What next? Brake Question

Platonic Solid · Jun 26, 2005

I’ve replaced the distribution block and bled the brakes about 5 times now and the brake pedal still sinks all the way to the floor. At one point it seemed to be maintaining pressure, but that soon faded. The front calipers are new and there are no visible leaks anywhere. The only parts left that could be replaced are the rear wheel cylinders, master cylinder, and the brake booster. Any suggestions or recommendations?
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degins · Jun 26, 2005

Make sure that the calipers are installed on the correct wheels. The bleeder screws should be located at the high side of the caliper. If you installed the calipers right on left, and left on right, the bleeders will be at the low end of the caliper and will allow a bunch of air to remain behind the caliper pistons. With 70-73 and Granada calipers I believe the bleeders should point nearly straight upward.

Platonic Solid · Jun 26, 2005

Good Advice, but Calipers are installed correctly.

jst6 · Jun 26, 2005

the reason i did the ssbc brake kit was b/c my master cylinder went out. i had the brakes pro bled by a machine and the pedal would still sink to the floor. the mc will go out before the wheel cylinders. i'd replace the mc and go from there.

Platonic Solid · Jun 26, 2005

jst6 said:
the reason i did the ssbc brake kit was b/c my master cylinder went out. i had the brakes pro bled by a machine and the pedal would still sink to the floor. the mc will go out before the wheel cylinders. i'd replace the mc and go from there.

That's what I was thinking too. I'll replace the mc first and see if that solves it. Thanks

I've been looking for pressure bleeders. Anyone know where to get one that installs on old style master cylinders?
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Platonic Solid · Jun 28, 2005

OK, I bench blead and replaced the Master Cylinder. I don't have time to bleed the brakes tonight, but I though I'd just try to see what the pedal feels like now. Pedal feels perfect with the engine off, but still goes to the floor with the engine on. Is this right?

2nd Mustang · Jun 28, 2005

I saw an article a few years ago about a home made type pressure bleeder. I bought a quarter inch thick plate of aluminum at a metal scrap yard, big enough to cover the top of the MC, drilled a hole through one end to fit a compressor fitting through it. The fitting will fit over the front bowl first, then turn it around for the rear bowl. The pressure should be less than 15 pounds if I recall, so rather than risk using my compressor, I use a two gallon garden sprayer to pump pressure into the MC. I screwed an air pressure gauge into the body of the tank to monitor pressure. This method works great, but you do have to periodically check on the fluid level in the MC. Good luck.

Oops, forgot to mention that I also got some universal rubber gaskets to seal the plate to the top of the MC and used a small C-clamp to hold it in place on the MC.

a.vannoy · Jun 28, 2005

2nd Mustang said:
I saw an article a few years ago about a home made type pressure bleeder. I bought a quarter inch thick plate of aluminum at a metal scrap yard, big enough to cover the top of the MC, drilled a hole through one end to fit a compressor fitting through it. The fitting will fit over the front bowl first, then turn it around for the rear bowl. The pressure should be less than 15 pounds if I recall, so rather than risk using my compressor, I use a two gallon garden sprayer to pump pressure into the MC. I screwed an air pressure gauge into the body of the tank to monitor pressure. This method works great, but you do have to periodically check on the fluid level in the MC. Good luck.

Oops, forgot to mention that I also got some universal rubber gaskets to seal the plate to the top of the MC and used a small C-clamp to hold it in place on the MC.

This should work great

Platonic Solid · Jun 29, 2005

2nd Mustang said:
I saw an article a few years ago about a home made type pressure bleeder. I bought a quarter inch thick plate of aluminum at a metal scrap yard, big enough to cover the top of the MC, drilled a hole through one end to fit a compressor fitting through it. The fitting will fit over the front bowl first, then turn it around for the rear bowl. The pressure should be less than 15 pounds if I recall, so rather than risk using my compressor, I use a two gallon garden sprayer to pump pressure into the MC. I screwed an air pressure gauge into the body of the tank to monitor pressure. This method works great, but you do have to periodically check on the fluid level in the MC. Good luck.

