Anybody using a 15/16" bore master cylinder
- Thread starter hunt2elk
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i have very little travel
Hmmm. I have a lot more than I think I should. With the weight off the car, all wheels will lock up with about 3 inches of travel. However when I push the pedal with all I have, it will go darn near to the floor. I have bled this thing more than any car I have ever owned and haven't gotten any air out for quite awhile now. The brake light in the dash is also on and goes off when I unhook the wire from the prop valve.
my Bee stops nice and no lockup. Firm pedal just as good as PB
Do you have the rear brakes adjusted properly? If they are excessively loose it would cause the problem you are describing.
Yes, just checked them again yesterday.
dsd1967
Well-Known Member
Is your MC designed for drum brakes and are using drums on the rear? I bought a drum brake MC but have 4 wheel disc and it said to remove the residual valves. They are designed to act as check valves to hold some pressure in the drum system. If yours aren't working properly you may be getting excess fluid return to the MC
15/16" bore is probably the smallest bore made. It will take a lot of pedal travel to fill the calipers and cylinders - even more as the pads wear in. The upside is it takes less effort. Small bore = less effort = more travel. Large bore = more effort = less travel. Did you bench bleed the master before installing it - that is critical.
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Had the light issue and long pedal stroke on the Bird, until I brought the rear shoes out to a light drag on the drums and then all was just fine. OE booster and master, front discs with the equalizer valve in the mix.
Also remember the fight I had with the Bee, hours of bleeding the master on the car and ended up lifting the *** end of the car to dislodge a trapped air bubble before I finally got a hard pedal.
Also remember the fight I had with the Bee, hours of bleeding the master on the car and ended up lifting the *** end of the car to dislodge a trapped air bubble before I finally got a hard pedal.
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I got everything from Dr Diff and he knew exactly what the application was going to be. Pretty sure there is a residual valve in the rear cylinder port because fluid does not run out that one like it does the front brake port.
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Cass explained the same thing to me and said a lot of guys are preferring the 15/16 bore for my setup. Like you stated it takes more pedal travel than what I am accustomed to on my other cars. I just don't know what it should be like and am surprised that @davek says he has very little travel. I did bench bleed the mc before bolting it in the car.
MW 413
Well-Known Member
Your front MC port(farthermost from the firewall) feeds the rear drum brakes and needs the residual check valve in it, not the rear port that feeds the front disc brakes. You will have a very low pedal with it in the rear MC port.
I have the 15/16 in my cuda and it has a lot of pedal travel and just a little spongy. I have bled and bled but no help and believe the silicon fluid is the problem. I know fluids aren't supposed to compress but evidently silicon traps air bubbles. The residual valve is generally not needed if you have replaced the rear cylinders as they compensate to hold pressure.
MW 413
Well-Known Member
If you have drum brakes on any axle you have to have a residual check valve in the MC port or an external aftermarket one in the line just outside the port or you will have a lazy/low pedal. The drum type wheel cyls do not have check valves internally or do they compensate as they have to have a 1-2lbs of pre-loaded pressure to fully apply on the first hit as opposed to disc brakes that do not.
Yes, that is where it is. Smaller front reservoir which feeds the rear drums. I didn't type it clearly in my earlier post.
My MC reservoir has same size front and back feeds,my front discs do drag a little. Other then that like I said I have a firm pedal.My question is what is a residual valve? Is that a pressure valve and if so I do not have that on my car.
The valve looks like a little office which is pressed in the mc line port.
threewood
Well-Known Member
I probably have the exact same set I bought from Cass, 15/16" master cylinder, manual discs up front. My first MC would go pretty low and get air in them. Slow enough so that it was inconsistent. I could have a great, firm pedal for a week. Let it sit for a day and it would drop down low on first press but be fine afterwards. I was also seeing airbubbles out of the wheel cylinders and caliper occassionally.
Cass sent me a new one so I put it in and it has been fine. The only mod I did do was add a return spring to the pedal because the internal spring in the MC never pushed the pedal all the way to the top. Kind of annoying but an easy fix. No issues since.
If you aren't seeing air in the fluid I wouldn't suspect a leak anywhere. My pedal stops well above the carpet but I haven't actually measured it. More travel than my 4 wheel drum 62 Ply.
Cass sent me a new one so I put it in and it has been fine. The only mod I did do was add a return spring to the pedal because the internal spring in the MC never pushed the pedal all the way to the top. Kind of annoying but an easy fix. No issues since.
If you aren't seeing air in the fluid I wouldn't suspect a leak anywhere. My pedal stops well above the carpet but I haven't actually measured it. More travel than my 4 wheel drum 62 Ply.
I also have the Dr Diff kit with 15/16 Master Cylinder. All I can say is the pedal travel takes some getting used to as the brakes do really work well.
In most of my 35 45MPH driving light pedal effort stops the car easily.
In most of my 35 45MPH driving light pedal effort stops the car easily.
I am not seeing any bubbles, so don't think I have a leak. Just took a video, but can't figure out how to post it here. I measure 7" from the top of my pedal to the floor. When I push it down it gets real hard at 2.5" off the floor and I can get it to go another 1/2" by really standing on it. So I am getting 5" max travel, although I would imagine the car will normally stop well before it gets to that point. Is that about what yours is? Maybe that part is normal and I just have a bad switch in the prop valve.
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