Boxster S 986 spongy brakes

[Tiberious0]

Hi!

I have this problem with the brakes on my 986 Boxster S (with PSM): the pedal feels spongy, there is no bite; almost like there is some air in the system.
- The ABS works - I can feel the grinding when braking hard.
- The braking power looks OK, so it stops the car.
- It is not the perception issue. I drove another Boxster S and the brakes there felt normal; also all the previous mechanics confirmed it.

I had braking fluid changed and brakes bled twice, also the front and rear brakes discs + pads were replaced. That didn't fix the issue. Now one very trusted independent Porsche specialist has done some diagnostics and is suggesting to replace the brake master cylinder and servo and if that doesn't fix the issue, then the ABS pump.

So could anyone comment on my questions please:
- Has anyone had a similar issue?
- Is there a simple way to check that the master cylender/servo is the cause?
- Do you think it is realistic to have a some type of proper diagnostics somewhere instead of going and simply replacing parts till the issue is gone?

P.S.: Another suggestion from another independent garage (which had a customer with brake issues similar to mine) was "We did the master cylinder and ABS pump but still had a spongy pedal, I think the fault was in the wiring but the customer didn't want me to proceed any further. I think something to do with the pressure sensor wiring maybe."

 

[Tiberious0]

Any thoughts from anyone? I am really desperate with the situation :/

 

[GrahamW]

A couple of queries. Was the pedal feeling soft before you had the fluid changed or since the change? Sometimes the technician is a little "lazy" when flushing out the system with the new fluid and doesn't bleed all of the nipples on the calipers. Have you checked this? It will be quite apparent if they have all been bled as the nipples will show signs of use. Secondly, sometimes with age the brake pipes corrode and develop small holes. Has this been checked? They are hidden from view behind the underside floor panels and may not be apparent to the naked eye or by spots on the garage floor.

Finally is the slave cylinder or the calipers leaking fluid?

 

[AndrewCS]

No experience of this but looking through the parts diagram I don`t see a brake sensor. There is a regulator (valve ?) between the master cylinder and the ABS unit ... that`s not mentioned by your previous investigations

I assume that the pedal linkage is OK, NB ... the switches 17 & 18, not sure what they are for ?

There are a few things ^ that would be easier ? to change / test than removing - replacing the brake booster / servo and ABS unit ...

Porsche Classic Genuine Parts Catalogue - Porsche Great Britain

 

[Tiberious0]

A couple of queries. Was the pedal feeling soft before you had the fluid changed or since the change? Sometimes the technician is a little "lazy" when flushing out the system with the new fluid and doesn't bleed all of the nipples on the calipers. Have you checked this? It will be quite apparent if they have all been bled as the nipples will show signs of use. Secondly, sometimes with age the brake pipes corrode and develop small holes. Has this been checked? They are hidden from view behind the underside floor panels and may not be apparent to the naked eye or by spots on the garage floor.

Finally is the slave cylinder or the calipers leaking fluid?

Thanks for replying, Graham!

>Was the pedal feeling soft before you had the fluid changed or since the change?

The issue was there before; I had the fluid changed 2 times at 2 different (and trusted) Porsche specialists that didn't have any impact.

>Secondly, sometimes with age the brake pipes corrode and develop small holes.

I think they should have checked this, but it is a good point! But I didn't see any effect at all after the fluid change, even immediately after it.

>Finally is the slave cylinder or the calipers leaking fluid?

I understand that I would see a drop in fluid level in the tank in this case, right?

 

[GrahamW]

A couple of queries. Was the pedal feeling soft before you had the fluid changed or since the change? Sometimes the technician is a little "lazy" when flushing out the system with the new fluid and doesn't bleed all of the nipples on the calipers. Have you checked this? It will be quite apparent if they have all been bled as the nipples will show signs of use. Secondly, sometimes with age the brake pipes corrode and develop small holes. Has this been checked? They are hidden from view behind the underside floor panels and may not be apparent to the naked eye or by spots on the garage floor.

