Brake issues

[Manu Mach1]

I finaly finished to work on the mechanic part of my Grandé.

Last thing to be done is to fix a problem I have with the brakes.

Front calipers are rebuilt completly.

MC is rebuilt with a new kit.

Rear brakes are in good condition.

I have no leak anywhere.

Symptom: when I hard brake, rear wheels get to much power, I mean all hydraulic power, or most of it is blocking the rear wheels. I suspect the proportioning valve to don't do his job.

Proporting valve is the original one I guess, nothing like some of the ones you can adjust it.

I found some kit to repair, seals, springs etc...

My question is: should I change it by a new one or should I repair it using a repair kit?

Thank you,

Manu

 

[Don C]

I would rebuild it.

Was the MC bled after the rebuild? Also, make sure the calipers are completely bled and no air remains in the system.

If you still have the problem I would suspect that something went wrong with the MC rebuild and it has an internal leak.

 

[Manu Mach1]

Don,

I noticed that the brakes were stronger at the rear from the first day I bought the car.

Then when I started to work on my car, I saw a small leak that came from the MC.

I removed the complete brake fluid and change it all, and the system is completly flushed of air.

So I will follow your recommendation and repair the proportioning valve.

Need now to find a brand new kit.

Merci.

 

[jeff8877]

Here is the link for instructions on rebuilding...I just finished mine and it is very easy and takes about 15 minutes. These guys sell the kit.

https://www.musclecarresearch.com/valve-rebuild-kh

 

[Manu Mach1]

Jeff,

Is your problem was the same as mine?

Thanks for the link.

When ordering the kit it asks me:

Ordered $32.55 including shipping.

Just have to wait, I will come back after the repair.

 

[jeff8877]

Jeff,

Is your problem was the same as mine?

Thanks for the link.

When ordering the kit it asks me:

Ordered $32.55 including shipping.

Just have to wait, I will come back after the repair.

Mine leaked but worked...so not same issue.

 

[Bentworker]

Personally I think the stock combo valves are evil. I have a habit of tossing them and putting in a Wilwood adjustable proportioning valve. I think the Ford combo valves are similar to the GM ones. For sure the GM ones can get troublesome when bleeding brakes as the shuttle spool that is supposed to actuate the warning light will move to one far end of it's travel when brake fluid flows through the combo valve unrestricted. I do not know for a fact but I think the Ford ones are similar and could give you trouble. The GM ones required a tool to keep the shuttle valve cented while bleeding the brakes... Again I think the Ford ones are similar. The point of the combo valve was to give you a fixed rear proportion valve and a failsafe for your front brakes. If you had a brake hose or piston failure up front the shuttle spool was supposed to slide to one end, the groove in the spool would activate a warning light switch and the spool valve was supposed to cut off flow to the severed side.

Wilwood makes an adjustable proportioning valve that is similar to the stock combo valve. I like the ability to adjust brake bias to make up for tire size, non stock brakes etc. However it does not have the shuttle spool / warning light.

If you are staying all original I'd say a rebuilt combo valve is a must, as there are moving parts and seals inside that little chunk of brass.

 

[rocket366]

Throwing this out there for people that don't know.

If there is ever a leak or too much air in the front or rear system or

the master has run dry in front or rear reservoir the combo valve piston will

move (doing it's job) and shut off the fluid to the front or rear system.

When this happens the piston in the combo valve needs to be "re-centered".

Example;

When I first got my 73 the front reservoir was dry in the master. I was driving

with front brakes only. The rear wheel cylinders were leaking which is why the

master was dry and the combo piston shut off fluid to the rear brakes.

To re-center the combo valve piston after repairs/bleeding;

Mostly a few "hard as you can" stomps on the brake pedal will re-center the

piston.

If not the piston may have gotten stuck in the muck of the bore.

Now in that case you need to loosen a brake bleeder on THE END OF THE CAR

THAT THE BRAKES WORK...then a couple hard stomps to get the piston to center.

Hope this helps somebody.

Regards

Paul

 

[Manu Mach1]

Hello,

So I received the repair kit for the proportioning valve



I couldn't remove the proportionning valve from the car, one nut didn't want to loose, anyway I rebuilt it like that



After work I will bleed of the system and check if it brakes like it should.

 

[Manu Mach1]

Throwing this out there for people that don't know.

If there is ever a leak or too much air in the front or rear system or

the master has run dry in front or rear reservoir the combo valve piston will

move (doing it's job) and shut off the fluid to the front or rear system.

