Brake warning light after brake sys flush - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Austin C10 · 01-03-2006, 01:40 PM

Immediately after purchasing my 1972 LWB Cheyenne, I had it in Firestone getting 2 matching rear Firehawks. I also had them drain and "flush" the brake system. About a week later, I had a pretty hard stop coming off the highway into a traffic jam. Since then, my brake warning light on my dashboard won't go off. Additionally, the brake pedal needs to be pressed harder to keep the truck stopped at idle.

Indications point to unequal pressure between the fronts and rears. Other than returning to Firestone, what are the first steps that I need to take to re-equalize? What else could be wrong?

Thanks!

badpeanut · 01-03-2006, 02:48 PM

When I had this problem with mine, I had to bleed the brakes some more.

Sweet72 · 01-03-2006, 06:59 PM

Check for leaks first and then bleed the system. If yours is like my '72, there's a button at the front of the proportioning valve that must be depressed and held during bleeding. Remove the rubber boot, and you'll have to be creative to hold the button depressed unless you have a extra set of hands. This should reset the switch.

jhow66 · 01-03-2006, 10:49 PM

You need a new master cylinder. You blew the seal in one side of your master cylinder. That is what the light is for to tell you that you only have 2 wheels doing the braking (front or rear).

**truckdude239** · 01-03-2006, 11:07 PM

the light tells you that the prop vavle has been triped closing off the front or the rear brakes easly done when bleeding brakes now how to reset to the prop vavle don't ask me lol

Brento72 · 01-04-2006, 01:37 AM

Proportioning valve switched internally. There is a small button covered by a rubber boot at the front of the proportioning valve. When a loss of or diffferential in line pressure is detected between the lines coming from the proportioning valve, the valve moves to block fluid flow to the system with the problem. At the same time the wire going to the valve connects to a switch that is tripped, completing the ground circuit of your BRAKE light. DO NOT ASSUME RESETTING WILL FIX YOUR PROBLEM. You need to examine the master cylinder for leaks, lines for leaks, the calipers and wheel cylinders for leaks, and check all bleeder screws for, once again, leaks. If you have no leaks bleed the system with the valve button depressed. You can use a strong zip tie and a hunk of something to hold the valve in and bleed the system. Bleed it thoroughly starting with the master cylinder. I usually run 1 1/2 quarts through a system when bleeding. Do not re-use any old fluid. It will seem to take forever but if it was flushed poorly this should remove any air just in case you got a mechanic that didn't have it in him to do it right.

01-03-2006, 01:40 PM	#1
Austin C10 1972 C10 Cheyenne LWB Join Date: Dec 2005 Location: Redwood City, CA Posts: 41	Brake warning light after brake sys flush Immediately after purchasing my 1972 LWB Cheyenne, I had it in Firestone getting 2 matching rear Firehawks. I also had them drain and "flush" the brake system. About a week later, I had a pretty hard stop coming off the highway into a traffic jam. Since then, my brake warning light on my dashboard won't go off. Additionally, the brake pedal needs to be pressed harder to keep the truck stopped at idle. Indications point to unequal pressure between the fronts and rears. Other than returning to Firestone, what are the first steps that I need to take to re-equalize? What else could be wrong? Thanks!

01-03-2006, 02:48 PM	#2
badpeanut Not a bad nut after all.. Join Date: Dec 2000 Location: ND Posts: 1,756	Re: Brake warning light after brake sys flush When I had this problem with mine, I had to bleed the brakes some more. __________________ '05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer

01-03-2006, 06:59 PM	#3
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Re: Brake warning light after brake sys flush Check for leaks first and then bleed the system. If yours is like my '72, there's a button at the front of the proportioning valve that must be depressed and held during bleeding. Remove the rubber boot, and you'll have to be creative to hold the button depressed unless you have a extra set of hands. This should reset the switch. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

01-03-2006, 10:49 PM	#4
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Brake warning light after brake sys flush You need a new master cylinder. You blew the seal in one side of your master cylinder. That is what the light is for to tell you that you only have 2 wheels doing the braking (front or rear). __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

01-03-2006, 11:07 PM	#5
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,230	Re: Brake warning light after brake sys flush the light tells you that the prop vavle has been triped closing off the front or the rear brakes easly done when bleeding brakes now how to reset to the prop vavle don't ask me lol __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

01-04-2006, 01:37 AM	#6
Brento72 resU deretsigeR Join Date: Dec 2005 Location: Belleville Illinois Posts: 27	Re: Brake warning light after brake sys flush Proportioning valve switched internally. There is a small button covered by a rubber boot at the front of the proportioning valve. When a loss of or diffferential in line pressure is detected between the lines coming from the proportioning valve, the valve moves to block fluid flow to the system with the problem. At the same time the wire going to the valve connects to a switch that is tripped, completing the ground circuit of your BRAKE light. DO NOT ASSUME RESETTING WILL FIX YOUR PROBLEM. You need to examine the master cylinder for leaks, lines for leaks, the calipers and wheel cylinders for leaks, and check all bleeder screws for, once again, leaks. If you have no leaks bleed the system with the valve button depressed. You can use a strong zip tie and a hunk of something to hold the valve in and bleed the system. Bleed it thoroughly starting with the master cylinder. I usually run 1 1/2 quarts through a system when bleeding. Do not re-use any old fluid. It will seem to take forever but if it was flushed poorly this should remove any air just in case you got a mechanic that didn't have it in him to do it right.



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