70 Gmc Brake problem still - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kevmic28 · 11-16-2009, 07:45 PM

My brakes travel to the point the light comes on, If I pump it a couple times its good but give it a second or two and its bad again. I have replaced the master cylinder and all the wheel cylinders. I am totally stumped and cannot drive my truck the way it is now. Drums all around and no booster. No brake fluid loss either.
Im beginning to wonder if I got a bad master cylinder from the auto parts store.

mbgmike · 11-16-2009, 08:22 PM

Quote:

Originally Posted by kevmic28

My brakes travel to the point the light comes on, If I pump it a couple times its good but give it a second or two and its bad again. I have replaced the master cylinder and all the wheel cylinders. I am totally stumped and cannot drive my truck the way it is now. Drums all around and no booster. No brake fluid loss either.
Im beginning to wonder if I got a bad master cylinder from the auto parts store.

Very possible their are failure rates on all parts
You may want to blank off the ports with a plug and see if the pedal will stay firm if not its bad. You many still have air in the lines also. if it still does it check your front brake lines. If old I would replace them. How long has it been since they were done.

PanelDeland · 11-16-2009, 08:24 PM

It's possible the MC was bad but you may also have air in the lines causing this.Have you bled the brake system fully?Did you bench bleed the MC? Those are the two things I would check first.

mbgmike · 11-16-2009, 08:35 PM

Its definetly possible the mc can be bad. We sell brake parts all the time. A one in 200 failure rate is not that uncommon on some brands. The lower the price the less quality control usually.

kevmic28 · 11-16-2009, 09:39 PM

Yeah this was the bottom of the line MC from Advanced. This is something I have been trying to fix for months. New Mc in August. All new wheel cylinders two weeks ago. I thought I had it fixed two weeks ago when I realized the adjusters were frozen but I am back to the drawing board.
I did bench bleed the mc and have bled the brakes to the point of having all new fluid throughout the system. How do I block off the mc to check it?

kevmic28 · 11-17-2009, 12:31 AM

Ok I went up under the dash tonight and listened to the master cylinder while I pumped the brakes. I could hear the fluid pump as I pumped the brakes but when I held pressure on it I could still hear fluid moving throught the MC. So I think it may be bad. Is this normal??

mbgmike · 11-17-2009, 08:16 AM

Quote:

Originally Posted by kevmic28

Yeah this was the bottom of the line MC from Advanced. This is something I have been trying to fix for months. New Mc in August. All new wheel cylinders two weeks ago. I thought I had it fixed two weeks ago when I realized the adjusters were frozen but I am back to the drawing board.
I did bench bleed the mc and have bled the brakes to the point of having all new fluid throughout the system. How do I block off the mc to check it?

You just get two plugs w/correct taper and screw them in. Then apply pressure to the pedal and it should stay firm.

kevmic28 · 11-18-2009, 05:46 PM

Well I think I fixed my problem. I bled the crap out of my brakes and still had no pressure. So I was checking autozone online for parts and decided to read their help section. I started reading about the parking brake adjustment and remembered that I had to install new cables for my parking brake. Well it seems I never tightened the cables up. This caused the back brakes to not be seated correctly. Which explains why when the parking brake was set I had good pressure.
Now its not as tight as I would like it to be but that might just be the difference between power brakes and non power brakes.

68gmsee · 11-18-2009, 07:40 PM

Loose parking brake cable shouldn't have any thing to do with your original problem. I'd go back and recheck all of your brake shoe adjustments to make sure they're just barely scraping the drum as you turn it by hand. And make sure your parking brake isn't too tight -it may throw off your adjustments.

The way I do it is to tighten the adjuster until the drum won't turn and then back it off until it barely scrapes the inside. Then bleed some more.

If you still have trouble, then your master cylincer could be the problem. I've had to take couple of them back at Auto Zone because of internal seal failure. Finally went to a different auto parts and got a different brand and it worked fine.

kevmic28 · 11-18-2009, 08:16 PM

Ok Ill double check them again tomorrow, Its too dark and cold to be out there now. Especially with no garage or carport.

68gmsee · 11-18-2009, 09:00 PM

I hear you. My garage is so full of stuff, I can't do any work in it. I don't like the cold either but I bet those guys up north laugh their a$$ off when we complain it's too cold at 50-60 degrees...

