having trouble bleeding brakes

[edcalli]

my friend has a 92 chevy 1500 and we tried bleeding brakes but the peddle doensnt get any better we were told there is a button on the master cylinder that has to be pressed in in order to bleed the brakes.it is a new master cylinder and we bench bled it before putting it on and weve bled all 4 wheels.and still no peddle any suggestions were out of ideas

Topic

[ChrisR1987]

There is a button on some systems that resets the proportioning valve you have to have it pressed in while bleeding the brakes, im not sure if that applies to your particular year truck or not. Assuming you do have a new MC. My next step would be verify that your power booster is good and that you dont have any leaks in the lines, calipers, or rear wheel cylinders, you may want to try adjusting your back brakes as well as this can affect brake pedal feel. Usually the proportioning valve is just under the MC but it can be in other places too such as just over the rear axle or somewhere on the frame. Best advice I can give is follow your brake lines from the MC out if you dont see it under the MC

[djhughes]

Either your rear brakes need to be adjusted or you need to hold the button on the combination valve. The combination valve is the proportioning valve, metering valve, and brake warning light switch all in one. The metering valve is the one that needs to be held open, but if you have someone pumping up the brakes for you there should be enough pressure to open it without using the button on the combination valve. I would say you have a leak somewhere or your rear brakes are out of adjustment.

[college man]

check that the rear drums are adjusted correctly.
does fluid come out when bled?

[Daniel]

Some times breaks just like to be a pain. That button you mentioned is called a combination valve. Out of curiosity, why are you bleeding the breaks?

[EricTheCarGuy]

As pointed out you may need to seat the ‘button’ on the combination valve however you don’t push it but hold it up. There’s actually a special tool for this that is very inexpensive. You may be able to purchase it at your auto parts supplier. Also the rear brake adjustment is important for brake pedal feel so be sure they’re adjusted correctly. Lastly you might have a problem with the master cylinder. If the master cylinder is leaking internally it won’t provide enough pressure to the wheels to remove any trapped air.

[Author]

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