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Discussion Starter #1
Okay guys, I am soliciting your experience and troubleshooting abilities, I am seriously stumped on the brakes on my car (and so is Mike, 1970FastCat who has the same issue). The symptoms are:

- half a pedal that feels as if you go through a mushy first circuit and then the pedal is solid

- no discernable wear-in on front rotors after nearly 50 miles

- rear brakes can be made to lock up on wet pavement but only by standing on the pedal, fronts nothing

What I have done:

- replaced one new master cylinder with another brand new master cylinder and bench bled both to death each time I tried to use them

- vacuum bled, regular (pump, hold, bleed) bled over and over with same results, half a pedal and car is stopping on rear brakes only (which obviously feels like not much brakes)

- checked rear brake shoes for tightness, I hear them drag slightly as they should when I turn the rear wheels

- removed and disassembled previously rebuilt proportioning valve, was put together correctly and found nothing wrong

- checked booster pushrod length against master piston hole depth, pushrod is right length, not too short, not too long

What the brake system consists of:

- all new stainless lines front to back

- all new brake hoses

- rebuilt calipers

- new wheel cylinders

- new pads and new shoes

- cleaned up booster that was working in my first Cougar when taken out of service

WTF is going on, I wish I knew. I am down to the idea of plugging the rear brake port on the master with a fine thread botl and teflon tape and seeing if the fronts will work that way. I don't know what else to do.

Any ideas?

Questions about what I have or the condition or this or that? Ask away.

Thanks,

Bob
 

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Out of the blue... is there a way to tap in a pressure gauge at the end of the lines?
or with 2 people, one breaking and the other looking for movement at the disks?

don't forget this is from someone that knows less than nothing about it, but if the pros are stumped. it might just need a oddball perspective to solve it.
 

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Bob,
Any chance you have a leak in the system? And any chance that you mixed up the brake lines either going into or coming out of the master cylinder or the proportioning valve?

Antonio
 

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Discussion Starter #5
Bob,
Any chance you have a leak in the system? And any chance that you mixed up the brake lines either going into or coming out of the master cylinder or the proportioning valve?

Antonio
No leaks, but I was thinking the same thing about reversing of the lines, like master front circuit going to rear brakes and vice versa, that could explain how things are behaving, but each time I look I find that the lines are connected correctly. Will look once again however.
 

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Sure you have the correct master cylinder? Some of the parts stores are selling a truck master cylinder as a replacement for the correct one. Post a pic of the master if you're not sure.
 

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Pull the pads. Pump the pedal. See if the pistons are moving under pressure.
Could be several bad things. I'd start at the caliper and go backward.

If you're bleeding the fronts, then you have fluid movement and some pressure. Doesn't mean the pistons are moving and doesn't mean the seals are good in the new master cylinder. So, that's why I say start at the caliper and work backward.

Or, nuke it from orbit. It's the only way to be sure.
 

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Discussion Starter #8
Jeff,

How does this imposter truck cylinder differ? I can post pictures of both of the cylinders I have if that would help. Each are somewhat different but fit the application.
 

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Discussion Starter #9
Pull the pads. Pump the pedal. See if the pistons are moving under pressure.
Could be several bad things. I'd start at the caliper and go backward.

If you're bleeding the fronts, then you have fluid movement and some pressure. Doesn't mean the pistons are moving and doesn't mean the seals are good in the new master cylinder. So, that's why I say start at the caliper and work backward.

Or, nuke it from orbit. It's the only way to be sure.
Does the fact that the (front) wheels lock when someone steps on the pedal on the car (in the air) make a difference? I think it means that the pistons are indeed moving under pressure. I am of course grateful for every insight and suggestion, one should lead to the problem and its resolution.
 

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With two assistants open both front bleeders and push the pedal to the floor and verify fluid coming out. Tighten bleeders and release pedal. Do this a couple of times until no more air is spotted. I've had to do this on several cars after new master and calipers. Bleeding one at a time can push air back and forth into the other front line.
 

