Soft Brakes (pedal to floor)

[mpierce9]

Hello - Been working on this a month and have exhausted all the options I have found in these forums. 1975 Chevy blazer disc front, drum rear.

My brake pedal travels to the floor before stopping. Slamming the brake pedal to the floor at about 30 MPH takes about 30-40 yards to come to a complete stop.

The pedal also returns slowly after being applied.


Done so far:
Overall System:

• I've been through two master cylinders (I've bench bleed both extensively)
• I want to clarify that I "pumped" each MC up to 150 times and saw zero air bubbles
• New brake booster
• Extended pedal link to booster to engage the booster immediately
• Resolved all leaks
• Bleed the entire system multiple times with the "One person pumps the pedal five times and holds it down, while the other person opens the bleeder" resulting in no visible air bubbles.
• Confirmed the Combination / Proportioning valve is working as expected (i.e. the light isn't on)

Front brakes:

• Replaced both calipers, discs & rotors
• Replaced both soft brake hoses, banjo bolts and washers

Rear brakes:

• Replaced both wheel cylinders
• Tightened both shoes to sit very close the drum

General notes

• Each bleeder has excellent fluid flow when bleeding
• With the engine powered off, the brake pedal returns quickly
• With the engine powered on, the brake pedal returns slower
• Feels like most of the braking is being done by the rear brakes
• This started with a bad wheel cylinder resulting in my proportioning valve becoming tripped
• On the MC I plugged the ports and attempted to press the brake pedal down this resulted in a completely firm & unmovable brake pedal (which I believe indicates the MC has been properly bleed and is working as expected.

Any help or direction would be greatly appreciated. Minus the hard lines, and Combination/Prop valve almost everything has been replaced.

[donut]

Seems to me that there's either more air or a leak. Loosing any fluid?
If using a helper, only push the brake pedal once, then while they're holding it down, crack the bleeder. Pushing the pedal 5 times may be aerating the fluid.

I usually do it myself, but I have a small bottle (brake bleeder kit) Tubing goes from the bleeder screw, under the fluid level in the small bottle. That way your pushing out air, and not taking the chance of introducing air in through the bleeder screw.

[hatzie]

Don't pump the pedal between opening the bleeders it aerates the fluid making air pockets that will not work out.
Push the pedal down with the bleeder open and then close the bleeder before the assistant lets off the pedal.

You can build one of these or buy one. I built one and bought a Master Cylinder cover from Motive Power. Makes one man bleed jobs a piece of cake.
http://www.amazon.com/Motive-Products-105-System-B...
Use a C-Clamp to hold the cover on, if you can find a place to put it, rather than the Rube Goldberg J-Hook and Chain arrangement that comes with the Motive Power cover.

[86c20]

sounds like the ford i had. try bleeding with it running

[hatzie]

One thing nobody usually mentions is to start with the longest tube run first and work your way to the shortest.
On the squares this is usually the Left Rear Wheel Cylinder and then RR then RF caliper then LF...

[sgr60]

I thought the procedure was push the pedal down, open the bleeder, close the bleeder, then release the pedal? That's how I always did it...

Wouldn't opening the bleeder with the pedal not depressed allow air in?

[mrolds88]

Originally Posted by sgr60

I thought the procedure was push the pedal down, open the bleeder, close the bleeder, then release the pedal? That's how I always did it

Thats the way I do it. Now if you have someone else there that is mechanically inclined, your helper can lightly hold their finger over the bleeder and it acts as a one way valve.

When you do push the pedal, do it slowly and to its full stroke.

[lahnen]

had similar issue with my suburban last year, one of my lines to the prop. valve had just a slight leak(bad flare job) had no visible air when I bled the system but wasn't getting a lot of pressure when I opened the bleeders up.

[mpierce9]

Is there such a thing as a pressure gauge that screws into the bleed valve spot?

[enaberif]

When was the last time the master cylinder was changed out? My pedal goes right to the floor and I know for fact my master cylinder is to blame.

[mpierce9]

MC has been changed twice in the last 30 days. MC testest to be working well.

[hatzie]

Originally Posted by sgr60

I thought the procedure was push the pedal down, open the bleeder, close the bleeder, then release the pedal? That's how I always did it...

Wouldn't opening the bleeder with the pedal not depressed allow air in?

I should've added "Only open the bleeder after you tell your assistant to push the pedal down." I mistakenly figured that was self explanatory.

[donut]

Not self explanatory, but I did mention it. However, I didn't mention to close it again before you release the pedal...
Of course the OP didn't ask for a step by step procedure.

[spspspspoon]

tube on bleeder
"Quick Bleed" between the 2 hoses
usually seen on race bikes
it IS a 1 way check valve but IS a bleeder valve
also u can do like we do in VW
put valve stem like a tire(one with threads and O rings)
and place it In the top
then pressurize

[WyattTX]

Does the pedal feel harder with the engine off?

[WyattTX]

I don't know if a GM booster has an adjustable push rod, but this would be worth looking into: https://www.google.com/amp/s/techtal...%3fhs_amp=true

If the booster push rod is too long or too short (very possible in today's low standards of manufacturing) you'll never get get a hard pedal with the engine running. If you have no air in your system, and still have a soft pedal, this is a likely culprit.

[hatzie]

Originally Posted by WyattTX

I don't know if a GM booster has an adjustable push rod, but this would be worth looking into: https://www.google.com/amp/s/techtal...%3fhs_amp=true

If the booster push rod is too long or too short (very possible in today's low standards of manufacturing) you'll never get get a hard pedal with the engine running. If you have no air in your system, and still have a soft pedal, this is a likely culprit.

Chinese garbage parts that don't meet any reasonable spec poisoning the supply chain...

If you want a real exercise in futility... Try buying ball joints and tie rod ends that last more than 5,000-10,000 miles.
Wheel bearings are another fun excursion into pulling out gobs of your hair.

[kwmech]

Still bleeding the brakes after 5 years..??? damn

[WyattTX]

Oops, did not realize I posted in a zombie thread. I hope OP got his brakes to work.

[hatzie]

Originally Posted by WyattTX

Oops, did not realize I posted in a zombie thread. I hope OP got his brakes to work.

You posted useful relevant information on the thread subject. Don't feel too bad.