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Hello all,

I've been working on my 1969 mustang coupe for the last 3 years and now the only thing standing between me and driving it are the brakes. This car is a factory drum-drum setup and I upgraded it to 4 piston front discs using Wilwood's kit a while ago.

My issue is that ever since I upgraded to these discs, the front brakes drag when I let go of the pedal. With sufficient force I can turn them by hand when the car is in the air but they both drag evenly from side to side when the pedal is not depressed. I have read about residual pressure valves being the culprit but I've replaced the master cylinder a while ago for one that is drum-drum (I know for performance its not ideal but its what I have for now) and there isn't a residual valve threaded into the port.

Any thoughts on what could cause this? This is actually my second brand new master cylinder as I returned the other one in case it had bad seals or something, but the problem has not been fixed. The rear brakes apply pressure fine and let go once I let go of the brake pedal, but the front calipers never retract. Upon disconnecting them at either the caliper itself or at the master, the front brakes turn much more freely but I can still see the caliper lightly contacting the rotor.

Please help, I'm dying to get back on the road and I'm at a loss. Thank you!
 

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First, you should get the proper MC for disc/drum brakes. Insure you have the correct Distribution Valve and the MC does or does not have the rear built-in residual valve.
What is the condition of your front flexible brake lines? New, original? If original, replace with either OEM (rubber) or braided lines.
Also know disc pads do not "back off" the same distance as shoes and may even drag, a "hair" but, not be tight. Also check your wheel bearings are set properly
 
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Hello all,

I've been working on my 1969 mustang coupe for the last 3 years and now the only thing standing between me and driving it are the brakes. This car is a factory drum-drum setup and I upgraded it to 4 piston front discs using Wilwood's kit a while ago.

My issue is that ever since I upgraded to these discs, the front brakes drag when I let go of the pedal. With sufficient force I can turn them by hand when the car is in the air but they both drag evenly from side to side when the pedal is not depressed. I have read about residual pressure valves being the culprit but I've replaced the master cylinder a while ago for one that is drum-drum (I know for performance its not ideal but its what I have for now) and there isn't a residual valve threaded into the port.

Any thoughts on what could cause this? This is actually my second brand new master cylinder as I returned the other one in case it had bad seals or something, but the problem has not been fixed. The rear brakes apply pressure fine and let go once I let go of the brake pedal, but the front calipers never retract. Upon disconnecting them at either the caliper itself or at the master, the front brakes turn much more freely but I can still see the caliper lightly contacting the rotor.

Please help, I'm dying to get back on the road and I'm at a loss. Thank you!
This diagnosis at the pro-level is done by determining how much pressure is remaining at the caliper.....
that is causing the calipers to drag.

At the DIY level, here are your bullet points-
  • Power brake car? If it is, the rod adjustment from the booster probably needs attention.
  • All masters need to be checked internally (inside the port) for a umbrella-like residual pressure valve. You can check with a carefully inserted paper clip.
Those are the main things that cause the problem you're describing.

ex-Global West GM
1991-1995
 

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Please elaborate on what you mean by the proper parts.
The others in the thread @kenash and @CHOCK have elaborated. FYI Chock is Dan from Chockostang considered by many, including myself, to be one of the most authoritative sources for classic Mustang steering and braking systems in the business. Ken also knows what he’s talking about. You’re getting some good advice.
 

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Discussion Starter #9
Thank you all! I didn't realize the residual valve was hidden in the port, and as such I never realized it was there as I didn't see it by looking at it. I found it and I ordered a proper disc setup wilwood master cylinder to complement my brakes, rather than simply removing it and not having a bigger bowl for the discs.
 
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