Simple Brake Question (project update) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**j_cst_10** · 09-25-2010, 08:55 AM

This may seem like a dumb question, but here it goes anyway. I am converting my 70 CST to power disc brakes and I was wondering...

Coming off of the proportioning valve, what side feeds the front brakes?

The fitting towards the rear of the truck (closest to the firewall) has the larger fitting. I would assume this to be it but on my CST now, the rear line feeds the rear brakes and front line feeds the front.

How my truck is set up now is usually the convention, is it switched on disc brake C10's?

**MikeB** · 09-25-2010, 09:09 AM

OEM or aftermarket prop valve? Do you have a picture?

TobyArnot · 09-25-2010, 09:42 AM

Do you have a drum/disc proportioning valve? Usually the larger fitting (rear facing on most) feeds the rear and either (or both front) feed the front calipers.

**j_cst_10** · 09-25-2010, 11:04 AM

I will post a pic. It is a factory prop valve.

The reason I am unsure about all of this is because the disc brake flex line accepts the 1/4" brake fittings (larger) while the prop. valve has the 1/4" fitting towards the rear and the smaller 3/16" fitting towards the front.

I am just wondering why the flexible brake line for disc brakes takes a 1/4" line if the prop valve is 3/16" on the front and 1/4" for the rear??

**Drum/disc prop valve

13lazer · 09-25-2010, 11:28 AM

The larger reservoir on your master cylinder should be piped to your disc brake calipers. I had to run different diameter lines on my 70 blazer when converted it to disc brakes. I'm not 100% sure, but I think the pipe diameter should be left the way GM designed them.

**Classic Heartbeat** · 09-25-2010, 11:35 AM

What mastercylender/booster combo are you using? Factory for a disk/drum truck or factory for a drum drum truck? Either way the rear resivour is for the rear brakes and the front one is for the front. If you are using a drum/drum set up, you will need to at the very least add an adjustible proportioning valve in the line going back to your rear brakes. WES

**MikeB** · 09-25-2010, 02:27 PM

It's not very pretty, but here's a nearly stock setup from a 71-72.

As you can see, the front circuit uses 3/16" line; the rear 1/4" from M/C to prop valve to tee fittings.

**j_cst_10** · 09-25-2010, 07:29 PM

Thanks MikeB, that helps a lot.

That is pretty much what I thought it was going to be (conventional). What I still don't get is that my flex line to my caliper takes the larger 1/4" line, while the prop valve/master cylinder is plumbed with the smaller 3/16". (This is using factory DISC brake parts, not my original drum)

Oh well, I guess I'll have to make it work somehow.

68anniversary · 09-25-2010, 08:36 PM

Unless I'm wrong your front 3/16 line comes off the front of the prop valve and goes down into a "T" fitting on the drivers side frame with one offshoot line going to the drivers side hose and the other line off the "T" continues across to the pass side hose. Those front lines are 3/16. That rear line coming off the prop valve just follows along side the 3/16 line across the front crossmember and then heads rearward to a fitting, then on to the rear of the truck. I just worked on mine tonight and this is how it was setup. Hope this helps

ERASER5 · 09-25-2010, 09:12 PM

FYI, Since no one has specified C10 or C20, MC plumbing for a C20 is reversed from a C10.

**j_cst_10** · 09-26-2010, 08:36 AM

Well did they send me the wrong flexible brake line to the calipers? The fittings are definitely 1/4", not 3/16".

** Just checked the catalog and I ordered the correct part. This is a mystery, and not a good one. I just dropped my now lowered/disc brake converted truck on the ground and I want to drive it! All that is left is to bend a few brake lines.

RCbowtie69 · 09-26-2010, 09:49 AM

I brought my disc brake system from MP brakes, but others are out there,CPP,i did disc to drums,they will know what proportion valve you'll need,you can check them on line

**j_cst_10** · 09-26-2010, 12:49 PM

I am using the factory disc brake proportioning valve off of a 72 C10

Pont406 · 09-26-2010, 04:07 PM

there is a T where both front line come together. I am using inline tube kit but changed to 73 and up hoses. From what I remember I had to get an adaptor for the right side when trying to use 72 hoses but again it was for inline tube kit. Do hoses fit the lines? Which kit are you using? Here is a pic. Hope its helps.

**j_cst_10** · 09-28-2010, 01:08 AM

I ordered 71/72 flexible line and I am using a master cylinder/prop valve off of a 72 C10 that I parted out for the disc brake set up.

The flexible line is set up for 1/4" line while the prop. valve is set up for 3/16".

This seems like a fairly unique problem. Maybe I should just call LMC truck and ask them why these lines are set up for 1/4 rather than 3/16 if that is factory.

09-25-2010, 08:55 AM	#1
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Simple Brake Question (project update) This may seem like a dumb question, but here it goes anyway. I am converting my 70 CST to power disc brakes and I was wondering... Coming off of the proportioning valve, what side feeds the front brakes? The fitting towards the rear of the truck (closest to the firewall) has the larger fitting. I would assume this to be it but on my CST now, the rear line feeds the rear brakes and front line feeds the front. How my truck is set up now is usually the convention, is it switched on disc brake C10's?

09-25-2010, 09:09 AM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,489	Re: Simple Brake Question (project update) OEM or aftermarket prop valve? Do you have a picture? __________________ 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!

09-25-2010, 09:42 AM	#3
TobyArnot Quit if it's not FUN!!! Join Date: Jul 2010 Location: Indian Trail, N.C, Posts: 864	Re: Simple Brake Question (project update) Do you have a drum/disc proportioning valve? Usually the larger fitting (rear facing on most) feeds the rear and either (or both front) feed the front calipers.

