Soft brake pedel

Dom2door · Dec 4, 2021

I have a 1999 two door Tahoe
I am sure this has been talked about, read all I could find on line but no real fixes.

I did replace all of the flex lines , calipers, pads, shoes, master cylinder and rear cylinders.

I bleed the system every witch way , presser, two person, pressure and two person, and reverse bleeding by pushing fluid up to the master cylinder. I also did bleed the ABS system via automatic bleeding.
I tracked it down to my calipers. I pinched off the flex lines an I get a good hard pedal this tells me that there is no air in the lines. I don't know what would cause this in my front calipers and the back could be a little out of adjustment.
Pedal gets better with just the back flex line pinched. Pinching the passenger front has more effect on the pedal then the driver side front. Could it be bad calipers?
Thanks for any help, Dom

Frank Enstein · Dec 4, 2021

Make sure the calipers float properly.

Remove the pads and bolt the calipers without them.

See if you can push the calipers in and out on the slides with 1 finger. You may need to push FIRMLY but with one finger.

If you cant free up the caliper slides and lube with brake lubricant.

Check the drum backing plates for grooves where the shoes contact the backing plate.

Smooth and lubricate the contact points.

Adjust the shoes until they JUST touch the drums. Apply the brakes and the parking brake a few times and re-adjust until there is no difference in the sound before and after applying the brakes.

Test drive and bed in the pads per the manufacturer's instructions.

If there are no bedding instructions make several back-to-back medium stops from 40 mph to 10 mph until the brakes start to smell and the brakes change how they feel.

Medium means stopping at a yellow light because there is a cop across the street.
NOT both feet on the pedal bending the steering wheel back because a kid ran out in front of you chasing a ball.

They will either stop really really well or stop really really bad. When the feel changes you have the pads and rotors up to temperature.

Drive for a half hour trying to let the brakes cool. Do not set the parking brake or hold the vehicle with the brakes if you can help it.

Repeat the bedding procedure again tomorrow.

Generally this will help your soft pedal issues.

Dom2door · Dec 4, 2021

Frank Enstein said:
Make sure the calipers float properly.

Remove the pads and bolt the calipers without them.

See if you can push the calipers in and out on the slides with 1 finger. You may need to push FIRMLY but with one finger.

If you cant free up the caliper slides and lube with brake lubricant.

Check the drum backing plates for grooves where the shoes contact the backing plate.

Smooth and lubricate the contact points.

Adjust the shoes until they JUST touch the drums. Apply the brakes and the parking brake a few times and re-adjust until there is no difference in the sound before and after applying the brakes.

Test drive and bed in the pads per the manufacturer's instructions.

If there are no bedding instructions make several back-to-back medium stops from 40 mph to 10 mph until the brakes start to smell and the brakes change how they feel.

Medium means stopping at a yellow light because there is a cop across the street.
NOT both feet on the pedal bending the steering wheel back because a kid ran out in front of you chasing a ball.

They will either stop really really well or stop really really bad. When the feel changes you have the pads and rotors up to temperature.

Drive for a half hour trying to let the brakes cool. Do not set the parking brake or hold the vehicle with the brakes if you can help it.

Repeat the bedding procedure again tomorrow.

Generally this will help your soft pedal issues.

I did replace the drums at the same time I replaced everything else.
Calipers seem to move feely. I preyed the piston in and the hole caliper moved easily.
I can't say that I bad the pads in correctly.
Would not bedding the pads make the pedal low? Making a gap between the pads and rotors.
The truck is on jack stands.

Erik the Awful · Dec 4, 2021

No, bedding the pads wrong will have a good pedal, but the brakes just won't slow your truck fast enough.

x2 on the shoe adjustment. If the star wheel is adjusted in too far you have to pump the brakes out further for the shoes to meet the drums, which makes the pedal low.

The fact you can pinch the brake hoses and get better brakes says you don't have them fully bled. You do have the bleeder screws at the tops and not the bottoms of the calipers, right?

Schurkey · Dec 4, 2021

Erik the Awful said:
The fact you can pinch the brake hoses and get better brakes says you don't have them fully bled.

