When will it stop? Brake question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

K2Orion · 11-18-2009, 04:11 PM

I have a 72 C10 custom deluxe that I bought this summer that I can't stop. I'm running out of ideas and I want to make sure I'm not missing something before I throw any more parts at it. So here's some history.

The truck was originally a 72 C10 custom deluxe with a 350/350 2wd with tilt and air. I bought a 4wd truck with a 350/350/203 amd 44/60 with 3.73s.

When I bought the truck I knew it had a few issues. The brakes would not stop the truck when it was in gear and would barely stop it when it was in neutral. I assumed it needed a master cylinder.

First, I tried bleeding the system. After 2 qts. of dot3 the system ran clear and had no bubbles. No change in pedal feel or stopping ability.
FAIL

Second, I found some hard lines that were rusted and started leaking after some movement. I replaced them and bled the system again.
FAIL

Third, I discovered that the truck was missing a proportioning valve. I bought a used MC and PV from a board member (whose name I forgot) that came from a 72 C10. I installed these and bled the system again.
FAIL

Fourth, I bought a reman. MC for a 72 K20 but it would not fit. It used a different length pushrod and reversed the position of the lines from the MC to the PV. So I bought a MC for a C10 and installed it. I bled the system again.
FAIL

The first 2 attempts I just bled the system by having somebody depress the pedal as I cracked the bleeder screw. Each time the fluid ran clear with no bubbles.

The second 2 attempts I vacuum bled the system with a Mity-vac.
I am going back to the garage to try to put together a pressure bleed setup. I hope that will work.

So what should I try next? Replace the fex lines? New calipers? The previous owner daily drove the truck as I bought it for a while before he parked it. Then it sat for 10 years. But this combo of parts should work, right? I shouldn't need a MC for a K20, should I?

Help?

cdowns · 11-18-2009, 04:36 PM

have you tried new pads and shoes and adjusted the real drums manually?

PowerPro · 11-18-2009, 04:47 PM

I'm assuming this is power brakes. Have you checked the vacuum line coming from the engine? If there is a crack in that line or if the plastic fitting or gasket at the brake booster is cracked, you will have all of these symptoms. You could also have a bad brake booster.

Good luck and I hope this helps!

joedoozer · 11-18-2009, 04:50 PM

Since you didn't say the pedal was going to the floor, I can only assume you don't have a leak. If the pedal is hard and you can't stop the truck, then you have an assist problem. The vacuum hose to the booster could be bad, or the booster itself.

hayhauler71 · 11-18-2009, 04:57 PM

Jack up all 4 wheels and have a friend press on the brakes and see if you can turn the tires by hand.

K2Orion · 11-18-2009, 06:00 PM

Yes, power brakes.
Doesn't seem to be a problem with the booster. I'll check to see if it holds vacuum. It doesn't take much effort to depress the pedal. It just goes almost to the end of its travel before any braking occurs. I can't find any leaks in the hydraulic side or were you referring to the vacuum booster? If the booster were bad, it should still stop, but require more pedal effort, right?
I've been working in the garage with it on stands each time. Each corner moves fine by hand and the brakes will stop the wheels while it is running and in gear on stands. But not until the pedal is fully depressed and just barely then. The brake performance is basically the same as when I bought it despite the new parts.

K2Orion · 11-18-2009, 06:03 PM

I also found that my factory service manual says that the pin on the front of the proportioning valve should be held in during bleeding. Anybody heard of this?

How do you bleed your brakes?
step by step.

BB72CHEVKT · 11-18-2009, 06:08 PM

How about the rear wheel cylinders?

WFAPS · 11-18-2009, 06:32 PM

I ran into a problem with a customer a the parts store I used to work at. We went round and round trying to figure out why the pedal went almost to the floor before any braking was applied. Come to find out when he was restoring/reassembling the truck he swapped the calipers side to side. This positioned the bleeders on the bottom of the caliper and as you well know air risesin fluid. The previous owner had installed different brake hoses that allowed you to be able to install the caliper upside down.

