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Old 06-10-2012, 09:21 AM
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Brake pedal and residual valves

I have converted my '32 chevy to all discs and a new power booster/MC combo mounted below the floorboard. All works good except occasionally the brake pedal will stay down after stopping. Can be pulled up manually. I have residual valves to install and have been told this will cure my problem. Does anyone know where I can find a 3/8" - 24 IFF to 1/8" NPT nipple so I can plumb the valves directly into the MC?

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Old 06-11-2012, 04:14 AM
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Residual valve

From my understanding the residual valve keeps a minimal amount of pressure applied at the caliper piston. For my car i have a 2 psi willwood residual valve ( blue) which is plumbed into the rear line only as i have a 4 wheel disc brake conversion. This reduces the amount of pedal travel slightly when you apply the brakes. My master cylinder is typically a tandem and has two internal springs for pedal return + a tension spring off the steel pedal arm. (standard)
If you have to pull the pedal back manually my guess its a spring issue. ????
I read somewhere if your mc is below the floor then the residual valve also stops the syphoning of the brake fluid back to the mc. That would give you a long pedal travel but the springs compressed down to their min length should be pushing back just as hard as the spring would be totally compressed. Theres your 5 cents worth.
Al.

Last edited by 67Mustang Al.; 06-11-2012 at 04:21 AM.
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Old 06-11-2012, 06:21 AM
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Quote:
Originally Posted by Jim7231
I have converted my '32 chevy to all discs and a new power booster/MC combo mounted below the floorboard. All works good except occasionally the brake pedal will stay down after stopping. Can be pulled up manually. I have residual valves to install and have been told this will cure my problem. Does anyone know where I can find a 3/8" - 24 IFF to 1/8" NPT nipple so I can plumb the valves directly into the MC?
Speedway has a lot of brake parts, adapters, etc...

Russ
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Old 06-27-2012, 08:19 AM
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Thanks for response

I will have to check my MC for internal return springs. It is interesting that when I have to pull up the brake pedal, it takes quite a bit of pull. I do have external return springs and I am going to recheck those as well.

In my mind, I can't see how residual valves will fix this but I'm not a hydraulic engineer.
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Old 06-27-2012, 09:42 AM
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Depending on the MC, you may not be able to find a direct to MC fitting.

I would also suspect the MC as well - it sounds like fluid is getting by the internal piston cup and when you pull it back - it goes the other way. There is at least one spring plus a cup expander inside of that MC

As far as plumbing resid valves - I suggest that you do them close by the MC - and use 2# versions with disc's fron and rear. An adjustable proportioning valve would also be a good addition.

In the photo you can just see one of the two RPVs, the prop valve and the stoplight switch - and it all works with a Corvette type MC and using simple SAE or AN fittings.



Dave W
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Old 06-27-2012, 10:33 AM
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Brake pedal

Thanks so much for the additional info. I do have a proportioning valve in the system already. It was there before I converted the rear drums to discs. The MC and booster were new purchases from Speedway however I have read that sometimes new MCs have problems.
Not being a brake system guy, do I pull the MC and find an expert or what is the way to determine if fluid is getting by the piston?
Another bit of info is that when the pedal stays down, it pulls up with more effort than I think should be with two external springs on the actuator rod.
Again, thanks. I learn something new everyday.
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Old 06-27-2012, 11:56 AM
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Quote:
Originally Posted by Jim7231
Thanks so much for the additional info. I do have a proportioning valve in the system already. It was there before I converted the rear drums to discs. The MC and booster were new purchases from Speedway however I have read that sometimes new MCs have problems.
Not being a brake system guy, do I pull the MC and find an expert or what is the way to determine if fluid is getting by the piston?
Another bit of info is that when the pedal stays down, it pulls up with more effort than I think should be with two external springs on the actuator rod.
Again, thanks. I learn something new everyday.
Jim - as much as I like Speedway, a lot of their parts have become less then great lately, being from somewhere overseas(China, etc). If the MC has an incorrectly drilled reservoir return holes, porous or internally cracked casting, poorly bored cylinder, etc - you might chase the problem for a long time.

As far as a return spring, that really doesn't have to be much if the system is 'right'

I would probably pull the MC, do an inspection and if OK, find a kit and install when I did RPV's. If it's a Corvette type, Rock Auto has them as rebuilts from about $30 to $80 - and their quality overall for many parts for various vehicles of mine that I've purchased has been 100%.
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Old 06-27-2012, 04:11 PM
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Mc

Thanks for the info again. I'm not a builder, just a one car guy and I really appreciate the expertise and experience you have. I will pursue the MC inspection and / or replacement.

Thanks for taking to time to communicate.

Jim
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