Don't overlook the fact that the mc may be the culrpit. Once you do all the adjustments and make sure you don't get any bubbles when you bleed, then I'd try another one just to make sure. I know it's a pain in the rear and my wife hates it when I holler at her to pump the brake but, it's part of the fun of owning these old trucks.

kevmic28 · 11-18-2009, 10:39 PM

They might laugh, but it was pretty chilly at 35 degrees this morning on my Harley.

68gmsee · 11-19-2009, 12:01 AM

Yep, I agree there. I got rid of mine long time ago but I do remember they will suck the heat right out of you when it's cool. Won't be as cold tonight. They say high 40's down here.

kevmic28 · 11-19-2009, 12:07 AM

One question.... Shouldnt the the self adjusters keep the pads tight with all the pumping I have done??

wzuke · 11-19-2009, 02:33 AM

The rear brakes "self" adjust when you are backing up and apply the brakes not by just pumping the pedal.

68gmsee · 11-19-2009, 10:14 AM

That's correct... Take a look at this site and scroll down. It has a good pic of how the self adjuster works.
http://auto.howstuffworks.com/auto-p...rum-brake2.htm

Forgot to mention earlier that once you tighten the brake shoes you have to push on the pawl to allow backwards movement of the adjuster. I usually use two tools -the brake adjuster and a long thin screwdriver to push on the pawl to back off the adjuster.

Now the reason I do this is to make sure the shoes are centered on the drum. They have slight movement front to back on the plate and if you adjust until it barely touches, it may just be one shoe that's touching.

kevmic28 · 11-19-2009, 10:23 AM

Ok well I should have said more than just pumping the brakes. More like yard driving forwards and backwards in the yard. But Ill get to looking at that this afternoon. I have never had such an issue with brakes before.

68gmsee · 11-19-2009, 10:39 AM

Actually, for the rear brakes to self adjust, you have to do it on hard surface and really step on the brakes. In other words, the brakes shoes have to lock up and force the backwards rotation of the mechanism. There may not be enough traction on soft or wet surface.

Actually, this is not the correct way to adjust your brakes. The self adjuster was introduced as a means of keeping the rear brakes adjusted as they gradually wore down.

Now, I know this more info than you want, but I was asked this by a friend. Why keeps it from getting tighter and tigher until the shoes no longer turn?

They're designed to allow less pawl action the closer to the rim the shoes are. Once they're at the correct distance, the pawl moves very little and no adjusting action will occur.

kevmic28 · 11-19-2009, 10:53 AM

Ah ok.
I am wondering now if the adjusters are on the right way. There is no telling what previous owners have done and I have been having brake problems since I bought the truck. The first thing I bought was a new master cylinder thinking that was the problem. Then new wheel cylinders, then new shoes.
Im thinking I might just buy a new spring kit and a new adjuster kit for all 4 wheels.
Anybody have some detailed pictures of their brakes they can post. Im wondering if the adjusters are backwards and backing the brakes off instead of tightiening them.
When I got the truck there was only one parking brake cable on the pax side of the truck so there is no telling what might else be missing.

fleetimus · 11-19-2009, 02:52 PM

http://www.pbase.com/nufsed/drumbrake

kevmic28 · 11-19-2009, 03:31 PM

Thanks. Based on those pics I am missing some springs and parts for my brakes. Ill tear into it this afternoon when I get home.

kevmic28 · 11-19-2009, 07:40 PM

Ok I got the springs in the right place. Oh and the front adjusters were flipped from side to side. So instead of tightening them, they were loosening them. Brakes finally fixed.
You know in theory when you replace your brakes you reinstall them the way they came off but if the previous owner had them screwed up to begin with you are screwed..... lol

cdowns · 11-19-2009, 08:07 PM

that's why it's nice to have the service manual and look at the pictures

kevmic28 · 11-19-2009, 08:41 PM

Yeah I have a Haynes manual but its a joke. I have been fighting this issue for months. What a pain.
Thanks for all the help yall.

mclairmo · 11-19-2009, 08:42 PM

Great discussion and a good reminder to check those little springs and doodads in the drum. I have all drums on my 68 C10 and used my manual to confirm everything was correct. I once did the rear drums on my father in law's van and it was missing all kinds of parts. I was amazed the van stopped at all. Good thing the fronts do most of the braking.

