Soo the other day I noticed that my brake fluid cap was missing. Looked all over town but couldn't find one. The one I ordered won't be in until later. However, when I got in my car earlier today I noticed my brake, vdc, and traction lights were on and very little pressure from the pedal, had to press as hard as I could to stop. I went and put fluid in, the lights went off but still no pressure at the pedal.

When I get off I plan on trying to bleed my brakes but I'm really concerned that maybe I have damaged my master cylinder or something, since it was running fine before today.

 

Brake fluid is hygroscopic- which means that the fluid absorbs moisture from the atmosphere.

I would plan on doing a complete flush of the brake system. If there is even the slightest bit of water- or even air- in the system the brakes will never feel right. Unless you have the proper tools you might consider having a reputable shop do the work.

 

Do you think I should just go ahead and get a new master cylinder while I'm at it? I know people say that air and moisture can ruin them even though it's only been without the cap a few days

 

You're not still driving around with the reservoir uncovered, are you? My guess is there's air in the line. If you still can't get a hard pedal after bleeding, possible there's air in the abs module. I believe special tools are needed to force it to cycle during bleeding.

 

To mirror what Jsolo recommended, at the very least you should fully bleed the brake system which will, in essence, flush the system out. The FSM does not call for any special tool though many people prefer to use those "power bleeder" tools:



There is no reason to start replacing parts based on maybe's and what-if's. Bleed the system thoroughly and go from there.

 

^^IIRC, normal bleeding doesn't bleed the abs module as it's off. A scan tool or some other tool is used to modulate it, allowing for fluid within to be flushed.

 

Per the 2008 Coupe FSM no special tools or procedures are needed. The key is that you do NOT want the ABS module to cycle hence why the FSM recommends disconnecting the electric connector at the ABS module/disconnect the battery:

If the procedure changed for later model years I do not know and will stand corrected if so. Also, not trying to start a pi$$ing contest here. Been down this road before and there is really nothing to the procedure. Hardest part for me was ensuring the damn bleeder screws didn't get stripped.

 

No need to change the master cylinder, but you should change your brake fluid.
Here is a step by step video for the G37 Sport. The non-sport will be the same, except for the calipers only having 1 bleed screw.

 

@ILM-NC G37S No pissing match. The concern is if the cover was off and air got inside the system, there's a possibility of air being in the abs unit. It's my understanding normal bleeding will not fix this.

 

All good. We are both on the same/similar page.

 

Thank you all. I just left AutoZone to get a small one man bleeder kit and some fluid. Got 3 hours to see if it works before I have to go back to work

 

Only had time to do 2 wheels. But nothing has changed.

 

Just my 10¢:
I, personally, never had much luck with those power bleeder kits. Many use them and love them, just not my cup of tea. I would get a helper and bleed the brakes the old fashioned way. Again, just my preference.

All four corners have to be done before you will feel results at the pedal. Remember, if you have the sport brakes you have to bleed both sides of the calipers.

 

Many of us (self included) have good results with the motive power bleeder. It pressurizes the master. The bleeding process is to then just open each bleeder screw in proper order while maintaining pressure on the master. Two quarts is usually enough (for the sport).