Brake feel - master cylinder, pushrod, pedal linkage

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68ss

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Hey guys,

I'm a member of the B body forums too and sometimes you A body guys have some great advice, so I'd like to get some feedback from you on this one too. I have a 1968 Satellite. I installed a new upgraded system last year and then yanked part of it out and replaced some parts with new parts of a different brand. Neither setup really dialed in like I wanted it to feel or perform. The pedal effort is OK, the pedal is not too hard and not too soft and things stop, but I don’t feel confident in doing so. I may be a little biased in my assessment though because when I got the car it had a single diaphragm booster from a ’73 E body and when I would hit the brakes it would grab so hard I would do a faceplant, but it also pulled to one side, which is why I swapped it all out. Now things are not snappy at all (which is actually a good thing), but I would like it to brake a lot better when I stomp on it, but still allow some feathering of the pedal, which I don’t feel like there’s much of now. I’ve put about 500 miles of stop and go driving on the new pads, so they should be well broken in. I also had a brake shop adjust the proportioning valve so the rear end wouldn’t slide sideways when I lock them up.

First off, in another thread Meep-Meep mentioned something about “the power brake cars had a link assembly that multiplied the pedal travel, and because of the way it's set up, the MC rod will not align with the pedal rod directly.” Do I have the correct link assembly here or am I missing something? I had a shop install this kit and I’ve always thought that the rubber baffle seal looked like it was bunched up due to the rod going in at a weird angle. You can kind of see this in the photo. I tried adjusting things, but no luck so far.

I’ve also read that for power brakes, the pedal linkage should be connected to the lower hole farthest from the pivot point. From the photo, is my pedal connected properly? When I sent this photo to MP brakes, they said yes, but it sounds like it could be backwards.

The last thing I need clarification on is my MC push rod length requirement, which I think may affect pedal feel and stopping power? Take a look below at my list of parts. Unfortunately, I don’t know the pushrod length of what’s installed without disassembling and measuring.

Original aftermarket kit installed all from Master Power Brakes”
10.75” rotors
8-inch dual diaphragm booster
1-1/8” master cylinder
pedal linkage and pushrod
calipers
Combination valve

Then I swapped out the calipers, Rotors, and MC. Now I have:

11.75” Napa rotors with caliper adapters from AREngineering
Wilwood forged dynanlite calipers with their BP-10 pads
Wilwood adjustable proportioning valve
New Raybestos 15/16” master cylinder for disc/drum
Same as before MP brakes combo valve, 8-inch dual diaphragm booster, push rod, and pedal linkage.

Any input is greatly appreciated.
 

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  • BrakePedalLinkage.jpg
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One thing I found that may be causing some issues is the pushrod length. Can anyone confirm if I switched from a 1-1/8" bore MC to a 15/16" bore if I need a different length pushrod? My new MC didn't come with one. I'm using the Raybestos MC 36406.
 
The linkage does multiply the travel, so you would want a smaller diameter master cylinder to compensate. This would help you with "feathering the pedal". You will have more pedal travel and therefore greater ability to control the amount of braking force.

On A bodies the linkage is in the engine compartment, but it has the same effect. 15/16 bore MC is what's called for on an A-body with power disc brakes. A larger bore is called for without power. This is counter intuitive until you consider the linkage multiplying the travel.

On A bodies, I believe the push rod is the same for power or manual brakes.
 
That photo looks funny to me. The linkage parts are shiny and new looking and the push rod and boot appear to be angling down. Is that a stock setup? I don't know anything about B-Bodies.
 
65DartGTConv said:
That photo looks funny to me. The linkage parts are shiny and new looking and the push rod and boot appear to be angling down. Is that a stock setup? I don't know anything about B-Bodies.
Click to expand...

I know, the angling down thing has been bothering me too, but two mechanics looked at it and said it's fine. That's the new replacement linkage that came with the Master Power brakes kit. I would think it should be horizontal and then the rubber boot wouldn't be bunched up on the bottom. I should have taken a photo of the old setup while it was still in the car before I got rid of it. The car is in for paint and body for a few months, so I'll have to tackle this after it's back, but I couldn't resist checking into this while I have some time.

Thanks for your quick feedback by the way.
 
Ahhhh! Looks different than mine. However, I originally bought this as a complete kit from Master Power Brakes. Their linkage is based off of a 79 Cordoba and should be complete. Maybe a different design? Anyway, I have no trouble with everything attaching correctly as that poster did, but visual inspection tells me that my pushrod is not completely horizontal.

I wonder if I can buy that extra linkage and make it work with what I have to try it out?
 
I think you need to modify your backing plate as described in the thread or find one from a power brake car.
 
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