prop. valve problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

shelby987 · 06-08-2006, 07:46 PM

I am upgrading from drums to discs, and as such will be upgrading my MC and needing a new prop. valve. When I bought my 3/4t booster, it came with a prop. valve, but it is definately different from my drum/drum setup. The disc/drum valve has one spot for a line from the MC on top that is smaller than the fitting on the MC, one spot on the rear that is larger than the line for the MC, and two fittings on the bottom that appear to be the same size as the fittings on the MC (I assume these are the same size as the fitting currently on the lines going to the front and rear brakes).

Anyway, can I buy these lines at an autoparts store or do I need to hunt down some adaptors? Does anyone have a pic. of a 3/4t MC and prop. valve......I swear, the way this is suppose to go together looks like its upside down

JimKshortstep4x4 · 06-08-2006, 09:02 PM

Here is a picture of the 3/4 ton master cylinder/prop valve/booster setup.

Jim

shelby987 · 06-09-2006, 10:20 AM

Thanks, that helps a ton.....I was looking at it upside down....that would have been bad, not to mention had I been looking at it the correct way, I would have run front to front and rear to rear on the valve.
Next question, is there enough length in my original brake line to run it to that rear port?
And where do I buy the lines from the MC to the prop valve? The store I go to has the same size fittings on each end of the flared pipes, can I but larger fittings to accept the smaller line???

shelby987 · 06-09-2006, 05:52 PM

ok, now I am confused, I just checked my LMC catalogue, and they show the line from the front of the MC going to the front of the prop. valve, and the lines from the rear going to the rear of the prop. valve.

And JimK, you seem to have a smaller tube for the rear of the MC than for the front.....are these custom bent lines?

**truckdude239** · 06-09-2006, 05:57 PM

if you need lines i recomend www.inlinetube.com

**john** · 06-09-2006, 06:42 PM

The LMC catalog shows c10 lines. The c20 lines are reversed like pic shows.

Americanrider · 06-09-2006, 08:07 PM

3/4 & 1 tons have the back MC to front P-valve & front MC to back of P-valve.
1/2 tons are front-front & back back.
This is a one ton system pic.

shelby987 · 06-09-2006, 08:52 PM

Is there anyway to be positive that I have a 3/4t prop. valve and not the 1/2t version? (does the 1/2t version look anything like the 3/4t?).

Will my original brake lines work, I think they are both the same diameter.

Americanrider · 06-10-2006, 02:35 AM

You will need new lines for the front, smaller lines raise the pressure and you need high pressure for the disk calipers.

I'll let someone else weigh in on the 1/2 vs. 3/4 ton P-valve issue. Personally I'd just change the top lines and run it.... but then I sorta red-neck stuff as long as it works I'm happy.

shelby987 · 06-10-2006, 10:00 AM

That's kinda what I am worried about, my front resevoir in my MC is larger than my rear, so that is the resevoir that should be feeding my rear brakes, and looking at the above pics the front res. is feeding the rear lines, is the MC on stock MC's setup so the rear resevoir is larger????

American, I am tempted to work this redneck style for the time being, I just want it to stop, looking at buying new stainless steel lines down the road.

Americanrider · 06-11-2006, 12:00 PM

I'm not sure which side is larger, the divider plate in the center of the MC chambers is tilted toward the back. It only looks like the front chamber is larger but I think it will hole the same amount of fluid as the rear. On DANA 44's the calipers are the same between 1/2 & 3/4ton axles. Your 1st post says that you Booster & P-valve came off a 3/4 ton, am I right?

As long as you can put this puppy together without it leaking it should work OK.

06-08-2006, 07:46 PM	#1
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	prop. valve problem I am upgrading from drums to discs, and as such will be upgrading my MC and needing a new prop. valve. When I bought my 3/4t booster, it came with a prop. valve, but it is definately different from my drum/drum setup. The disc/drum valve has one spot for a line from the MC on top that is smaller than the fitting on the MC, one spot on the rear that is larger than the line for the MC, and two fittings on the bottom that appear to be the same size as the fittings on the MC (I assume these are the same size as the fitting currently on the lines going to the front and rear brakes). Anyway, can I buy these lines at an autoparts store or do I need to hunt down some adaptors? Does anyone have a pic. of a 3/4t MC and prop. valve......I swear, the way this is suppose to go together looks like its upside down __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-08-2006, 09:02 PM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: prop. valve problem Here is a picture of the 3/4 ton master cylinder/prop valve/booster setup. Jim Attached Images

06-09-2006, 10:20 AM	#3
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: prop. valve problem Thanks, that helps a ton.....I was looking at it upside down....that would have been bad, not to mention had I been looking at it the correct way, I would have run front to front and rear to rear on the valve. Next question, is there enough length in my original brake line to run it to that rear port? And where do I buy the lines from the MC to the prop valve? The store I go to has the same size fittings on each end of the flared pipes, can I but larger fittings to accept the smaller line??? __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-09-2006, 05:52 PM	#4
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: prop. valve problem ok, now I am confused, I just checked my LMC catalogue, and they show the line from the front of the MC going to the front of the prop. valve, and the lines from the rear going to the rear of the prop. valve. And JimK, you seem to have a smaller tube for the rear of the MC than for the front.....are these custom bent lines? __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-09-2006, 05:57 PM	#5
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,237	Re: prop. valve problem if you need lines i recomend www.inlinetube.com __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

06-09-2006, 06:42 PM	#6
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: prop. valve problem The LMC catalog shows c10 lines. The c20 lines are reversed like pic shows. __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

06-09-2006, 08:07 PM	#7
Americanrider Registered User Join Date: Dec 2004 Location: NW, WA. Posts: 1,421	Re: prop. valve problem 3/4 & 1 tons have the back MC to front P-valve & front MC to back of P-valve. 1/2 tons are front-front & back back. This is a one ton system pic. Attached Images

06-09-2006, 08:52 PM	#8
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: prop. valve problem Is there anyway to be positive that I have a 3/4t prop. valve and not the 1/2t version? (does the 1/2t version look anything like the 3/4t?). Will my original brake lines work, I think they are both the same diameter. __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-10-2006, 02:35 AM	#9
Americanrider Registered User Join Date: Dec 2004 Location: NW, WA. Posts: 1,421	Re: prop. valve problem You will need new lines for the front, smaller lines raise the pressure and you need high pressure for the disk calipers. I'll let someone else weigh in on the 1/2 vs. 3/4 ton P-valve issue. Personally I'd just change the top lines and run it.... but then I sorta red-neck stuff as long as it works I'm happy.

06-10-2006, 10:00 AM	#10
shelby987 Registered User Join Date: Mar 2005 Location: Just outside Durham, NC Posts: 894	Re: prop. valve problem That's kinda what I am worried about, my front resevoir in my MC is larger than my rear, so that is the resevoir that should be feeding my rear brakes, and looking at the above pics the front res. is feeding the rear lines, is the MC on stock MC's setup so the rear resevoir is larger???? American, I am tempted to work this redneck style for the time being, I just want it to stop, looking at buying new stainless steel lines down the road. __________________ 1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM!

06-11-2006, 12:00 PM	#11
Americanrider Registered User Join Date: Dec 2004 Location: NW, WA. Posts: 1,421	Re: prop. valve problem I'm not sure which side is larger, the divider plate in the center of the MC chambers is tilted toward the back. It only looks like the front chamber is larger but I think it will hole the same amount of fluid as the rear. On DANA 44's the calipers are the same between 1/2 & 3/4ton axles. Your 1st post says that you Booster & P-valve came off a 3/4 ton, am I right? As long as you can put this puppy together without it leaking it should work OK.



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