(And yes I know that I need to replace the flex lines before really trusting it)

PB

[Ron Dame]

Funny thing... I have only bench bled a MC once... and it was the only time I had trouble getting a decent pedal. But the problem was not related to bench bleeding, still it's ironic.

Going way on back, when I was a kid and did not know what bench bleeding was, I've changed maybe a dozen or more MCs of various make cars and trucks, and had no trouble. All were firewall mounted, and maybe that's part of it. Even once I knew what it was, since I had no problems, I did not see it as truly necessary. And none really required an extraordinary amount of effort to bleed them.

Still it appears that most have problems if they don't bench bleed.

Am I just lucky?

[aftontrix]

I installed a complete brake system including new lines. My problem was trying to bleed the system by myself. This was difficult to do so I installed "self bleeders". I opened each one, pumped several times each and I ended up with a full pedal. I refilled the master cylinder after bleeding each wheel. I had never heard of bench bleeding so I did not know to do it. Next time I will do it as it would not be that much trouble.

[doofus]

recent experience; replaced complete brake system on '56 2dr wagon, steel lines rubber hoses m/c & w/c's. with wagon on 4 jack stands i opened r/r wheel bleeder and added small hose from bleeder screw to a small jar with an inch of brake fluid in it. filled m/c and gave it 4 slow pumps and left for lunch. later closed r/r bleeder and did same procedure on r/f and let stand for several hrs. that evening closed r/f and topped up m/c. now have good brakes! have had good brakes for 3 yrs now while i do body work and build r/1. Doofus

[JoeHall]

Most every new MC comes with instructions to bench bled first, but they probably don't know what they are talking about

I too, do not normally bench bleed a new MC before install, but (keeping the reservoir topped off) lightly pump the pedal many times (maybe 100) and watch till every last one of the tiny bubbles stop coming out. Then and only then, do I move to the right rear wheel to begin bleeding.

I am guessing, if bench bled first, there'd be no need for pumping the pedal till the bubbles disappear (same thing bench bleeding accomplishes). Further, if one began bleeding immediately at the rear wheel, without getting the bubbles out first (on bench or in car), it would make the bleeding process seem endless, with bubbles chasing bubbles, basically.

[E. Davis]

The Doofus system of brake bleeding is probably okay on a new clean system but since flushing the brake system is one of the most overlooked maintenance items on the car I use brake bleeding as an opportunity to flush all the old fluid out until new clean fluid comes out the bleeder screws. Dot 3 gathers lots of water over time and brake fluid is cheap compared with the cost of neglecting this vital maintenance.

[BobPalma]

I'm about to pick up a running 59 Silver Hawk that has no brake pedal.

I was just going to fill it with fluid to see

1: if if works at all once there's fluid
and
2: where it might be leaking

Obviously I'm not planning on removing the master cylinder and bench bleeding it first - but do I take this to mean that I will never have a good system unless I eventually do?

(And yes I know that I need to replace the flex lines before really trusting it) PB

Phil, you are more likely to have success NOT bench-bleeding a single-piston master cylinder as when not bench-bleeding a dual-piston one. Which is to say, if you assemble a single-piston master cylinder system without bench-bleeding the master cylinder first, you might get lucky and it might work.

It is the dual-piston cylinders that are killers to get a pedal if they aren't first bench-bled. If fact, you usually can't get a pedal, period, with a dual-piston M.C. that wasn't bench-bled.

So on your '59 project, sure; just fill the master cylinder and see if you can get a pedal by pumping and bleeding. Of course, don't go very far with the car , if anywhere, until you have checked and overhauled everything as needed. BP

[Ron Dame]

It is the dual-piston cylinders that are killers to get a pedal if they aren't first bench-bled. If fact, you usually can't get a pedal, period, with a dual-piston M.C. that wasn't bench-bled.. BP

Guess I am special then... from the dual MC now in my '63 Champ, to Oldsmobubbles, Valv-os, Volkswagens, Honduhs, Furds, and more, duals were never problem.

Not disputing you Bob, but why do some of us have no problem, others nothing but problems if they don't bench bleed?

[pbrown]

Bob

Thanks for the response - I'll give it a try as I planned then!

Phil, you are more likely to have success NOT bench-bleeding a single-piston master cylinder as when not bench-bleeding a dual-piston one. Which is to say, if you assemble a single-piston master cylinder system without bench-bleeding the master cylinder first, you might get lucky and it might work.

It is the dual-piston cylinders that are killers to get a pedal if they aren't first bench-bled. If fact, you usually can't get a pedal, period, with a dual-piston M.C. that wasn't bench-bled.

So on your '59 project, sure; just fill the master cylinder and see if you can get a pedal by pumping and bleeding. Of course, don't go very far with the car , if anywhere, until you have checked and overhauled everything as needed. BP

[BobPalma]

Guess I am special then... from the dual MC now in my '63 Champ, to Oldsmobubbles, Valv-os, Volkswagens, Honduhs, Furds, and more, duals were never problem.

Not disputing you Bob, but why do some of us have no problem, others nothing but problems if they don't bench bleed?

Ron, a lot might have to do with how and where the master cylinder is positioned on the vehicle.

Quite often, dual-piston master cylinders are mounted going "uphill," with the front of the cylinder higher than the rear. That might be a contributing factor, whereas single-piston master cylinder OEM positions are nearly always flat, parallel to the ground.

And, yes, luck might be a factor! BP

[pbrown]

Quite often, dual-piston master cylinders are mounted going "uphill," with the front of the cylinder higher than the rear.

So maybe put the car on an incline to flatten the dual-piston master cylinders? But since you have no brakes, wheel chocks might be a good idea too!

[Skip Lackie]

It's been many years since I bought a new master cylinder that DIDN"T include instructions that mandated bench bleeding. And as bob noted, most new cars have a m/c that points up hill. I have found a steeply sloping driveway to be a big help in installing such master cylinders.

[jclary]

Another characteristic of the "STUDEBAKER PERSONALITY" seems to be contrarianism. This thread validates it. No matter what the subject, or how much credibility the source of a subject is...someone will post an opposite view.

Really...what harm is there in bench bleeding? Depending on how quick, and dexterous you are with your fingers, some will re-introduce more air that others when connecting the fittings after bench bleeding. However, getting the device installed full of fluid has got to be, at least, a little better than hanging it on guaranteed "full of air."

[BobPalma]

Another characteristic of the "STUDEBAKER PERSONALITY" seems to be contrarianism. This thread validates it. No matter what the subject, or how much credibility the source of a subject is...someone will post an opposite view.

Really...what harm is there in bench bleeding? Depending on how quick, and dexterous you are with your fingers, some will re-introduce more air that others when connecting the fittings after bench bleeding. However, getting the device installed full of fluid has got to be, at least, a little better than hanging it on guaranteed "full of air."

An astute observation, John. BP