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Old 07-02-2015, 08:50 PM
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65 mustang disc brake conversion issues

Hi everybody, i am working on a friends 65 mustang fastback. A beautiful car, it needed a few things so im helping him out.
he bought an ebay 4 wheel disc conversion kit, it was a complete kit with the worst set of installation instructions ive ever seen.
im having a problem bleeding the system, ive been at it for a couple days now. Ive probably taken the master cylinder out 4 times to bench bleed it, its still not bleeding properly. I noticed when it is in my vice and im stroking it the front resevior give a healthy flow but the rear resevior appears to be quite a bit less flow. When pumping the brake pedal it does not firm up hardly at all. Could it be a bad madter cylinder?
When bleeding the calipers the fronts give a good solid flow when opening the bleeders and the rears are considerably less.
also the brake booster is an issue. The engine has a huge cam so i went to the wrecker and bought a vacuum pump from a deisel pickup. I have installed it and it pulls 18" of vacuum, however the booster doesnt appear to be doing anything at all.
Could the booster be junk as well?
Hopefully ive just missed something obvious.
any thoughts?☺

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Old 07-02-2015, 09:27 PM
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Have you a master cylinder that is intended for 4 wheel disk brakes. That may be a source of difficulty. The booster may not show much effect when the car is setting still. Sounds like separate issues to me.

Sam
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Old 07-02-2015, 09:34 PM
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The kit is a 4 wheel disc kit, im assuming the mc is correct. How can you tell the difference between a disc/disc and a disc/drum mc?
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Old 07-02-2015, 10:33 PM
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Hi
There are a couple of differences between these mc's. One is the amount of fluid, drum drakes need a lot less fluid as the wheel cylinders only move a small amount then retract, where disc. Move a fair amount and don't retract thus needing more fluid to take up that space the Pistons moved. Also the drum mc has a 10# residual valve, and if used for disc. You wouldn't have enough fluid and the disc. would drag because of the residual valve. Also if you use a drum mc without a residual valve, you will have a spoungy pedal, and the brake pedal will have to be pumped several times to get it to stop.
Good luck
Rich
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Old 07-02-2015, 10:45 PM
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hello again.
About the booster, power brakes have a larger piston in the mc then a manual mc. So if you think the booster isn't working try pushing the pedal, with engine off very hard to push, now try it with the engine running, is it still very hard to push, or is it easer to push indicating the booster is working.
Rich
Ps the larger the piston, the harder it is to push the pedal.
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Old 07-03-2015, 05:53 AM
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Good info on the mc and booster, i think i have the right parts. It just wont firm up. I guess ill bleed the thing yet again. The booster does nothing, car running or not .
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Old 07-17-2015, 05:38 PM
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FWIW, I did a conversion on a 65 Mustang and had about the same problem, could not get enough fluid moving to have adequate brake function. I moved the pivot point on the pedal in order to get alot more pushrod travel and got acceptable braking, but still not ideal. I dont know that any of the low dollar kits out there are really engineered properly, as the combination of the calipers, the booster, the pedal ratio, the rotor diameter, etc. all play a part in getting really good brakes. But they are cheap.
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