Hi,

Lately I've noticed that when I'm holding the brake pedal for a few moments (i.e. at a stoplight) the pedal becomes soft, it keeps going down and makes a hissing sound.
What could be causing this?
Thanks

 

sounds like your master brake cylinder going bad

 

You need to look at the brake booster. The booster uses engine vacuum to make braking easier (less foot power). I think you may be hearing a vacuum leak. Check the booster and the hose going to it from the intake manifold. Maybe have a friend hold the brake pedal with the engine running and with the hood up listen in the firewall area on the driver's side. Try to find the hissing sound.
With no hissing sound your diagnosis is easy....air in the system, which means you need to have the system bled. Hope this helps.

 

how does the brake fluid look- clear, or cloudy and colored?
Supposed to change that every year - moisture gets in and will give a soft pedal overall.

at stoplight- does the pedal still hold the car stopped?, or does it sink and no brake..
A slight pedal drop is normal at idle -especially if the AC kicks on

I replaced the Master on mine along with the calipers- fluid had never been changed and messed up the system.
M/C runs about 85 iirc, online store, comes with new cap too.

 

Thanks all for the input.

Chuck:
I'll try to locate the hiss from under the hood.

01tl:
Fluid looks dark, close to 10yrs not sure whether it's been changed before, but will do now. At stoplight, the pedal still holds the car stopped, pedal sinks, hisses and ac on all the time (live in the caribbean!)

I really hope it's just a vacuum leak that I can solve with a new hose...

 

hmmm... i think i have the same issue on my accord v6, makes that hissing noise, think the brake fluid is dirty?

 

Definately change that fluid, have the system bled, all four calipers. Brake fluid attracts water, so in your humid environment it will deteriorate more quickly.

 

black is not ari mon!
Use DOT3 or DOT 4 spec fluid
Bleed/flush order on the TL is different than normal cars due to ABS

Correct order is LF= driver front, then clockwise around the car
LF RF RR LR

 

Is this something you can do by yourself or best left to pros? Any DIY out there?