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Old 10/17/2020, 03:05 PM   #1
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Trouble shooting brakes & booster

I'm finally getting back to work on my '68 HCS and having issues with the brakes. The car sat for several years and the brakes were shot. I could only get brake fluid to come out of 1 of the 4 bleeders. So I replaced the soft lines, blew out the hard lines, replaced the master cylinder, front calipers & pads, rear shoes, hardware and wheel cylinders. (my car has factory power front disc brakes, drum rears)

This work was all done 2 years ago and unfortunately the car sat again during that time with just a few trips around the block to keep things from drying out.

My issue is the brakes still do not work well. Backing out of my sloped driveway I can't totally stop, only keep to a slow roll even with my foot mashed on the brake pedal. (C4 automatic) Going forward I can stop, but not quickly.

The only thing I did not replace is the power booster, so that's what I'm focused on trouble shooting now. I've bled the brakes twice and I don't think there's any air or old fluid left in the system. The check valve appears to work fine. I can blow air from the booster side of the valve, but can't suck in air.

My pedal is firm, but just doesn't stop. It travels easily for the first 1 1/2" or so, then firms up quickly and doesn't travel after that. If I push hard on the brake pedal with the engine off, then hold it while I start the car, the pedal travels maybe another 1/2". Shouldn't it travel more than that if the booster is working correctly?

I unplugged and capped the vacuum to my booster and drove around the block. No change in brake performance or pedal feel. But with the booster vacuum unhooked the pedal no longer travels any further down when I start the engine.

So I'm thinking my booster is shot. I think it's working only marginally (hence the little bit of extra pedal travel when I start the engine and apply vacuum).

Thoughts? Any other tests I can do to verify it's the booster?

My booster is the original Midland style, but a factory Ford replacement, not original to the car. I remember replacing it about 25 years ago.

I see West Coast Classic Cougars has a replacement for $350. Other shops seem to sell mostly rebuilt or aftermarket units that aren't factory correct.

What about sending it off for a rebuild? I obviously have the time. I've seen Booster Dewey recommended here. Looks like he charges about $175 per his web site: http://boosterdeweyexchange.com/

Any other rebuilders I should check out?

Thanks for reading this far!!!

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Old 10/17/2020, 06:18 PM   #2
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Did you replace the front brake calipers? If you get the switched around you can not ever get all of the air out of them. The bleeders should face rearward not up.

It sounds likely the booster is going bad. I use booster Dewey. If you have time that is the path I would take.

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Old 10/17/2020, 10:25 PM   #3
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Quote:
Originally Posted by Ruppstang View Post
Did you replace the front brake calipers? If you get the switched around you can not ever get all of the air out of them. The bleeders should face rearward not up.
Yes, new calipers. I believe they're installed on the correct side.
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I forgot to mention that my brake light has been on for forever. I haven't been able to reset it. I don't know if the distribution block could be part of my issue or not.

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Old 10/18/2020, 07:08 AM   #4
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The piston in your distribution block might not be centered. Brake warning light on, or disconnected?
Power Brake Booster Exchange, is now owned by Booster Steve. Booster Dewey retired and sold to Booster Steve, a long time employee.

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Old 10/18/2020, 08:00 AM   #5
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The brake light is on. I tried re-centering it when I last worked on the brakes, but no luck. Will the piston being off center affect my braking ability or is it purely to control the brake warning light? I bled the brakes again yesterday and had no problems getting fluid to flow at all 4 wheels.

Thanks for the info on Booster Steve.

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Old 10/18/2020, 11:54 AM   #6
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Quote:
Originally Posted by admin View Post
Yes, new calipers. I believe they're installed on the correct side.
Attachment 23843

I forgot to mention that my brake light has been on for forever. I haven't been able to reset it. I don't know if the distribution block could be part of my issue or not.
It appears that you have the calipers on correctly. I do not think that if the piston is not centered it will affect braking. If your booster is 25 year old it is time for a new one anyway.

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Old 10/18/2020, 12:59 PM   #7
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Quote:
Originally Posted by Ruppstang View Post
If your booster is 25 year old it is time for a new one anyway.
For my car that equates to only about 10,000 miles. But I get your point.

I pulled the plug off the brake light switch on top of the distribution block and my brake light went out. My understanding is that this switch grounds itself when the plunger/shuttle inside the distribution block slides over, thereby completing the circuit and turning on the brake warning light. So that fact that my light goes out when I pull the switch should confirm that my switch is not faulty and that it's indeed the plunger/shuttle that needs to be recentered.