Another thing you can do is install plugs/caps on the brake lines and remove the calipers and wheel cylinders out of the loop. If the pedal get firm then you would know it is a caliper or wheel cylinder problem. Reattach them one at a time and when the pedal gets bad the last one hooked up is the problem. If the pedal did not get firm then it would be a mastercylinder or prop valve problem.

budman k20 · 11-18-2009, 06:38 PM

It not clear to me but it sounds like you have a K20 (4 wheel drive 3/4 ton) pickup now. If that is true then you should know that 3/4 ton trucks use a reversed MC (compared to 1/2 ton trucks) and you would need to use the 3/4 ton MC. K20's also use a double brake booster. You may also have to use the correct P valve (for a K20) in your truck as well. Hope this info helps!

rsavage · 11-18-2009, 09:19 PM

There is a rod in the front of the booster that contacts the back of the master cylinder. It is adjustable. You can usually unbolt your MC without unhooking lines and move it out enough to adjust the rod. Try adjusting it out (making it longer) to see if you get booster assist. This may be all that is wrong.

K2Orion · 11-18-2009, 09:21 PM

The bleeder screws are on top of the calipers where they belong.
Yes, it has rear wheel cylinders and they have been bled in the correct order each time.

Budman, I think we are wondering about the same thing. Does it matter what position each half of the MC is in relation to the firewall? Assuming that if the chamber on the MC meant for the front brakes is plumbed to the port on the prop valve for the front and on to the front calipers. And the chamber for the rear goes to the rear portion of the PV and down the line to the rear drums.

Are there different prop valves for different applications? I know there are different valves for disc and drum. What about the difference between 10 and 20or 2wd and 4wd? LMC only lists 1 for 72.

The truck was running minus a PV for years. And it seems to have the same symptoms with the PV as without.

K2Orion · 11-18-2009, 09:23 PM

How should I adjust the rod? It's not threaded. It just pops in and out.

mclairmo · 11-18-2009, 11:06 PM

Quote:

Originally Posted by K2Orion

How should I adjust the rod? It's not threaded. It just pops in and out.

The part bolted to the brake pedal should be adjustable. Also, make sure the rod coming from the booster and into the MC bore has very little slack before it bottoms out in the MC piston.

Murphy IRE · 11-19-2009, 12:09 AM

Sounds like the same stuff, that I'm going through. I difinetely have a '71 K20 and I replaced both WC & the flex lines, they just looked old. The drums and rotors were worn out. And new shoes and pads. The PO replaced the MC and booster. I have the same problem the pedal doesn't fad, but it just doesn't engage early and get the wheels to stop for an emergency stop. I will adjust the rear drums manually tomorrow. I will re-read budman's,rsavage and some of the other threads.
Murphy

mclairmo · 11-18-2009, 11:04 PM

Fluid on the pads/shoes will cause your symptoms. Sometimes the pads/shoes are saturated from a leaky caliper/cylinder but you can't really see it.

wzuke · 11-19-2009, 02:25 AM

Yes, replace the rubber lines on the front. Just one of mine was collapsed and it pulled hard to one side.

rsavage · 11-19-2009, 05:41 PM

The small round tip on the end of mine had a hex on it and threaded out from the rod. Do you have the same rod on your booster? Mine is a 69/70 type dual diaphragm. I put a rebuilt unit on and instructions with it specifically talked about adjusting it. Of course I didn't at first and had the same symptoms you are experiencing. I had replaced eveything on the brake system as a part of the restore so I knew it had to be related to booster in my case.

K2Orion · 11-19-2009, 05:53 PM

I'll try adjusting the rod on the booster. Anybody know what length supposed to be?

K2Orion · 11-21-2009, 08:26 PM

There is no slack between the rod coming from the booster and the mc.

What else should I try?
How can I test the booster? Other than buying a new one and trying it.

PowerPro · 11-21-2009, 09:09 PM

Copied from google search:

Vacuum Brake Booster Test Procedure
by H Steve Dolan

--------------------------------------------------------------------------------

If the booster is working correctly, it should have no noticable effect on the engine, but if it is leaking, it will cause big problems. Use the following procedure to check yours.

Things you need:

Vacuum guage
Cap for vacuum port on the intake manifold
Friend to work brake pedal
Pencil and paper
Procedure:

Hook up the vac guage. Start the engine. Note the reading. This is your "base" reading.

