need some help, In a bind here

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boosted

boosted

Life Needs Air
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My 67 barracuda has 74 Dart front disk and an aftermarket rear disk brake setup. All new, new master cylinder new proportioning valve new harn and soft lines. Her eis the problem and this is what has been done... So what would be next?

I can bleed the brakes and get a good pedal. Walk away for a few minutes and come back and the pedal will go to the floor.

I have swap out the master cylinder with a working one from another car same issue

I have blocked the back brake line off so only the front has fluid and the problem goes away. So I am thinking something in the rear. Nothing is leaking anywhere that I can see.

The rear system is the one that uses the 85 Cadillac calipers. It is like the fluid is returning back to the master cylinder and not holding the piston in the caliber in place. The proportioning vale is a disk to drum new one for a 74 dart.

What is next? Could it be in the valve? They are not cheap and getting it in and out with this big motor in it is not going to be easy.
 
If its holding with the rear blocked I think you have localized the area. Have you tried pumping the brakes with the engine running and booster activated? That will provide more pressure and possibly a leak might show up with the increased pedal pressure. Sounds like air in the system.
 
I had the same problem. First put a two pound residual valve in the rear line. The bleeder valve needs to be strait up to bleed them. You will also need to adjust the throw on the E brake arm to get the pads touching the disc. there are some videos on Youtube showing what to do.
 
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Not sure I feel like this guy knows 100% what he is saying but....



70s Versailles rear disk had a similar adjusting procedure.


If the piston was not adjusted correctly you had issues. On the Ford you removed the e brake lever, used a tool to turn the piston into the caliper, reattached the e brake lever and the piston would self adjust.
 
Ok so just throwing this out there, most rear e-brake calipers are to be ratachted out before you pump up the pedal , I will pump the e-brake handle or pedal many times before bleeding them . Hope this helps worst case you’ve pulled the guts out of the rear piston . :popcorn:
 
No, you do not use a residual line pressure valve with disc brakes.

Check that the rear calipers are not reversed, if they are of a type that fit L or R. Bleed nipple needs to be up.
 
Bleed nipple is up top, and the piston is out to a measurement of .060 from pad to rotor. What would be the harm to put a 2lb valve n the rear line? This is a street race car so no real daily driving.

20180804_103400.jpg
 
boosted said:
. What would be the harm to put a 2lb valve n the rear line? This is a street race car so no real daily driving
Click to expand...
Your pads will always be dragging and as such heating up.


Are you loosing fluid out of the master?

If not there is no leak. And if you have a firm pedal one day and it goes to the floor the next I would say faulty master allowing fluid around the piston.
 
I believe it might also be possible you simply have a bad seal in one or both rear calipers. The reason residual valves are used in drum systems is that the master can return fast enough to cause a slight vacuum and draw air in past the cups on the drum pistons, eventually building up air. Most disk systems don't need them because the pistons dont really return much. If you read the explanation in some of the old shop manuals, the flex in the lip of the piston seal causes the caliper pistons to return a tiny amount. Maybe the seals have gotten a bit hard
 
Well, I initially asked if the shoes were adjusted. Then I re-read the post and decided I was 'tarded.

Now I'm gonna catch hell for suggesting adjusting the parking/rear brakes, because I'm completely unfamiliar with that particular system, but someone else said it too.
 
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