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"BRAKES" light

J

Jonathan

1/2 ton status
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Apr 14, 2001
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Location
Little Rock, Arkansas
\"BRAKES\" light

The "BRAKES" light on the dash of my 77 K5 comes on during hard braking. Does this mean I need to add brake fluid or need new brakes or what?
 
Re: \"BRAKES\" light

That light is activated by the switch in the combination valve(proportioning valve). It means that there is a pressure difference from front to rear that shouldn't be there. This is caused by the seals in your master cylinder going out.

You need to replace your master cylinder.

It can last a while longer, but why push it on something like brakes.

Lu95735.jpg
 
Re: \"BRAKES\" light

I just bought it friday and the guy I bought it from said he redid the brakes last (pads, shoes. ect.) and said it probably needs new drums in back. Could that be it? I think I can probably do without rear brakes for a while.

<P ID="edit"><FONT SIZE=-1>Edited by jonathan on 04/16/01 07:38 PM (server time).</FONT></P>
 
Re: \"BRAKES\" light

If it has new shoes, but the drums need replaced, that shouldn't cause your brake light to come on. I would take the drums off and see what kind of shape they are in.

Lu95735.jpg
 
Re: \"BRAKES\" light

I dont think master cylinders are too much. Less than 30 bucks.

"My blazer may be slow, but it goes faster at higher speeds"

Jim
 
Re: \"BRAKES\" light

They sell rebuild kits, but for the price of a rebuild one plus the time you save, the rebuilt ones are the way to go. Any auto parts store has them.

Lu95735.jpg
 
Re: \"BRAKES\" light

Could I get a used one at a junk yand or something? If so, what years and models used that specific master cylinder? I have a 62 C10 at my disposal but I really don't think that would work.
 
Re: \"BRAKES\" light

I wouldn't go the junk yard route. Brake fluid attracks water, and one sitting in the junk yard won't have typical use or maintenace and would likely not last long. The 62 C10 would be wrong. Any 1/2 ton chevy/gmc truck/blazer/jimmy from about 73 to 87?? should work. Maybe not that much of a range.

Lu95735.jpg
 
Re: \"BRAKES\" light

It could also be something besides a master cylinder. A leaking caliper or wheel cylinder could also cause the brake light to come on. My guess would be the wheel cylinders in the rear (if going bad and new shoes are put on sometimes the seals go real quick after becouse of being moved from where they were). Pull off the wheel and drum and check under the dust boot for fluid. If there is any on fluid on either side rebuild or replace both (rebuild kits are about $5 each)

'71 Blazer CST with alot of rust
 
Re: \"BRAKES\" light

He's right...even low fluid or air in the lines can cause this..all that is needed for the brake light to come on is a difference in pressure between the front and rear brakes, IE air in the system, leak, low fluid, etc.


Dorian
My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
 
Re: \"BRAKES\" light

I checked the fluid in the master cylinder and it was full to the top then drove around in a very hilly neighborhood this afternoon and gave the brakes a real good work out a the light didn't come on one single time. I don't know what the deal is. It will be a while before i get enough time to check the drums. But I know there is no bad leakage.
 
Re: \"BRAKES\" light

From what I could tell from the factory service manual, the proportioning valve SHOULD re-center itself when the problem is corrected and pressure is applied. Even when bleeding the brakes, if you leave the key in the "run" position, the light should come on, since there is a pressure "leak" in the system, which should move the proportioning valve trigger internally, activating the brake light. According to GM, if you lose the front or rear half of the brakes, the end that didn't fail should still work. But I've heard of that not happening and losing all braking. Don't think I'll test that one.

Dorian
My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
 
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