1970 c10 brakes problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

travisfraughton · 11-13-2009, 04:55 PM

ok, so this last week the brakes started feeling like i had to push a little too hard to engage the brakes, so I adjusted all 4, tightened and adjusted all the drum brakes like i always do. now in the last 2 days it grabs much better, buuuutttttt, when i slow down, or am waiting at a stop light, the pedal will slowly get softer and softer and i've even had it go as far as it can and my brake light comes on. The front shoes are fine, the rears will need to be replaced in the next couple of months, but I am clueless as to why they are all of a sudden going soft when i'm waiting for the light. They are power boosted, and i'm stumped. HELP!
seriously any help is very appreciated.
Thanks.

smn69 · 11-13-2009, 05:03 PM

Quote:

Originally Posted by travisfraughton

ok, so this last week the brakes started feeling like i had to push a little too hard to engage the brakes, so I adjusted all 4, tightened and adjusted all the drum brakes like i always do. now in the last 2 days it grabs much better, buuuutttttt, when i slow down, or am waiting at a stop light, the pedal will slowly get softer and softer and i've even had it go as far as it can and my brake light comes on. The front shoes are fine, the rears will need to be replaced in the next couple of months, but I am clueless as to why they are all of a sudden going soft when i'm waiting for the light. They are power boosted, and i'm stumped. HELP!
seriously any help is very appreciated.
Thanks.

Check all the rubber lines to make sure they are in good condition. It is possible that you may have gotten some air in the system too. You may try bleeding them to see if that helps.

travisfraughton · 11-13-2009, 05:18 PM

hey you live right down the road from me.
I will try that, my first thought was booster, but i guess that'd make the pedal stiff not soft. hmmm.
will go out and play with it this weekend.

71tahoe · 11-13-2009, 05:42 PM

If you're not pumping fluid out the wheel cylinders then you probably have a bad master cylinder. Fluid is bypassing inside.

smn69 · 11-13-2009, 05:44 PM

Let me know how it goes, I just did the brakes on my 69 (I converted to front disc though). I have manual brakes too, so maybe someone else can chime in on if the booster could cause the pedal to go soft. My guess is no. If you can't get it maybe I could come by and help out.

joedoozer · 11-13-2009, 05:48 PM

Yeah definitely sounds like a bad wheel cylinder or a bad master cylinder. If it is triggering a brake light, the the metering valve is moving. So I would look at the wheel cylinder first.

smn69 · 11-13-2009, 06:00 PM

Ok, sorry for the double post, and some one can correct me if I am wrong, but a couple more questions:
Is the fluid level staying the same or do you have to fill it often?
Do you have good braking initially?
I just checked with the auto teacher at the high school I work at and he said the booster just aids in stopping and will not cause to pedal to go to the floor while sitting (that's what I thought). If you are not loosing fluid check to make sure the rubber hoses are not ballooning anywhere. If the rubber hoses are good and you are not loosing fluid, it may be an internal leak in the master cylinder. If that is the case, I have a new cylinder for a drum, drum setup that I can't use that I would be willing to let you have.
Let me know how it turns out.

travisfraughton · 11-13-2009, 06:13 PM

Now that i think of it, i had this problem with my 77 like 6 years ago and it was a wheel cylinder. that sounds right but i will let ya know what happens this weekend.

dwcsr · 11-13-2009, 06:32 PM

Quote:

Originally Posted by 71tahoe

If you're not pumping fluid out the wheel cylinders then you probably have a bad master cylinder. Fluid is bypassing inside.

My thinking also. If the pedal slowly goes down under pressure its a bad master.

sleepertruck72 · 11-13-2009, 09:54 PM

A quick way to rule out the master cylinder is to undo your brake lines, and plug the m/c lines, your pedal should be rock hard. But if you are having to add fluid because the brake light is coming on, then possibly your wheel cylinder(s) is leaking, causing the pressure differential switch or low fluid sensor to activate the brake light. If you have air in your lines, that would cause the low brake pedal also.

Longhorn Man · 11-13-2009, 11:50 PM

just look under the truck at the backside of the tires. If there's a leaking cylinder, you'll know it.
Otherwise (and more likely IMO) it needs a master cylinder.