Stop the engine, disconnect the booster vacuum line and cap the port on the manifold. Start the engine, look at the guage. If this reading is substantally higher than the base, you have a leak in the system, probably in the lines leading to the booster.

Stop the engine, remove and test the one-way valve (should be able to blow into it one way but not the other). Air should only pass in the direction indicated by the arrow printed on the top of the valve (make sure to reinstall it in the correct direction).

Reconnect the one way valve and vacuum line to the manifold and start the engine. Watch the vac guage as a friend depresses the brake pedal. It should dip as the pedal is depressed and return to the base reading. If it drops slowly, but returns, you have a blockage/collapse in the vac line. If it falls and does not return, you have a torn diaphram in the booster. Especially indicative of a torn diaphram is a hissing when the pedal is depressed.

rsavage · 11-21-2009, 10:03 PM

If your booster tests out okay, adjust the rod coming out from the booster out further (lengthen it) even if you don't see any slack. Try like a 1/4" and see if you get some assist. then another 1/4" if that didn't change pedal feel. I had to lengthen mine to get power assist feel and it took a few times. I could, however, feel a positive change as soon as I lengthened it. Perhaps vacuum it pulls back in somewhat when the engine is running? In any event, it worked for me and at this point you don't have anything to lose by trying it before you start throwing money into a new booster.

11-18-2009, 04:11 PM	#1
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	When will it stop? Brake question I have a 72 C10 custom deluxe that I bought this summer that I can't stop. I'm running out of ideas and I want to make sure I'm not missing something before I throw any more parts at it. So here's some history. The truck was originally a 72 C10 custom deluxe with a 350/350 2wd with tilt and air. I bought a 4wd truck with a 350/350/203 amd 44/60 with 3.73s. When I bought the truck I knew it had a few issues. The brakes would not stop the truck when it was in gear and would barely stop it when it was in neutral. I assumed it needed a master cylinder. First, I tried bleeding the system. After 2 qts. of dot3 the system ran clear and had no bubbles. No change in pedal feel or stopping ability. FAIL Second, I found some hard lines that were rusted and started leaking after some movement. I replaced them and bled the system again. FAIL Third, I discovered that the truck was missing a proportioning valve. I bought a used MC and PV from a board member (whose name I forgot) that came from a 72 C10. I installed these and bled the system again. FAIL Fourth, I bought a reman. MC for a 72 K20 but it would not fit. It used a different length pushrod and reversed the position of the lines from the MC to the PV. So I bought a MC for a C10 and installed it. I bled the system again. FAIL The first 2 attempts I just bled the system by having somebody depress the pedal as I cracked the bleeder screw. Each time the fluid ran clear with no bubbles. The second 2 attempts I vacuum bled the system with a Mity-vac. I am going back to the garage to try to put together a pressure bleed setup. I hope that will work. So what should I try next? Replace the fex lines? New calipers? The previous owner daily drove the truck as I bought it for a while before he parked it. Then it sat for 10 years. But this combo of parts should work, right? I shouldn't need a MC for a K20, should I? Help?

11-18-2009, 04:36 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: When will it stop? Brake question have you tried new pads and shoes and adjusted the real drums manually? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

11-18-2009, 04:47 PM	#3
PowerPro Registered User Join Date: Sep 2009 Location: Spokane, WA Posts: 68	Re: When will it stop? Brake question I'm assuming this is power brakes. Have you checked the vacuum line coming from the engine? If there is a crack in that line or if the plastic fitting or gasket at the brake booster is cracked, you will have all of these symptoms. You could also have a bad brake booster. Good luck and I hope this helps! __________________ 1970 C20 LWB Fleetside with a 472 Caddy engine! TH400 Restoration in progress 07 Yamaha 650 V-Star Custom 83 Honda V-45 Magna

11-18-2009, 04:50 PM	#4
joedoozer is Certifiable Join Date: Feb 2008 Location: Hinesville, Georgia Posts: 160	Re: When will it stop? Brake question Since you didn't say the pedal was going to the floor, I can only assume you don't have a leak. If the pedal is hard and you can't stop the truck, then you have an assist problem. The vacuum hose to the booster could be bad, or the booster itself. __________________ 1972 Chevy C10 LWB 350 Auto Blue with a white roof.

