Intermittent Brake Fade

[ølaf]

Hi all.

New pads, new rotors, Tundra calipers. Last brake bleed about 2 years ago (who I installed the tundra calipers). Brakes feel very strong right after start-up, but every once in a while, I get a hard pedal and the braking power feels very weak. Is this a sign of trapped air, or could the booster or master cylinder be on the way out. Both are original. Any other ideas?

Thanks for any ideas!

1999
240k.

 

[nevada]

Hi all.

New pads, new rotors, Tundra calipers. Last brake bleed about 2 years ago (who I installed the tundra calipers). Brakes feel very strong right after start-up, but every once in a while, I get a hard pedal and the braking power feels very weak. Is this a sign of trapped air, or could the booster or master cylinder be on the way out. Both are original. Any other ideas?

Thanks for any ideas!

1999
240k.

a hard pedal and weak braking would be a sign of a booster failing. possibly the check valve, but at that mileage I would suspect the booster itself.

 

[Kyngfish]

I'd try a re-bleed as well though. I actually had the same exact issue after the Tundra upgrade.

It certainly could be the booster failing or (according to what I've read) it also could be the master cylinder letting some fluid seep by. But in my case, I didn't have any problems before the TBU and I got the occasional problem only after the upgrade. I re-bled the brakes and I haven't had the problem at all in months.

Anyway, worth a try.

 

[ølaf]

Thanks guys! ills tart with a bleed. Far to near, correct?

As far as the booster ... any way to check it?

Thanks!

- olaf

 

[Kyngfish]

Thanks guys! ills tart with a bleed. Far to near, correct?

As far as the booster ... any way to check it?

Thanks!

- olaf

I believe the best approach is passenger rear - driver rear - passenger front, driver front. No idea on the booster. I'll let others sound off.

I hope you check back in once you find a solution though and let us know what it was.

Good luck

 

[nevada]

Thanks guys! ills tart with a bleed. Far to near, correct?

As far as the booster ... any way to check it?

Thanks!

- olaf

with the engine off, pump the pedal a few times to drain all the vacuum. then while holding the pedal down, start the engine. the pedal should sink about 3/4" or so. that is a sign its working.


but, if as you said the pedal gets hard, the booster is not working.


air in the system would give you the opposite symptoms. you would have a soft or low pedal.

 

[pokeyman]

Sounds like a master cylinder to me.

 

[ølaf]

Sounds like a master cylinder to me.

Interesting ... I can't feel a failing booster or air in the system in the parking lot / firing up the engine type of scenario, since this will only happen about once a day or every other day.

How would I diagnose a leaking master cylinder?
How are the symptoms different than a failing booster?

Thanks!!!!

 

[pokeyman]

A bad master would be the pedal sinking slowly with your foot on the pedal . Everytime you pump on the pedal the pedal would rise and then slowly go down again.