When this happens the piston in the combo valve needs to be "re-centered".

Example;

When I first got my 73 the front reservoir was dry in the master. I was driving

with front brakes only. The rear wheel cylinders were leaking which is why the

master was dry and the combo piston shut off fluid to the rear brakes.

To re-center the combo valve piston after repairs/bleeding;

Mostly a few "hard as you can" stomps on the brake pedal will re-center the

piston.

If not the piston may have gotten stuck in the muck of the bore.

Now in that case you need to loosen a brake bleeder on THE END OF THE CAR

THAT THE BRAKES WORK...then a couple hard stomps to get the piston to center.

Hope this helps somebody.

Regards

Paul

I read you with attention.

When I reassembly all together, i set the piston like that



Than I bleed off the air, start with rear right cylinder, left rear, front right caliper then left one.

At the end I still have the same problem, to much power to the right brakes, first the rear right wheel block and i can feel the car while braking is going to the right.

So at least I have the same problem as before.

Any idea?

 

[rocket366]

have a look at the left front caliper.

caliper piston may be frozen

caliper may be rusted to spindle and not sliding

 

[Manu Mach1]

Front calipers have been completly dissassemblied and rebuilt with new seals kit.

 

[rocket366]

Are you sure no air in system?

Master was bench bled?

in that case I would revisit the combo valve

there may be a blocked passage

this is a tough one

 

[Manu Mach1]

No I didn't do the bench bleed, I even ner did on any car. Is it absolutly necessary?

 

[72HCODE]

additional things to check:

* have you replaced both front soft lines from the engine bay apron to the front calipers, they are known to collapse internally and choke off the brake fluid getting to the front disc calipers?

on the rear drums:

* were the correct springs used during rebuild?

* is the parking brake cable adjusted too tight?

* are the adjusters set too tight, if you back them off a couple of clicks it would reduce the rear brakes engaging early?

* were the correct wheel cylinders installed?

(they had 2 different sized rear wheel cylinders there was a 29/32" and a 7/8" size, i have seen people accidentally install front wheel cylinders on the rear, those are 1-1/8" sized and 1-1/16" sized,, the 29/32 is slightly larger. the V8 cars got the larger 29/32" versions)

* correct brake shoe width and correct drum size there are 3 different sizes that can get miss matched.

10x2-1/2" and 10x1-3/4" and 10X2"

on the front disc:

* have the pins been greased inside the rubber caps, without the grease the calipers will not float they can get stuck and reduce braking function?

* correct pads for the disc size? i've seen people get the wrong part number and install undersized pads.

just some extra things to check

 

[Manu Mach1]

Since I got this Mustang, the brakes were doing a bad job, blocking first the right rear wheel and I can feel the car going to the right (while breaking).

You give me a lot of things to check and I gonna do that.

-I didn't replace the soft lines.

-I didn't touch the rear brakes, no leaks and the shoes are in good condition.

-The parking break is adjusting enough to immobilise the car while parking, and I have to push the pedal to it maximum for that.

-need to check the adjusters.

-need to check the rear cylinders.

-need to check the rear drums size and shoes.

front:

-the pins have been greased.

-need to check if are the correct pads, but looks like.

Thanks for those more indications.

 

[mrmach1]

There are two things on a car I don't fool with and I want working perfectly one is Tires and two are the brakes. I would take it to a professional and not skimp to save a few bucks. Just my opinion for what it's worth. I value my life and the life of others to much to do otherwise.

 

[Manu Mach1]

There are two things on a car I don't fool with and I want working perfectly one is Tires and two are the brakes. I would take it to a professional and not skimp to save a few bucks. Just my opinion for what it's worth. I value my life and the life of others to much to do otherwise.

I totally agree with you, but here to find a professional to work on this old car is not easy, only garage where they connect the computer to tell you that you have to change this or that, and most of the time the prblem is coming from something else, but still you have to pay for what you didn't need.

If I knew a guy who would spend time to analyse where is my brake issue, I wasn't here to share with you guys.

 

[T-Tom]

I would definitely replace the soft lines. You've done everything else so why not replace those. Check them by disconnecting them from the caliper, placing the end in a container, and push down on the pedal. See how much fluid you've moved. 72HCODE has also given you a lot of other issue to check. Hopefully you didn't mismatch your parts but at this point it would be good to recheck everything. Best wishes on resolving the issue.