1968 C10 disc brake conversion- MC question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jbrem010 · 03-13-2022, 02:14 PM

Hey all,

I'm looking to convert my '68 C10 to front disc brakes. I understand I'll need to change the prop valve; do I need to replace the MC in this pic? Sorry if I haven't given you enough info. The front chamber of the MC is larger and the line fittings measure 7/16" and 9/16".

68Gold/white · 03-13-2022, 05:09 PM

Man, I don't know exactley what you've got there for a booster, m/cyl snd prop valve. It all looks like disc brake stuff to me looks like a setup from a 73-up Chevrolet pickup.

All the GM m/cyls I've seen with a larger fluid compartment were for front disc/rear drum.
Of course I have not seen them all, but I worked in a parts store for 13 years, from 1985-1998. Some all drum fords had a larger compartment on one end of some of their m/cyls, your m/cyl is NOT a ford...

Jbrem010 · 03-13-2022, 05:49 PM

Okay, thank you 68G/W. Is there a specific PV you would recommend assuming the MC is correct? I currently have drum/drum brakes now. Thanks again for your input.

**MikeB** · 03-13-2022, 06:02 PM

Yes, very strange setup. I'd use a manual prop valve in the rear line and adjust to maximum pressure. Then reduce pressure as necessary if the rears lock up before the fronts during a panic stop.

Wilwood 260-12627

Jbrem010 · 03-14-2022, 12:45 PM

Okay guys, what's odd about the setup? I don't know as much as you all do. Would the Wilwood adjustable PV go in place of the current PV? What about the front brakes? Sorry for all of the questions.

68Gold/white · 03-14-2022, 01:05 PM

You might look for a part number on the Prop valve?

THe all drum and disc prop valves look nearly the same. I'm sure you can find a disc/drum prop valve here, used....to be safe. New may not be that much.

If you could get a look at a 73-up prop valve, that might be nice...

geezer#99 · 03-14-2022, 01:54 PM

The wilwood adjustable is spliced into the rear line. Leave the rest as it is.
Somebody is gonna come along and say that’s not right but I’ve done it like that several times. Not all prop valves are the same. You’d need to find one that’s sized right for your system.

**Steeveedee** · 03-14-2022, 02:14 PM

That's right. Keith Seymour posted some charts for the various equipment for brakes. If the OP's truck doesn't have disc brakes, he should buy a disc brake master cylinder. imo. No telling what the current master is, and if it's currently a drum/drum system can't possibly be plumbed right for disc/drum. I ended up putting the Wilwood valve on my truck, like MikeB posted. The brakes work great.

**MikeB** · 03-14-2022, 02:23 PM

Steeveedee -- Well said.

Jbrem010 · 03-14-2022, 09:58 PM

Okay, thanks guys. I think I'll pick up a disc/drum prop valve. You've confirmed the MC should work. Thanks again.

**70STOVEBOLT** · 03-15-2022, 11:02 AM

You have what appears to be a 3/4 ton master cylinder and booster. The valve below the master is not a proportioning valve, but a distribution valve that will not work with disc brakes. You will need to get a master cylinder, booster, and prop valve for a 71-72 half ton and you can either use the original hard lines or buy new lines and you will need new hoses for the calipers, along with the spindles. Member Pickmup (Frank) sells a complete master/booster/prop valve kit for 1/2 tons.

Jbrem010 · 04-11-2022, 08:43 AM

Hey everyone, I grabbed a set of 2.5" drop spindles and the disc brake conversion kit from CPP. The previous owner heated the front springs and they are uneven so I'm replacing them with 2" drop springs. The brake hose that came with the conversion kit has a 7/16" inverted flare fitting and the OEM brake is a 3/8" inverted flare. The adapter is BR550 (reminds me of Hee-Haw if anyone gets that one. :-) I read the brake hose 88466 would be what would be needed since it is shorter and I found it has a 3/8" inverted flare fitting. Awesome, no adapter!! Got them installed last night after paying around $13 ea at Autozone. 88466 is 4" shorter than the hose that came with the kit and I had to file out the hose frame hole to fit and secure the fitting. I hope it is long enough, an inch or two longer would have made it just right.

