Intermittent brake fade (1 Viewer)

[deaddrift]

Just lately sometimes my brake pedal is soft. It travels further and I experience less stopping power. Tis only happens sometimes and is unrelated to driving conditions, i.e., it's not boiling fluid because it can happen the first time I apply the brakes in the morning.

If I release the pedal and then reapply foot pressure, it becomes firm and the truck stops normally. (Most of the time it works normally anyway.) The pedal does not sink while applying steady pressure, for instance at a stop light. There is no effect on the engine from braking at any time.

I have 4runner calipers and a rebuilt MC I replaced last summer. (I did have the rotors ground down to minimum thickness at that time.) The system was working fine until this week. There are no visible leaks at the wheels or elsewhere along the lines.

The parking brake is frozen at one wheel and only works a little bit. I have a diesel and I use engine compression in 1st gear for parking in most cases.

Haven't bled the lines yet but will... hoping for other ideas to try at the same time or subsequently.

Thanks for having a look.

 

[ntsqd]

My first thought is the rebuilt master.

 

[gregnash]

Same here... seems to be similar symptoms to when my master cylinder went out. Check around the brake booster around the bottom of it where the m/c and booster mate. See if it feels wet there, if so then your m/c is leaking.

 

[Godwin]

The parking brake is frozen at one wheel and only works a little bit.

One use of the parking brake is to adjust the rear wheel cylinders so you might check those first.

As the others stated could also be your MC. A friend had a bad MC in her 60 that exhibited a soft pedal when the brakes were applied more gently. A firmer application of the pedal did not result in a sinking pedal. I think the slower application of the brake pedal allowed fluid to pass around the seal. Changing the MC fixed her Cruiser right up.

 

[asmith2081]

I would say it is the master cylinder, too. I believe there is a cylinder that goes through a hole to create the hydraulic pressure to assist the brakes. When they cylinder of the hole gets worn out it can't always create the pressure needed for the assist because. At least I think that is they way it works. The problem will get worse over time if not fixed.

 

[lehiguy]

Check your wheel bearings as well. If loose, the rotor will "walk" back and forth in the caliper pushing the pistons in. Then more pedal movement is required to get it back to normal.

 

[TobyB]

Yup.

Bearings or master can do it.

Warped rotor, too...

and keep an eye on fluid level- I had a caliper that
started leaking just a bit into its boot. The first symptom
was that the pedal would drop farther than usual- but only the
first time you went for the brakes.

BTW, fade is when you stand on the pedal and it doesn't stop so well..

t

 

[deaddrift]

Thanks guys, just got back from several days backpacking in WA with my ten year old.

So... this is annoying. The MC is literally a year old. It came from NAPA and is a rebuild. Anyone have a source for one that won't cr@p out in a year? Or some suggestions for preventive maintenance to keep it in good shape?

 

[stockhorse]

Your brake system can not work at it's best if not all components are working properly.Fix the park brake and adjusters so they can do the job properly. having your discs machined to minimum thickness was only a stop gap measure and new discs are needed.
I am not a fan of changing brake system components as I have found the originals in good condition are as good as anything else, the best upgrade for these rigs is better pads, but that is personal choice and just MHO.
Don't skimp on brakes, they keep your rig and everyone who travels in it or around it a lot safer.

 

[ntsqd]

Does NAPA offer an warranty?

The turning of rotors is intended to sell new rotors. I don't do it. Toyota FJ60's (& 4wd Mini Trucks) don't have enough brake rotor mass to start with, turning them just makes this worse. Instead I use a body work long board with 80 grit paper on it to scuff the rotors when changing pads.