11-18-2009, 04:57 PM	#5
hayhauler71 Registered User Join Date: Aug 2009 Location: St. Paul MN. Posts: 1,996	Re: When will it stop? Brake question Jack up all 4 wheels and have a friend press on the brakes and see if you can turn the tires by hand.

11-18-2009, 06:00 PM	#6
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question Yes, power brakes. Doesn't seem to be a problem with the booster. I'll check to see if it holds vacuum. It doesn't take much effort to depress the pedal. It just goes almost to the end of its travel before any braking occurs. I can't find any leaks in the hydraulic side or were you referring to the vacuum booster? If the booster were bad, it should still stop, but require more pedal effort, right? I've been working in the garage with it on stands each time. Each corner moves fine by hand and the brakes will stop the wheels while it is running and in gear on stands. But not until the pedal is fully depressed and just barely then. The brake performance is basically the same as when I bought it despite the new parts.

11-18-2009, 06:03 PM	#7
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question I also found that my factory service manual says that the pin on the front of the proportioning valve should be held in during bleeding. Anybody heard of this? How do you bleed your brakes? step by step.

11-18-2009, 06:08 PM	#8
BB72CHEVKT Junior Member Join Date: Mar 2007 Location: Hideaway, TX Posts: 4,950	Re: When will it stop? Brake question How about the rear wheel cylinders? __________________ 71 Suburban 350/700R4 Project Trixie 72 CHEVY,Highlander,SWB,396,T400

11-18-2009, 06:32 PM	#9
WFAPS Registered User Join Date: Oct 2009 Location: College Station, TX Posts: 15	Re: When will it stop? Brake question I ran into a problem with a customer a the parts store I used to work at. We went round and round trying to figure out why the pedal went almost to the floor before any braking was applied. Come to find out when he was restoring/reassembling the truck he swapped the calipers side to side. This positioned the bleeders on the bottom of the caliper and as you well know air risesin fluid. The previous owner had installed different brake hoses that allowed you to be able to install the caliper upside down. Another thing you can do is install plugs/caps on the brake lines and remove the calipers and wheel cylinders out of the loop. If the pedal get firm then you would know it is a caliper or wheel cylinder problem. Reattach them one at a time and when the pedal gets bad the last one hooked up is the problem. If the pedal did not get firm then it would be a mastercylinder or prop valve problem.

11-18-2009, 06:38 PM	#10
budman k20 1972 K20 Join Date: Apr 2008 Location: Greenfield MN Posts: 360	Re: When will it stop? Brake question It not clear to me but it sounds like you have a K20 (4 wheel drive 3/4 ton) pickup now. If that is true then you should know that 3/4 ton trucks use a reversed MC (compared to 1/2 ton trucks) and you would need to use the 3/4 ton MC. K20's also use a double brake booster. You may also have to use the correct P valve (for a K20) in your truck as well. Hope this info helps!

11-18-2009, 09:19 PM	#11
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: When will it stop? Brake question There is a rod in the front of the booster that contacts the back of the master cylinder. It is adjustable. You can usually unbolt your MC without unhooking lines and move it out enough to adjust the rod. Try adjusting it out (making it longer) to see if you get booster assist. This may be all that is wrong.

11-18-2009, 09:21 PM	#12
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question The bleeder screws are on top of the calipers where they belong. Yes, it has rear wheel cylinders and they have been bled in the correct order each time. Budman, I think we are wondering about the same thing. Does it matter what position each half of the MC is in relation to the firewall? Assuming that if the chamber on the MC meant for the front brakes is plumbed to the port on the prop valve for the front and on to the front calipers. And the chamber for the rear goes to the rear portion of the PV and down the line to the rear drums. Are there different prop valves for different applications? I know there are different valves for disc and drum. What about the difference between 10 and 20or 2wd and 4wd? LMC only lists 1 for 72. The truck was running minus a PV for years. And it seems to have the same symptoms with the PV as without.

