Master Cylinder Question

[NAPA 68]

After bench bleeding a 1 1/8" bore C3 master cylinder (shallow piston), I noticed the rears come in a fair amount after the front. I currently have the same master on my car (59 Bel Air) and I am getting very little volume and pressure to the rears. I have an adjustable Wilwood proportioning valve on the system and have it opened up all of the way (the car is 4 wheel disc).

While this may sound like an elementary question, is there a M/C that is evenly proportioned through the piston stroke so the valve can do it's job?

In advance, thanks for the consideration.

Tim

[Vince@Meanstreets]

Originally Posted by NAPA 68

After bench bleeding a 1 1/8" bore C3 master cylinder (shallow piston), I noticed the rears come in a fair amount after the front. I currently have the same master on my car (59 Bel Air) and I am getting very little volume and pressure to the rears. I have an adjustable Wilwood proportioning valve on the system and have it opened up all of the way (the car is 4 wheel disc).

While this may sound like an elementary question, is there a M/C that is evenly proportioned through the piston stroke so the valve can do it's job?

In advance, thanks for the consideration.

Tim

When you say "I noticed the rears come in a fair amount after the front" is this while bench bleeding or on the car.
Off car...its by design. One port will have more volume.
On car... You may need to bleed again or you have a possible push rod issue.

[kwhizz]

Originally Posted by NAPA 68

After bench bleeding a 1 1/8" bore C3 master cylinder (shallow piston), I noticed the rears come in a fair amount after the front. I currently have the same master on my car (59 Bel Air) and I am getting very little volume and pressure to the rears. I have an adjustable Wilwood proportioning valve on the system and have it opened up all of the way (the car is 4 wheel disc).

While this may sound like an elementary question, is there a M/C that is evenly proportioned through the piston stroke so the valve can do it's job?

In advance, thanks for the consideration.

Tim

Glad I'm not the only one...........LOL.....

[NAPA 68]

Originally Posted by Vince@MSperfab

When you say "I noticed the rears come in a fair amount after the front" is this while bench bleeding or on the car.
Off car...its by design. One port will have more volume.
On car... You may need to bleed again or you have a possible push rod issue.

Vince,

The notable difference is while the M/C is one the car (to the rear calipers). After watching and talking to Kwizz, I was suspecting perhaps I had an issue with the M/C as well. Hence, I tried an other M/C. While bench bleeding, that is where I noticed the rear port came in notably later than the fronts. While the pedal while on the car is good, there is hardly any rear brake in the car (on jack stands). Just trying to think this one through before firing anymore parts at it.

Thanks,

Tim

[NAPA 68]

Originally Posted by kwhizz

Glad I'm not the only one...........LOL.....

You know it well!

[Vince@Meanstreets]

I have had a lot of these issues with customer cars and there are a lot of things to check.

Just a few questions:

Power booster?
Is this a previous manual to power conversion? Having the wrong ratio can effect piston travel. Your master cylinder piston should travel at least 1" - 1.20".

When you bench bleed the master is it totally out of the car and you are pushing the piston by hand? If it is still on the car the piston may not be traveling far enough.

Are you noticing the lack of fluid at the rear calipers or at the master port?
Check flow at the master. If it is good keep going rearward. Go to prop valve, then after the valve, then at the rear diff hose. I have had a few bad rear hose preventing fluid flow.

Turn your prop all the way on. Knob all the way in or down, no threads showing. Adjust after you get the fluid flowing.

What calipers are you running in the rear.
How much air gap do you have between the pads and rotor?
Are the rear pads seated already?
Integral parking brake?


Things to look for.

When bench bleeding measure how far the piston travels.
With the master off, have a helper depress the brake pedal. Measure how much the push rod travels. Compare what you find.

If your pedal travel is less then you have a ratio issue.

Do you have an air gap between the push rod and master register? The push rod should not depress the master cylinder piston when mounted. That will cause a bunch of issues. Brake drag and the piston will be in partial travel and you can loose volume/flow there.

Hope that helps a bit.

[Vince@Meanstreets]

I almost forgot.

How are your brake lines arranged coming out of the master? Front port to front brakes? Rear port to rear brakes? Sorry, gotta ask.

Im hopin Tobin chimes in.

[NAPA 68]

Originally Posted by Vince@MSperfab

I almost forgot.

How are your brake lines arranged coming out of the master? Front port to front brakes? Rear port to rear brakes? Sorry, gotta ask.

Im hopin Tobin chimes in.

Yes they are. The rear calipers are from a C5 Corvette. Not sure about the air gap but I can assure it is minimal. This was a manual conversion. I have checked my pedal ratio (6 to 1).

Thanks,

Tim

[Vince@Meanstreets]

Sorry, so this is power to manual or man to pow?

6:1 (approx 2" from pivot shaft)is the top hole for a manual master rod.

[Apogee]

How are you bench bleeding the master cylinder? Recirculation or plugged port method? It sounds like you might still have air in the piston assembly for the rear brakes.

Tobin
KORE3