Seemingly lack of vacuum, wooden brakes.

[phazed]

Bit of advice please. New to Porsche so a learning curve......

I recently became the owner of a tidy 2008 3.4. The brakes while driving at normal speeds are excellent, no complaints but, very low speeds, rolling on idle and the brake peddle is hard/wooden feeling and lacks stopping power.

I am sure that all vacuum is lost at idle/very low speeds. I did notice this on my brief test drive, the seller stated this was normal, obviously b@llox!

i drove a friends 986 a few days ago and I couldn't get the car to loose vacuum even when pumping the peddle at idle!

Any tips, hints as to what the problem may be before I ram the rear of someone in slow moving traffic.

Thanks.

[sa utah]

If you’re used to heavily servo assisted cars you’ll find the Porsche system very odd at first.  
mot definitely needs a good hard prod to get the desired results compared to other cars.  Maybe it’s just a lack of familiarity

[phazed]

Absolutely not. The brakes are practically non existent at low very speeds, plain dangerous......

[Nobbie]

What happens after you turn off the engine? Normally the system holds vacuum for a while and takes two or three pushes to go away and then the pedal goes hard. If it goes away quickly then you may have a leak in the servo somewhere. 

[Lennym1984]

Are they wooden all the time (at low speed)? My old car used to be awful until the brakes had heated up a bit (it was a second car so I didn't drive it all the time) 

[phazed]

Wooden at low speed, bloody awful! That is never right!

[sa utah]

Probably worth stripping the brakes down then and going from there with new parts were applicable.   It’s not expensive now to replace the whole lot.  
the discs may look ok from the wheel side but are possibly corroded on the inboard side.  
A fluid swap / bleed is always good if you can’t find any history mentioning that for the last couple of years also. 

[phazed]

New pads and discs recently fitted.

 

Brakes are excellent at normal speeds. Just very low speeds they loose their vacuum.

i thought this may be a common fault?

[Lonewolfgjp]

Definitely not! 
I drove mine yesterday for the first time in ages and I had forgotten how good the brakes were!

[topradio]

Usually if you stop the car and pump the pedal a few times to dissipate any vacuum then start the car with your foot on the pedal, you will feel it sink under your foot as the servo kicks in.  If it doesn't do this I would suggest that you have a fault with the servo. 

[red rocket]

5 hours ago, phazed said:

thought this may be a common fault?

+1 for definitely not. Must be a fault somewhere.

[DaveEFI]

15 hours ago, phazed said:

Wooden at low speed, bloody awful! That is never right!

Do you know what pads it has fitted? Some only grip well when hot. But if you operate the. pedal many times with the engine stopped to exhaust the vacuum, then start the engine while pressing the pedal, you should feel it move down slightly

[phazed]

Back home a bit later so will try the engine starting with foot on the pedal but I’m pretty certain that it just has insufficient vacuum which works at speed and loses it at very low engine speeds or idle.

 

I had this with my TVR With a highly tuned engine with a highlift camshaft that produced very little vacuum at low revs. I’ve got over this by fitting an electric vacuum pump specifically meant for these circumstances which completely cured the low vacuum.

Obviously Porsche would never let this happen in the first place so I’m sure I have a fault.

[phazed]

Started the engine with my foot on the break and it sank as you would normally expect it to.

Brakes fitted by the previous owner are Sebro discs and Brendon pads.

 

 

[phazed]

It seems Siri can’t spell brake, (break)!

just been for a spin down the road. Warm engine, 50 miles an hour, foot on the clutch and throttle closed.
First prod of the brake pedal, great braking, Second prod without raising revs from idle and only about half as effective, third prod and it is rock hard with hardly any braking!

Returned home, rolling down our quiet road at about 5 mph on Idle, pedal rockhard and no servo assistance.

Either a problem with the servo or there may be a minor leak on the system is my guess.

First thing to do is expose the servo and see what the vacuum is like at that point, checking for leaks

I guess the servo is accessed from somewhere under the bonnet having never been in there before!

[Lonewolfgjp]

Sounds like he fitted decent parts, I wonder if he hasn’t bled them off and you’ve got air in there ?

Only a guess as I’m not overly mechanical but it maybe worth checking before digging out the servo.

[sa utah]

Have you checked the fluid level?   I bought a car a few years back where the owner had topped up the brake fluid level..... then fitted new pads and disc etc.  Later on 

when I did my usual full check over when I got it home the fluid was brimmed to the top so the was no gap in the reservoir.   
worth a look 

[Greenman]

It does sound like a vacuum problem but it’s not a fault that I’ve seen as common at all.  Lack of fluid or air locks or old fluid would (as far as I know) result in a spongy peddle feel. 
 

I'm not familiar with Brendon pads, these aren't track/race pads are they? That might also give the results you are seeing.

 

[Lonewolfgjp]

I’m guessing he means Brembo👍

[phazed]

Absolutely!

I use Siri too much and the bugger AutoCorrects just before I post!

[phazed]

Pedal is firm, not spongy.

You should definitely get more than 1 1/2 pedal depressions before losing the vacuum.

[topradio]

I'm not near a manual at the moment, so I can't check, but is the vacuum produced by a dedicated pump rather than scavenging it from the manifold. If so, perhaps it's a fault with the pump? 

[phazed]

Interesting post I found on a site, (Planet9): A guy had a similar problem with a Cayman.

 

"

"Brakes:
The 2006 Cayman S gets the 'Big Red' brakes from the Boxster S, sporting 12.5" rotors up front, 11.8" rotors in the rear, both clamped by patented 4 piston monobloc calipers made for Porsche by Brembo. The open top design of the calipers makes brake pad swaps possible without removing the caliper.  

Brake boost is provided by a mechanical vacuum pump so boost levels will not drop from long applications of wide open throttle like systems that use manifold provided vacuum. Cooling is well thought out, using the air flow from the radiators to keep the braking system cool, but not so cool that aggressive brake pads can't be safely used."

I pulled the line off the booster and it is pulling some suction and the engine didn't change speed so it appears to be working. Anyone know where is this Mechanical Vacuum Pump located? Any check valves I need to check?"

 

Worth investigating tomorrow.

[phazed]

https://www.frazerpart.com/acatalog/Porsche-987-997-tandem-vacuum-pump.html

[phazed]

 I have just found this on the web. At the bottom of the second page on Google. Absolutely amazing that there isn't any technical information regarding the tandom vacuum pump renewal before! 

https://f01.justanswer.com/tracker40/b94fe2ee-7789-4a85-9506-0b7bc46a1391_124.pdf

 I must say, if this was a problem with a TVR there would be untold pages of information/diagrams/how to do's/links to PistonHeads or similar showing how to replace it .

 It seems there are very few Porsche owners that actually do any sort of major work on their own cars preferring to leave this to independents and main dealers.  

 I have pretty much taken every nut and bolt apart from my TVR including completely rebuilding the 5.5 L V8 engine and carrying out untold performance modifications and upgrades. I am not alone, I have several friends who have done the same.

Not knocking you guys, it is just obviously a different demographic that buys a Porsche.

 Anyhow,  I will put the car on the ramp this morning and see if I can see the offending article, run up the engine and see if it is working. That's the plan!