Master Cylinders
#1
Hey guys I was thinking of replacing the master cylinder. I have found various sources that state there are multiple part numbers depending on the manu date of the car (either 2/72 or 7/72 was the change). Anyone have any experience with this? Can anyone recommend a part number for a 72 with power disc (manu date 3/72)?
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#2
I suggest take it out and down to your local brake component rebuild shop. They will recognise it by the bore, ports etc and be able to either rebuild or supply components.
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#3
I kind of doubt that such a "local brake component rebuild shop" exist in most U.S. areas. Kind of a thing of the past for us.

I don't have the personal experience that you are requesting either. I would recommend a call to Don Witt at Ohio Mustang Supply for competent professional help and knowledge.
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#4
Wagner shows a new one part # MC86130 ...
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#5
Whatever you do, try not to buy a rebuilt master cylinder and try to avoid rebuilding yours. Usually the bores are pitted. Plus any honing to clean up the bores puts a rougher finish inside the bores than the manufacturer originally had. This rougher finish increases seal wear on the pistons. It's just not as good as a new master cylinder. I would only rebuild if new is not available.

In general its not good to rebuild master cylinders and drum brake wheel cylinders. Disk brake calipers are safer to rebuild because the seal doesn't continuously rub on the same part of the piston so the pistons are more often than not is good condition.

Regards,
Mike
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#6
I just replaced my master cylinder with a new one that i bought at napa. I was surprised they had it for a 69 mach 1 power front disc / rear drum.
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#7
I got the new MC and installed it yesterday. I bleed the brakes and I cant seem to get all the air out. I don't see any leaks and when everything is closed up no fluid leaves the MC so I am pretty sure I don't have a leak. I have never had any issue like this in the past with other cars. I will say that the bleeders seem to be pulling air around the threads so I am going to replace them tonite. Any other places I should look? Prop valve maybe?
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#8
If you changed calipers - they are L & R specific
If installed wrong you won't get all air out.
Don
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#9
(09-17-2015, 12:35 AM)ohiomustang Wrote: If you changed calipers - they are L & R specific
If installed wrong you won't get all air out.
Don

Nope just installed the MC. I was getting a leak from the piston so I swapped it. I just ordered some speed bleeders since I don't really have a helper to assist me bleeding. I was using a vacuum system pump deal to do it.
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#10
Did you thoroughly bench bleed the master cylinder? If not it can be difficult to get all the air out. I would try cracking the fittings loose at the master cylinder one at a time while another person pushes down on the brake pedal. Do it a few times and use the same method as when bleeding the brakes at a wheel. Don't forget to tighten the fitting before the brake pedal is released. This will usually get any air out that is trapped in the master cylinder. These fittings were not intended to be loosened and tightened repeatedly so don't go nuts when tightening them during the bleeding process. Then go back to the wheels and bleed at the wheels.

Usually if you bench bleed the master cylinder. Then bleed at the master cylinder fittings after installing it there is no need to bleed at the wheels.

If you are vacuum bleeding at the wheels some air will seep in through the threads of the bleeder but not get into the system. I put downward pressure on the bleeder screw while vacuum bleeding to reduce the air seeping past the threads. Tighten the bleeders while there is still a vacuum on the system so air cannot get into the brake system.

Regards,
Mike
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