1968 C10 4 wheel drum brakes are spongey - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HeavyHauler · 04-22-2019, 12:34 AM

The manual four wheel drum brakes on my 1968 C10 were very mushy and would barely stop the truck. I noticed there was alot of what looked like stain from brake fluid on the old really rusty mastercylinder so I decided to replace that for starters. It was rusty inside as well I noticed after I took it off.

I purchased a new mastercylinder and now the brakes are hard but barely stop the truck. What could be the issue with the brakes barely wanting to stop the truck.

saxart · 04-22-2019, 06:27 AM

Two things come to mind:
1) Rusted wheel cylinders (internal rust)
2) Brakes hoses that have collapsed inside
3) Old water-logged brake fluid

I guess that's three things....

**special-K** · 04-22-2019, 06:52 AM

What you have is a K/10, not a C/10. The rusty inside the master cylinder is not good. That means the entire system has moisture affecting it and most likely all is as bad as the m/c. Brake fluid needs to be pure and I'm sure you have particles from the rust contaminating the fluid. The particles can block orifices. Also, if there is actual water in the system you will get that hard and high pedal with weak brakes

HeavyHauler · 04-22-2019, 11:12 AM

Quote:

Originally Posted by special-K

What you have is a K/10, not a C/10. The rusty inside the master cylinder is not good. That means the entire system has moisture affecting it and most likely all is as bad as the m/c. Brake fluid needs to be pure and I'm sure you have particles from the rust contaminating the fluid. The particles can block orifices. Also, if there is actual water in the system you will get that hard and high pedal with weak brakes

My truck does not have 4 wheel drive and is a C10.

**Jason Banks** · 04-22-2019, 07:26 PM

First thing I would replace is the rear brake hose, that runs from the frame to the rear end. That alone made a world of difference on my truck.

**Steeveedee** · 04-22-2019, 10:47 PM

When you replaced the master cylinder, did you do a complete brake system flush? Or just a bench bleed and then replace? It is possible to replace the master cylinder and not bleed the rest of the brakes- not a procedure that I recommend. I worked for a guy back in the '70s that did that.

04-22-2019, 12:34 AM	#1
HeavyHauler Registered User Join Date: Nov 2011 Location: USA Posts: 409	1968 C10 4 wheel drum brakes are spongey The manual four wheel drum brakes on my 1968 C10 were very mushy and would barely stop the truck. I noticed there was alot of what looked like stain from brake fluid on the old really rusty mastercylinder so I decided to replace that for starters. It was rusty inside as well I noticed after I took it off. I purchased a new mastercylinder and now the brakes are hard but barely stop the truck. What could be the issue with the brakes barely wanting to stop the truck.

04-22-2019, 06:27 AM	#2
saxart Registered User Join Date: Aug 2012 Location: St. Croix River Valley, WI Posts: 795	Re: 1968 C10 4 wheel drum brakes are spongey Two things come to mind: 1) Rusted wheel cylinders (internal rust) 2) Brakes hoses that have collapsed inside 3) Old water-logged brake fluid I guess that's three things.... __________________ Meet "Old Roy": http://67-72chevytrucks.com/vboard/s...d.php?t=707801

04-22-2019, 06:52 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 1968 C10 4 wheel drum brakes are spongey What you have is a K/10, not a C/10. The rusty inside the master cylinder is not good. That means the entire system has moisture affecting it and most likely all is as bad as the m/c. Brake fluid needs to be pure and I'm sure you have particles from the rust contaminating the fluid. The particles can block orifices. Also, if there is actual water in the system you will get that hard and high pedal with weak brakes __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

04-22-2019, 07:26 PM	#5
Jason Banks Senior Member Join Date: Dec 1999 Location: TX Posts: 1,623	Re: 1968 C10 4 wheel drum brakes are spongey First thing I would replace is the rear brake hose, that runs from the frame to the rear end. That alone made a world of difference on my truck.

04-22-2019, 10:47 PM	#6
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,677	Re: 1968 C10 4 wheel drum brakes are spongey When you replaced the master cylinder, did you do a complete brake system flush? Or just a bench bleed and then replace? It is possible to replace the master cylinder and not bleed the rest of the brakes- not a procedure that I recommend. I worked for a guy back in the '70s that did that. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

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