**Grumpy old man** · 04-11-2022, 09:21 AM

Quote:

Originally Posted by Jbrem010

Hey everyone, I grabbed a set of 2.5" drop spindles and the disc brake conversion kit from CPP. The previous owner heated the front springs and they are uneven so I'm replacing them with 2" drop springs. The brake hose that came with the conversion kit has a 7/16" inverted flare fitting and the OEM brake is a 3/8" inverted flare. The adapter is BR550 (reminds me of Hee-Haw if anyone gets that one. :-) I read the brake hose 88466 would be what would be needed since it is shorter and I found it has a 3/8" inverted flare fitting. Awesome, no adapter!! Got them installed last night after paying around $13 ea at Autozone. 88466 is 4" shorter than the hose that came with the kit and I had to file out the hose frame hole to fit and secure the fitting. I hope it is long enough, an inch or two longer would have made it just right.

This thread has some good info . You want to watch for chaffing .

https://67-72chevytrucks.com/vboard/...d.php?t=818077

72c20customcamper · 04-11-2022, 09:08 AM

Quote:

Originally Posted by Jbrem010

Hey all,

I'm looking to convert my '68 C10 to front disc brakes. I understand I'll need to change the prop valve; do I need to replace the MC in this pic? Sorry if I haven't given you enough info. The front chamber of the MC is larger and the line fittings measure 7/16" and 9/16".

That unit looks like a Buick olds setup.

Jbrem010 · 04-23-2022, 08:41 PM

Hey guys, I've moved on to installation of a Summit Racing adjustable proportioning valve and I'm building lines from it to the MC. I have everything figured out except the 1/4" OEM rear brake line is a 1/2-20 fitting and I need to reduce this to 3/8-24 to fit the prop valve. Has anyone came across a 1/2-20 inverted flare female to 3/8-24 inverted flare male fitting? I've been scouring the Internet with no success.

**jocko** · 04-23-2022, 10:34 PM

Quote:

Originally Posted by Jbrem010

Okay, thanks guys. I think I'll pick up a disc/drum prop valve. You've confirmed the MC should work. Thanks again.

Actually, I think people have confirmed you still need a correct disk/drum MC. Note that all your lines in post #1 are 1/4". Stock disk/drum lines are 3/16" (to front disks) and 1/4" to rear drum. Will it work if you just install a prop valve and do nothing else? Perhaps. Will it work correctly? Not likely - or at least not like a stock disk/drum system was engineered to work. Recommend not skimp on the parts or go crazy with mixing and matching systems - a new correct MC is not very expensive and GM engineered the original brake systems to the truck (71-72 C10 brake systems is the model you'd want to emulate).

03-13-2022, 05:09 PM	#2
68Gold/white Registered User Join Date: Sep 2011 Location: Ark City, Kansas Posts: 3,319	Re: 1968 C10 disc brake conversion- MC question Man, I don't know exactley what you've got there for a booster, m/cyl snd prop valve. It all looks like disc brake stuff to me looks like a setup from a 73-up Chevrolet pickup. All the GM m/cyls I've seen with a larger fluid compartment were for front disc/rear drum. Of course I have not seen them all, but I worked in a parts store for 13 years, from 1985-1998. Some all drum fords had a larger compartment on one end of some of their m/cyls, your m/cyl is NOT a ford...

03-13-2022, 05:49 PM	#3
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	Re: 1968 C10 disc brake conversion- MC question Okay, thank you 68G/W. Is there a specific PV you would recommend assuming the MC is correct? I currently have drum/drum brakes now. Thanks again for your input.

03-13-2022, 06:02 PM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,464	Re: 1968 C10 disc brake conversion- MC question Yes, very strange setup. I'd use a manual prop valve in the rear line and adjust to maximum pressure. Then reduce pressure as necessary if the rears lock up before the fronts during a panic stop. Wilwood 260-12627 __________________ 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; 04-24-2022 at 12:29 PM.

03-14-2022, 12:45 PM	#5
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	Re: 1968 C10 disc brake conversion- MC question Okay guys, what's odd about the setup? I don't know as much as you all do. Would the Wilwood adjustable PV go in place of the current PV? What about the front brakes? Sorry for all of the questions.

