FYI FORD MustangSteve's Ford Mustang Forum » Brake issue

Mark Z · 4/06/2013 8:57 AM

Ok, I've brought this up before but the weather is better here in NY and I'm about to try to fix these brakes.68 mustang 289 aod. I have factory rear drums adjusted properly bled and no leaks. Front are four piston kh conversion from SSBC. I have a powerbrake pedal, disc drum master and powerbooster from Master power brakes. Original distribution block and adj proportioniong valve installed in rear line. I have plenty of vacum. Ok what is happening is, when you intially step on the brake pedal and do not release the car stops. If you lift off the pedal and bake again as what you do when normally brake , you can barely stop the car. With the rear wheels off the ground and spinning , they stop when brakes applied initially but when off pedal and brake again they spin! I have an original 68 powerbooster, and a proportioniong valve from a 70 mustang that I am going to install. This would eliminate the adjustable one (which I tried turning each was with no change) and the smaller after market booster. I hate to just change out parts for no reason but knowone seems the have seen thei before or have an answer? Maybe someone here know what is going on.

Thanks Mark

Mark Z · 4/08/2013 12:54 PM

I guess no one has seen this before? I wish someone would just say , ya thats a bad mastercylinder or something else before I just replacing parts blindly.

Hornman · 4/08/2013 2:17 PM

OK, I have seen something similar, on my 63 Galaxie wagon, except I got no good stops. My problem was a bad booster, it had a huge vacum leak. Your problem could be a wounded booster and a bad proportioning valve. If you have adjusted the prop valve both ways and still cannot make the rear wheels stop, the prop valve is a problem since you should be able to manually generate enough rear brake line pressure to stop the rear wheels.

Mark Z · 4/08/2013 2:59 PM

Thanks for the response. The booster tests fine, no leaks. like you said not too sure about that adjustable valve. Not sure if the symptoms are coming from it?

MS · 4/08/2013 3:19 PM

The valve in the booster that allows atmospheric pressure or vacuum to come in is probably stuck. Replace with a factory Bendix (my favorite) or Midland Ross that is in known good condition and you will be way ahead.

Mark Z · 4/08/2013 3:35 PM

I have one of those boosters and the plan was to replace the aftermarket one with it. I can't wait to drive the car and beable to stop!! I also have one of the disc/drum proportioning valve from a 1970 mustang i was going to install at the same time. OMG pic works too a good sign
Thanks

MS · 4/08/2013 8:37 PM

I really like that white 68. Looks sharp!

jollem · 4/08/2013 11:11 PM

if your really getting no where,make sure inside of vacume hose is 100% and no rubber dangling to affect vacume

Last edited by jollem (4/08/2013 11:11 PM)

50vert · 4/09/2013 2:10 AM

I don't know where it is on a 68, but no one has mentioned it, residual pressure valve?
Needed to hold the brake shoes close to the drums after releasing the brakes.
Just a W.A.G. and post # 2

Mark Z · 4/09/2013 3:19 PM

MustangSteve wrote:
I really like that white 68. Looks sharp!

Thanks, I had the same car in high school. Was trying to figure out how to respond to an individual post, I hope this is it

Mark Z · 4/26/2013 1:07 PM

MustangSteve wrote:
The valve in the booster that allows atmospheric pressure or vacuum to come in is probably stuck. Replace with a factory Bendix (my favorite) or Midland Ross that is in known good condition and you will be way ahead.

Well I finally replaced the booster with an original ford midland. Only to find out it was bad! I was told when I bought it , it was good. I ordered a new rebuilt one. Not even sure this will fix my brake issue. Just love these cars

GPatrick · 4/26/2013 2:05 PM

This is probably unrelated but was this a PB car originally? There was a thread a few days ago regarding the firewall cutout for manual m/c or booster. From what I saw in Steve's post, the original firewall hole for manual brakes is smaller than the hole for the booster and it can cause the booster to hang up. I didn't see in your thread what brakes were stock on your car. There is a link and template here. Ignore if it was already boosted. http://www.mustangsteve.com/fyi_brakepedals/msFAQbrakepedals.html

Mark Z · 4/26/2013 2:21 PM

Was originally a manual brake car that I converted many years ago to power disc. I cut the hole out years ago. This booster just plan old leaks. New one ordered, these things are made of gold

terry · 4/26/2013 5:53 PM

Mark Z wrote:
If you lift off the pedal and bake again as what you do when normally brake , you can barely stop the car.

Mark, not to poke at you or pick on you,But I was told when you get ready to stop your car you should place your foot on the brake and start pressing enough to start slowing the vehicle then keep pressure on the brake until completely stopped. You shouldn't press on the brake pedal and lift off then press again or as they call it "pumping the brakes". Seems the pumping action causes warping of the rotors in disc brake cars.
Only reason I bring this up is I never knew this bit of Info until I took one of my cars in for brake work, the car was surging as I went to stop. The mechanic asked me if I pumped the brakes when I stop. Then He informed me of the cause of the surging, warped rotors, caused by pumping the brakes while stopping. well I learned something that day many years ago!!

Hornman · 4/26/2013 6:37 PM

terry wrote:
Mark Z wrote:
If you lift off the pedal and bake again as what you do when normally brake , you can barely stop the car.
The mechanic asked me if I pumped the brakes when I stop. Then He informed me of the cause of the surging, warped rotors, caused by pumping the brakes while stopping. well I learned something that day many years ago!!

Terry, I think you are the victim of an urban legend. The rotors (or drums) don't know or care how you use the brake pedal. Their job is to turn forward momentum into heat, resulting in the car stopping. Pumping the pedal actually gives the brakes (a little) time to dissapate some of that heat. Guess how modern antilock brakes work: the computer very rapidly pulses the brakes. If that caused warpage, there would be a large pile of discs and drums outside every brake shop and dealership. What I have heard about brakes is that you should apply them early and gently to minimize heat buildup. Supposedly, panic style stops (like in road racing) builds up heat the fastest which could cause warpage if that rotor style is prone to warp. I had a Taurus SHO that warped a set of rotors every 20,00 miles. I finally learned that Ford missed the design on those rotors. I bought some aftermarket rotors at Autozone and the problem went away.

Mark Z · 4/27/2013 7:14 AM

Trying to find a booster for my 68, Are the Bendix and midland dimensionally the same? I hate bending brake lines. And is one better?
Thanks

MS · 4/27/2013 10:39 AM

Bendix is a little shorter. Lines should be OK if you are replacing a Midland. I have a really nice rebuilt Bendix that has the BENDIX stamp and all the patent numbers showing very well if that kind of stuff matters to you. I prefer the Bendix. It doesn;t has so many small parts to go bad.

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