Oops, forgot to mention that I also got some universal rubber gaskets to seal the plate to the top of the MC and used a small C-clamp to hold it in place on the MC.

OK, something like this: Inexpensive Brake Pressure Bleeder with a cover like this:

If the booster is shot, is it safe to simply disconnect and plug the vacuum line and use it that way?
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DarkBuddha · Jun 29, 2005

Platonic, is this a conversion or just a good old fashioned rebuild? Did you add the power booster, or is it original to the car? The reason I ask is that conversions sometimes cause problems with pedal travel and master cyl plunger rod, which can cause lots of wierd symptoms.

Assuming it's just a rebuild, here are a couple thoughts... First, are you sure you've got the "right" master cylinder? If you've got front discs and rear drums, then the master should have one small well and one large well. Then make sure you've connected the hardlines to the master correctly. The large well feeds the front discs, the small well feeds the rear drums. Also, if the pedal is fine before starting the engine, make sure the pedal is actually working the brakes. Raise the front of the car and spin the wheel and then have someone press the pedal and make sure the brakes stop the wheel from turning.

Finally, I read a letter in this month's Car Craft that indicated that some distribution/proportioning valves have a built in safety feature that causes the valve to close off pressure to a line when line pressure drops. If our Mustangs have this feature, then the moment the valve was exposed to an empty line (i.e. like before you first poured fluid into the system), then the valve may need to be reset... I don't know much about this, so you might consult a Ford manual or Haynes book about it.

Hope this helps...

Platonic Solid · Jun 29, 2005

This is just a rebuild (typical front disk - rear drum). I have been very careful to make sure that I'm using the right parts (which has involved some returns to NAPA of parts that didn't look identical). I'm going to replace the rear cylinders tonight to eliminate that from the equation. I am also going to pick up a rebuilt booster to have on hand just in case everything else fails - though I hope I'll be returning it.

I have more manuals than I know what to do with, yet not one of them tells me what the symptoms of a bad booster are.
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Edit: OK, so I’m a bone-head. I did a simple google search on: “Symptoms of a bad booster”, and everything I see seems to indicate that a faulty booster would cause a hard pedal, since it would be failing to assist.
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monk302 · Jun 29, 2005

Hey Platonic,

I have a pressure bleeder at my house right now that I borrowed from a friend of mine. If you really need it maybe we could meet up. The thing is big though. It has a several gallon reservoir on wheels connected to the top plate like you have shown above. Let me tell you this though, the thing is a pain in the ass to use. Getting it to seal to the MC without leaks proved to be a hassle. Once it is on though, it shoots brake fluid through the system like a champ. In addition the this one I used another handpump type setup that worked pretty well. Ultimately it turned out that I had put my Granada calipers on the wrong side which did not allow all the air out. I felt like such a dummy.

krash kendall · Jun 29, 2005

Just a note - When a car with power brakes is not running, the pedal will get rock hard within a pump or two. That is why on older cars and trucks the brake pedal is twice as big on cars with power brakes than those without. In the event of an engine failure or the car car rolling without the engine running you could press with both feet on the pedal.

2nd Mustang · Jun 29, 2005

Yes, that is what my homemade pressure booster looks like. I think the total cost was well under $10.

Re-reading your original post, did you replace the MC or just removed it and bench bled it? When the pedal goes to the floor after bleeding the system, it might be that the MC pistons are not making any pressure and the pistons are just sliding back and forth. A tell tale sign would be fluid looking like a fountain in the MC bowls.

Platonic Solid · Jun 30, 2005

2nd Mustang said:
Yes, that is what my homemade pressure booster looks like. I think the total cost was well under $10.

Re-reading your original post, did you replace the MC or just removed it and bench bled it? When the pedal goes to the floor after bleeding the system, it might be that the MC pistons are not making any pressure and the pistons are just sliding back and forth. A tell tale sign would be fluid looking like a fountain in the MC bowls.

Replaced with new (rebuilt) MC. I didn't get to bleed them last night due to rain.

What next? Brake Question

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