73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: itapippo on March 01, 2011, 09:56:55 am
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As I wrote in welcome section (wrong section), I have a brake problem. Sometimes the brake pedal goes down with a little load and the truck doesn't brake. I think may be a pressure loss in the master cylinder. Is it possible to find a rapair kit or I need a new master cylinder? Has anyone had the same problem?
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Check that there is no brake fluid leaks first. If the pedal slowly drops to the floor or almost to the floor with no fluid leaks than you probably need to replace or rebuild the Master Cylinder. I suggest replacing it if your parts place has one.
Check that there is no air trapped in the brake lines. This could be from a leaking line or the brake fluid was boiled inside the calipers or line when the brakes were over heated at one time.
If the pedal only travels a little bit(less than half way) make sure the rear brakes are adjusted correctly. Using up most of the pedal travel to engage the rear brakes will effect the front brake engagement.
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Are these power assisted brakes. You said 'sometimes' so along with what autorepr said, I'd check for a vacuum leak and also perhaps the diaphragm in the booster has a hole (if they are power assist). Also, is it an absolute loss of braking power or will it stop if you jam on the brake pedal?
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Yes, sometimes the pedal travels a little bit (less than half way) and the red brake lamp lights. If I jam on the pedal brake it stops properly. The brake fluid level is ok so I don't think there are leaks.
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The e-brake light goes on? I'm assuming you are referring to the rear brake lights.
If there are no fluid leaks than I would pull the master cylinder away from the power brake booster, careful with the lines, and open up the booster and check the diaphragm. If it looks good than I'd bleed the breaks to make sure there are no air pockets in the line, PITA I know :(, than I would certainly follow autorep suggestion and just get a new master cylinder.
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I'm referring to the dashboard red light "BRAKE"
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That light will come on for 2 reasons:
1- E-Brake is on
2- The proportioning valve has a switch in it which sits centered, and when 1 of the 2 "systems" (front/Rear) has more pressure than the other, it slides over and makes contact, and comes on.
I am betting you have an issue with either Air in the lines or you have an axle set with brakes that have a leak, causing the switch to slide over...
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there is a difference in brightness in the idiot light for the brakes, e brake versus other problem. Next time the light comes on, push down on the e brake pedal to see if it is brighter then. If not, it may be at its brightest signifying e brake. If it becomes brighter when ebrake is pushed down, the problem lies elsewhere.
There is a way to differentiate between a booster problem and a M/C problem...
http://forum.73-87chevytrucks.com/smforum/index.php?topic=5202.15 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=5202.15)
I read up on how to check to see if booster works. You depress the pedal several times with engine off. Then turn on the engine, the pedal should fall about an inch. Mine didnt and i replaced the booster. problem solved.
I tried this too:
Shut engine off, place gear selector in neutral and pump pedal until all reserve vacuum in booster is depleted. Press and lightly hold brake pedal: if pedal doesn't hold pressure and falls away master cylinder is leaking internally. If pedal maintains pressure, start engine in neutral and if pedal falls away slightly then holds firm proceed to Booster Test Procedure. If no pedal action is noticed the Power Booster or Vacuum Check Valve is at fault.
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my dads 87 r30 dually has an issue when you are stopping, the pedal will go 3/4 of the way to the floor, then if you let off almost all the way and press it again it has good pedal. now the brakes are run off of hydraulics from the power steering pump and I think that there is no vacuum power on these if i remember right. I dad thinks that it is the master cylinder, but it hasn't used and fluid and i just put all new back brake lines on it, so it isn't leaking. if you try to press the brakes when the engine is off you reilly have to step on them in order for them to brake and when you start the engine the pedal drops almost to the floor and grabs.
What is your guys thesis on this?? :P
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westernhauler, your problem is either air/moisture in the lines or master cylnder. Bleed thoroughly. Then see what you have. Look for signs of leaks along lines/wheelcylinders/calibers, etc...
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it hasn't used any fluid for over a month now, and we bled them fairly well I thought when we did the back lines and front pads.
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westernhauler, your problem is either air/moisture in the lines or master cylnder. Bleed thoroughly. Then see what you have. Look for signs of leaks along lines/wheelcylinders/calibers, etc...
I agree with Sgt
Also check to see that your rear brakes are not to worn and adjusted properly.