I own a STR6 convertible with only 7000 miles. The vehicle has been sitting awhile uncover in storage. I decided to start it up the other day and take it for a drive when I noticed the brake pedal went straight to the floor. I could pump the pedal rapid and get a little braking but after the pedal would go straight to the floor. I did notice though with the engine not running I would have brake pressure near the top. Only with the engine running did I lose all brake pressure. I have NO LEAKS whatsoever. Any advice is greatly appreciate.

 

I would say the master cylinder has a leak internally. Have someone push on the peddle while you look inside the open brake fluid reservoir you might see the oil getting disturbed near the bottom of the tank as it comes back through the seals.

 

If the master cylinder was leaking would I also not have brakes with the engine not running (without booster).

 

With no boost does the pedal slowly go to the floor?

 

Without the engine running, with power brakes, it will "feel" as though you have a full pedal, while actually you don't.

Try this :
Find an open non public area.
get up to about 20 MPH, put it in neutral, switch off the engine and see if you REALLY have any brakes.
My bet is you will coast for a while until you start the engine back up.

If I were you, I'd do this :
1. rebuild or replace the master cylinder.
2. flush out all the old brake fluid with a complete bleeding job.

 

I've seen the distribution block fail and not apply pressure to certain calipers. My advice would be to start by flushing the system. 11-year old vehicle with 7K miles makes me think no one bothered to bleed the brakes before.

 

My first action would be to change the fluid. My brake pedal would go to the floor board and hardly stop when I got air into the lines. One time I only had rear brakes but that was from boiling the fluid repeatedly in the front calipers. Felt/is the same as air in the lines, pedal to the floor and almost no brakes at all. I've never had a master cylinder fail and don't know the symptoms but it sounds plausible too.

Les

 

Front and rear seals in the MC would have to go but an old car sitting, who knows. No wheel cylinder leak seen but ...?
Old fluid is a distinct possibility as noted, the extra force of the booster might make the seals leak easier.
The pistons inside the MC must get pushed as that part is mechanically linked. So if the pistons move the oil has to move somewhere. Low fluid in the reservoir would allow air to get pushed around, but that should be seen easily.

 

Yes the pedal does go to the floor with no boost. Can I assume then it's the master cylinder?

 

No leaks and no pressure I would expect MC problems. Have you looked inside the reservoir for oil movement when the pedal is pushed?

 

or if there is any brake fluid at all in the mc.

 

Same issue here. Second year in a row. I had the fluid changed last year and it seemed to do the trick (crossfire peddles are generally pretty soft anyway). However, it has returned again this year. It sits a lot I the winter but I drive it occasionally. Seems to get worse the longer it sits though.


No leaks, no appearance of issues externally, etc.


I'm done diagnosing. I'm taking it to a auto facility that specializes in German cars. I told him I had a Crossfire and he didn't blink. Fine, bring it in and we'll take a look. I need it fixed so I can drive it with confidence..............

 

The answer to your problem is to drive it more and let it sit Less, it's as simple as that.

 

Yeah, I'm sure driving it more may be a factor but weather up here isn't always advantageous to driving my car. Also, commuting into Washington DC can destroy any car and I have another car I'd prefer to beat up more than my Crossfire, so it's saved for decent weather on the weekends when the salt and sand isn't spread all over the place. Given there seems to be a rash of this condition cropping up on these cars now, there has got to be something more to it than it just sitting for a few weeks at a time. I'm hoping to get to the bottom of it tomorrow. The good news is..........it's driving weather NOW!

 

Please share the solution.

 

U*pdate. I took it in this morning to have the brakes checked. The BAS light went off on the way to the shop. Long story short. They checked every thing out. Brakes, rotors sensors, lines everything looked great. He said the fluid did look a little dirty and the light was on due to a code thrown for the brake switch. He said let's do the flush, clear the code before determining if the switch is actually bad. I, and he thought given the pedal was traveling to the floor, that it may have been triggering the sensor light. So, flushed the fluid, cleared the code and all is well. I now am back to regular brake feel and power and the BAS light has not returned. I drove it about 20 miles and all seems good.

Recommendation is to do the flush and reset the code (logical first step of course) and see if that fixes it. If not, next step is likely the master cylinder. Hope this helps. Good luck and report back.

 

Does the reservoir just hold onto the master by the one visible bold and as O-ring between the reservoir and the pump itself? I have had trouble with leakage with no help for some time and will take a chance on that O-ring, just need to confirm the way the reservoir is attached, Thanks, Mark

 

I think you'll find there are two seals on there. I have had mine off but I cannot remember a bolt. It may just push on there.