Brakes won't hold pressure

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Dustert73

Dustert73

Stripping bolts since ‘10
Joined
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Hey everyone, I just swapped to 1973 single piston front disks and 10 in rear drums. The car used to have 9 in drums on all four corners. All brake lines, hoses, calipers, wheel cylinders, and correct disk/drum MC are either brand new or 2 years old at most. Only thing that isn't new is the old drum/drum distribution box (never had issues with the dist. Box with the old drum setup). Have tried multiple master cylinders with no change In results. I have a wilwood adjustable prop. Valve plumbed into the rear brake line. Bleeder screws are on top.

Now for the problem, I can't seem to get the brakes to bleed. If I pump the brake peddle around 4 times the peddle is firm and doesn't seem to decrease if I hold it. But if I let the peddle return, wait for a few seconds, and try to press the brake pedal again there is no pressure behind it and it goes to the floor. I have gravity bled, pressure bled (by pumping/holding the brake peddle), and used a vacuum bleeder on the system starting from the furthest point and working my way in many times. Always seemed to have good pressure/no air bubbles coming from fluid when I would crack the bleeder screw. All connections don't appear to have any leaks.

Could it be the old dist. Box causing this? Figured I'd ask here before I spend anymore money. My apologies if this has been answered before, I couldn't find a solution through all the treads I read that I haven't already tried. I'm trying not to get frustrated with this car but it's starting to get hard
 
First question is "are the bleeders at the tops" of the cylinders / calipers?

Next, tighten up the rear shoes, or temporarily, try setting the parking brake. See if this improves the pedal. If so, the rear shoes either need adjustment, or there's 'wrong parts' back there.

Bleeding..........you DO know? that when you bleed by "pumping" that you must pump and hold..........open the bleeder............close the bleeder BEFORE releasing the pedal
 
67Dart273 said:
First question is "are the bleeders at the tops" of the cylinders / calipers?

Next, tighten up the rear shoes, or temporarily, try setting the parking brake. See if this improves the pedal. If so, the rear shoes either need adjustment, or there's 'wrong parts' back there.

Bleeding..........you DO know? that when you bleed by "pumping" that you must pump and hold..........open the bleeder............close the bleeder BEFORE releasing the pedal
Click to expand...

Yes, bleeders are above.

Rear shoes have been tightened up.

Yes :) this isn't my first brake bleed rodeo
 
70DartMike said:
You didn't swap out the drum/drum for a disc/drum? Did you bench bleed the matter cylinder? Are your bleeder screws facing up?
Click to expand...

No I didn't, I was kinda hoping I could skip that by adding in the adjustable prop. valve to the rear main body brake line. Jury is still out if that was a good call or not.

Yes I bench bled the MC before installing it.

If by facing up you mean the bleeders are above the brake hoses/lines then yes I do.
 
That block is a pressure differential switch. It's not a proportioning valve. It shouldn't affect bleeding of the brakes. Is the dash warning light on? I can't say I have ever seen one suck in air. It could happen, but I would bet that you would be seeing it leak, also.

You did bench bleed the master cylinder, right?
 
Revhendo said:
That block is a pressure differential switch. It's not a proportioning valve. It shouldn't affect bleeding of the brakes. Is the dash warning light on? I can't say I have ever seen one suck in air. It could happen, but I would bet that you would be seeing it leak, also.

You did bench bleed the master cylinder, right?
Click to expand...

That's good to hear, and to be completely honest I don't think I've ever seen the brake warning light come on in that car. Maybe it's burned out or bad wiring?

Yes I did bench bleed.
 
Well I have no idea. Here's what I'd do.

Go downtown and buy some fittings, including some inverted flare plugs. Pull the rear line loose at the distro block and plug that port. See if the pedal "hardness" improves, and it should be absolutely hard. If so, concentrate on something in the rear.

If you conclude that it's "fronts" I would pull the calipers and pads and "rig" a 2x4 or other block in the caliper. Slowly actuate the pedal until you have the pistons out against the blocks. Be sure to monitor fluid in the master so it doesn't "hit air."

Next, take a C clamp on the longest line (pass?) and retract the piston. this will force fluid (and air) back up to the master. You can pull the front fed line off the master, and collect fluid. Use a second clamp to force the remaining piston back in. Keep the hoses at the tops of the calipers. This should create an absolutely air-free pair of calipers.

If that doesn't fix it, then it surely is something in the rears.

Dustert73 said:
Rear shoes have been tightened up.
Click to expand...

I would REALLY tighten them up, until the rears simply will not turn
 
Dustert73 said:
That's good to hear, and to be completely honest I don't think I've ever seen the brake warning light come on in that car. Maybe it's burned out or bad wiring?

Yes I did bench bleed.
Click to expand...

Yep, 4 wheel drum brake systems don't use prop valves. The adjustable in your rear line should do just fine.

Your going to have to figure out which part of your system isn't working for you. Try disconnecting the brake lines at the master, get some brass fittings and block the ports at the master. Pump your brake pedal and see if it holds. If it does, hook up the front brake line and bleed the system and then see if it holds. If it doesn't, you need to check the front system out. If it does, well, I would hook up the rear and try to bleed that out. If it doesn't hold, then you know for sure where your problem lies. If it does hold, I would guess you had some real pesky air hiding in there.
 
