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Old 12-31-2004, 08:31 PM
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residual valve ?what location

I'm putting under cab power brakes on a 57 chev truck (disc/drum). It's been suggested I use a residual valve for the rear brakes. I'm just wondering where the valve should be installed, right off the master cylinder? after the proportioning valve? Does it really matter? Can it go anywhere on the line going to the rear before it divides? Depending on where it needs to go it may require some adapter fittings so if it can go anywhere I'll try to put it somewhere where the fitting sizes match.

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Old 01-01-2005, 12:02 AM
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Anywhere in the line going to the rear brakes is fine. The factory puts them in the outlet port of the master cylinder. And yes, you do need one for sure.
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Old 01-01-2005, 10:35 AM
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residual valve

Do all brake systems have a inline residual valve to the rear brakes? I thought most factory systems have them built in, using what they call a combination valve ? ( Looks like a block where the brake lines are split to the front and rear )
Im not positive about this but I think some master cylinders may have the valve built into them.
Are you using all new parts? used ?
Check out www.mpbrakes.com. there was/is a tech article about brake system setups.
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Old 01-01-2005, 10:46 AM
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I put a 78 Chrysler front torsion bar ifs on this truck. I got the proportioning valve from the same donor car. The master cylinder is a 73 Vette 1 1/8" master which is what most of the aftermarket kits are using. I don't think this master cylinder has a built in residual valve but I'm not sure about the proportioning valve.

Wilwood's residual valves are 1/8-27 at both ends and the ports on the master cylinder are bigger than this so I guess I'll install anywhere from the out port of the prop. valve to the divider at the rearend where it's all 1/8-27.

I guess if you put one on the front brakes it would have to go somewhere between the mast. cyl. and the prop. valve because there's two ports heading to each front wheel coming out of the prop. valve.
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Old 01-01-2005, 01:02 PM
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You only need a normal 10psi residual check valve on front brakes if they are drum brakes. If your master cylinder is above the height of the brake calipers, disk brakes should NOT have a residual valve. They are intended to bias the system against brake shoe spring pressure so it takes less time for the shoes to expand when you mash the pedal. If you put this much residual pressure on disk brakes that have no springs to overcome, it will apply the brakes all the time! Not a good idea. They do make a 2psi disk brake residual valve for applications where the master cylinder is under the floor board and below the calipers to prevent the fluid draining back into the master cylinder. It isn't necessary for systems with a firewall mounted master cylinder.
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Old 01-01-2005, 06:35 PM
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Re: residual valve ?what location

Quote:
Originally posted by murrsue
I'm just wondering where the valve should be installed, right off the master cylinder? after the proportioning valve?
After the proportioning valve (If you are use a stock non-adjustable proportioning valve) and as close to the master cylinder as possible is the correct location for the residual valve.

If you are using an after-market adjustable proportioning valve on the rear brake lines only, then put the residual valve as close to the master cylinder as possible and then plumb the adjustable proportioning valve after it.

Since you stated that the master cylinder is "under the cab" you should use a 2 p.s.i. residual valve for the front disc brakes and a 10 p.s.i. residual valve for the rear drum brakes.
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