03-14-2022, 01:05 PM	#6
68Gold/white Registered User Join Date: Sep 2011 Location: Ark City, Kansas Posts: 3,319	Re: 1968 C10 disc brake conversion- MC question You might look for a part number on the Prop valve? THe all drum and disc prop valves look nearly the same. I'm sure you can find a disc/drum prop valve here, used....to be safe. New may not be that much. If you could get a look at a 73-up prop valve, that might be nice...

03-13-2022, 02:14 PM	#1
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	1968 C10 disc brake conversion- MC question Hey all, I'm looking to convert my '68 C10 to front disc brakes. I understand I'll need to change the prop valve; do I need to replace the MC in this pic? Sorry if I haven't given you enough info. The front chamber of the MC is larger and the line fittings measure 7/16" and 9/16". Attached Images

03-14-2022, 01:54 PM	#7
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,541	Re: 1968 C10 disc brake conversion- MC question The wilwood adjustable is spliced into the rear line. Leave the rest as it is. Somebody is gonna come along and say that’s not right but I’ve done it like that several times. Not all prop valves are the same. You’d need to find one that’s sized right for your system.

03-14-2022, 02:14 PM	#8
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,279	Re: 1968 C10 disc brake conversion- MC question That's right. Keith Seymour posted some charts for the various equipment for brakes. If the OP's truck doesn't have disc brakes, he should buy a disc brake master cylinder. imo. No telling what the current master is, and if it's currently a drum/drum system can't possibly be plumbed right for disc/drum. I ended up putting the Wilwood valve on my truck, like MikeB posted. The brakes work great. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

03-14-2022, 02:23 PM	#9
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,464	Re: 1968 C10 disc brake conversion- MC question Steeveedee -- Well said. __________________ 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!

03-14-2022, 09:58 PM	#10
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	Re: 1968 C10 disc brake conversion- MC question Okay, thanks guys. I think I'll pick up a disc/drum prop valve. You've confirmed the MC should work. Thanks again.

03-15-2022, 11:02 AM	#11
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,254	Re: 1968 C10 disc brake conversion- MC question You have what appears to be a 3/4 ton master cylinder and booster. The valve below the master is not a proportioning valve, but a distribution valve that will not work with disc brakes. You will need to get a master cylinder, booster, and prop valve for a 71-72 half ton and you can either use the original hard lines or buy new lines and you will need new hoses for the calipers, along with the spindles. Member Pickmup (Frank) sells a complete master/booster/prop valve kit for 1/2 tons. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Power windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

04-11-2022, 08:43 AM	#12
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	Re: 1968 C10 disc brake conversion- MC question Hey everyone, I grabbed a set of 2.5" drop spindles and the disc brake conversion kit from CPP. The previous owner heated the front springs and they are uneven so I'm replacing them with 2" drop springs. The brake hose that came with the conversion kit has a 7/16" inverted flare fitting and the OEM brake is a 3/8" inverted flare. The adapter is BR550 (reminds me of Hee-Haw if anyone gets that one. :-) I read the brake hose 88466 would be what would be needed since it is shorter and I found it has a 3/8" inverted flare fitting. Awesome, no adapter!! Got them installed last night after paying around $13 ea at Autozone. 88466 is 4" shorter than the hose that came with the kit and I had to file out the hose frame hole to fit and secure the fitting. I hope it is long enough, an inch or two longer would have made it just right.

04-23-2022, 08:41 PM	#15
Jbrem010 Registered User Join Date: Jun 2021 Location: Harrisonville, MO Posts: 11	Re: 1968 C10 disc brake conversion- MC question Hey guys, I've moved on to installation of a Summit Racing adjustable proportioning valve and I'm building lines from it to the MC. I have everything figured out except the 1/4" OEM rear brake line is a 1/2-20 fitting and I need to reduce this to 3/8-24 to fit the prop valve. Has anyone came across a 1/2-20 inverted flare female to 3/8-24 inverted flare male fitting? I've been scouring the Internet with no success.



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