Not at all. Even with a fully-bled, zero-air system, pinching the hoses--front or rear, or all of them--eliminates the fluid flow that would push the pistons out and move the pads/shoes.

No fluid flow = high, hard pedal.

If you pinch the hoses and don't have a high, hard pedal, you've got air in the system between the pinch and the master cylinder (including the master cylinder.)

Erik the Awful said:
You do have the bleeder screws at the tops and not the bottoms of the calipers, right?

Beat me to it.

Dom2door said:
I also did bleed the ABS system via automatic bleeding.

Did you bleed the system AFTER bleeding the ABS?

Perhaps a moderator will move this thread out of "Engine Performance" and into "Axles and Brakes".

Dom2door · Dec 5, 2021

Yes the bleeder screws are on top , yes I bleed after doing the ABS system.
I just installed NBS master cylinder and the pedal only goes down half way, better then to the floor and stops ok , I did not try to stop hard, setting in the pads.
The dalema for this problem still has no answer.

I have a 1993 k1500 Blazer and the pedal has a way better feel being closer to the top. The blazer has a different ABS system and bleeds different.

Rob7233 · Dec 5, 2021

Did you actually bench bleed the master and follow the proper procedure?

Have you confirmed the booster is operating properly? I had a similar low pedal issue and lived with it for a year until I decided to replace the booster. That fixed it.

Schurkey · Dec 5, 2021

Dom2door said:
I just installed NBS master cylinder

That was almost certainly a mistake.

If you have low-drag front calipers--brake option JB5 or JB6--that is a completely WRONG master cylinder. It does not have the third high-volume/low pressure fluid chamber needed by the low-drag calipers.

Dom2door said:
and the pedal only goes down half way, better then to the floor and stops ok ,

As said...verify that there's no air in the master cylinder. Most folks think they're doing a "good" job bench-bleeding, and they often leave air in the master. Because the master cylinder is often tipped "up" at the front when installed on the vehicle, that air bubble is trapped. No amount of bleeding will remove it. Lifting the rear of the vehicle and LIGHTLY pumping the brake pedal, or disconnecting the master from the booster and pushing the front end "down" then "tickling" the primary piston with a Philips screwdriver or wood dowel allows the trapped air to bubble into the reservoir.

If all else fails, re-bleed the ABS.

Dom2door said:
I did not try to stop hard, setting in the pads.

Bedding the pads requires hard "slows" (not "stops") so that the rotors/drums keep turning which allows the fins molded into them to pump cooling air.

I start with firm 40-to-20 mph "slows", increasing both speeds as the process goes on. I generally end up with very firm 70+ mph slows to 40-ish mph, with several miles in between.

Dom2door said:
The dalema for this problem still has no answer.

Sure it does. You just haven't found it yet.

Dom2door · Dec 5, 2021

Yes I benched bleed the master by following the instructions, as I was doing it I tilted it every witch way tapping it.
I read all of what I found on line and found no real answers.
I have the tool to holed in the pin on the perportioning valve when bleeding, I tried every thing I when through 1.5 gal of brake fluid, I swap out an ABS system from a junk yard with the same results no matter what I did.
I think the problem is in the calipers after pinching the flex lines.
When I get more funds I will change them with high end ones. For now the NBS gets the pedal higher.

rtaylor93 · Dec 6, 2021

How did this issue come about? Been there for a while or did it happen after you replaced all those parts? From my most recent experience with a super soft pedal on my truck, make sure those rear brakes are adjusted really well. Put some good drag on them. Helped resolve my headache.

Maybe some of my thread can help you?

Brake bleeding issues

97 K1500 W/Kelsey-Hayes ABS- A few days ago the brake pedal went extra low and on came the brake light. Still able to stop but extremely low pedal. Fluid level was perfect. Bled brakes starting at right rear using 2 person method. No change. Replaced master cylinder - bench bled and bled...

www.gmt400.com

Soft brake pedel

Dom2door

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Frank Enstein

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Dom2door

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Erik the Awful

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Schurkey

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Rob7233

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Brake bleeding issues

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