Viperbob1

OK had issues with 997 S posted few weeks back. Turned out the ABS unit (second one in car) was bad. So another ABS pump (also new master cylinder and Cup 3.15 vacuum pot) and the damn brakes are as spongy as can be. Last ABS pump and was hard as a rock. Now mushy. Bled brakes with Durametrics going to each channel to bleed (did this 3 times) and then did a ABS pump general on for 2 more bleeds (using foot and Motive for all these). NOTHING is coming out air wise.

Last weekend spoke to some other teams and 997 racers (apparently similar issues with racing Caymans) at Daytona and they say it is normal (spongy pedal that then goes to floor after a few seconds to me is not normal). This apparently is one of the reasons Grand Am allows Bosch ABS now for these cars. Several theories as to the cause. 1) The Durametrics while it says it can bleed the pump really cannot. Have not had issue with other pumps, but Porsche and others say 997 requires their tools only to work. 2) In a Race car evolved from street car the HUGE number of errors from all the now non-existant systems (doors, seats, climate, turn signals, etc) causes a degradation (or I would guess fail safe operation) of the ABS system. While the ABS does function, it reduces somehow the general braking operation causing this pedal. One team said they plugged in the door modules and that significantly helped.

One last thing. When car is off, the brake pedal almost does not move it is so hard. Start and pure mush. Disconnect vacuum and pedal is again hard as a rock (although no vacuum assist so MUCH more effort needed to stop).....

So question is what is going on here? Is the PIWIS the only tool that can bleed these if air in the ABS, or is a wipe of the Gateway needed to purge these other systems and maybe restore some braking operation. Thoughts are greatly appreciated.

924RACR

Don't know the product, and don't like to slam with no data... but it's sounding rather as if this is the case.

Whatever team finds the ABS works better with the doors plugged in... well, I guess that says a lot about their knowledge of ABS systems. Be sure to wave when you pass 'em on the brakes.

To imagine that we'd design an ABS system - a safety system, mind you - that'd rely on such useless inputs is pretty absurd. We're not designing iPhones, here.

The ABS should have exactly ZERO effect on pedal feel, till such point as the valves start cycling - which isn't gonna happen in the garage, standing still. So if you're having a crappy pedal feel while parked - you've just answered your own question.

Hope that helps... hope you have a sympathetic and willing dealer as a resource?

PedroNole

Bob-

Why don't you just yank out the ABS and put in a dual master cylinder, non-power setup and be done with it once and for all?

mobonic

Bob,

I have run into the same issue 2 times now in my 997S race car.

I chased no existant air and went through 5+ full bleeds with SRF (not cheap)

First time I changed, the ABS unit and master cylinder... still spongy. Then changed the whole front calipers and BAM.. rock hard pedal.

Now after I swapped pads last month at laguna seca.. the spongy pedal just came back, I think it might be piston knock back.. but my shop bled the whole system with new brembo fluid and i still cant get back to a rock solid pedal and its pissing me off!

My new guess is that my rear calipers are shot and I might have to change those to stoptech's just as I did on the fronts.

I really want to go to a full dual master cylinder set up as pedro suggested but I want to retain abs as its an advantage in my GT race class.

Viperbob1

That is what you would think Vaughan. But it still does not seem right

I wish I could Peter. My 996tt and 997 customers grew into racing with their current cars. They do not have any idea about this concept of threshold braking. Go fast, slam on brake. The ABS is so smooth anymore that it is a crutch that racers do not even know they are using. When there is an ABS issue, the one customer smoked his tires everywhere and spun 3 times on one lap at Sebring.

Mobonic we are not even moving the car to get any possible piston knock back. But as you described spongy pedal when car is turned on. Thing is, ABS pump went bad in an instant on track. Replaced it (which means calipers were fine then, no leakage of fluid etc) and pedal is junk. We ran with rock hard pedal for 2+ years (new calipers were installed F & R about a year ago and maybe 15 track days on them). Pads never made a difference. So if pedal hard as a rock with car off, and when car is on the pedal is soft and continues sinking to the floor "Where is the fluid going?" Has to be the valves in ABS are opening. Like you new master cylinder, no fluid leaks in any seals, stainless lines so no ballooning. Gonna take it to dealer and have then 1) Bleed with PIWIS and 2) we are going to remove all the other systems that are no longer applicable to the car. Will try #1 first and check. Then #2 and check. Will let you know what I find.

