67442nut

Did a front disc brake conversion on my '67 post coupe CS using the '71-'72 proportioning valve and '69-'72 single piston calipers.
This system has EVERYTHING new- calipers, rotors, booster, master cylinder rear wheel cylinders,
prop valve and all hard lines and flexible lines.
We bled the brakes a few weeks ago and had good peddle.

We used a parastolic pump to pump fluid from each wheel back to the master cylinder.
We did each wheel until no air appeared at the master cylinder.
This process seemed to do the trick as we attained very good peddle.
We've done this before on later model vehicles without a problem.

The car remained on the stands while I completed other work under the car to get it road worthy.
Got in today to start it, pushed the brake peddle and it went to the floor.
Would not pump up.

When the peddle was gone today, we re-bled the brakes the old fashioned way by wearing out our legs pumping.
Got a little air at one wheel, but, peddle still goes to the floor.
Was pumping fluid from the wheel to the master cylinder a mistake?
Is it possible the seals in the prop valve or master cylinder may have been damaged by doing this?
I'm at a loss.
Any help or ideas will be appreciated.

Rickman48

Did you bench bleed the master??

Run to Rund

I'd disassemble the master cylinder and check the seals and valving.

Tony72Cutlass'S'

You absolutely 100% need to bench bleed your Master. There should have been a disclaimer in the box saying how you should go about it.

In any case, Lay your master cylinder horisontally on a table or something and pump until you see no bubbles coming out of the reservoir. Pump Slowly. Unless you want a brake fluid shower.

67442nut

I DID bench bleed the master cylinder,
Today, I removed it and returned it for a replacement.
After installing it and re-bleeding the system, there was no change. Same problem.

67442nut

I don't think we put enough pressure on the system to invert any seals.
Used a piece of neoprene hose from the pump to the bleeder at the calipers/wheel cylinders.
Hose was slipped over the end of the bleeder. No clamp was used.
I had to hold the hose on the bleeder to keep it from coming off.
Pump is variable speed. I only ran it up fast enough for my buddy to see air/fluid flow at the master cylinder.
Even a small amount of pressure would have blown the hose off the bleeder.
If not, I think the neoprene hose would swell before any seals would invert.
However, since I replaced the first master cylinder and have the same problem, and since I'm at a complete loss,
I think disassembling the master cylinder is a good idea.
I'll be out of town until next week. I'll tear it down when I return.
I'll let you know what I find.
I've been wondering if the prop valve could possibly be the problem.

67442nut

With the help of a couple of fellows at ROP who are smarter than myself,
I think my problem has ben diagnosed.
The primary diagnosis is stupidity, mine. the secondary is I've put the calipers on the wrong side!
For details, http://72.22.90.30/phpBB2/viewtopic....=asc&highlight=

Rickman48

And we took that one for granted - I guess brain farts can come at all ages.