I suspect M/C is bottoming out. (Boy, have a hard time explaining this) Inside the M/C the piston has two halves with a spring between the halves. If one side is spongy the outer half compresses down then pushes on the second piston!
You can feel this happen.... Hope one the guys here can explain it better....
Howard

A little crazy that you could get a power booster added to the car after purchase and that there was apparently enough demand for the Ford engineering group to issue a drawing set. What was on pages 1 & 3?

Thanks for the replies guys, I appreciate it.
barnett468: You're right in that guess.  Although I've had the car for 19 years, I've never really had a reason to go looking for what was original and what wasn't in the brake system.  I found the build sheet under the back seat, but it's tattered and torn enough that I can't make out what was originally in the braking system (disk front or not).

MustangSteve's idea of a binding booster boot (that rolls off the tongue, huh?) is interesting.  I noticed that the boot on the first booster was torn when I took it out and it's difficult to get through the firewall hole.  Same with the booster I installed, after how many times I've had it in and out.

I'll take the driver seat out tomorrow and lay on my back and take some photos.  I clearly remember torque-ing down the booster bolts pretty well - using a universal joint on the ratchet.  Maybe it's in there crooked and/or the hole's too small.  That would be a nice fix if I didn't have to screw around with the proportioning valve and fabricate new lines.  (Well, nice is relative:  laying on my back reaching up under the dash isn't one of my favorite pastimes.)

Thanks for the suggestions everyone, that gives me new things to try.
Hutch

BTW, in answer to a question I missed answering:  The hard spot is a full-stop, not a temporary spot you can push through.  The amount of force I need to apply to get the car to stop isn't linear at all with the braking response - which is now sounding more like something mechanical binding somewhere when it's under pressure (hence it not binding when the brake drums or front pads are off).

Last edited by jhutch (4/15/2015 8:48 PM)

H all,

I pulled the master cylinder to double-check the push rod setting.  It looks to me like the MC is bad.  I have lots of brake fluid in the booster, as you can see in this photo:

Also, the piston in the MC seems to be way inside the cylinder and stuck there.  Here are also some score marks in the cyliner wall, but I'm not sure if they'll show up here in these pics:




One more question please:
Is this the correct orientation for the booster push rod?  That is, should the washer be installed with the convex side fasing the MC?

Thanks, looks like I'm shopping for a new MC

Hutch
 

The booster may not be long after that master. Brake fluid has a way of doing bad things to rubber, that are not intended to come in contact with it.

barnett468 wrote:

.
you master does not look like it is leaking to me . . it looks bone dry . . if it is bone dry, it is not leaking and the fluid in the master is from a previously leaking master.

the rod direction is correct . . the end must easily go in the ,aster and contact the end of the piston.

your piston is exactly where it shoud be . . the piston is against the circlip . . there is simply a hole drilled in it for the rod.

Thanks guys, I appreciate the continued feedback.
That picture of the master cylinder with rod resting on the flashlight is misleading; it's a picture from last year.  That's when I was measuring the rod depth into the cylinder, as you can see by the Sharpie marker line on the rod.  The current master cylinder, when turned with the side facing the booster facing down, drips fluid out the piston end rapidly.  What doesn't show clearly on the pictures I posted looking into the end of the MC is that the piston is way deep in the cylinder and stays down there.  There is an obvious irregular mark in the end of the piston from the booster rod.

MachTJ:  Ugh, that's not what I wanted to hear.  That's a new booster as of last year..  I guess I'll leave it in there to see how long it lasts.  Although I'm an old-hand at removing/installing boosters, I don't enjoy the experience at all, my back doesn't stand being twisted and contorted like it used to.

My mechanic buddy, who looked at the car extensively earlier this week, said he had the MS off and the booster was dry - that was one of the first things he looked at.  He did back the adjuster out on the proportioning valve, which is on the rear line only.  That direction is marked "decrease" on the knob, which I assume means decrease braking to the rear.  Perhaps that resulted more pressure to the front (and overall) and pushed the malfunctioning MC too far and caused it to leak?  In any event, I'll be replacing the MC tomorrow and will see how it behaves after that.

Is this the seal you're referring to?  At the moment it's in the booster and the booster push rod goes through it.

Last edited by jhutch (4/18/2015 9:11 PM)

Just for the sake of completeness, here are a couple of photos I took with a better camera that show how far in the piston is sitting.  I don't think it showed up clearly enough on the other photos:

Ok, sorry for being dense.  I see now after using a screwdriver to push the piston in that what I thought was the cylinder is actually the piston itself.  The fog lifts... perhaps I need new glasses.

On the last MC, I seem to recall the hole in the piston not being as deep, but I could simply be losing my mind over time.  The MC looks bone-dry in the photos because I cleaned it up prior to bringing into the house.  The replacement part number I was given by Advance Auto is 13-1378, which also is the part number recommended by Summit Racing's website and CJPony Parts when I specify make/model/year/engine size.  Advance says it's a "new" Cardone MC, not rebuilt.