11-16-2009, 07:45 PM	#1
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	70 Gmc Brake problem still My brakes travel to the point the light comes on, If I pump it a couple times its good but give it a second or two and its bad again. I have replaced the master cylinder and all the wheel cylinders. I am totally stumped and cannot drive my truck the way it is now. Drums all around and no booster. No brake fluid loss either. Im beginning to wonder if I got a bad master cylinder from the auto parts store. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-16-2009, 08:24 PM	#3
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	Re: 70 Gmc Brake problem still It's possible the MC was bad but you may also have air in the lines causing this.Have you bled the brake system fully?Did you bench bleed the MC? Those are the two things I would check first. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

11-16-2009, 08:35 PM	#4
mbgmike Registered User Join Date: Aug 2005 Location: Pasadena,Tx /Pto Pta DR Posts: 5,415	Re: 70 Gmc Brake problem still Its definetly possible the mc can be bad. We sell brake parts all the time. A one in 200 failure rate is not that uncommon on some brands. The lower the price the less quality control usually.

11-16-2009, 09:39 PM	#5
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Yeah this was the bottom of the line MC from Advanced. This is something I have been trying to fix for months. New Mc in August. All new wheel cylinders two weeks ago. I thought I had it fixed two weeks ago when I realized the adjusters were frozen but I am back to the drawing board. I did bench bleed the mc and have bled the brakes to the point of having all new fluid throughout the system. How do I block off the mc to check it? __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 11-16-2009 at 09:41 PM.

11-17-2009, 12:31 AM	#6
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Ok I went up under the dash tonight and listened to the master cylinder while I pumped the brakes. I could hear the fluid pump as I pumped the brakes but when I held pressure on it I could still hear fluid moving throught the MC. So I think it may be bad. Is this normal?? __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 11-17-2009 at 08:32 AM.

11-18-2009, 05:46 PM	#8
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Well I think I fixed my problem. I bled the crap out of my brakes and still had no pressure. So I was checking autozone online for parts and decided to read their help section. I started reading about the parking brake adjustment and remembered that I had to install new cables for my parking brake. Well it seems I never tightened the cables up. This caused the back brakes to not be seated correctly. Which explains why when the parking brake was set I had good pressure. Now its not as tight as I would like it to be but that might just be the difference between power brakes and non power brakes. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-18-2009, 07:40 PM	#9
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: 70 Gmc Brake problem still Loose parking brake cable shouldn't have any thing to do with your original problem. I'd go back and recheck all of your brake shoe adjustments to make sure they're just barely scraping the drum as you turn it by hand. And make sure your parking brake isn't too tight -it may throw off your adjustments. The way I do it is to tighten the adjuster until the drum won't turn and then back it off until it barely scrapes the inside. Then bleed some more. If you still have trouble, then your master cylincer could be the problem. I've had to take couple of them back at Auto Zone because of internal seal failure. Finally went to a different auto parts and got a different brand and it worked fine.

11-18-2009, 08:16 PM	#10
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Ok Ill double check them again tomorrow, Its too dark and cold to be out there now. Especially with no garage or carport. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-18-2009, 09:00 PM	#11
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: 70 Gmc Brake problem still I hear you. My garage is so full of stuff, I can't do any work in it. I don't like the cold either but I bet those guys up north laugh their a$$ off when we complain it's too cold at 50-60 degrees... Don't overlook the fact that the mc may be the culrpit. Once you do all the adjustments and make sure you don't get any bubbles when you bleed, then I'd try another one just to make sure. I know it's a pain in the rear and my wife hates it when I holler at her to pump the brake but, it's part of the fun of owning these old trucks.

11-18-2009, 10:39 PM	#12
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still They might laugh, but it was pretty chilly at 35 degrees this morning on my Harley. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-19-2009, 12:01 AM	#13
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: 70 Gmc Brake problem still Yep, I agree there. I got rid of mine long time ago but I do remember they will suck the heat right out of you when it's cool. Won't be as cold tonight. They say high 40's down here.