11-13-2009, 04:55 PM	#1
travisfraughton Registered User Join Date: Jun 2008 Location: provo, ut Posts: 69	1970 c10 brakes problem ok, so this last week the brakes started feeling like i had to push a little too hard to engage the brakes, so I adjusted all 4, tightened and adjusted all the drum brakes like i always do. now in the last 2 days it grabs much better, buuuutttttt, when i slow down, or am waiting at a stop light, the pedal will slowly get softer and softer and i've even had it go as far as it can and my brake light comes on. The front shoes are fine, the rears will need to be replaced in the next couple of months, but I am clueless as to why they are all of a sudden going soft when i'm waiting for the light. They are power boosted, and i'm stumped. HELP! seriously any help is very appreciated. Thanks.

11-13-2009, 05:18 PM	#3
travisfraughton Registered User Join Date: Jun 2008 Location: provo, ut Posts: 69	Re: 1970 c10 brakes problem hey you live right down the road from me. I will try that, my first thought was booster, but i guess that'd make the pedal stiff not soft. hmmm. will go out and play with it this weekend.

11-13-2009, 05:42 PM	#4
71tahoe Registered User Join Date: May 2006 Location: Jonesboro, AR Posts: 916	Re: 1970 c10 brakes problem If you're not pumping fluid out the wheel cylinders then you probably have a bad master cylinder. Fluid is bypassing inside.

11-13-2009, 05:44 PM	#5
smn69 Registered User Join Date: Oct 2007 Location: Orem, Ut Posts: 132	Re: 1970 c10 brakes problem Let me know how it goes, I just did the brakes on my 69 (I converted to front disc though). I have manual brakes too, so maybe someone else can chime in on if the booster could cause the pedal to go soft. My guess is no. If you can't get it maybe I could come by and help out.

11-13-2009, 05:48 PM	#6
joedoozer is Certifiable Join Date: Feb 2008 Location: Hinesville, Georgia Posts: 160	Re: 1970 c10 brakes problem Yeah definitely sounds like a bad wheel cylinder or a bad master cylinder. If it is triggering a brake light, the the metering valve is moving. So I would look at the wheel cylinder first. __________________ 1972 Chevy C10 LWB 350 Auto Blue with a white roof.

11-13-2009, 06:00 PM	#7
smn69 Registered User Join Date: Oct 2007 Location: Orem, Ut Posts: 132	Re: 1970 c10 brakes problem Ok, sorry for the double post, and some one can correct me if I am wrong, but a couple more questions: Is the fluid level staying the same or do you have to fill it often? Do you have good braking initially? I just checked with the auto teacher at the high school I work at and he said the booster just aids in stopping and will not cause to pedal to go to the floor while sitting (that's what I thought). If you are not loosing fluid check to make sure the rubber hoses are not ballooning anywhere. If the rubber hoses are good and you are not loosing fluid, it may be an internal leak in the master cylinder. If that is the case, I have a new cylinder for a drum, drum setup that I can't use that I would be willing to let you have. Let me know how it turns out.

11-13-2009, 06:13 PM	#8
travisfraughton Registered User Join Date: Jun 2008 Location: provo, ut Posts: 69	Re: 1970 c10 brakes problem Now that i think of it, i had this problem with my 77 like 6 years ago and it was a wheel cylinder. that sounds right but i will let ya know what happens this weekend.

11-13-2009, 09:54 PM	#10
sleepertruck72 Registered User Join Date: Nov 2007 Location: Turlock California 95380 Posts: 2,075	Re: 1970 c10 brakes problem A quick way to rule out the master cylinder is to undo your brake lines, and plug the m/c lines, your pedal should be rock hard. But if you are having to add fluid because the brake light is coming on, then possibly your wheel cylinder(s) is leaking, causing the pressure differential switch or low fluid sensor to activate the brake light. If you have air in your lines, that would cause the low brake pedal also. __________________ 72 C20 Longbed 05 1500 Z71

11-13-2009, 11:50 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: 1970 c10 brakes problem just look under the truck at the backside of the tires. If there's a leaking cylinder, you'll know it. Otherwise (and more likely IMO) it needs a master cylinder.



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