Master Cylinder issue???

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gtgto

gtgto

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Was out and about in my car over the weekend, 70 Duster and had issues with braking yesterday. The car has factory KH Discs up front and Drums in back and no power assist. I still have to check the fronts today when I get home but I adjusted the drums and bleed the rear brakes. Saw no sign of brake fluid and the MC is full. The pedal was solid at times and a minute later it was traveling close to the floor and my dash brake light even came on. I'm thinking my 2 year old Rock Auto MC has bought the farm already. If that is the case I'm hoping to find a better quality one and one that looks correct for a 70 340 Duster. Should both the reservoirs be equal in size or should they front reservoir be the larger of the two? Thanks in advanced
 
Typically disc drum, the rear resivor (closest to the firewall) is the larger and for the front discs.
 
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I just had the same MC failure a week ago, on the last leg of my trip back from Arizona to Washington in my 69 Barracuda. The brakes behaved pretty much as you described, but no sign of leakage from any wheel cylinders. I did note the large reservoir fluid was down slightly. As it turned out, upon removal, there was a slight leak from the back of the MC, but not enough to cause the loss of breaking. The shop said the MC seals had failed and the fluid was bypassing the piston when I stepped on the brake pedal. If you want to maintain the original look, then purchase a new premium quality MC that's correct for your year/make car and brake setup. I've bought a few things from Rock, but not the replacement MC. I would shy away from a rebuilt MC in any case.
 
Napa is not remanufactured. Rebuilt brake parts are a waste of money. Seen it many times including at the end of a 1/4 mile run. Went thru the trap a 117mph and short braking area. Lucky I remembered the e brake.
 
When my brakes went the other day I was able to remove both back wheels for inspection and then bleed the brakes. I ordered a new MC before checking out the fronts. Last night I took both front wheels off and found one of them to have brake fluid on it. As it turned out the crossover hard line was seeping some. I put a line wrench on it and tightened it down more since I must not have tightened it enough. Had my son sit in the car and hold the brake pedal down for a while with no more leak. I still am going to replace the MC at some point since I am getting the correct one for a disc/drum car.
 
gtgto said:
When my brakes went the other day I was able to remove both back wheels for inspection and then bleed the brakes. I ordered a new MC before checking out the fronts. Last night I took both front wheels off and found one of them to have brake fluid on it. As it turned out the crossover hard line was seeping some. I put a line wrench on it and tightened it down more since I must not have tightened it enough. Had my son sit in the car and hold the brake pedal down for a while with no more leak. I still am going to replace the MC at some point since I am getting the correct one for a disc/drum car.
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Which MC did you settle on? P/N?
 
512Stroker said:
Was it recommended by Summit or did you pick it out?
MC piston diameter looks rather large for disc brake application?
I could be wrong
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I could be wrong too.....I didn't call and speak to anyone and picked it.
 
gtgto said:
I could be wrong too.....I didn't call and speak to anyone and picked it.
Click to expand...
You may want to research the piston dia here on the forum.
I remember reading something about using smaller dia MC pistons for higher pressure that is required for disc brakes.
Watch that video on the Summit link you posted
 
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