Low brake fluid level, how to add more..
 

My brake fluid on my fluid reservoir is low. Can I just open the top and add more or is that going to let air into the brake system.

Sure you can, but Warning.

When you replace the brake pads the fluid will over flow.

Fluid does not evaporate. If you have a leak in the system then air will get in.

Low levels are directly linked to brake pad wear and it is normal in a sound system.

Simple answer, yes top it up, just make sure you wipe off the top to get dust off before you pour in new fluid. If you're using excessive fluid that's a different story.

Don't think I am using excess fluid. Have not had to add fluid for a long time, years.. Thanks for the help !!!

Sorry, to answer your question. No, adding fluid at the resevoir will not introduce air into your system.

If it's been years since the last time anything was done to the fluid, you may want to consider having the system bled/flushed.

+1 If the fluid is dark it would be a good idea to flush and replace.

Then you can start on the slippery slope and replace the calipers & rotors. A few suspension upgrades, new wheels and a fresh paint job will be a nice start. :)

To combine all the previous posts and add a bit:

The reservoir is actually two reservoirs as it is devided at the low end of acceptable level. This allows one circuit (front or rear) to run low (or out) while the other circuit remains functional.

As the fluid level drops, the space above the fluid is made up with outside air. If you push a caliper piston back with high fluid level, the fluid will overflow with a tube to the outside.

There are two common ways for the brake fluid level to become lower than ideal: First, the normal wear of the pads allows the caliper pistons to move closer to the rotor. The difference in caliper volume is made up with fluid from the reservoir. As the pad wears and you continue to add fluid, be aware that this ‘extra’ fluid must be removed when you replace the brake pads with new.

The other critical cause of low fluid level is a leak. A common leak is at the master cylinder seals. On boosted brakes, the fluid can disappear into the vacuum booster and not be obvious.

On a non-booster brake system (’65-’76) the fluid typically leaks into the boot around the pedal push rod and then into the pedal assembly. With the floorboard removed, a ‘digital exam’ will find most leaks.

Of course you should inspect the calipers and flex hoses. There should never be any sign of brake fluid leak anywhere. A ‘little leak’ is not acceptable.

Both the master cylinder and the flex hoses have a service life. While the exact life is somewhat controversial, I like to err on the conservative safe side.

Old fluid and long periods of inactivity are particularly hard on components.

The brake fluid reservoir cap commonly cracks and should be replaced occasionally. The later ‘warning light‘ type cap can be fitted to an earlier car.

Best,
Grady

Absolutely, flushed and replaced.