I was unaware that there are different models of the booster and master cylinder that fit a 1969 Mach 1 (different piston sizes, single/multiple diaphragms).  I've only ever had one option available from parts suppliers.  What supplier and part numbers would you recommend?  I just want the normal power braking that was designed as stock for this car.

I don't know how to tell if I have a dual or single diaphragm booster.  Is there an easy way to tell by looking at it?
Thanks,
Hutch

.
ok based on your info and since we have no idea what is factory on your car and what is not, especially since you have an adjustable proportioning valve on your car, i would buy one of the masters below . . they will, cause the pedal to travel around 3/4 inches more than it did when you first installed your new booster and master providing you had the proper clearance between the master and booster rod . . if you had more clearance and you now reduce the clearance, your pedal will not travel farther thsan it did before, so if this additional amount of pedal travel is acceptable and reduced pedal force is what you want which is what it sounds like then this is the key.

 
DORMAN Part # M36445  Bore: 15/16 In.  $22.79  
 
CARDONE SELECT Part # 131602 bore size $22.89  
 
RAYBESTOS Part # MC36445  bore Size=15/16"   $23.89 
 
WAGNER Part # MC86130 bore size 15/16" $40.79 
 
CENTRIC Part # 13061029 check bore size $26.99
 
A-1 CARDONE Part # 101602 check bore size $20.79    


PROPORTIONING VALVE ADJUSTMENT

You mentioned your friend adjusted your valve so after your brakes are bled, i would find a safe strip of as phalt and go around 20 mph then mash on the pedal and adjust the brakes until you know the rears are locking up first after this, reduce the pressure to the rear a little then try the same thing from 40 if you are brave enough and repeat the adjustment process.

you must finbd the point where the rear brakes lock up first then adjust until you think they stop the best.

once the brakes actually lock, you can let off the pedal so you donyt put flat spots in your tires.

it is helpful if you have a friend watch the wheels as you do this.

some people do this rest on the grass or the dirt or the gravel . . since i at least try to drive on the asphalt, this is where i test them.

 

Last edited by barnett468 (4/19/2015 2:09 PM)

.

Mustang Steve wrote:

Why deviate from proven factory design 1" bore master cylinder?

I rarely if ever do and I posted the reason why in my post but I will try to explain it better . . in just the shop that we had we were doing probably 2 brake jobs a week and many of those included installing after market systems so I am very familiar with what affects what within a braking system and know that in some cases, the factory systems or some of the home installed, pieced together systems can be improved upon much like people installing brake pads and shoes that are more effective than the typical crummy ones available from the local auto stores and which are also more effective than the originals in many cases . . also, a big part of one of my previous jobs was developing and testing brake systems for a major vehicle mfg.
 
I organized his comments to make the chronology of his brakes easier to follow.
 

jhutch wrote:

I'm another Mach 1 owner that's new to this forum.  I'm also having problems with my brakes.  Here's a summary; I'm hoping someone will have some ideas.
 
I have a 69 Mach 1 351W
 
When I first bought this car in 1997, it was a stock 351W.  and the brakes were almost too good.
 
Eventually I needed to replace the booster and decided to also replace the master cylinder at the same time… The brakes worked ok after that and weren't so touchy.
 
I had the engine rebuilt… …to 410… and afterwards the brakes still worked ok, this was last spring.
 
Around about August, I decided to replace the stock Ford steering and slave cylinder mess with a Borgeson gearbox.
 
Afterwards, the brakes have a hard-spot in the pedal.  (I can't definitively say that this occurred right after replacing the steering. 
 
I have a 18 inches of vacuum at the booster, have tested the booster off the car with a vaccuum pump (it works)…

.
.

Mustang Steve wrote:

Why deviate from proven factory design 1" bore master cylinder?

1. His brakes worked too good before the new master and booster and sucked after installing them.
 
2. We have no idea what, if any of the parts on his car are factory original type for his model.

3. He has an adjustable proportioning valve so that is obviously not factory and was obviously installed because the brakes were unacceptable to one of the previous owners for unknown reasons.

4. imo, since he says his were marginal after the installation of the new master and booster, it would simply increase the safety factor if they were less marginal . . also, he stated the installation of these parts, reduced the braking performance.

Mustang Steve wrote:

The 15/16" bore MC is designed for manual brakes.

The masters I posted are stock for 1979 granadas with power disc brakes which actually have larger calipers than a 69 mustang . . this means that with the same pedal ratio and rear wheel cylinder size, the pedal will travel farther before the brakes lock but it will be easier to depress, and since the stock pedal stops well above the floor on the 69's with power discs, additional travel caused by the smaller master will not cause any problem.
.

Last edited by barnett468 (4/19/2015 4:15 PM)

Can you verify which type pedal you have?  Power brakes requires the long one in the center.  I have seen alot of botched booster installations.  With the wrong pedal, you will get really touchy brakes and possibly bad pedal geometry.