mrg

Still having a problem with aa soft brake pedal. The installation is a dual outlet master cylinder to replace the single.

Here's the set up:
7/8" dual outlet disc/drum master cylinder.
The rear larger chamber of the master feeds the front brakes through a 1/4" line.
The front smaller chamber of the master feeds the rear brakes through a 3/16" line. This line also has a Wilwood 10# residual pressure valve installed near the master outlet.

From what I gathered online the rear main master cylinder chamber feeds the front brakes, the front master chamber the rear brakes. ..
For thar reason, along the lines of a front disc/rear drum master cylinder the RPV was installed only on the 3/16" line that feeds the rear drum brakes. No RPV was used on the 1/4" line that feeds the front brakes.
Is this the right way to do it? .. I'm wondering if I got it backwards and/or should have installed a second RPV on the 1/4" line. The new brake line connections were made at the junction block on the left frame rail.

Speed bleeders were installed and the system again bled. Brake pedal feel improved but only a little. Pedal stiil soft.

Starting over.........the brake line fittings at the master cylinder were loosened and moved out of the way. Plastic fittings were installed with foot long hoses to return brake fluid back to each master cylinder chamber.

Working the brake pedal a small geyser of sorts was seen to jump up from the rear chamber, followed by air bubbles. No bubbles from front chamber. . One pump, 2 pumps, 3......air bubbles continuing to flow.

It just seems incredible that air bubbles would still be inside the master cylinder after a few go-rounds bleeding a quart of brake fluid through the system.

PITA that's it been.....taking a break right now to watch a little baseball and clear the noggin.

Should a second RPV valve be installed on the 1/4" line? .. Seems like it couldn't hurt . . . If anyone might have anything further to add to the above, thanks.
John

ILBMF

I wouldn't doubt the master cylinder may have a flaw and possibly drawing air in through the piston seal...I have experienced that with master cylinders and wheel/slave cylinders without any fluid leaks.

ohiovet

I believe the 1/4" line should go to the rear brakes and the 3/16" to the front brakes.
A residual valve should only be necessary if the master cylinder is located below the wheel cylinders.
Are you using a GM type proportioning valve?
If so you need a screw in gizmo to keep the brake warning sensor piston in the center position or it is close to impossible to bleed the brakes.

vmaxpwc

I was always told on C2s to jack up the rear end so the master cyl was level so all the air could easily be bleed and not be trapped in the front of the master cyl. I always bench bleed mine also, but maybe you have already done this.

Mike (Naples)

I had a very similar experience and I found that I wasn't able to get all the air out except by bench bleeding. My master cylinder has a port on either side of each reservoir and bench bleeding allowed me to tilt the MC fore and aft and side to side until eventually the bubbles stopped. Also, I found that the plastic fittings needed to be tightened more than I expected, as air was being sucked in even though there didn't appear to be any fluid seepage.

MikeM

I never did see a satisfactory answer to post #13 in your first thread on brakes.

https://www.corvetteforum.com/forums...g-problem.html

mrg

Mike, the master cylinder was installed and level on the car on the first go-round with bench bleeding. .. Looks like it wasn't done adequately.

After redoing the bench bleed again and purging any remaining bubbles from the master the plastic fittings with return hoses were removed. Tube nuts with a short section of crimped end tube were installed as plugs to test the master.

Working the brake pedal, the pedal now holds in place and is firm. Need to bleed the wheel cylinders again. I hope the problem is now resolved. ..

A proportioning valve isn't being used. The 3/16 and 1/4" lines are plumbed from the master cylinder to their connect points. Thanks, guys.
John