itsmike177

iTrader: (3)

Never had this problem until this week. Last changed brake fluid ~5000 miles ago. 2011 ISF, ~29k miles.

After letting the car sit for 10+ minutes after driving, I notice the brake pedal is really stiff. As if I had pumped the brake pedal a few times with the engine off. Because of this, I have to really press down hard on the brake pedal in order to start the car or else the warning will say, "depress brake pedal before starting" or something like that.

When I start the car, the brake pedal goes down a little, and it feels "normal" as it always has for the past 20k miles. The brake fluid level is completely level and I don't see any leaks at the master cylinder or at the bleeder valves. Brake performance and pedal feel is normal when driving and I doubt there is air in the system as this didn't occur until this week, and the pedal doesn't slowly sink down when I am sitting at a stop.

Just wondering what could cause this, which does not seem normal?
Thanks for anyone's input.

caveman

So this is the first time you've seen this in 20k or so miles?

I've had the stiff brake at start up if the car was not driven for a day or longer. It's always been like this since I purchased it new so I thought it was normal.

itsmike177

iTrader: (3)

Yes, this just started up this week. Before, it would take 4-5 pumps on the brake pedal (engine off) before it got stiff.... even if the car has been sitting undriven for 1+ weeks.

stick

My pedal has also been very hard to press down at start up when I have not driven it for a few days.

flowrider

iTrader: (9)

I believe this is caused because the Vacuum in the power brake system bleeds off. This is normal, and if it returns to normal when you pump the pedal a few times, it's fine.

Lou

9aristo

iTrader: (10)

I just parked for about 30 minutes, the first pump of the brakes is normal for me. The next consecutive ones make it stiff.

the pedal should be soft enough so that you don't have to plant your weight on it to start the car. It should be like a standard stop. If it's stiff before ignition, maybe the vacuum pressure in the brake booster leaked out as Lou pointed out.

WhatYaGot

It's also a know issue with the Is 250 and 350s. I have had this issue for a while. I purchased a new booster check valve and gasket, but haven't installed it yet.

itsmike177

iTrader: (3)

Dealer is changing the booster check valve, will find out next week. Getting headlights replaced too due to bubbling black trim.

itsmike177

iTrader: (3)

Update and resolution: dealer replaced brake booster check valve which was found to be leaking.

Part numbers replaced:
90480-24015 Grommet
44730-28030 Vacuum valve assembly

9aristo

iTrader: (10)

nice. wonder how it got damaged...