Poking around more I found my proportioning valve has a small leak. That explains why my front reservoir was about half low after sitting for a couple of years.

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So my plan is this:
  1. Pull out the master cylinder and booster. Send the booster in for a rebuild.
  2. Pull the brake distribution block & proportioning valve. Get a rebuild kit from WCCC. Probably replace the hard lines while I'm at it.

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Old 10/18/2020, 01:46 PM   #8
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A little more testing with a vacuum guage. With the booster hooked up I get 9 inches of vacuum at the back of the manifold. If I disconnect the booster and cap that port I get 15 inches.

Another indication the booster is shot.

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Old 10/18/2020, 05:33 PM   #9
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The proportioning valve could also be stuck or plugged causing your brake issues.
I sounds like you have a good plan. I would buy or make the tool that locks the piston centered while you bleed the brakes. It is a time saver.

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Old 10/19/2020, 06:16 AM   #10
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My understanding of the distribution block, and someone can correct me if they want, is that if you have a failure in either the front or rear brake system, the piston moves to block that side so you can maintain braking pressure in the other side. Once the failure is repaired, and you are ready to bleed the brakes, you can open one of the bleeders for the side that didn't fail and gently apply brake pedal pressure to reseat the piston in the middle. Press too long or hard and the piston will go the other way. The fact that you can get fluid from all 4 corners tells me the seals on the piston in the distribution block are bad. The piston has a relief/narrow spot in the middle that a plunger on the warning light switch drops in to. When the piston is centered, the switch is off. When the piston moves away from center (brake failure), the plunger moves up and the contacts are made, turning on the light.

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Old 10/25/2020, 06:40 PM   #11
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Steve, that's my understanding as well. Based on the factory cut-away diagram below I first thought that if the piston slid over due to a brake failure it would also cut off the pressure to that side (front or rear brakes). But I don't believe that's the case.
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Old 10/25/2020, 07:51 PM   #12
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My 14 yr old son and I made some disassembly progress on the brakes today, although I also damaged the distribution block, so two steps forward, one step back.

We took out the power booster, master cylinder, distribution block and proportioning valve. The booster is all boxed up and ready to ship out tomorrow to Booster Steve to be rebuilt. They have about a 6 week lead time at the moment, but I have plenty to do on my HCS, so not a problem for me.

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A few shots of the booster and the spacer to the master cylinder. The rebuild will include the foam filter that's supposed to be there, but was missing from mine.

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Old 10/25/2020, 07:57 PM   #13
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We disassembled the brass distribution block and proportioning valve with the intent of rebuilding them w/ a kit from West Coast Classic Cougar. They have a great video on rebuilding these here: https://www.youtube.com/watch?v=9kOCpaFGWGw

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But... on the distribution block I screwed up freeing up the piston inside that triggers the brake warning light. I used the wrong size punch to force out the piston and mushroomed out the brass flare seat. So that's an original part going in the trash unfortunately.

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Here's the distribution block disassembled. The 2nd photo shows the internal piston and how brake warning light switch has a pin that rides in the piston groove when the brake pressures are balanced.

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And here's the proportioning valve disassembled. The original o-rings were so brittle they broke as we were prying them off, which explains why the proportioning valve was slowly leaking. The piston inside the valve actually did spring when you pushed on it, so it wasn't totally shot.

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Last edited by admin; 10/25/2020 at 08:10 PM..

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Old 10/25/2020, 09:17 PM   #14
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https://youtu.be/PGO0aWJkrmo

We did a video with Booster Steve.

Scott Behncke
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Old Yesterday, 03:08 PM   #15
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Is a slight hijack to this thread okay? Thanks, I appreciate it.

I have 69 Bendix booster on my '68 GTCS with factory front disks. Brakes work great. I picked up a correct Midland booster and will be sending it to Booster Steve shortly. The prior owner had put on a new MC about four years ago so I do not have to get one. So here is my question which I know is probably dumb. Is there anyway to remove the booster without disconnecting the lines to the MC. I am wondering if I unbolt the distribution block/prop valve and any line retainers if I could swing the MC/booster out far enough to remove it from the booster and then sneak the booster out.

Just hate to remove the lines and then go through the whole bleeding thing again.

Thanks.

Dave
'68 GTCS
8R01J140036 2/8/1968
C4/PS/PB/AC
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