Disc/drum master cylinder

[r.e.c.enthusiasts]

Okay. So I purchased a while back a western chassis Master cylinder for my disc /drum setup. But now my front discs are dragging. When I release the pressure at the bleeder valve the brakes release and wheel spins freely. Sadly I know when I was installing the setup some debris got in the reservoir. I thought I cleaned it out. But it's possible I got some tree pollen in there.


So that's where I will start. I don't like Western chassis any after dealing with them. Where can I get a suitable Master cylinder to replace what they had? My truck 69 Chevy c10 front disc rear drum, the discs, prop valve, and all other hardware are from cpp through summit racing.

[dmjlambert]

Power or manual brakes?

[r.e.c.enthusiasts]

Manual.

[weq92f]

.

I have some air in my lines in the front. When that air heats up after repeated braking events like stop-n-go, my front discs drag a little.

I suspect your issue is not that, but it's worth a mention.

-klb

[dmjlambert]

I recommend NAPA part M36280 new master cylinder for manual-brake 1/2 ton C-10 disc/drum. https://67-72chevytrucks.com/vboard/...39#post9169739

First, bleed the brakes to make sure you don't have air in the lines. If you have old rubber brake hoses, replace those because they could be your problem.

[r.e.c.enthusiasts]

Thank you.
No issues with the rubber hoses. All new.

I will try to reverse bleed again.. When I put the new master on I'll be reverse bleeding into it after bench bleeding.

[MikeB]

What type of master cylinder was on the truck previously, and why did you replace it?

Are the calipers also new to the truck?

[dmjlambert]

Originally Posted by r.e.c.enthusiasts

Thank you.
No issues with the rubber hoses. All new.

I will try to reverse bleed again.. When I put the new master on I'll be reverse bleeding into it after bench bleeding.

If you reverse bleed after bench bleed, wouldn't that just push air up into the master cylinder and you would lose any benefit of bench bleed?

[Sheepdip]

Double Check your MC push rod for proper clearance from the M/C piston contact point. Should be 1/16"-1/8" ....Sounds like your vent port is getting slightly covered and holding pressure

[r.e.c.enthusiasts]

So I know there is a decent clearance between pushrods and MC on full release

[MikeB]

Originally Posted by Sheepdip

Double Check your MC push rod for proper clearance from the M/C piston contact point. Should be 1/16"-1/8" ....Sounds like your vent port is getting slightly covered and holding pressure

I know you meant "holding vacuum", but good call.

[r.e.c.enthusiasts]

Originally Posted by MikeB

I know you meant "holding vacuum", but good call.

When brakes are applied pressure is applied all the way to the pads. When brakes are released. There should be release vacuum but there is not. It is holding pressure at the caliper. When I release the bleeder screw the pressure that is still lightly holding the rotor is then released.

I did have the fluid flushed and filled at Les Schwab. The brakes to engage well. But after a while begin to drag.

[lil hoodlum]

My first thought is the brake hoses are failing, but you said the brake hoses are new.

[geezer#99]

Does your master cylinder have residual check valves in it?
If it’s a drum/drum master then it might have a 10# check valve for the front when it should have a 2# in it.

[Rust_never_sleeps]

Originally Posted by geezer#99

Does your master cylinder have residual check valves in it?
If it’s a drum/drum master then it might have a 10# check valve for the front when it should have a 2# in it.

Interesting. I was not aware there was a residual valve built into the MC at all.