proportioning valve question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dinnut · 07-19-2006, 03:05 AM

im converting my drums over to discs... is the proportioning valve specific to 71-72 or can i use off say a newer truck i could find at junkyard.... if i cant find one locally ill have to order i guess

Jim_PA · 07-19-2006, 08:12 AM

There is a little more to consider -- are you using the 71-72 master cylinder and related lines?

If you look at a 71-72 versus the earlier years, the lines are very different, and I don't think you could just put a 71-72 prop valve into an earlier setup, unless you are going to try to bend some custom lines? The 71-72 master cylinder is much larger as well.

The choice for me was easy... I needed all new lines, and a new master cylinder anyway, so I just put all 71 brake hardware on my 68.

68speedalert · 07-19-2006, 09:50 AM

A prop valve is technically specific for a particular application. But you MUST have one for disc/drum set up. I can't say for sure, but a newer app (from a c-10) would probably work. Make sure you know the routing of the lines; which outputs go to the front & rear, and make the you know which outputs of the new master cylinder go to the front & rear and route them accordingly.

I've not done one myself, but the easiest way to convert is to change the entire front subframe from a 73-87 c-10. The prop valve is mounted low on the front, main frame crossmember.

You should change the master cylinder to a disc/drum type as well, although I'm sure the swap has been done without it. The disc/drum master has different valving in it for disc. A drum type would, in theory, hold pressure on the front brakes.

dinnut · 07-19-2006, 01:29 PM

well i know what all needs to be done to convert it over. i know about the master cylinder. ive bought all the correct equiptment to put the 71-72 spindles on my 70 suspension. i just needed to know about the proportioning valve. my prop valve is RIGHT off of the master cylinder... so i guess one off a newer truck wont work. ill just use all 71-72 parts then.

Jim_PA · 07-19-2006, 01:58 PM

You seem to know what to do-

Good luck, I ran into a few things when doing mine.

SoCal71K20 · 07-19-2006, 02:22 PM

Would an aftermarket prop valve like from Summit be able to be plumbed in and work too.

**clay68c10** · 07-19-2006, 11:12 PM

I used the aftermarket valve and it works just fine.

krue · 07-20-2006, 12:06 AM

The only difference (externally) that I can tell between the 71/2 and the 73 up is one port that has a line on it on the newer pv is plugged on the older version.

07-19-2006, 03:05 AM	#1
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	proportioning valve question im converting my drums over to discs... is the proportioning valve specific to 71-72 or can i use off say a newer truck i could find at junkyard.... if i cant find one locally ill have to order i guess __________________ 70 longbed 496/th400/Ford 9"

07-19-2006, 08:12 AM	#2
Jim_PA Registered User Join Date: May 2005 Location: PA Posts: 2,696	Re: proportioning valve question There is a little more to consider -- are you using the 71-72 master cylinder and related lines? If you look at a 71-72 versus the earlier years, the lines are very different, and I don't think you could just put a 71-72 prop valve into an earlier setup, unless you are going to try to bend some custom lines? The 71-72 master cylinder is much larger as well. The choice for me was easy... I needed all new lines, and a new master cylinder anyway, so I just put all 71 brake hardware on my 68.

07-19-2006, 09:50 AM	#3
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	Re: proportioning valve question A prop valve is technically specific for a particular application. But you MUST have one for disc/drum set up. I can't say for sure, but a newer app (from a c-10) would probably work. Make sure you know the routing of the lines; which outputs go to the front & rear, and make the you know which outputs of the new master cylinder go to the front & rear and route them accordingly. I've not done one myself, but the easiest way to convert is to change the entire front subframe from a 73-87 c-10. The prop valve is mounted low on the front, main frame crossmember. You should change the master cylinder to a disc/drum type as well, although I'm sure the swap has been done without it. The disc/drum master has different valving in it for disc. A drum type would, in theory, hold pressure on the front brakes. __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab Last edited by 68speedalert; 07-19-2006 at 09:52 AM.

07-19-2006, 01:29 PM	#4
dinnut Registered User Join Date: Apr 2003 Location: missouri city, tx Posts: 4,486	Re: proportioning valve question well i know what all needs to be done to convert it over. i know about the master cylinder. ive bought all the correct equiptment to put the 71-72 spindles on my 70 suspension. i just needed to know about the proportioning valve. my prop valve is RIGHT off of the master cylinder... so i guess one off a newer truck wont work. ill just use all 71-72 parts then. __________________ 70 longbed 496/th400/Ford 9"

07-19-2006, 01:58 PM	#5
Jim_PA Registered User Join Date: May 2005 Location: PA Posts: 2,696	Re: proportioning valve question You seem to know what to do- Good luck, I ran into a few things when doing mine.

07-19-2006, 02:22 PM	#6
SoCal71K20 Registered User Join Date: Jan 2002 Location: Lemon Grove, California Posts: 152	Re: proportioning valve question Would an aftermarket prop valve like from Summit be able to be plumbed in and work too.

07-19-2006, 11:12 PM	#7
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,990	Re: proportioning valve question I used the aftermarket valve and it works just fine. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

07-20-2006, 12:06 AM	#8
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	Re: proportioning valve question The only difference (externally) that I can tell between the 71/2 and the 73 up is one port that has a line on it on the newer pv is plugged on the older version. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

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