Any other thoughts or experiences?

2BWise

With a new ABS unit I wouldn't expect an issue with seepage past any of the valves. There is the potential for several other issues to be going on. Any evaluation of the system with the car off or no vacuum supplied is worthless. There is so much mechanical advantage provided thru the booster that you aren't going to be able to feel any issue thru the pedal. You almost physically can't match the force output without straining yourself. The ABS unit when unpowered and powered defaults to inlet valves open and outlet valves closed. If you don't get seepage with the unit unpowered then you shouldn't get any with it powered. Unless there is an internal electrical issue that is opening the valves but I find that highly unlikely.

Things that I would consider chasing: piston seal wear, pad taper, and rotor wear. Try all new hardware on each corner and then check the pedal feel. It is surprising how much pedal travel that can be caused thru normal wear of the braking components and especially when you start applying very high pressures thru the system. Any uneven wear in the brake components will show thru the pedal as added travel and a spongy feel to pickup all the compliance. Another thing to note. The factory bleed process is amazing. Once you crack the system you might not be able to reproduce that pedal feel ever again. Seen it in development cars and never reached the same pedal feel as when the car was first built.

Really should teach customers how to threshold brake or at least point them to someone who can. That's a pretty basic race technique that really should be in their bag of tricks. Especially considering one such person is so bad as to smoke all tires and spin 3 times in a lap.

mdrums

Bob have you spoken with John over at BGB in Daytona. They have tons of 997 and Cayman race car experience.

Have you tried to plug back in all the nannies and clear the fault codes and see if the brakes feel better. I was also told buy Porsche that Durametric will not run the ABS pump properly to bleed the brakes.

By the way...I got, once again at over 130 on the banks PSM and Drive Off Assistant failure...lights! Kicks the car into the soft normal shock setting and into the slow normal PSM shifting!

Viperbob1

Using a Cup booster you only have a 3.15 leverage advantage on the pedal. Why do you not think you could feel that? And yes what some people are saying is that a build up of error codes through the CAN bus potentially causes, intentional or not who knows, the valves to open and bleed off some of the pressure.

Come on. The system had a catastrophic failure. From perfect pedal during race (new pads and rotors just installed before car went onto track) to failed ABS unit on track. All components other components were fine and after just replacing ABS pump car acts like many other 997s apparently that have been turned into race cars.

The car is on the third ABS pump (second work just like first for 2+ years as dedicated race car. Same rock hard pedal. Third pump had exact same Porsche and Bosch part numbers) and third Master Cylinder. The system was far from being a virgin before this episode.

Easier said than done anymore with guys starting racing with the newer cars

2BWise

Is 3.15 the boost ratio or the pedal ratio? I don't know how the stock booster or pedal ratio compares to the Cup equivalents. What you could try is to pull the ABS fuse with the car running. If the pedal travel is the same then its not the ABS unit.

Still don't understand how that's plausible. If its an error code for one of the ABS sensors, maybe, but the safest failure mode for an ABS controller is full brake control to the driver. In no situation would it be safer for the ABS unit to bleed off pressure.

So start of race perfect pedal, ABS failure during (how did it fail; was this the "pedal falls all the way to the floor issue"?), and afterwards replacing the unit you have a spongy pedal. If we make the assumption that the unit is bled properly isn't it at all possible that your 997, turned race car, has base brake issue that doesn't show up until strong track usage. Something that may not have been designed for on a prominently street based car. Have you trying running a session back to back with ABS fuse in and ABS fuse out? That would give you a direct comparison of the foundation brake components.

Viperbob1

OK as a follow up. Took the car to Porsche. Bleed with a PIWIS instead of the Durametrics (which was used repeatedly on the individual channels and then also numerous times just running the pump before hand) and removed like 30+ entries in the Gateway for now non-existant devices (doors, seats, memory, etc, etc). Glad to say the car is MUCH better. Pedal is back to probably 70-80% the firmness prior to all this mess. Pedal no longer sinks when holding down. Oddly enough, the PIWIS bleed did maybe a little to help the pedal, but it seems removal of all the systems in the Gateway did the most. Strangest thing I have seen....