11-18-2009, 09:23 PM	#13
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question How should I adjust the rod? It's not threaded. It just pops in and out.

11-19-2009, 12:09 AM	#15
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: When will it stop? Brake question Sounds like the same stuff, that I'm going through. I difinetely have a '71 K20 and I replaced both WC & the flex lines, they just looked old. The drums and rotors were worn out. And new shoes and pads. The PO replaced the MC and booster. I have the same problem the pedal doesn't fad, but it just doesn't engage early and get the wheels to stop for an emergency stop. I will adjust the rear drums manually tomorrow. I will re-read budman's,rsavage and some of the other threads. Murphy

11-18-2009, 11:04 PM	#16
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: When will it stop? Brake question Fluid on the pads/shoes will cause your symptoms. Sometimes the pads/shoes are saturated from a leaky caliper/cylinder but you can't really see it.



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11-19-2009, 02:25 AM	#17
wzuke Registered User Join Date: Nov 2007 Location: Marion, IL Posts: 112	Re: When will it stop? Brake question Yes, replace the rubber lines on the front. Just one of mine was collapsed and it pulled hard to one side.

11-19-2009, 05:41 PM	#18
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: When will it stop? Brake question The small round tip on the end of mine had a hex on it and threaded out from the rod. Do you have the same rod on your booster? Mine is a 69/70 type dual diaphragm. I put a rebuilt unit on and instructions with it specifically talked about adjusting it. Of course I didn't at first and had the same symptoms you are experiencing. I had replaced eveything on the brake system as a part of the restore so I knew it had to be related to booster in my case.

11-19-2009, 05:53 PM	#19
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question I'll try adjusting the rod on the booster. Anybody know what length supposed to be?

11-21-2009, 08:26 PM	#20
K2Orion Registered User Join Date: Jan 2009 Location: St. Louis, MO Posts: 75	Re: When will it stop? Brake question There is no slack between the rod coming from the booster and the mc. What else should I try? How can I test the booster? Other than buying a new one and trying it.

11-21-2009, 09:09 PM	#21
PowerPro Registered User Join Date: Sep 2009 Location: Spokane, WA Posts: 68	Re: When will it stop? Brake question Copied from google search: Vacuum Brake Booster Test Procedure by H Steve Dolan -------------------------------------------------------------------------------- If the booster is working correctly, it should have no noticable effect on the engine, but if it is leaking, it will cause big problems. Use the following procedure to check yours. Things you need: Vacuum guage Cap for vacuum port on the intake manifold Friend to work brake pedal Pencil and paper Procedure: Hook up the vac guage. Start the engine. Note the reading. This is your "base" reading. Stop the engine, disconnect the booster vacuum line and cap the port on the manifold. Start the engine, look at the guage. If this reading is substantally higher than the base, you have a leak in the system, probably in the lines leading to the booster. Stop the engine, remove and test the one-way valve (should be able to blow into it one way but not the other). Air should only pass in the direction indicated by the arrow printed on the top of the valve (make sure to reinstall it in the correct direction). Reconnect the one way valve and vacuum line to the manifold and start the engine. Watch the vac guage as a friend depresses the brake pedal. It should dip as the pedal is depressed and return to the base reading. If it drops slowly, but returns, you have a blockage/collapse in the vac line. If it falls and does not return, you have a torn diaphram in the booster. Especially indicative of a torn diaphram is a hissing when the pedal is depressed. __________________ 1970 C20 LWB Fleetside with a 472 Caddy engine! TH400 Restoration in progress 07 Yamaha 650 V-Star Custom 83 Honda V-45 Magna

11-21-2009, 10:03 PM	#22
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: When will it stop? Brake question If your booster tests out okay, adjust the rod coming out from the booster out further (lengthen it) even if you don't see any slack. Try like a 1/4" and see if you get some assist. then another 1/4" if that didn't change pedal feel. I had to lengthen mine to get power assist feel and it took a few times. I could, however, feel a positive change as soon as I lengthened it. Perhaps vacuum it pulls back in somewhat when the engine is running? In any event, it worked for me and at this point you don't have anything to lose by trying it before you start throwing money into a new booster.

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