Finally is the slave cylinder or the calipers leaking fluid?

Thanks for replying, Graham!

>Was the pedal feeling soft before you had the fluid changed or since the change?

The issue was there before; I had the fluid changed 2 times at 2 different (and trusted) Porsche specialists that didn't have any impact.

Are you sure all the nipples have been bled?

>Secondly, sometimes with age the brake pipes corrode and develop small holes.

I think they should have checked this, but it is a good point! But I didn't see any effect at all after the fluid change, even immediately after it.

They would had had to remove the panels to check, did they?

>Finally is the slave cylinder or the calipers leaking fluid?

I understand that I would see a drop in fluid level in the tank in this case, right?

Correct, but maybe not as much as you'd think

If the above are all OK then I'd start with replacing the Master cylinder as the rubbers do/can wear over time.

 

[Tiberious0]

No experience of this but looking through the parts diagram I don`t see a brake sensor. There is a regulator (valve ?) between the master cylinder and the ABS unit ... that`s not mentioned by your previous investigations

I assume that the pedal linkage is OK, NB ... the switches 17 & 18, not sure what they are for ?

There are a few things ^ that would be easier ? to change / test than removing - replacing the brake booster / servo and ABS unit ...

Porsche Classic Genuine Parts Catalogue - Porsche Great Britain

>There are a few things ^ that would be easier ? to change / test than removing - replacing the brake booster / servo and ABS unit ...

Thanks! Yes, that sounds exactly like the possibilities I would want to explore; in theory I would come to some garage with the list of those and ask to check those.

 

[Tiberious0]

A couple of queries. Was the pedal feeling soft before you had the fluid changed or since the change? Sometimes the technician is a little "lazy" when flushing out the system with the new fluid and doesn't bleed all of the nipples on the calipers. Have you checked this? It will be quite apparent if they have all been bled as the nipples will show signs of use. Secondly, sometimes with age the brake pipes corrode and develop small holes. Has this been checked? They are hidden from view behind the underside floor panels and may not be apparent to the naked eye or by spots on the garage floor.

Finally is the slave cylinder or the calipers leaking fluid?

Thanks for replying, Graham!

>Was the pedal feeling soft before you had the fluid changed or since the change?

The issue was there before; I had the fluid changed 2 times at 2 different (and trusted) Porsche specialists that didn't have any impact.

Are you sure all the nipples have been bled?

>Secondly, sometimes with age the brake pipes corrode and develop small holes.

I think they should have checked this, but it is a good point! But I didn't see any effect at all after the fluid change, even immediately after it.

They would had had to remove the panels to check, did they?

>Finally is the slave cylinder or the calipers leaking fluid?

I understand that I would see a drop in fluid level in the tank in this case, right?

Correct, but maybe not as much as you'd think

If the above are all OK then I'd start with replacing the Master cylinder as the rubbers do/can wear over time.

> Are you sure all the nipples have been bled?

Jaz Porsche (https://jazweb.co.uk/) did the fluid change - if they didn't do it right, I don't know which indie to trust then :/

> If the above are all OK then I'd start with replacing the Master cylinder as the rubbers do/can wear over time.

I see! Do you think there is any definitive way to diagnose it, or at least some specific signs that are related to MC - rather than this being the next most likely thing?

 

[Motorhead]

All of the above Artem. Finding the source of spongy brakes can be a bit of a rabbit hole! A faulty master cylinder or ABS unit could be the problem, and as Graham has said, techs aren’t always diligent when it comes to bleeding both nipples on the calipers (assuming there are inner and outer nipples on your 986?). Watch out though if you’re planning to check the inner nipples as it’s most likely that they’ll shear off if they’ve never been cracked open.

Good luck!

Jeff

PS: The 2-switches 17 & 18 that Andrew mentions are purely to monitor brake and clutch operation (the latter to ensure that the clutch is depressed before starting the engine) and shouldn’t (won’t?) have any bearing on your problem.