09-25-2010, 11:04 AM	#4
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Re: Simple Brake Question (project update) I will post a pic. It is a factory prop valve. The reason I am unsure about all of this is because the disc brake flex line accepts the 1/4" brake fittings (larger) while the prop. valve has the 1/4" fitting towards the rear and the smaller 3/16" fitting towards the front. I am just wondering why the flexible brake line for disc brakes takes a 1/4" line if the prop valve is 3/16" on the front and 1/4" for the rear?? *Drum/disc prop valve Last edited by j_cst_10; 09-25-2010 at 07:32 PM.*

09-25-2010, 11:28 AM	#5
13lazer 13lazers' blazers Join Date: Jul 2005 Location: San Pedro, CA Posts: 152	Re: Simple Brake Question (project update) The larger reservoir on your master cylinder should be piped to your disc brake calipers. I had to run different diameter lines on my 70 blazer when converted it to disc brakes. I'm not 100% sure, but I think the pipe diameter should be left the way GM designed them. __________________ 1970 2wd blazer 1972 1ton blazer 4x4 in progress 1966 mustang coupe (modified) 1985 c20 suburban tow rig 1996 462 ranger with a 150 efi merc. a former B.A.S.S. tournament boat almost all exempt from california smog laws intentionally.

09-25-2010, 11:35 AM	#6
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,770	Re: Simple Brake Question (project update) What mastercylender/booster combo are you using? Factory for a disk/drum truck or factory for a drum drum truck? Either way the rear resivour is for the rear brakes and the front one is for the front. If you are using a drum/drum set up, you will need to at the very least add an adjustible proportioning valve in the line going back to your rear brakes. WES __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys

09-25-2010, 02:27 PM	#7
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,489	Re: Simple Brake Question (project update) It's not very pretty, but here's a nearly stock setup from a 71-72. As you can see, the front circuit uses 3/16" line; the rear 1/4" from M/C to prop valve to tee fittings. __________________ 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! Last edited by MikeB; 09-25-2010 at 02:28 PM.

09-25-2010, 07:29 PM	#8
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Re: Simple Brake Question (project update) Thanks MikeB, that helps a lot. That is pretty much what I thought it was going to be (conventional). What I still don't get is that my flex line to my caliper takes the larger 1/4" line, while the prop valve/master cylinder is plumbed with the smaller 3/16". (This is using factory DISC brake parts, not my original drum) Oh well, I guess I'll have to make it work somehow. Last edited by j_cst_10; 09-25-2010 at 07:33 PM.

09-25-2010, 08:36 PM	#9
68anniversary Registered User Join Date: Jul 2010 Location: Peculiar, Missouri Posts: 125	Re: Simple Brake Question (project update) Unless I'm wrong your front 3/16 line comes off the front of the prop valve and goes down into a "T" fitting on the drivers side frame with one offshoot line going to the drivers side hose and the other line off the "T" continues across to the pass side hose. Those front lines are 3/16. That rear line coming off the prop valve just follows along side the 3/16 line across the front crossmember and then heads rearward to a fitting, then on to the rear of the truck. I just worked on mine tonight and this is how it was setup. Hope this helps

09-25-2010, 09:12 PM	#10
ERASER5 Registered User Join Date: Jun 2006 Location: Indiana Posts: 4,859	Re: Simple Brake Question (project update) FYI, Since no one has specified C10 or C20, MC plumbing for a C20 is reversed from a C10. __________________ '70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60

09-26-2010, 08:36 AM	#11
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Re: Simple Brake Question (project update) Well did they send me the wrong flexible brake line to the calipers? The fittings are definitely 1/4", not 3/16". ** Just checked the catalog and I ordered the correct part. This is a mystery, and not a good one. I just dropped my now lowered/disc brake converted truck on the ground and I want to drive it! All that is left is to bend a few brake lines. Last edited by j_cst_10; 09-26-2010 at 08:43 AM.

09-26-2010, 09:49 AM	#12
RCbowtie69 Registered User Join Date: Dec 2003 Location: Thomasville, NC Posts: 1,877	Re: Simple Brake Question (project update) I brought my disc brake system from MP brakes, but others are out there,CPP,i did disc to drums,they will know what proportion valve you'll need,you can check them on line

09-26-2010, 12:49 PM	#13
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Re: Simple Brake Question (project update) I am using the factory disc brake proportioning valve off of a 72 C10

09-26-2010, 04:07 PM	#14
Pont406 Registered User Join Date: Aug 2007 Location: West Hills, California Posts: 679	Re: Simple Brake Question (project update) there is a T where both front line come together. I am using inline tube kit but changed to 73 and up hoses. From what I remember I had to get an adaptor for the right side when trying to use 72 hoses but again it was for inline tube kit. Do hoses fit the lines? Which kit are you using? Here is a pic. Hope its helps. Attached Images

09-28-2010, 01:08 AM	#15
j_cst_10 Senior Member Join Date: Nov 2008 Location: Cleveland, OH Posts: 591	Re: Simple Brake Question (project update) I ordered 71/72 flexible line and I am using a master cylinder/prop valve off of a 72 C10 that I parted out for the disc brake set up. The flexible line is set up for 1/4" line while the prop. valve is set up for 3/16". This seems like a fairly unique problem. Maybe I should just call LMC truck and ask them why these lines are set up for 1/4 rather than 3/16 if that is factory.



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