Another spongy brake pedal

[JT1930]

I don’t come on here much at all anymore asking questions but this one is killing me.
Brake pedal is spongy and goes to floor.

System.
-Boling bros Lincoln style brakes.
-3/16” brake lines
-‘67 mustang dual pot drum/drum 1” bore MC
-willwood 10# residual valves.
-tee for brake lights.
-shoes aligned and adjusted for slight drag.
-dot 3 fluid

Yes I’ve done a search and have tried everything I read on here and ford barn. Ive pretty much done every method of bleeding under the sun. Latest method I’ve done is as followed.

- Re-bench bled master cyl. Good no bubbles.

- Cap rear port. Bleed fronts first. For stiff pedal. Hand vacuum first then pump pedal and hold bled. Good.

- Connect rear brake line to MC. Vacuum bleed first then pump pedal and bleed. Good.

While bleeding I notice a stream of small bubbles coming out of all 4 bleeder. Thinking it’s the bleeder letting air by threads but have a bit of teflon tape on them to try and reduce that.

After all bleeding is done push pedal. Feels firm. Promising. Goes about half way down and gets firm. Move car back and forth pedal basically goes to floor but stops car. Jam on brake pedal stops car but not fast enough. Park car pedal gets firm as before moving car.

Suggestions? 1.25” bore mc? Should I just can the dual pot for a single ? Help !

Pictures are attached to just show if lines off master are what is causing air in system still. Rear backing plates are nothing new of what others have done when using model a rear end.

[slowforty]

Check on YOU TUBE. For Brake bleeding. There may be a solution for you.

[glennpm]

Regarding brake bleeding, you should always start with the wheel that has the longest run of brake tubing to it, not the fronts as you mentioned.
What was the last change you made prior to this issue?


Glenn

[JT1930]

Glenn, yes you are right but from what I read and someone who does many brake setups I went that route. Also. The MC is basically in the middle of these little cars to begin with. Right front and right rear are likey to be almost same length.

The system is all new. Ditched the mech brakes for hydro now.

[solidaxle]

Check your adjustment on the MC push rod, it may be too long, you don't want any extra length pushing on the piston at rest.

[glennpm]

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Yes with a dual reservoir system, you could do the left front first and for the rear whichever line is longest.


I'd block the brake pedal to mimic brake application, leave it for a few hours or over night and then look for leaks. Sometimes this helps to migrate air bubbles back to the master cylinder but not so much with the MC not mounted above the rest of the brake system.

[JT1930]

Will do. Worth a try.

Only other thing I can think of is I used sealant on the threads for front brake hoses to wheel cylinders. Will be getting and putting copper washer there today. But I have yet to see any leaks.

[V8 Bob]

Having the rear brake assemblies upside down not only creates bleeding problems, but also positions the lines in harms way. NOT good. I would do what's necessary to position the brakes properly.



The ONLY sealant that should be used on a brake system is on tapered pipe thread, NOT ANY straight thread fittings. IF you need sealant on straight threads, you're doing something wrong.


Bleeding the longest line first doesn't really apply to dual masters. You want ALL the lines connected, then go around the vehicle several times bleeding each brake until no air is seen.


After a preliminary bleed, leak check with a hard pedal apply. Use iso/denatured alcohol to clean all the fittings for easier leak detection and general cleanup.

[flathead4rd]

You don't mention what type of brake fluid you are using. DOT-3 or synthetic (silicone).