Brake Proportioning Valve Differences

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Nov 27, 2004 | 01:58 AM

WillFordTruck

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Cross-Country

Joined: Oct 2003

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From: N. CAL

Brake Proportioning Valve Differences

Anyone know if the proportioning value used in a 1972 F250 7500 GVW front drum truck can be used with front disc brakes for the same truck? They have a different number of outlets (drum config has more, since one output line goes to each front brake versus disc brake which has one outlet that goes to the front that splits off a "valve" (bolted to the cross member above the I beams) to each wheel?

NOTE: by all appearances, the spindle used for this GVW (and 8100) are identical whether for drum or disc application.

Thanks,

Will

Nov 27, 2004 | 05:28 AM

jowilker

Fleet Owner

Joined: Jun 1999

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From: Creedmoor, North Carolina

Don't monkey around with your life, use the one designed for the system that you are going to. Be able to stop and tell about it.

John

Nov 29, 2004 | 01:54 PM

talisker

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From: Bridgeville,CA

I believe that the valve in question is for operating the indicator light that lets you know when one of the independent systems has failed. As long as you have all drums you don't really need a porportioning valve. At least on my '69 the only valve is down in the frame rail and just turns on a "brake" light down by the parking brake release.

Nov 30, 2004 | 01:55 PM

boneman01

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Joined: Sep 2003

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From: Sunny NM

I believe talisker is right. My 70 has what is called a differential valve that just senses different pressures and turns on the light if one side is low. Front disc brakes require the proportioning valve to send different pressures to the discs and the drums.

Nov 30, 2004 | 03:05 PM

michaelbrainardatwor

More Turbo

Joined: Mar 2004

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From: manson

do the disk breaks require more or less pressure?

Nov 30, 2004 | 03:14 PM

talisker

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From: Bridgeville,CA

Disc brakes require a LOT more pressure. Drum brakes are almost self activeting once you engage them. Just look at the little electro magnet that runs electric treailer brakes.

Nov 30, 2004 | 04:12 PM

rebocardo

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Joined: Jun 2002

Posts: 13,873

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From: Atlanta GA

Disc brakes require a constant pressure to keep them within a minimum distance of the rotor so they just glide on the rotor surface for many reasons. The Bendix type drum system works by having the front shoe (minor) hit the drum and in doing so pivots the bigger (rear) shoe against the drum. fwiw.