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So, still haven't taken the master cylinder apart?? Do it, if for no one else, me, so that once u verify that All piston cups are present AND oriented correctly, I can stop bugging you about it. I know It's your 2nd new one, but it could have been assembled incorrectly. At this point buy a rebuild kit (inexpensive) and redo it all and take pics so you KNOW its been done right. I speak from experience being burned by this very thing.
Kevin
 

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Is the proportioning valve centered properly? Are you getting a brake warning light? Is the light hooked up? Have you tested the light to see if it works.

Just a shot in the dark but sometimes those valves tend to work their way to one side while bleeding the system which will change the pressure (primary to secondary) The only way to tell it's off to one side is the brake warning switch light. If the warning switch or light doesn't work you'll never know. See your 69 service manual.
 

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Jeff,

How does this imposter truck cylinder differ? I can post pictures of both of the cylinders I have if that would help. Each are somewhat different but fit the application.
I don't know how it differs internally but it does look different and performs differently. I used one of these on a prior Cougar and had the same symptoms you're describing. The truck master is a little wider and not quite as deep. The correct part number for the replacement master cylinder is TS-101378. The original Bendix part number is 11378.
 

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Discussion Starter #14
I don't know how it differs internally but it does look different and performs differently. I used one of these on a prior Cougar and had the same symptoms you're describing. The truck master is a little wider and not quite as deep. The correct part number for the replacement master cylinder is TS-101378. The original Bendix part number is 11378.
Hi Jeff,

Thanks for this. My second master (a new Cardone) is 13-1378, so sounds like I have a correct part there. Not sure about the first one as I bought it long ago but it has the same basic shape, length and size. Both look the same (within reason).
 

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Discussion Starter #15
Is the proportioning valve centered properly? Are you getting a brake warning light? Is the light hooked up? Have you tested the light to see if it works.

Just a shot in the dark but sometimes those valves tend to work their way to one side while bleeding the system which will change the pressure (primary to secondary) The only way to tell it's off to one side is the brake warning switch light. If the warning switch or light doesn't work you'll never know. See your 69 service manual.
Catman,

On '69 the prop valve is separate from the distribution block (which contains the shuttle for the brake light). I think you are mixing the two functions up. I went through the proportioning valve again last night just to be sure all was as it should be but I cleaned it well, lapped the end of the top nut (that the piston sits against at rest) and assured the piston moved freely with its spring. Put all back together and installed, bled, same thing.

As for the shuttle, I am sure it is off center at the moment and I have the switch contact partially unscrewed temporarily so the light stays off. The position of the shuttle should not affect the operation of either circuit but will slide toward the side with a pressure problem, the front in my case.

Thanks,

Bob
 

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Discussion Starter #16
Kevin,

I'll take the new Cardone apart just to make sure, I reinstalled the original new one. Will let you know what I find. In the meantime, toward this end, anyone have a diagram of the pistons/seals for this cylinder? Perhaps the shop manual does.

Thanks,

Bob
 

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Discussion Starter #17
Clawit,

Will try this for sure and look closely at the fluid that comes out (for bubbles, etc...)

Thanks,

Bob
 

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Long shot here but have you checked actual rotor thickness to be sure it's in spec? I had this problem with my old wagon one time I did the brakes. 1 rotor was out of spec thickness wise. It may have been the wrong part in the box even who knows. I noticed it right away before I started and returned it for another.
 

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Bob, I recall that you can swap the calipers from side to side resulting in an upside down situation that prevents the air from ever getting bled out (bubble forms at top). My understanding is that it looks right, but doesn't work right, when they are swapped side to side.
 

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Is the piston in the distribution block just a switch or is it a valve? If it is a valve, wouldn't it close off one of the circuits (front or back) if not centered? If it is just a switch.... nevermind.

What kind of pads are you using on the front disks? Did you try roughing them up a little? Might be glazed (which wouldn't effect pedal, so, again.... nevermind.)
 
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