11-19-2009, 12:07 AM	#14
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still One question.... Shouldnt the the self adjusters keep the pads tight with all the pumping I have done?? __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-19-2009, 02:33 AM	#15
wzuke Registered User Join Date: Nov 2007 Location: Marion, IL Posts: 112	Re: 70 Gmc Brake problem still The rear brakes "self" adjust when you are backing up and apply the brakes not by just pumping the pedal.

11-19-2009, 10:14 AM	#16
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: 70 Gmc Brake problem still That's correct... Take a look at this site and scroll down. It has a good pic of how the self adjuster works. http://auto.howstuffworks.com/auto-p...rum-brake2.htm Forgot to mention earlier that once you tighten the brake shoes you have to push on the pawl to allow backwards movement of the adjuster. I usually use two tools -the brake adjuster and a long thin screwdriver to push on the pawl to back off the adjuster. Now the reason I do this is to make sure the shoes are centered on the drum. They have slight movement front to back on the plate and if you adjust until it barely touches, it may just be one shoe that's touching.

11-19-2009, 10:23 AM	#17
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Ok well I should have said more than just pumping the brakes. More like yard driving forwards and backwards in the yard. But Ill get to looking at that this afternoon. I have never had such an issue with brakes before. __________________ 1970 GMC truck 1988 Harley 1200 Sportster



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11-19-2009, 10:39 AM	#18
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: 70 Gmc Brake problem still Actually, for the rear brakes to self adjust, you have to do it on hard surface and really step on the brakes. In other words, the brakes shoes have to lock up and force the backwards rotation of the mechanism. There may not be enough traction on soft or wet surface. Actually, this is not the correct way to adjust your brakes. The self adjuster was introduced as a means of keeping the rear brakes adjusted as they gradually wore down. Now, I know this more info than you want, but I was asked this by a friend. Why keeps it from getting tighter and tigher until the shoes no longer turn? They're designed to allow less pawl action the closer to the rim the shoes are. Once they're at the correct distance, the pawl moves very little and no adjusting action will occur.

11-19-2009, 10:53 AM	#19
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Ah ok. I am wondering now if the adjusters are on the right way. There is no telling what previous owners have done and I have been having brake problems since I bought the truck. The first thing I bought was a new master cylinder thinking that was the problem. Then new wheel cylinders, then new shoes. Im thinking I might just buy a new spring kit and a new adjuster kit for all 4 wheels. Anybody have some detailed pictures of their brakes they can post. Im wondering if the adjusters are backwards and backing the brakes off instead of tightiening them. When I got the truck there was only one parking brake cable on the pax side of the truck so there is no telling what might else be missing. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

11-19-2009, 02:52 PM	#20
fleetimus Registered User Join Date: Jul 2000 Location: Auburn,Ca USA Posts: 369	Re: 70 Gmc Brake problem still http://www.pbase.com/nufsed/drumbrake __________________ 68 Chevy l/b, 4 whl disc in the foothills of No Calif

11-19-2009, 03:31 PM	#21
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Thanks. Based on those pics I am missing some springs and parts for my brakes. Ill tear into it this afternoon when I get home. __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 11-19-2009 at 03:34 PM.

11-19-2009, 07:40 PM	#22
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Ok I got the springs in the right place. Oh and the front adjusters were flipped from side to side. So instead of tightening them, they were loosening them. Brakes finally fixed. You know in theory when you replace your brakes you reinstall them the way they came off but if the previous owner had them screwed up to begin with you are screwed..... lol __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 11-19-2009 at 08:02 PM.

11-19-2009, 08:07 PM	#23
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 70 Gmc Brake problem still that's why it's nice to have the service manual and look at the pictures __________________ 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

11-19-2009, 08:41 PM	#24
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: 70 Gmc Brake problem still Yeah I have a Haynes manual but its a joke. I have been fighting this issue for months. What a pain. Thanks for all the help yall. __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 11-19-2009 at 09:08 PM.

11-19-2009, 08:42 PM	#25
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: 70 Gmc Brake problem still Great discussion and a good reminder to check those little springs and doodads in the drum. I have all drums on my 68 C10 and used my manual to confirm everything was correct. I once did the rear drums on my father in law's van and it was missing all kinds of parts. I was amazed the van stopped at all. Good thing the fronts do most of the braking.

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