Brake Question

[Salonika]

Brake pedal goes to floor on first pump while providing moderate braking power. Second pump provides fully effective braking power. Not losing fluid. After second pump, pedal doesn’t move down if you maintain pressure on pedal. Calipers are working normally, pads and rotors are in spec and not overly worn. I may be overdue to bleed fluid but fluid is less than 5 years old. Any time I service my brakes I bleed as you are suppoaed to. Been doing my own brake service for 3 cars and 15 years…… Any ideas why I need to double pump to get a good hard pedal? This behavior is fully repeatable, does it every time unless you are reapplying brakes within 30 seconds or minute or so.
My only plan right now is to re-bleed all 4 corners.

 

[nwoods]

Air in the fluid. Time to bleed the brakes and replace the fluid with new clean fluid.

 

[Salonika]

Air in the fluid. Time to bleed the brakes and replace the fluid with new clean fluid.

How did air get in there? I’m not losing fluid……and haven’t serviced the brakes for 6 months, problem only seemed to start in the last couple hundred miles

 

[Salonika]

I will bleed system and report back.

 

[nwoods]

How did air get in there? I’m not losing fluid……and haven’t serviced the brakes for 6 months, problem only seemed to start in the last couple hundred miles

Brake fluid is hydroscopic (I think that is the term) in nature. Over time, the fluid absorbs air and moisture which reduces its resistance to compression. The more air and moisture in the system, the more you have to compress the fluid to get it to apply pressure on the other end. I don't know what the recommended periodicity is on replacing brake fluid, but I do it on my vehicles generally every 50,000 miles, because its easy and fairly inexpensive to do.

 

[nwoods]

I will bleed system and report back.

That might help, (results can be dramatic sometimes), but depending on the age of your fluid, you should be thinking in terms of fluid replacement by flushing out the old and replacing it.

 

[Salonika]

That might help, (results can be dramatic sometimes), but depending on the age of your fluid, you should be thinking in terms of fluid replacement by flushing out the old and replacing it.

I should have said that, I’ll flush…….on that topic, I’d love any recommendations on a tool to assist…… I hate the pump and and bleed process. I think you need a pretty good little vacuum pump to pull the fluid through right? I tried using the hand vac once but it didn’t work

 

[nwoods]

I use the pump and bleed, following Eric the Car Guy's method:

Chris Fix has a decent video also:

 

[CharlieNorth]

Check that the pedal is returning fully to allow the fill ports from the reservoir to keep the cylinder full.

 

[Salonika]

Check that the pedal is returning fully to allow the fill ports from the reservoir to keep the cylinder full.

Where do I observe / measure this?

 

[CharlieNorth]

Reaching up under the dash you need to get your fingers on the pushrod from the pedal into the master, it should have a touch of play. The boot can make it hard to feel. You can also thread out the brake light switch if needed.

When looking in the open resevoir with someone to assist pressing the pedal, many times you can see a slight movement of fluid as the pedal starts to move before it generates pressure.

 

[Salonika]

Now that you describe this I think there is a spec / evaluation procedure for this in the FSM. Thank you, I will refer to it.

 

[CharlieNorth]

Might not be the issue unless something has changed during other changes or service.

 

[Salonika]

Well so far rear pads were both at less than 50% but that shouldn’t create a double pump situation. I decided to just go ahead and replace both rear calipers since they’re nearly 6 years old, so I won’t be able to test only flushing the brake fluid by itself.

 

[Salonika]

new pads and calipers + bleeding rear lines and produced zero change in behavior. Unfortunately looks like my next target will be the master cylinder.