Bleeding problem

[RedLightBrew]

1964 Monza Coupe. Installed Dual master cylinder. Front brakes bled beautifully. Rear brakes won't bleed. The rear brakes were functional before installing the new dual MC. I am reverse bleeding and like I said the front brakes were cake! I can't get any fluid to even push through on the rear brakes. Am I missing something? or will I need to just jack up the car and follow all the lines looking for kinks? Thanks for your help.

[UNSAFE]

Did you bench bleed the MC before installing ?

If you did , did you get good similar streams out of both ports ?

Do you have a combination valve or are both lines plumbed directly to MC ?

It's possible that you need to adjust the pushrod length - if the piston in the MC does not fully retract it may be the cause of your problem.

The first thing I would do is bleed the rear line right at the MC and see what kind of flow you get

[terribleted]

Are you sure that the pedal rod isadjusted correctly. Often the rod need to be adjusted to allow the dual master piston to return fully when it is released (tends to be adjuted too long for the new master). If the piston can not move fully it will not pump correctly. There should be 1/8-1/4" play in the rod before it acts on the master cylinder piston.

[RedLightBrew]

I disconnected the line from the MC and it still wouldn't bleed, so it must be something with the lines. I'll jack it up and get under there to see what might have gotten kinked.

[UNSAFE]

"I disconnected the line from the MC and it still wouldn't bleed, so it must be something with the lines."

Maybe I'm not reading it right but if you disconnected the line at the master cyl and you do not get a good stream of fluid when you try to bleed the MC it has nothing to do with the brake lines .

It is pretty unlikely that a line is crimped since it worked before the new MC, but much more likely that the pushrod length needs to be adjusted as was twice mentioned above.

The rubber hoses can fail from the inside while still looking good on the outside but it seems pretty unlikely if the brakes worked before the swap.

It is also possible that the MC is defective from the factory.

I think the problem is at the MC

[terribleted]

Red you said something about reverse bleeding . I assume you meant you are using some sort of vacuum device and pulling fluid up to the master cylinder from a reservior attached to the bleeder valve at the wheel. If you can not suck fluid up the line to the Master cylinder end (with the master cylinder disconnected) then you may have a blockage in the lines. If there is such a blockage it would likely be in the main line somewhere the "New" rear brake feedfrom the master and the T-block above the left rear wheel as any restriction between this block and the left and right rear brakes would need to exisit on both sides for you to not get any fluid through from either side. Another tought, verify that you connected the dual master cylinder properly (the feed from the rear MC reservior goes directly to the main body line feeding the rear brakes after disconnecting that line from the 4 way block above th brake pedal and plugging the spot where it was originally plugged in). You do not mention what master cylinder you are using nor whether it has an external proportioning valve. The valve proportioning valve could cause this type of problem. If a valve is in the system open the rear feed line that comes out of the valve and see if you get flow there when pressing the pedal.

I would ditch the vacuum bleeder and try bleeding it normaly. Like Unsafe suggested, first try pushing the brake pedal down with the rear feed line disconnected from the Master and see if fluid comes out of the rear brake port of the master cylinder. If it does not you have a defective Master or a pedal push rod is not adjusted for free play. If it does then reconnect the rear feed line at the master and open both rear brake bleeder screws. You can wait a while and see if any fluid gravity bleeds thru either or both sides. You can also trying pumping fluid with the brake pedal (this works best by opening the bleeders and then pressing the pedal down....while holding the pedal down close both bleeders...release pedal and repeat until fluid flows. Pumping without closing the bleeders will cause fluid to go down the line and get sucked back up the line some when the pedal is released slowing the filling of the lines). If no fluid on both sides there is a mainline blockage (before the rear T-block). If fluid at only 1 side, the side with no fluid has a blockage between the T-block and that rear wheel. Bear in mind that if the system is totally empty you might not see much fluid movement far a little while or a number of pumps as the lines will need to fill first before anything will come out the bleeders. Once you have fluid at both rear brakes, proceed to bleed the entire system in this order right rear, left rear, right front, left front using the Master to pump fluid to each brake...same routine press pedal and hold open bleeder...pedal goes down fluid and air comes out... close bleeder release pedal. Repeat until no more air is seen exiting the bleeder. I like to go around the car at least 2 times and often 3 times to ensure no air is left in the system, alway using the same order RR,LR,RF,LF.