67Dart273 said:
Well I have no idea. Here's what I'd do.

Go downtown and buy some fittings, including some inverted flare plugs. Pull the rear line loose at the distro block and plug that port. See if the pedal "hardness" improves, and it should be absolutely hard. If so, concentrate on something in the rear.

If you conclude that it's "fronts" I would pull the calipers and pads and "rig" a 2x4 or other block in the caliper. Slowly actuate the pedal until you have the pistons out against the blocks. Be sure to monitor fluid in the master so it doesn't "hit air."

Next, take a C clamp on the longest line (pass?) and retract the piston. this will force fluid (and air) back up to the master. You can pull the front fed line off the master, and collect fluid. Use a second clamp to force the remaining piston back in. Keep the hoses at the tops of the calipers. This should create an absolutely air-free pair of calipers.

If that doesn't fix it, then it surely is something in the rears.



I would REALLY tighten them up, until the rears simply will not turn
Click to expand...


See what happens when I try to do tech help and watch "Hell on Wheels" at the same time?
Del beats me to it.....
 
67Dart273 said:
Well I have no idea. Here's what I'd do.

Go downtown and buy some fittings, including some inverted flare plugs. Pull the rear line loose at the distro block and plug that port. See if the pedal "hardness" improves, and it should be absolutely hard. If so, concentrate on something in the rear.

If you conclude that it's "fronts" I would pull the calipers and pads and "rig" a 2x4 or other block in the caliper. Slowly actuate the pedal until you have the pistons out against the blocks. Be sure to monitor fluid in the master so it doesn't "hit air."

Next, take a C clamp on the longest line (pass?) and retract the piston. this will force fluid (and air) back up to the master. You can pull the front fed line off the master, and collect fluid. Use a second clamp to force the remaining piston back in. Keep the hoses at the tops of the calipers. This should create an absolutely air-free pair of calipers.

If that doesn't fix it, then it surely is something in the rears.



I would REALLY tighten them up, until the rears simply will not turn
Click to expand...

It's nice to have a game plan again! Thank you!
 
Thanks for all the replies guys. I'll be sure to report back to here with the fix once I can make it out to the garage.
 
Also check the adjustment on the brake pedal rod at the master, I had an similar issue that the master plunger was not going back so no new fluid got into the chamber.
 
No one mentioned this and probably doesn't need to be, but when you bleed lines you need to keep the master full of fluid. You can't just bleed everything, then go back and fill it back up and call it done. I think you may know this already, but it's all I got. The rest is baffling.
 
if you pump it and get a good pedal that indicates air.
i'd suspect a bad master if everything else has been checked.
just plug its outlets for a test
 
halifaxhops said:
Also check the adjustment on the brake pedal rod at the master, I had an similar issue that the master plunger was not going back so no new fluid got into the chamber.
Click to expand...

It's a non adjustable rod from the drum/drum master. The master doesn't seem to have any external adjustment either.
 
ir3333 said:
if you pump it and get a good pedal that indicates air.
i'd suspect a bad master if everything else has been checked.
just plug its outlets for a test
Click to expand...

I've had multiple reman MC's on it, and the one present on it now is a brand new one. None of them seemed to change the results.
 
i just had a problem similar to this last week. while my motor and trans are out i replaced all the brake lines and plumbed in a adj prop valve for a future disc brake swap. i bled the system like you and got good pedal pressure. after i let off it and pressed again it went to the floor. after a couple of times of bleeding the system with no improvement. so i made sure the prop valve was adjusted so the rear was getting less pressure. and had someone pump the brakes so i could look to see what was going on. i found the problem in a few minutes. as the brake were getting pumped i noticed it looked wet on a line coming out of the master cylinder. nut was tight but just not enough so it was sucking air. went 2 flats more, did a quick bleed and problem fixed. might be a good idea to get a helper so you can see whats going on. good luck
 
zombywoof said:
i just had a problem similar to this last week. while my motor and trans are out i replaced all the brake lines and plumbed in a adj prop valve for a future disc brake swap. i bled the system like you and got good pedal pressure. after i let off it and pressed again it went to the floor. after a couple of times of bleeding the system with no improvement. so i made sure the prop valve was adjusted so the rear was getting less pressure. and had someone pump the brakes so i could look to see what was going on. i found the problem in a few minutes. as the brake were getting pumped i noticed it looked wet on a line coming out of the master cylinder. nut was tight but just not enough so it was sucking air. went 2 flats more, did a quick bleed and problem fixed. might be a good idea to get a helper so you can see whats going on. good luck
Click to expand...

I'll check all the connections again
 
Just in case anyone comes back to this thread, the problem ended up being the brand new calipers I bought from summit racing. One thing I learned from this deal is that even though there was no leaks, anything that hard to fix has a major breakdown in the system somewhere.
 
From what I remember it was a seal or O ring in both calipers that had rolled or was bad. I ended up after months of messing with it throwing in the white flag and taking it to a local guy who found out the problem.
 
Would it be accurate to say that whatever the malfunction in the calipers was, it hindered the air from bleeding out of them?
 
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