Posted By: BadFishy
New Master Cylinder defective? - 05/25/08 07:07 PM
If a dual disc/drum master cylinder is properly bench bled, and then plugging the outlets ports with brass fittings, filling the reservoirs and putting the cap on, should I be able to push the piston in? It pushes in very easily for the first 1/4 - 3/8 inch, and then stops. Sort of like the rear (small reservoir) isn't working properly, but stops when the fronts (big resevoir) kick in. This might explains my rear brakes not engaging.
The reason I ask is that I installed it new on my car as part of a front disk conversion from Master Power. I bench bled on the car, then did bleeds all around - 4 times - and still had a soft brake with little resistance on the pedal. The rears only engage at about the last 1/2 inch of brake pedal travel.
I can't get any more air out of the MC - used a kit and made sure no more bubbles, etc.
I want to make sure my new MC isn't defective. It seems if it is bled and the ports are capped, full of fluid, and the lid is on, I wouldn't be able to push in the piston, correct? Just like if it were on the car, and capped, it should be rock hard, correct?
Posted By: therocks
Re: New Master Cylinder defective? - 05/25/08 07:26 PM
If its bled right and the ports on the master are plugged it should be rock hard.I had a preoblem with my disc conversion and i plugged the lines and it was a rock.I did find my calipers were upside down when I swapped them side to side.That fixed my problem.Rocky
Posted By: RapidRobert
Re: New Master Cylinder defective? - 05/25/08 07:32 PM
I've been following your dilemma on this. With the MC bled out & capped off & you getting 1/4"-3/8" pedal travel before it's solid the MC is GOOD. there's always slack in any system & it takes a slight bit of movement before everything is locked tight.
Posted By: BadFishy
Re: New Master Cylinder defective? - 05/25/08 07:38 PM
Rapid, would there also be that much travel without being mounted, just pushing in the piston itself while the MC is on the vise? I am thinking that if it is mounted there would be a little travel but not by pushing on the piston directly with nothing in-between. Thanks.
Posted By: 71rm23
Re: New Master Cylinder defective? - 05/26/08 03:10 AM
I know this might be a dumb question. Do you need to bench bleed the MC BEFORE you install it? Then bled it with it installed? I thought if its bled when installed, then it should be good.
Posted By: RapidRobert
Re: New Master Cylinder defective? - 05/26/08 03:22 AM
Fish I just got back in the door. The seal has to flex as you push,the port that feeds fluid down to the bore has to be covered & there's always a miniscule amt of air left so it will never be instantaneous but your MC is GOOD & to convince yourself go back to your 1st post where didn't you say that the pedal goes to the floor? On my deal they(Russell IIRC) sent me the wrong front braided lines for E body drums & I screwed them into my calipers & I had to bend them at a severe enough angle that the car acted just like yours, I would stand on them & couldn't get enough(pressure or volume??)to slow down any better than a crawl just like you & it was definitely not fit to be driven. Stay in touch!
Posted By: StandOnIt
Re: New Master Cylinder defective? - 05/26/08 12:04 PM
Soft at the hit then firms up? Check your rear wheel cylinders. Make sure the adjustment rod in the brakes are adjusted correctly.
Posted By: BadFishy
Re: New Master Cylinder defective? - 05/27/08 03:57 AM
Rapid, aha, I see that now. On the bench the MC has very little travel when capped, but when mounted in the car, the pedal goes almost to the floor before any braking action. By the way other guys, the pedal doesn't get firm until it almost hits the carpet. The wheel cylinders were fine before the conversion, with less than 2,000 miles on them, the caliper bleeders are on top, and the rear brakes were adjusted, but thanks for the notes.
I've got air! I''ve bled almost three quarts through it and just can't get it right. I am taking it to the local garage to have it pressure bled. My back is sore from all the stooping and crawling! THANKS GUYS!
Posted By: RapidRobert
Re: New Master Cylinder defective? - 05/27/08 06:10 AM
Fish dont give up on it yet! Get a good nights sleep & you'll be ready(sort of!)to attack it again in the am(or evening). I would reinstall the MC with the brass plug in the rearmost port(for the fronts) & connect the line to the rear drums & bleed them out & then attack the front discs. Be sure that you(or your helper) isn't opening the bleeder screws too far to where air is gettin pulled in around the threads which I did & until I caught on I couldn't get the air out for nothing.