Soft brake pedal

[sitdusa]

98 Chevy Silverado K1500 5.7L Vortec, 177K.

I have a soft brake pedal and I noticed it about 45K ago when I changed the brakes on the front. I replaced the calipers, rotors, pads, and adjusted the back brakes. While the engine is off I have a firm pedal, but when I start the engine the pedal travels almost to the floor, I have bled the brakes, changed the Master Cylinder.

Any and all help is greatly appreciated!

Steve

[GOLIATHGMC]

Assuming that nothing is leaking anywhere, there are two possibilities I can see. First one is about the bleed - After you did the work up front and bled the system, did you bleed all 4 corners or just the front? It is possible that ONLY bleeding the front might not be enough. Also, (in case you are unfamiliar) Bleed the corners in this order: RR, LR, RF, LF (furthest to closest to the master).
It is also possible that the replacement Master was bad, especially if it was a rebuilt from a store like Strauss or Auto Zone. Sometimes they get the bottom of the barrel in terms of rebuilders. You might also check the 3 soft brake lines in the system for bulges or damage.
Good luck, hope this helps.
George
REBEL Motorsports

[2000CAYukon]

How far does your parking brake pedal move when you set the parking brake? If it goes to the floor and still not hold the truck, the rears are probably not adjusted properly.

You should be able to feel the brakes drag when you turn the wheel by hand.

//2000CAYukon

[wedser]

after you have checked everything in the first post (espically where you got the master cylinder from and the bleed procedure/order) and that is all good you should replace the check valve that comes off the power booster, and goes to the intake manifold. I had to go to the dealer to get it and it took about 2-3 days but the normal autoparts stores did not carry the same check valve. i have a '97 silverado so it should be pretty close, and i had a slightly soft pedal but that check valve helped a lot.

Sam

[offroadjoe]

Hey guys i got a 1988 sierra and i have the same problem but the pedal is soft even with the car off.. i have to pump it in order to stop alright... i got a master cylinder at a scarp yard, worked for a month than rigth back to pumping it than i bought a brand new one at c-tire.. but no same crap i bleed them twice after that same thing... i bought it about a year ago so i never really touched the front brakes but theres no leaks what do you think the problem is front brakes? i'm gunna go get them checked out later on this week i'm going to kill myslef lol ...

[Mr. Smith]

Originally Posted by sitdusa

98 Chevy Silverado K1500 5.7L Vortec, 177K.

I have a soft brake pedal and I noticed it about 45K ago when I changed the brakes on the front. I replaced the calipers, rotors, pads, and adjusted the back brakes. While the engine is off I have a firm pedal, but when I start the engine the pedal travels almost to the floor, I have bled the brakes, changed the Master Cylinder.

Any and all help is greatly appreciated!

Steve

I have found it you put a reman on (usually aluminum) they are junk in my opinion. I have noticed they bore and sleeve them. I guess the whole bore flexes causing internal bypassing of fluid.

The new cast iron units from Advance or Autozone work the best and with proper bleeding you can get a solid pedal. I have done my 97 and my buddies 91 with excellent results.

[Bob B]

If you clamp carefully the flex hose in the rear lines, then test the pedal, This will eliminate the rears from the test and you might be able to decide which wheels are acting up. You can then do it to each front one at a time to eliminate them or not.
BTW the rears are self adjusting, but only adjust when applied while backing. So if you back up then pull it into drive, they aren't adjusting. If the parking brake takes a lot of motion to hold, this might be the problem.
Also spongy pedal means needs bleeding. Low but hard pedal menas need adjusting, I don't know if ABS affects those statements though.
Bob B

[jlwalsh]

I had the same problems with a 98 chevy 4x4 1/2 ton. After a couple of master cylinders and a whole lot of bleeding still spongy and pedal went almost to the floor but still have brakes. The rear would have air in the lines almost instantly after bleeding, mine is a front disk and rear drum system, I replaced the rear drum cylinders even thought there was no signs of leaking, it is possible for them not to leak and suck air when returning to a normal position. They cost about $20 for both and 2 bolts holding them on, it was worth the money to eliminate them and to my surprise it worked and have full pedal again. On a disk/drum system the drums determine your pedal distance before braking, as long as they are adjusted correctly, if adjusters are on the bottom they get set by backing up, if there on top they get adjusted by the emergency brake. Do not put anti seeze on the threads cause this can cause them to stick. On a completely drum system any cylinder can cause the same problem.

[777stickman]

Welcome to AF. Very interesting concept. Even though this thread is 10 yrs old, hopefully it will benefit others.

[mrbeenjamin]

1995 Chevy PU 5.7 kelso-hayes antilock brake 2 wd. low brake pedal. new master, slaves, ft calipers. Bleed 1 qt fluid through no air. still low. 3/4 down pedal stops solid but too low. adjusted shoes and new drums. i dislike upper adjuster system

[j cAT]

the drums wear out being now too big and do not match the shoes so only a small portion of the shoe contacts the drum .

[Schurkey]

Originally Posted by mrbeenjamin

1995 Chevy PU 5.7 kelso-hayes antilock brake 2 wd. low brake pedal. new master, slaves, ft calipers. Bleed 1 qt fluid through no air. still low. 3/4 down pedal stops solid but too low. adjusted shoes and new drums. i dislike upper adjuster system

1. Did you bleed the anti-lock mechanism? Mine has one or two bleeder screws on the anti-lock itself. Had crappy, low pedal until I moved a big air bubble out of the ABS.

2. Yes, faulty wheel cylinders can allow air to enter without allowing fluid to escape.

3. Be sure all the air is out of the master cylinder. This often means raising the rear of the vehicle so that the master cylinder is tipped slightly down in front--then the air bubble will escape through the compensating ports in the master cylinder back into the reservoir.

4. I got rid of the original rear brakes including the upper adjuster mechanism on my '88 K1500. By installing a 14-bolt, semi-floating (9.5 inch differential) I got a stronger rear axle assembly and larger rear brakes that use the self-energizing style brakes which have the adjuster on the bottom. The axle is a bolt-in except for needing a "conversion" rear U-joint. I got mine from a light-duty 3/4 ton pickup that had the same gear ratio and 6-bolt hubs as my truck. I needed new U-bolts also--I think this is fairly common. The original U-bolts on the 14-bolt were too corroded. Be sure to retain the emergency brake cables that attach to the "new" axle, along with the matching U-bolt bottom plates. The U-bolts, brake cables and plates are different on the 14-bolt axle than the 10-bolt original.

[j cAT]

Originally Posted by mrbeenjamin

1995 Chevy PU 5.7 kelso-hayes antilock brake 2 wd. low brake pedal. new master, slaves, ft calipers. Bleed 1 qt fluid through no air. still low. 3/4 down pedal stops solid but too low. adjusted shoes and new drums. i dislike upper adjuster system

I would check that the drums are the proper size. many after market drums have problems .see that the shoes are contacting the drum properly this is revealed by observing the wear on the shoes. can also be the shoes messed up.