I tried the search, but "soft brake pedal" returned 13 pages of results, none of which seemed to address my issue.

Rather spontaneously, my brake pedal has started to lose firmness while sitting at stoplights with my foot on the pedal, and as I bring the car to a stop. It seems that, all of a sudden, the car is almost unsafe to drive as it require increasing amounts of pressure to bring the car to a gradual stop.

Would a brake bleed serve as brake pedal Viagra? What is the period on which this process should be done? Quarterly? Annually?

Thanks for you help, I've parked the car until I know what to do next!

 

If the pedal fails to hold pressure, even though being a 'long pedal', you may have a master cylinder going or gone bad. Check for any fluid leaks aroud each caliper near their bleeder nipples, also around the master cylinder itself.

 

Hi Randy,

As Chris said, check for leaks and check your fluid level. But a sinking break pedal at a stop is the textbook example of a dying master cylinder. The master cylinder's piston is "pushing through" the fluid within the cylinder bore instead of pushing the fluid to actuate the brakes ...the dying seals are "leaking" the brake fluid past the piston. If you spot no leaks and the fluid level is normal (most likely), but pedal continues to sink under foot pressure while at a dead stop, you have a bad master cyl.

Edward

 

Thanks for the rapid response.

The pedal does fail to hold pressure, but the pedal returns to firm if I release the pedal and immediately stab it again. In essence, stepping on the brake yields the normal firm pedal feel, followed by decreasing pedal pressure.

Where would I find the master cylinder? I will check the bleeder valves on the calipers.

 

Remove the LF tire/wheel. Also, for better access, remove the plastic undertray. You'll see it right there.

 

Ah ha. I understand this explanation, and how it relates to the symptoms.

Sounds like a visit to the garage is in order. Dang. Expensive fix?

 

Thanks, Chris. As always, incredibly helpful advice!

 

One other question about replacement: is the cylinder the same for both NB and WB? As they have different brake calipers, not sure if the part number is the same. A quick search on Pelican's catalog yields only something for a Carerra 4, but no mention of S cars.

 

FWIW, your symptoms are the same as when my ABS controller failed. The MC is the more likely and less expensive part to replace, but don't be shocked if it doesn't solve the problem. I used a salvaged ABS controller as the new one was stupid expensive.

 

All sage advice...But it's possible your symptoms may go away with a good brake flush. Actually what you need to flush is the ABS controller, but a thorough brake flush should do that. Dealers are notorious for throwing ABS controllers at the problem when confronted with your symptoms...

 

I was told I needed the abs controller when I had the same symtoms. It turned out just a $70 flush job (suggested by a rennlister) at a different shop (and been going there since). That was about 5 yrs ago and my brake still work fine.

 

Hmm...I have had the ABS warning light come on briefly at startup, but it would go out again rather quickly.

Is there a recommended way to go about diagnosing which one of the three it could be, as opposed to "guess and check"? Great for long division, bad for car repair bills! It sounds like a failing master cylinder may be spotted visibly from leading brake fluid out the sides?

I will assume a failing ABS controller will not be as easily diagnosed without replacement?

EDIT: My goodness. ABS controllers run $1,800 a pop before labor. You weren't kidding when you said it was stupid expensive...

 

I've got a similar issue with my Targa. It's slight, but I assume it is a master cylinder losing its internal seal. I also assume it will cost more for that part than it did when I last replaced one (Pontiac GTO ... about $30). I'm not an expert with ABS systems or this controller mentioned here. Short of spotting a fluid leak, is there any way to diagnose with certainty what the cause is? Would the ABS controller throw an error light if it had an issue?

Thanks,
- Matt

 

I had assumed you had already done a thourough brake flush. If that's not the case, then that is the obvious first step. By thourough, I mean flush an entire liter through. Doing the clutch slave at the same time is a good idea.

Your ABS light should always come on at startup and then go out. Do you have a C2 or a C4? The brake boost is different and that could influence how you trouble shoot the problem.

My cars have never been to a dealer so I can't address that aspect. When the ABS was bad in my 964, it was the last thing we examined - after having changed the master cylinder, calipers and repeated brake flushes. There was no warning light in my case, just a soft pedal that could be pumped to get it firm. No leaks anywhere in the system (external leaks anyway).

 

I just had my brake system flushed by my mechanic this afternoon. He thought it would be worth the chance to see if that would solve the soft pedal. He also said that only a few cars he had ever tried this on actually gained normal pedal feel- about 20%. After driving home mine is falling into the 80% category. Dang it !!! Looks like the ABS pump (controller?) for me. He guessed part cost of $2500. Where can you get one for $1800?