Front Disc Brakes oddity

[Rons beast]

The proportioning valve could be part of the problem. In a front disc rear drum set up normally the valve allows fluid to flow to the rear brakes first allowing just about 5lbs of pressure before opening and allowing fluid to flow to the front calipers.  This gets the rear shoes set on the drum but not doing any real braking then the needed fluid in a lesser quantity is "proportioned to the fronts to allow proper braking bias. The lines to the front caliper are usually smaller because of the lower volume of fluid needed to pressurize the front brakes.  If the proportioning valve and or lines are not correct for the system you could have the poor pedal performance. The issue could be the proportioning valve is letting fluid flow to both front and rears and the return springs in the rears are pushing the fluid back toward the master. Then the second "pump of the pedal is getting the shoes in the rear set and finally the fluid pressure is even and applied to all 4 corners.  

If the PO put the front disc conversion on it may have been a problem from the beginning.

 

[Auggie]

Thanks.  I will check the lines, but to the Beast....this is OE...this 77 came with front disc and rear drums as did most 76 & 77's as stated by BB earlier in thread.

Bully....both reservoirs are full.  I have tried pumping with cap off and yes, I get fluid squirted up from side that supplies rear brakes. I also get some movement in the front brake side when the pedal is released. Only happens on first pump.......then brakes get hard.  Calipers on front moving as they should...just not securing the rotors as they should...obviously or I would be stopping better.  I have been recommended to unscrew all four bleeders and have my "garage associate" ( my Wife) push the brake pedal one time to the floor......makes a mess I hear, but can "reset" the proportioning valve?

I purchased the MC at Advanced Auto locally..compared to old one and was exact match...and has "limited lifetime warranty".  It was rebuilt. No Pads were missing, just realllllllllly worn.  Shoes were disintegrating.  Rotors however were in surprisingly good condition.

More later.

 

[Bully Bob]

Look'n in the book.., the proport. valve is adjustable.

Usually the dash light (with key on) indicates when it's out of adj. (If bulb isn't burned out)

It being out of adj. could cause the need to pump the pedal.  

What causes it to go out of adj. is improper pressure from the front or rear feeds from the M/C

------The old M/C may have pushed it out of adjustment.-----

What this all means is when a front or rear wheel system fails, the odd pressure pushes a piston in the

proport. valve..., forcing a switch to light up the brake warning light.

In turn.., the brakes are working only on front OR rear system.

Sounds like yours are working only on rear system.

 

[Auggie]

That is exactly what it feels like....I would think if the discs were catching th rotor I would be stopping much quicker.  You have once again given me a weekend project....thanks Bully.

 

[Bully Bob]

http://www.tomsbroncoparts.com   has the '76-'77 origonal shop manual on CD..!!

That would be a big help to you as it's 10 times better than Chillton or Haynes.

It says "Ford trucks, including Bronco"  (i would ask them if it's COMPLETE AS TO THE BRONCO

Jeffs Bronco Graveyard may still have it in hard-bound print copy, if memory serves.

I have the '66-'67 book & it's priceless..!!   (& pretty much wore out  :-B   /emoticons/[email protected] 2x" width="20" height="20" /> )

 

[Auggie]

Thanks Bully...I checked Jeff's and they have the CD...it is in my cart!

Thanks again

 

[Auggie]

Hello Bronco Brainiacs!

After replacing the front calipers, pads, rear shoes and wheel cylinders, new master cylinder and new front lines.  I was really trying to keep away from the proportioning valve since it seemed to be pushing fluid thru as it should.  I decided to replace the booster and abracadabra, I have brakes!!!! Nice to be able to stop as it should.  Thanks for all the input..especially Bully Bob who plainly said PV rarely fail! True story.  Now I just need to find an emergency brake for the beast. 

 

[Bully Bob]

Good news.., good work..!!  /

Start a new topic as to the E-brake...,  list what parts are missing, etc.

 

[BLADE262US]

What yr is this ? If the bronco originally had drum fronts and someone converted it the master cylinder may not be big enough bore to support the fluid volume of the caliper . I think its 1 1/16 bore is a standard front disk rear drum setup .  

 

[Auggie]

I should have posted up my results.....sorry everyone.  It was a combination of my MC and the Booster....replaced the booster after replacing the failed MC and bingo bango....I can stop.  Thanks again.