Weak Brakes...Master Cylinder or Booster?

[OK-944]

So...after having replaced all soft brake lines, rebuilding the calipers, installing new rotors and pads, and bleeding everything twice - the brakes are now only "so-so" as far as stopping the car. Very smooth, but just not great stopping power. Fine for general use...but I'd worry about a true "panic" stop scenario.

Brake fluid level remains constant...and I can find no leaks.

Question: given the above...should I be looking at replacing the brake master cylinder, or the brake booster?

[944 Ecology]

944s have always had "soft" brakes... certainly compared to 911 brakes.

It may be that the pads are not aggressive enough or need to bed into the rotors better.

I would do nothing for a month or so, then look at my options, starting with the easiest, which would be the master cylinder.

[mytrplseven]

I had what I thought was a great brake package in my restoration project: cross drilled rotors, Hawk street/competition pads, new master cylinder and stainless wrapped flexible hoses. I had also rebuilt my Brembo rotors, The brakes were hardly effective and downright soft. I replaced the booster, bled and re-bled the brakes and finally, after hearing about using standard rotors with semi-metallic pads vs what I was trying to use, and re-bleeding once more, I had BRAKES!

[OK-944]

...are you sure it wasn't just the new booster that gave you what you needed?

[c5pilot]

Could be the pad type. I face same issue but running EBC Yellow on street now where i got them a lot warmer when it was just a track car. I plan to try more street pad first as i have rebuilt calipers , lines etc as well. Just doesn’t feel like it did


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[jjeffries]

How many miles on these brakes now? Did you do proper “bedding-in” procedure?

[v2rocket_aka944]

If you think the booster is suspect, I will make you a deal on the one just pulled from my car, was brand new in 2008.

[88Silver924S]

So, what brand and model rotors and pads did you use? What brand soft brake lines? I assume you lubricated the sliding parts and pins during your caliper rebuild, what lube did you use?

[OK-944]

Brakes are actually starting to get better...still not quite there.

170K miles on the MC and Booster.

Textar pads and Zimmerman rotors - not top dollar for the pads but I've had good success with this combo in the past.

Not sure of the brake line manufacturer - but I got these through 944 Online and I trust them completely.

At any rate...I'll give these a bit more time to see if they acquire any more bite.

[drew1]

A booster diaphram generally gives an airleak sound when brake pedal mashed.

[walfreyydo]

Also worth looking into exactly how much vacuum is coming from the line connected to the booster. If normal, I would suspect the booster itself.

[mikepellegrini]

I struggled with that on my 951 and replaced the booster twice without getting any improvements. In the end, I found out it was a vacuum leak in the hoses underneath the intake manifold. I fixed that by doing a venturi delete and it's been great ever since.

[Rasta Monsta]

Originally Posted by OK-944

Texter pads and Zimmerman rotors.

This is the preferred setup, IMO, so nothing wrong here. However, they do need to be properly bedded for optimal performance. And by this I mean actually following the manual. Accelerate to 30 ten times and brake hard to zero. Then 50. When you get back four wheels should be smoking.

Done.