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

JJ · 10-25-2002, 12:19 PM

When I mount my disc brakes on the back of my K2500, do I have to use a proportioning valve? The calipers rotors and pads are all the same as the ones on the front.

**MikeB** · 10-25-2002, 01:29 PM

I would install w/o the prop valve. If the rears lock-up prematurely, you can add one of those adjustable valves to get it just right.

kpf · 10-25-2002, 02:11 PM

jj

I would definitly use a prop valve.

**MikeB** · 10-25-2002, 02:58 PM

Stock prop valves were for front disc/rear drums and may not work properly for a disc/disc setup. For example, Brother's Trucks sells different valves for disc/drum and disc/disc. However, your best bet is an adjustable valve that lets you tune your braking system so the rears don't lock up before the fronts. Summit Racing sells a couple different models for $39.50 to $75.95.

**1971Stepside** · 10-25-2002, 04:41 PM

From what I have read and with talking to different folks at various vendors they all seem to universily agree that you should not put disc brakes on the rear of our trucks (that is why I choose not to) but if you do go ahead and do it I would definately get a prop valve that is adjustable for disc/disc. CCP sells one, but I don't know how well it works.

JJ · 10-25-2002, 04:53 PM

What would be the reason for not using them on the rear axle? They seem to increase braking performance on the front axles. Seems like more and more vehicle manufacturers are using them all the way around now.

crazy longhorn · 10-25-2002, 05:37 PM

The @ss end is really pretty light,& probably doesnt need disc brakes unless you are hauling a lot of heavy loads(they will lock & slide). If you do opt for disc brakes, i think the adjustable valve would be the way to go. Good luck....crazy AL

Lightspeed · 10-25-2002, 10:57 PM

since we are on the subject of prop valves. would i have to get a new one to add power brakes to my disc/drum manual brake truck? or could i just bolt on a booster and go?

**MikeB** · 10-26-2002, 07:24 PM

I would expect the prop valve is the same for manual and power brakes. It's still working with the same pressure -- you just don't have to push as hard with power brakes to generate the pressure!

10-25-2002, 12:19 PM	#1
JJ Lurking Member Join Date: Feb 2000 Location: Forest Grove, OR USA Posts: 196	Disc proportioning When I mount my disc brakes on the back of my K2500, do I have to use a proportioning valve? The calipers rotors and pads are all the same as the ones on the front. __________________ JJ 72 GMC 1500 350 4 Speed, stone stock baby!!!!! 72 GMC K-2500 350TPI 700R4 For those who fought for it, Freedom has a flavor the protected will never know.

10-25-2002, 01:29 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,475	I would install w/o the prop valve. If the rears lock-up prematurely, you can add one of those adjustable valves to get it just right. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

10-25-2002, 02:11 PM	#3
kpf Registered User Join Date: Jun 2002 Location: Camas, Wa Posts: 58	jj I would definitly use a prop valve. __________________ 71 c-10 6cyl 68 Camaro (wifes) 65 dodge town wagon (wanna buy it?) 97 crew cab f350 psd

10-25-2002, 02:58 PM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,475	Stock prop valves were for front disc/rear drums and may not work properly for a disc/disc setup. For example, Brother's Trucks sells different valves for disc/drum and disc/disc. However, your best bet is an adjustable valve that lets you tune your braking system so the rears don't lock up before the fronts. Summit Racing sells a couple different models for $39.50 to $75.95. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

10-25-2002, 04:41 PM	#5
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	From what I have read and with talking to different folks at various vendors they all seem to universily agree that you should not put disc brakes on the rear of our trucks (that is why I choose not to) but if you do go ahead and do it I would definately get a prop valve that is adjustable for disc/disc. CCP sells one, but I don't know how well it works. __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

10-25-2002, 04:53 PM	#6
JJ Lurking Member Join Date: Feb 2000 Location: Forest Grove, OR USA Posts: 196	What would be the reason for not using them on the rear axle? They seem to increase braking performance on the front axles. Seems like more and more vehicle manufacturers are using them all the way around now. __________________ JJ 72 GMC 1500 350 4 Speed, stone stock baby!!!!! 72 GMC K-2500 350TPI 700R4 For those who fought for it, Freedom has a flavor the protected will never know.

10-25-2002, 05:37 PM	#7
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	The @ss end is really pretty light,& probably doesnt need disc brakes unless you are hauling a lot of heavy loads(they will lock & slide). If you do opt for disc brakes, i think the adjustable valve would be the way to go. Good luck....crazy AL

10-25-2002, 10:57 PM	#8
Lightspeed Registered User Join Date: Oct 2002 Location: Virginia Posts: 226	since we are on the subject of prop valves. would i have to get a new one to add power brakes to my disc/drum manual brake truck? or could i just bolt on a booster and go?

10-26-2002, 07:24 PM	#9
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,475	I would expect the prop valve is the same for manual and power brakes. It's still working with the same pressure -- you just don't have to push as hard with power brakes to generate the pressure! __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!



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