Dr Mitch

So, car was in for some final work prior to selling the bloody thing and due to some previously leaking valves, the brake booster is not holding adequate pressure anymore. So, they tell me it needs a replacement.
I found a new one for $1450 online, but wondering what other options are?

apanossi

Look at the 993 version. You will need a converter for the output, I believe but should be cheaper.

Dr Mitch

The part number is a 993 code:

993.355.953.1 Hydraulic brake booster

Or is there a different one as well?

-nick

The pump tends to leak rather than lose the ability to make pressure. The preesure accumulator, aka the "bomb", is what holds pressure. These have a pressure charged diaphram that looses pressure over time. Probably anyone who hasn't replaced theirs is due, i.e does your c4 beep and blink the brake/awd lights at you when you first start it up after a few days of sitting? Luckily the bomb is reasonable- just under $200 at Sonnen 964.355.109.16. Good luck!

Dr Mitch

Thank you! I'll have to check it out as it sounds like it pumping but not reaching proper pressure. With any luck the bomb may be the issue. Worth trying cost wise too!

Goughary

Note on the bomb...they tend to have a 5 year life. Though we have all seen them go a lot longer...seems they remain like new through approx five years and then over time trail off.

Most bombs I've seen fail seem to be from bad bleeding. The diaphragm in the bomb is delicate. When you bleed the bomb, if you open the bleeder and let the pressure out at full open, it's cool- cuz you get this explosion of fluid...fuuuuuuunnnnnnn....but it blows the diaphragm as well...and causes the bomb to fail early. So during the bleed stage where you fully pressurize the bomb, and then open the bleeder. Open the bleeder slowly and let the pressure out slowly. Don't just crack it open all the way.

I agree w nick. Change the bomb first. You'll know when the pump goes. Trust me. Mine just went last winter/spring. And when you lose all brakes, you'll know. If the system is just running all the time. Or taking a huge amount of time to pressurize, likelihood is it's just the bomb.

Dr Mitch

I never lost pressure with braking. They even tried replacing with a couple of used hydraulic pumps they had in the shop - sounds like they said they weren't maintaining the 100bar (or whatever number) of pressure - so, yeah sounds like the bomb may be the problem of why the pump keeps pumping but pressure never stabilizes! Would be wonderful if that's the issue!!

Dr Mitch

Ended up there was just some air in the system that needed to be flushed out. Some new oil hydraulic pressure valves and lines and new fluid and brakes are back and no more warning lights!