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Extreme Veteran
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| I did a front disc brake conversion using AAJ components leaving the rears drum. The disc callipers are 1976 Monte Carlo single piston. Ron’s recommendation was to use a 76 Dart master cylinder, 1.032” bore. All good at this point, that was until I pushed the pedal and it felt like you were putting your foot in a pail of cow dung. I went through buckets of brake fluid trying to bleed the suspect air out of the lines, callipers and cylinders. I disassembled the master cylinder, checked seals, put it back on. Still no good. Ordered another master, same crap. After a lot of cursing, kicking and pouting and a bit of research I dug through my stock pile and pulled out an old 1.125” master cylinder and installed it. Yahoo...I have a good solid pedal! Doesn’t make sense but I don’t care as it worked. The OE master cylinder was 1.00” bore and supplied enough fluid to front and read wheel cylinders. The piston travel in the 1.032” is just not enough to satisfy those silly little rear wheel cylinders. Go figure.
Del S |
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Expert 5K+
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Location: So. Cal | It doesn't make sense. I have used the Dart master on 4 vehicles now, a '57 Chrysler, '58 Dodge & 2 '56 Plymouths without issues. Definitely, the 1.125 is better with stock rear cylinders, but the 1.032 does work OK. I have found that some of these new Chinese masters don't seal well though, and I ensure that the rear brakes are adjusted properly so they don't have too far to travel. |
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Extreme Veteran
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| i Expert 5K+. Yu are correct! It does not make sense. This issue has annoyed me for months now. I Have bought 2 Master cylinder, 1 Raybestos, 1 Dorman. Neither gave me a solid Pedal. I blocked 1 port with the other open and back to reservoir....Solid as a rock, switched the plug, etc and again ...solid. I had the rear drums off so often they should have had a zipper on them. Mic'ed the drums and gauged the clearance and adjusted as tight as I dared and still like a sponge. I measured the push rod travel to make sure I was moving the piston all the way. That is when I dug through my stock pile and dug out the 1-1/8" Master. Solid pedal and no excessive pedal pressure required. Going on a 60 mile trek with it tomorrow.
Del S
Would you take a look at the thread I started on Wheel Studs and maybe help me out there.
Thanks,
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| Quick question. Will it gravity bleed? |
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Expert 5K+
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Location: So. Cal | I have gravity bled every one of my cars including some with original masters, later Dart style masters, Mitsubishi truck masters, & aftermarket ones. |
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Extreme Veteran
Posts: 345
| Gravity will bleed front disc brakes as there is no residual pressure valve as there is for the rear drum brakes.
Del S |
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Extreme Veteran
Posts: 371
| The rear should gravity flow if bleeders are opened. If they aren't I use a hand vac to pull the fluid. Once it is flowing I pull off the vac tube. If still doesn't flow majority of the time it's the master cylinder. If you haven't disconnected all the rubber hoses and shoot brake cleaner through the lines followed by compressed air I would recommend doing so. Did you replace all the rubber lines also? My '56 is a pain in the southern quadrants. From the master it goes over to the hydro boost then down from there. The hydro port is just a tad above the master. I just replaced all the wheel cylinders and it took about 4 hours to get the fluid flowing properly. |
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Expert
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Location: NorCal | dels56 - 2021-07-25 9:11 PM
kicking and pouting and a bit of research I dug through my stock pile and pulled out an old 1.125” master cylinder and installed it. Yahoo...I have a good solid pedal! Doesn’t make sense but I don’t care as it worked.
Actually it does make sense...sorta. The smaller diameter MC puts more pressure in the system and the floating single-piston calipers are known to cause a softer pedal because they flex under pressure.
My experience with such disc swaps has been the same as yours, smaller MC gives a softer pedal. In my last swap I had to go to a 1 1/4" MC to get a decent pedal. |
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Extreme Veteran
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| Thanks fellows. The hard lines are all new and flushed before I dumped any fluid in the 1st master and from there I have pumped bunches of fluid through. I do have a vac pump and used it. I am confident I do not have any air left in the system. I like the thought that the single piston callipers flex a bit it give a softer pedal, that will explain my soft pedal and I will live with it for now.
Del |
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56 brakes
