Spongy brake pedal but works fine

Tiny
CANNON1349
  • MEMBER
  • 1995 CHEVROLET 1500
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 349,000 MILES
Hi,

I did the front brakes on this truck, new rotors and wheel bearings, and the pedal is very spongy. With the engine off I can get a pretty stiff pedal, maybe with enough pressure it can be spongy but the real sponginess is with the engine on. The master cylinder/brake booster is very squeaky and also I can see the fluid inside the reservoir slush and bubble.

I've bled all four wheels in the proper sequence, and even bled the ABS unit looking thing. I'm almost convinced it's a weak master cylinder, it's original. Also the seals at the reservoir are seeping, just not pushing fluid out but they are looking a little wet.

And, when bleeding the brakes, as I crack the bleeder valve the brake fluid doesn't rush out, it just flows nice and smooth out of the tube.
Do you
have the same problem?
Yes
No
Friday, May 22nd, 2020 AT 5:02 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

It could be a master cylinder. When you bled the brakes, did you have a helper and what procedure did you follow? Also, this truck has rear drum brakes. Are you sure the brakes are properly adjusted? If they are out of adjustment, it will cause a spongy pedal.

Now, if the master cylinder reservoir is leaking at the rubber grommets, they need replaced. Also, can you explain what you mean by squeaky? One last thought, there shouldn't be bubbles in the brake fluid. I have a feeling there is air in the system at some point.

Let me know exactly what was done and how it was done.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Friday, May 22nd, 2020 AT 6:47 PM
Tiny
CANNON1349
  • MEMBER
The shoes in the drum are like new, still have numbers on the shoes but I didn't do those, at any point in time but seem okay in regards to drag and braking. I did have a helper hold down the pedal, crack the bleeder, close the bleeder, then release the pedal and pump 3 times. I did it in this order: RR, LR, RF, LF.

When pressing the brake pedal there's a squeak like a cabinet hinge that needs some wd-40, might be the arm in the booster. Who knows. It's not leaking per se, but is deteriorating and has a shiny/wet appearance.
Was this
answer
helpful?
Yes
No
Friday, May 22nd, 2020 AT 7:04 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Okay, the noise could even be where the brake pedal and push rod come together. That makes sense.

We have two things we can try. Since you have already manually bled the brakes (and it sounds like everything was done correctly), you can try pressure bleeding them or try to bleed the master cylinder. Since you are seeing bubbles in there, (if there is air in the system) that sounds like where it will be.

Here are directions for that. If this fails and there is no air in the system, chances are the master cylinder is bad.

______________________

1995 Chevy Truck C 1500 Truck 2WD V6-262 4.3L VIN Z TBI
Bleeding Master Cylinder
Vehicle Brakes and Traction Control Hydraulic System Brake Bleeding Service and Repair Procedures Master Cylinder Bleeding Without ABS System Bleeding Master Cylinder
BLEEDING MASTER CYLINDER
This procedure can be performed with master cylinder on or off vehicle.

1. Disconnect brake lines at master cylinder, if necessary.
2. Connect suitable lengths of brake lines to master cylinder and immerse other ends of lines in master cylinder reservoirs.
3. Apply master cylinder pushrod or brake pedal with full strokes until air bubbles have disappeared in reservoirs. It may require 20-30 applications to fully eliminate air bubbles.
4. Remove bleeding lines from master cylinder, then install master cylinder on vehicle, if necessary, and connect brake lines.

It is not necessary to bleed entire hydraulic system after replacing master cylinder, providing master cylinder has been bled and filled during installation.

_______________________________

Let me know if this helps.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Friday, May 22nd, 2020 AT 7:45 PM

Please login or register to post a reply.

Sponsored links