[RedLightBrew]

I have the Phoenix systems reverse brake bleeder where you push fluid from the wheel up to the MC. It bleeds the MC while you reverse bleed the brakes. And with the rear line disconnected from the MC it still would not push fluid through the line, so at this point it has nothing to do with the MC. When I get back out there to work on it some more I'll post more.

[RedLightBrew]

Alright, this is odd. THe right rear bled fine. The left rear still won't bleed. There must be a line issue between the left rear and the junction of the rear lines before they head up front. I closed up the MC and pushed on the brake. All brakes work fine. Pedal is firm. Even better than it was before. But still didn't get the left rear to bleed. But the left rear does engage when pedal is pressed.
MC is the clarks kit.

[terribleted]

I suspect the left rear brake hose. I may be broken down internally. I would bet a flap of the inner surface is broken loose acting like a door. It may be hinging closed when fluid is applied from the brake side. I have had this issue before when a brake would stay applied for seemingly no reason (pressed the pedal and the brake would apply but would not release until the car sat for quite a bit...fluid would slowly get back past the flap). Try disconnecting the left rear brake hose at the top and see if you can get any flow up thru it. If it is bad and the right one is of similar vintage change both of them.

[RedLightBrew]

Thanks, Ted. I was actually planning to replace all the rubber hoses in the next phase, so now would be as good a time as any to just do that. Thanks for the info.

[UNSAFE]

Here's how I bleed my brakes by myself . Works great and you can quickly detect blockage judging by the pressure stream.

Rubber lines do collapse as was mentioned a few times.

Here's a cross section from a rear hose on my Vette. Kinda hard to see but the center was collasped and acting like a flap/valve.

It would bleed ok but the hose held the pressure and the brake would drag severely.

[bbodie52]

This has certainly been an interesting and informative topic! The symptom of the flexible brake line internal collapse behaving like a one-way valve appears to be more common than I would have thought. I suppose that a dragging or overheating brake on one wheel, that might have been assumed to be caused by a sticking wheel cylinder or caliper piston, could, in fact, be a collapsing internal fault in the flexible brake line supporting the troubled wheel.

In fact, I currently have a sticking, overheating brake caliper on the left front disc brake of my '91 Toyota Supra. I will certainly keep this info in-mind when I work on that problem!

I'll bet a lot of people have learned something valuable from this "conversation"!

[UNSAFE]

I suppose that a dragging or overheating brake on one wheel, that might have been assumed to be caused by a sticking wheel cylinder or caliper piston, could, in fact, be a collapsing internal fault in the flexible brake line supporting the troubled wheel.

On my Vette I thought it was probably the caliper so I replaced it and still had the problem . I was getting ready to change the combo valve when that light-bulb in my brain lit up and I figured out that it was the hose . If the car sat for a while the brake wouldn't drag right away but after braking a few times the rotor would get hot enough to smoke.

When I cut the old hose apart I found that only a short section about an inch long had collapsed and the hose looked fine on the outside .

I was kinda surprised too . I had heard of collapsed hoses but was a bit doubtful .

In hindsight it happened on a front wheel on an old Nash Metropolitan I had years ago . The wheel would lock up after a few miles . Back then I just smashed the metal line flat and eliminated that brake

[bbodie52]

In hindsight it happened on a front wheel on an old Nash Metropolitan I had years ago . The wheel would lock up after a few miles . Back then I just smashed the metal line flat and eliminated that brake

From a Nash Metro to Corvettes and hot Corvairs... you've come a long way!



This might work for you in Alaska...



Or... when the snow melts...



Do you miss your Nash Metro?