1969 Rebuilt Brake Caliper Issues

[Cadillac Nut]

Yes, the rear bled fine. 

[Mike Baillargeon #15848]

It's time to start all over again with the bleeding.....If you don't have a power bleeder then this is a 2 person operation....one in the car at the brake pedal and one under the car opening and closing the bleeders....your proportioning valve has to be open....

Start at the right rear, furthermost from the master....bleeder gets opened someone pushes the brake pedal down.....air and or fluid comes out.....brake pedal held at the floor until you close the bleeder....keep do that process until just brake fluid comes out of that bleeder....go back to master and refill with fresh fluid....

Continue with left rear then right front then left front....don't let the master run out of fluid.....Then close proportion valve and see if you have brake pressure.....if you still don't, I'd look hard at the new master cylinder as being defective....

Wish I was there to help...

Mike

[Cadillac Nut]

Well bled the car again, the rears bleed fine like before. Proportioning valve was open. The fronts very tough to get all the air out, went through a lot of brake fluid.  I think I got all the air out.  Pedal does the same thing, maybe a slight improvement.  Step on it and it goes to the floor.  I don't think it's a bleeding issue now.  Master cylinder? What else could it be?  I have never had so many issues with brakes before and I have worked on a lot of cars   

[Dave Shepherd]

Pinch the front hoses off, see if the have a pedal, post back.

[TJ Hopland]

What bleeding method(s) are you using?

[Cadillac Nut]

Pinch off both brake hoses near the caliper? How do I do this, with a zip tie?    I am using the regular 2 person bleeding method like described above. 

[Dave Shepherd]

Use needle nose vise grips, if possible, clamp them closed as far from the caliper as you can. Even better is plug the port on the master that goes to the front brakes, an inverted flare pipe plug will work. Same size as the line. The see if you have some pedal.

[Cadillac Nut]

I plugged the front port on the master cylinder.  Now, I have pedal

[TJ Hopland]

So that tells us that something in the front has a leak and or has air in it.   Can you keep moving forward plugging things?   Like being able to isolate the sides?

[Cadillac Nut]

I'll try pinching off each side with a vise grips.  Would this indicate a master cylinder issue?

[Dave Shepherd]

Couple of possibilities here, air getting into one or both of lines supplying the front brakes, or if the master is sectioned off front to rear, could be air trapped in the portion that feeds the ft brakes. Your getting closer to a resolution  here.

[Cadillac Nut]

I clamped off each side with a vise grip, as tight as I could.  No pedal whatsoever.    It's a dual pot master cylinder.    I must have gone through a quart of brake fluid trying to get the fronts bled.  Thanks for the help guys

[Cadillac Nut]

The fronts never seemed like they bled 100% even though I went through so much fluid.  I can here gurgling sounds when I am bleeding them (not sure if that means anything but seems a little odd)

[V63]

If you have any 'leak' it's also opportunity for air to be introduced and therefore no bleeding can take place.

Once the leaks are addressed the bleeding takes place with the rear farthest from MC. I like to use clear aquarium hose fitted over the bleeder into a clear reservoir. Open the bleeder and have someone depress the pedal only. Watch for fluid/air  activity exhausting thru hose. Tighten bleeder and then raise pedal.

Technically air can be introduced via loosened bleeder, so to avoid that, I try to only depress the pedal for bleeding.

I also bleed right at the master cylinder by pumping the brakes and holding the pedal down, then crack the line at the master and fluid/air will exhaust while pedal sinks. Tighten line BEFORE allowing pedal to return.

Monitor fluid level at all times in reservoir or all gains will be lost.

[Cadillac Nut]

There are no leaks that I see.  That's exactly how I am bleeding the brakes (with clear tube) and it has worked for every other brake job I have ever done.  I did bench bleed the master cylinder.    I will try bleeding just the fronts at the master cylinder.  Something is going on with the front brakes that isn't normal. 

[Cadillac Nut]

I have done as suggested and bled at the master cylinder and both front calipers.   They seem like the bled okay this time,but still no pedal.  To me I would think this is a master cylinder issue.  Could the proportioning valve have anything to do with it?

[TJ Hopland]

Since you are running out of other things to try maybe loosen and install temporary spacers between the booster and MC just to make sure its returning fully?  Maybe the front and back are not perfectly aligned and the fronts are having an issue because its not fully returning?

Are those MC's hard to come by or expensive?  Since you have tried everything else maybe try a new one?  Are you sure you have the correct one for disc brakes?  There were still a lot of drums around in 69.


Since 69 is still fairly early in disc brakes I'm not sure what the prop valve was actually doing.  Many of them are mostly working with the rear.

[Cadillac Nut]

No, they aren't, I ordered another one which should come Thursday.  I need to get the brakes working ASAP as this car is blocking in another one.  I matched up the casting part number on the old master cylinder to the new one so I'm sure I have the right one.   At this point I don't see it being a caliper or brake hose issue.

[Cadillac Nut]

Is the proportioning valve rebuildable on these cars?   I cannot find a new one anywhere.

[Dave Shepherd]

Pretty sure you could fabricate some lines and adapt a generic  GM style disc /drum valve if you feel that would fix it, I don't  think that is the issue though, let's say it was blocking off the front, yes you couldn't bleed the front as no fluid could pass the valve, but you would have a pedal.