Spongey Brakes? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tink · 09-26-2003, 06:52 AM

The brakes on my 76 K5 are kind of spongey.... At first you get good pedal feel and then as you sit on the brakes the pedal goes to the floor. You have to pump it sometimes to keep it from rolling. The other day, I stepped down on it a little harder cause I was on a hill and I heard a pop and the brake light came on. Everything looks to be ok and the fluid is full (although a really dark color). The truck sat for 2 years before I bought it and it looks like at one time there was a leak between the brake booster and the master cylinder. What all should I check and replace?

**N2TRUX** · 09-26-2003, 08:44 AM

It sounds like you are ready for a new master cylinder. If there are no leaks anywhere else, the fluid has to be displacing somewhere to loose pedal pressure. That indicates the master cylinder has "blown" internally, so the fluid pressure is escaping past the piston seals.

I would consider replacing (or rebuilding) it, and flushing the entire system...

*Zilverado* · 09-26-2003, 04:36 PM

Quote:

Originally posted by N2TRUX
It sounds like you are ready for a new master cylinder. If there are no leaks anywhere else, the fluid has to be displacing somewhere to loose pedal pressure. That indicates the master cylinder has "blown" internally, so the fluid pressure is escaping past the piston seals.

I would consider replacing (or rebuilding) it, and flushing the entire system...

Bingo! I agree - that's exactly what mine was doing a while back. I actually noticed it wahile I was pulling a trailer

.

Especially if there are no other obvious leaks, I'd put money down on the MC.

ElGracho · 09-28-2003, 12:57 AM

I wouldn't just put money down on it being the Master Cylinder, I would replace it and look for further problems. Brakes aren't a place to try and save a buck. Replace the master cylinder, check your calipers and rear wheel cylinders for leaks and a do a go flush of the whole system. (Bleed until you think you are done, then start over)

Tink · 09-29-2003, 06:44 AM

There are no obvious leaks anywhere but on the frame below the master cylinder and brake booster. The pads on the front are real thin too.

I ordered a master cylinder, calipers, pads and hoses and will be picking them up today. Hopefully this will take care of it... she is a lot of truck to stop!

Tink · 10-03-2003, 06:58 AM

The brakes are loads better now. That old Master Cylinder had sludge in the bottom and the calipers had like those insect cocoon things in them!!

Anyhow, I bled the brakes to death and she stops much better but the brake light is still on. Any way I can get the light to go off?

**Captkaos** · 10-03-2003, 03:02 PM

check the switch under the dash at the brake pedal. You might need to moved it so it will contact the pedal tab.

Hard_Core_Hick · 10-03-2003, 04:29 PM

if havent allready check the rear wheel cylenders too just to be sure.

apstguy · 10-05-2003, 03:42 AM

There might be a switch on the proportioning vavle that can set off the light. I've never had a problem with it but others have. How about you guys chime in and tell him how to fix it?

09-26-2003, 06:52 AM	#1
Tink Registered User Join Date: May 2002 Location: VA Posts: 1,337	Spongey Brakes? The brakes on my 76 K5 are kind of spongey.... At first you get good pedal feel and then as you sit on the brakes the pedal goes to the floor. You have to pump it sometimes to keep it from rolling. The other day, I stepped down on it a little harder cause I was on a hill and I heard a pop and the brake light came on. Everything looks to be ok and the fluid is full (although a really dark color). The truck sat for 2 years before I bought it and it looks like at one time there was a leak between the brake booster and the master cylinder. What all should I check and replace? __________________ 69 Chevy C10 88 Sierra 02 2500 Suburban And too many S10s to list!

09-26-2003, 08:44 AM	#2
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	It sounds like you are ready for a new master cylinder. If there are no leaks anywhere else, the fluid has to be displacing somewhere to loose pedal pressure. That indicates the master cylinder has "blown" internally, so the fluid pressure is escaping past the piston seals. I would consider replacing (or rebuilding) it, and flushing the entire system... __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

09-28-2003, 12:57 AM	#4
ElGracho Gentleman Jim Driver Join Date: Nov 2002 Location: Poulsbo, WA Posts: 1,553	I wouldn't just put money down on it being the Master Cylinder, I would replace it and look for further problems. Brakes aren't a place to try and save a buck. Replace the master cylinder, check your calipers and rear wheel cylinders for leaks and a do a go flush of the whole system. (Bleed until you think you are done, then start over) __________________ Joe '75 GMC Gentleman Jim '84 Chev C10 Short Wide - Super duper plain (manual steering, manual brakes, no dome light, no cig lighter) '85 Chev C10 Short Wide - Super plain Vortec 4.8 4L60E trans also: '81 K30, '83 C30 Crew Dually, '84 M1028 CUCV, '85 M1009 CUCV, another '85 C10 SWB, '89 R3500 Flatbed

09-29-2003, 06:44 AM	#5
Tink Registered User Join Date: May 2002 Location: VA Posts: 1,337	There are no obvious leaks anywhere but on the frame below the master cylinder and brake booster. The pads on the front are real thin too. I ordered a master cylinder, calipers, pads and hoses and will be picking them up today. Hopefully this will take care of it... she is a lot of truck to stop! __________________ 69 Chevy C10 88 Sierra 02 2500 Suburban And too many S10s to list!

10-03-2003, 06:58 AM	#6
Tink Registered User Join Date: May 2002 Location: VA Posts: 1,337	The brakes are loads better now. That old Master Cylinder had sludge in the bottom and the calipers had like those insect cocoon things in them!! Anyhow, I bled the brakes to death and she stops much better but the brake light is still on. Any way I can get the light to go off? __________________ 69 Chevy C10 88 Sierra 02 2500 Suburban And too many S10s to list!

10-03-2003, 03:02 PM	#7
Captkaos www.73-87chevytrucks.com Join Date: Dec 1999 Location: Birmingham, AL Posts: 6,935	check the switch under the dash at the brake pedal. You might need to moved it so it will contact the pedal tab. __________________ Chris Lucas 1973 Chevy C-10 1978 GMC Jimmy (2WD) - SOLD 1987 R10 twin turbo LS 1991 R3500 SRW CrewCab 1985 K5 diesel swapped project 1989 K5 2WD conversion w/ Vette susp Project Captkaos Customs 73-87chevytrucks.com

10-03-2003, 04:29 PM	#8
Hard_Core_Hick Registered User Join Date: Apr 2003 Location: Canada Posts: 133	if havent allready check the rear wheel cylenders too just to be sure. __________________ I need a 454 4 barrel and dad wont let me get one

10-05-2003, 03:42 AM	#9
apstguy LED King Join Date: Jan 2003 Location: Sacramento, CA Posts: 2,087	There might be a switch on the proportioning vavle that can set off the light. I've never had a problem with it but others have. How about you guys chime in and tell him how to fix it? __________________ Tyler 1985 C10 305 w/ Bowtie OD TH700R4 3.42 LSD 202,000 miles 2006 Ford Focus ZX3 5-speed Stick 2016 Chevy Spark EV Gone: 2002.5 VW GTI 24v VR6 Gone: 2008 VW R32



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.