Power Drum Brake Conversion - Vintage Mustang Forums

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post #1 of 18 (permalink) Old 04-21-2017, 03:41 PM Thread Starter
TRC
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Power Drum Brake Conversion

I recently purchased and installed a power brake conversion kit for (4) wheel drum brakes from NPD. It includes a power booster and dual reservoir. I'm having an issue getting good stopping power and was hoping somebody else has had a similar issue and solution. I've bled the lines numerous times to ensure there is no air in the lines. I've also checked the vacuum I'm getting from the carb to the booster and it is sufficient (19 in). The pedal is solid and is not on the floor. However, when I apply the brakes, the car gently slows to a stop. It's impossible to lock them up. Any suggestions out there? Thanks in advance for your help!
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post #2 of 18 (permalink) Old 04-21-2017, 03:45 PM
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if you went from 4 drums to 4 discs, was there a proportioning valve for the rear line? I've seen (translated as I've done) calipers mixed side to side- it put the bleeder in a position that made it impossible to get all the air out of the piston. Double check that your bleeders are at the highest point on the caliper, you've gotten ALL the air out of the lines, your hoses aren't twisted, no leaks, and that you used the correct fluid. First few thoughts to mind anyway..

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post #3 of 18 (permalink) Old 04-21-2017, 10:56 PM
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I once did a drum brake P/B conversion on a '68 with no problem. (You do not need a proportioning valve with 4 wheel drum brakes.) I would suspect a faulty Master Cylinder or Booster.

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post #4 of 18 (permalink) Old 04-21-2017, 11:10 PM Thread Starter
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I didn't convert from drum to disc. It's still all wheel drum. I figured this was the most economical way to add stopping power and safety over the single reservoir manual system. I'm thinking faulty equip as well, but I'm new at this. Wanted to get some other opinions before going through the hassle of removal, returning and reinstalling. Thanks for your input.
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post #5 of 18 (permalink) Old 04-21-2017, 11:29 PM
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Quote:
Originally Posted by TRC View Post
I recently purchased and installed a power brake conversion kit for (4) wheel drum brakes from NPD. It includes a power booster and dual reservoir. I'm having an issue getting good stopping power and was hoping somebody else has had a similar issue and solution. I've bled the lines numerous times to ensure there is no air in the lines. I've also checked the vacuum I'm getting from the carb to the booster and it is sufficient (19 in). The pedal is solid and is not on the floor. However, when I apply the brakes, the car gently slows to a stop. It's impossible to lock them up. Any suggestions out there? Thanks in advance for your help!

OK, when you performed this conversion,
1. Did you have all 4 drums turned?
2. Did you bench bleed the MC?
What shoe material are you running?

Waiting.......

Ken ..
64 1/2 Poppy Red too!, Cvt. Resto-Mod
333 Cu.in. T5z, 3:55, Dual 40 mm DCOE Webers
Performer RPM, CI cam, TFS/TWs, Tri-Ys, Discs w/Shelby Drums
Severna Park, MD
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post #6 of 18 (permalink) Old Yesterday, 05:25 PM Thread Starter
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I did bench bleed the master cylinder, but had to bleed all the lines as well as I had to custom bend some new lines to the distribution block. I did not have the drums turned. Would this have a major effect if they were working properly just prior to the conversion?
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post #7 of 18 (permalink) Old Yesterday, 05:44 PM
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I did bench bleed the master cylinder, but had to bleed all the lines as well as I had to custom bend some new lines to the distribution block. I did not have the drums turned. Would this have a major effect if they were working properly just prior to the conversion?

"Would this have a major effect if they were working properly just prior to the conversion?"

Not really, unless they were glazed to some extent. You might re-bleed starting in this order RR> LR > RF >LF

What brand shoes you running?

Ken ..
64 1/2 Poppy Red too!, Cvt. Resto-Mod
333 Cu.in. T5z, 3:55, Dual 40 mm DCOE Webers
Performer RPM, CI cam, TFS/TWs, Tri-Ys, Discs w/Shelby Drums
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post #8 of 18 (permalink) Old Yesterday, 08:24 PM
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If your pedal is hard your booster isn't boosting.

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post #9 of 18 (permalink) Old Today, 08:38 AM
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I'm sure you don't want to hear this but the most economical way to add stopping power and safety would have been to go with manual front disk, Cool master cylinder though.

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post #10 of 18 (permalink) Old Today, 09:04 AM
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Perhaps you're expecting something from "power" brakes that doesn't exist. Power does nothing except reduce brake pedal effort or the amount of pressure that your leg/foot must apply to the pedal to stop the car. The actual stopping of the car is affected by the brake shoe lining material and the condition of the brake shoe rubbing surface inside the drum. If you have cheap organic shoes and overheated drums with hard spots you won't have much stopping power regardless of "power" or "manual" brakes.
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post #11 of 18 (permalink) Old Today, 09:11 AM
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Originally Posted by Woodchuck View Post
If your pedal is hard your booster isn't boosting.
Exactly. A working booster always feels a little soft.

He didn't get power boost to stop better, he got it to reduce pedal effort. It isn't working. Even manual drums will lock the wheels.

His booster isn't working. His stopping is worse because the stock-type booster he appears to have has a built-in lever to make the brakes less touchy. With the booster not working, this means he needs to press even harder to stop.

Amateur restorer. Well, sometimes I have been paid for it. But not right now.

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post #12 of 18 (permalink) Old Today, 09:26 AM
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Originally Posted by 2nd 66 View Post
I'm sure you don't want to hear this but the most economical way to add stopping power and safety would have been to go with manual front disk, Cool master cylinder though.
Which kit would you recommend?


1970 Sportsroof.
Parked in 1977 resurrected in 2015.
Original 302-2V, C4 trans, and 2.79 open differential.
Manual drums, manual steering.
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post #13 of 18 (permalink) Old Today, 09:35 AM
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Which kit would you recommend?
This one. Take a leisurely drive up to Marble Falls and pick one up.
CSRP discbrakeswap Mustang Disc Brake Conversion Kits SWAP1
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post #14 of 18 (permalink) Old Today, 09:40 AM
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Man!
That would men swapping out the 2 month old master again for the third time.
Any kit compatible with what I have now?
Sorry for the thread hijack.


1970 Sportsroof.
Parked in 1977 resurrected in 2015.
Original 302-2V, C4 trans, and 2.79 open differential.
Manual drums, manual steering.
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post #15 of 18 (permalink) Old Today, 10:52 AM
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I intend no offense, but just to be sure, the FRONT master cylinder reservoir is for the REAR brakes. The REAR master cylinder reservoir is the for the FRONT brakes. Is it possible you connected them backwards? This would be easy to do considering your previous master cylinder had only one reservoir.

A few years ago, a friend of mine had a disc brake kit installed on his '68 GTO. He had the same problem you describe. He took his car to another shop where the mechanic immediately noticed the brake lines were backwards on the master cylinder. Reconnecting the lines correctly solved the problem.

For anyone else in a similar situation, be aware for 12 years my daily driver was a 1969 Cougar with non-power drum brakes all around. I never had any braking problems with that system. The worst was reduced braking power if I drove through a deep puddle, but even that wasn't too bad. I could easily lock up all for wheels with minimal pedal effort in any situation. I never considered this system unsafe.

I put non-power KH front disc brakes on my 1970 Mach 1 only because I hope to do some occasional autocross and track events. If I was just going to do street driving, I would have been fine with the factory, 4-wheel drum brakes.

Currently working on a 1970 Mach 1 project. See it here: http://forums.vintage-mustang.com/vi...ode-build.html

Last edited by Klutch; Today at 10:59 AM.
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