Necessity of Bench Bleeding?

[DonaldSmith]

Re: Post # 21:  Huh?  Is he at a front brake or rear brake?  The springs look like rear springs.  But he talks as though it's the front of the car, with the front to the right. 

Later on, he says that the shoes are in wrong,  the left shoe with the short lining should have had the long lining, and vice versa.   I'm so confused. 

 

 

[MackTheFinger]

If you're sure of the adjustment I think more bleeding is needed. Make sure to not let the m/c run low on fluid while bleeding. I doubt the pedal will firm up with time. 

Edited May 9, 2020 by MackTheFinger

[Sniper]

4 hours ago, DonaldSmith said:

Re: Post # 21:  Huh?  Is he at a front brake or rear brake?  The springs look like rear springs.  But he talks as though it's the front of the car, with the front to the right. 

Later on, he says that the shoes are in wrong,  the left shoe with the short lining should have had the long lining, and vice versa.   I'm so confused. 

 

 

 

The front of the vehicle is to the right, he's working on the rear passenger brakes.

[squirebill]

Bleed the brakes some more.  A spongy soft pedal is an indication of compressible air some where in the hydraulic system.  A hard pedal is an indication of only incompressible fluid in the system.  Another indication of air in the system is if the brake pedal travel can be reduced by pumping the brakes.  A well bled brake system will have the same pedal travel regardless of pumping the brake pedal.  In a well bled system the pedal travel will get closer to the floor as the brake lining wears indicating the brakes need adjusting or replacement.  Bleed until you have a hard pedal.  Set the brake pedal free play to spec and you will be good to go.

[keithb7]

I recall when I tore down and rebuilt the master cylinder in my 53. I did not bench bleed the master. It did take considerable bleeding to get all the air out. A partner pumped while I bled at each wheel. Starting at the wheel furthest away and working closer to the master. Slowly the pedal started to feel more firm. It turned out feeling good. However in hind sight, it took me some more time learning to adjust and set the brakes properly. Developing some skills to get a good high and firm feeling pedal.

 

For some reason when I rebuilt the master in my '38 bleeding was a snap. Quick and easy it seemed compared to my 53. Way less bleeding was required to get a nice firm feel.

Edited May 10, 2020 by keithb7

[ChrisMinelli]

9 hours ago, keithb7 said:

I recall when I tore down and rebuilt the master cylinder in my 53. I did not bench bleed the master. It did take considerable bleeding to get all the air out. A partner pumped while I bled at each wheel. Starting at the wheel furthest away and working closer to the master. Slowly the pedal started to feel more firm. It turned out feeling good. However in hind sight, it took me some more time learning to adjust and set the brakes properly. Developing some skills to get a good high and firm feeling pedal.

Out of curiosity, do you bleed with the master cylinder refill cap on or off?  I have been taught on modern cars to keep the cap off the master cylinder; I wanted to make sure the advice is the same for these old under-floor cylinders. 

[keithb7]

I bleed with the fill cap on and sealing the reservoir. A few bleeds, I open it up and top it up. Rinse and repeat.  

[soth122003]

Bleed with the cap on. The return pressure from the lines causes the fluid in the MC to spurt up about 3-5 inches and can make a mess.

 

Joe Lee

[DJ194950]

Come on all- fess up- have we all not found that out- After the fact!!  ?

 

I know I did-several times over the years- Oh ya, Now - I remember that happens with the cap left off!  ?

 

DJ

[Dodgeb4ya]

I always bled those Mopar master cylinders that got too low and pedal was to the floor by cheating on minor air intrusion...

caused by a leakage that will be fixed ...I do this by

 

*Filling the master cylinder up

*leave the cap off and with good lighting to see the larger hole 1/8" in the bottom of master cylinder reservoir (intake port)

*While always watching that intake port hole push the pedal down slowly with your hand...then slowly let it all the way up... fluid level will drop down a tiny  bit each pedal push and release

* Again slowly push pedal down... and slowly release pedal all the way....do this several times always watching the silver or bronze master cylinder piston blocking and unblocking this 1/8" reservoir intake port hole.

*Soon you will notice the you need to refill the M/Cyl back up...the pedal should be getting a little firmer and lots of bubbles are coming up out of the return port when the piston returns all the way back uncovering the intake port.  

Also more bubbles will come up into the reservoir when you first begin to push the pedal down the first inch or so...( don't push the pedal down fast or release fast as fluid came come back up like a 6" geyser!

*As more and more fluid is pushed out of the M/cyl by cycling the brake pedal air is purged out of the return port in the master cylinder.

*When no more bubbles bleed up and out of the master cylinder intake port and the pedal is fairly high and firm you are done.

*This will easily bleed out a system with a leaky master cylinder where the fluid got low enough that air got to the master cylinder piston bore.

It will also bleed the master cylinder to start the complete bleeding process if the master was not previously bench bled.

This takes less than five minutes if the brake system has good rubber cups and not 20 years old and sitting and full of moisture.

It will not remove air from the wheel cylinders either.

I've done this dozens of times to get junkers going and get a pedal out of cars that sat too long and got a little low on fluid.

Now days though I just use a professional bleeder tank...quick and easy... no pumping.

I'm getting older and lazy.?

[kencombs]

50 minutes ago, Dodgeb4ya said:

Now days though I just use a professional bleeder tank...quick and easy... no pumping.

I'm getting older and lazy.?

Wrong description, the phrase is experienced and efficient.  At least that's what I try to tell people.

[Sam Buchanan]

54 minutes ago, Dodgeb4ya said:

 

I'm getting older and lazy.?

 

Wiser......... 

[Los_Control]

Probably to late to the game ... will just say my 2 cents.

I learned when I was under 20 years old, you need to bench bleed a master cylinder ... I really doubt modern tools such as a vacuum pump would replace bench bleeding a master cylinder.

I may be wrong but not changing my ways.

[Sam Buchanan]

8 minutes ago, Los_Control said:

 

I may be wrong but not changing my ways.

 

Not wiser....... 

[kencombs]

35 minutes ago, Los_Control said:

Probably to late to the game ... will just say my 2 cents.

I learned when I was under 20 years old, you need to bench bleed a master cylinder ... I really doubt modern tools such as a vacuum pump would replace bench bleeding a master cylinder.

I may be wrong but not changing my ways.

Every new or rebuilt I've purchased over the last 25-30 yrs have come with plastic tubes and adapters to attach to the ports and dip into the res.  Not sure when that became a standard for retailers, but I appreciate it.  Makes bench bleeding a snap.  No scrounging around for pieces to make a setup.

 

There must be a reason the manufacturers/retailers started doing that.  Probably returns of 'bad masters' by weekend warriors 'cause they couldn't get them to work. 

 

Of course all late models are firewall mounted too.  You can effectively 'bench bleed' with them mounted on the vehicle with those little tubes.

[Los_Control]

I have only understood it to be the travel of the push rod on the end of the brake pedal.

You need some play or you will end up with sticking brakes.

With the required play to prevent sticking brakes, you cant get all the air out, bleeding it on the car.

So we bench bleed the MC to remove all the air.

 

I guess I am just surprised bench bleeding a master cylinder went for 2 pages of answers.

[Dodgeb4ya]

1 hour ago, Sam Buchanan said:

 

Wiser......... 

At times I question that!