Very dangerous brake problem at the Nürburgring with 2 996 Turbos
#46
Now, I want to try the pre-charge disconnect job, to find out what it does exactly. Did anyone else try this? Does the core PSM function still engage, or try to engage?
Or does the disconnect give PSM error code/shutdown right away, or on the first time PSM is trying to work? I guess I am trying to find out that if ABS is working with this pre-charge pump disconnect trick, will that only shut off PSM, or also shut off what I call "core PSM"?
Or does the disconnect give PSM error code/shutdown right away, or on the first time PSM is trying to work? I guess I am trying to find out that if ABS is working with this pre-charge pump disconnect trick, will that only shut off PSM, or also shut off what I call "core PSM"?
You will have no interference at all from the PSM.
#49
(Great, thanks for the hint!)
#50
I did not feel it was unexpected at any time from PSM, or wrong either from PSM, it would be necessary to save the driver from a classic 911 spin out if this action was not fully intentional.
If now, as fellow Swede Speedfreak posted, the complete PSM function, incl PSM core function, is gone with the pre-charge pump disconnected then my problems are solved.
But I tested the car with 1 PSM fuse pulled out, that kept the ABS working and put the PSM failure light on, and it took three tailhappy turns to have core PSM go off again. I will check with a meter if this was the pre-charge pump fuse (it only says PSM in the fuse plan).
#51
Im, sure if the fuse is pulled that it disables both PSM & ABS... I haven't tried SpeadFreaks method as yet (was going to soon, just to see what happens) but I have not encountered these braking issues... I wonder if this has anything to do when brake fluid is boiled within one caliper!!!... lets face it the stock cooling isn't great under there and I run separate cooling hoses along with the Cup ducts, it does make a difference.
#53
Overall, this is a very RARE problem and I think smoother braking solves and helps but still this kind of thing should not exist. I am happy now as the improved yaw rate sensor (with all kinds of other tricks I tried along the way...) helped me. However, it is "good" that after some years some other members have commented about similar problems, as I was alone hitting my head against the wall quite a bit.
Back in the days I tried without ABS/PSM and the problem still existed.
Speed's recommendation of completely disabling the PSM is very good.
Just for all the members to know, now when you press PSM off it is off BUT it comes on if your tires are sliding over 7% and you are on the brake pedal (quite good feature for amateur drivers; PSM helps when you are in problems and you try to slow down the car, however, this brings additional problems with trail braking etc. and I believe this is the reason why a lot of 997 guys have had problems with rear pads and disks. Heck, even for me rear disks last only a season )
Good stuff again MrWhite, you remind me a lot of my favorite professional racing driver who is friendly and co-operative yet very knowledgeable.
When I talked on the previous message about Turbo's ABS not being suitable I did mean ABS including the PSM. So you are right with these comments again. The car I drive is one of the first Turbos ever rolled out from the factory (car was already on the streets of Finland in the beginning of June 2000). After that (do not know the date of change) Porsche changed the yaw-rate sensor which is a critical part in the system.
The part number for new "rate of turn sensor" is 996.606.145.00 and it can be only combined with the newer hydraulic unit 996.355.955.58 (there has been two previous units with same part number ending .51 and .57. The previous rate of turn sensor was 996.606.147.00 and they look different.
PM me if further instructions are needed as I have some handy files available.
I know this question is not pointed to me, but I want to emphasize I had this problem with stock sized tires and also with tires with a minor yet accepted difference (such as 235/295), LSD lockup 45%.
Cooling is very important in all brake related issues. I am very sure proper cooling helps even in this problem. However, I tried both Motul and Castrol racing fluid along with Cup ducts and still had the problem. Perhaps that was not enough but I think it should be.
Personally I'd try a safe track and take out the ABS PSM fuse and see if the problem occurs again. If not, then you have narrowed it down to the PSM and ABS systems at fault. If so, then you know it's one or the other. Then try Speed's recommendation and disable the PSM completely. And so on.
Speed's recommendation of completely disabling the PSM is very good.
Just for all the members to know, now when you press PSM off it is off BUT it comes on if your tires are sliding over 7% and you are on the brake pedal (quite good feature for amateur drivers; PSM helps when you are in problems and you try to slow down the car, however, this brings additional problems with trail braking etc. and I believe this is the reason why a lot of 997 guys have had problems with rear pads and disks. Heck, even for me rear disks last only a season )
Getting back on this thread, I had this lockup happen two days ago. It came gradually though, the fluid got overheated, the PSM/pump went frenzy and partially started to brake and within the next 1-2 seconds the brakes locked. Relatively slow place of track though and with a big banked turn so stayed on surface.
The problem for me seemed to be that with my car that has a little more "roatation" (oversteer) than the core PSM-function accepts (core PSM-function meaning even when the PSM is switched OFF), PSM was jabbing the brakes constantly and overheated the fluid in the brake system and somehow the whole brake unit went stiff pedal, pedal stayed in, and brakes would just lock. It took some cooling time and two restarts of the car before the unit would release the pedal again.
I removed the fuses from the entire PSM and ABS system and ran without and it worked fine, just had no ABS function anymore. It works but overall brake capacity sucks since basic bias is very much towards the front. My PBox shows I could brake 0.6G at best before locking up. At Cali Speedway in November I could brake at nearly 1.3G with electronic brake bias active (= ABS unit connected). At Cali speedway I did not have this problem, longer straights, less transitions to set off PSM.
Now, I want to try the pre-charge disconnect job, to find out what it does exactly. Did anyone else try this? Does the core PSM function still engage, or try to engage?
Or does the disconnect give PSM error code/shutdown right away, or on the first time PSM is trying to work? I guess I am trying to find out that if ABS is working with this pre-charge pump disconnect trick, will that only shut off PSM, or also shut off what I call "core PSM"?
2nd I want to know more about is the yawrate-sensor - is it just an improved sensor allowing wider "slides", which will still engage PSM if my slip angle is too large? (I suspect it will). Any part number for this?
It'd be nice for everyone to have this "myserious" brake issues fully sorted.
The problem for me seemed to be that with my car that has a little more "roatation" (oversteer) than the core PSM-function accepts (core PSM-function meaning even when the PSM is switched OFF), PSM was jabbing the brakes constantly and overheated the fluid in the brake system and somehow the whole brake unit went stiff pedal, pedal stayed in, and brakes would just lock. It took some cooling time and two restarts of the car before the unit would release the pedal again.
I removed the fuses from the entire PSM and ABS system and ran without and it worked fine, just had no ABS function anymore. It works but overall brake capacity sucks since basic bias is very much towards the front. My PBox shows I could brake 0.6G at best before locking up. At Cali Speedway in November I could brake at nearly 1.3G with electronic brake bias active (= ABS unit connected). At Cali speedway I did not have this problem, longer straights, less transitions to set off PSM.
Now, I want to try the pre-charge disconnect job, to find out what it does exactly. Did anyone else try this? Does the core PSM function still engage, or try to engage?
Or does the disconnect give PSM error code/shutdown right away, or on the first time PSM is trying to work? I guess I am trying to find out that if ABS is working with this pre-charge pump disconnect trick, will that only shut off PSM, or also shut off what I call "core PSM"?
2nd I want to know more about is the yawrate-sensor - is it just an improved sensor allowing wider "slides", which will still engage PSM if my slip angle is too large? (I suspect it will). Any part number for this?
It'd be nice for everyone to have this "myserious" brake issues fully sorted.
When I talked on the previous message about Turbo's ABS not being suitable I did mean ABS including the PSM. So you are right with these comments again. The car I drive is one of the first Turbos ever rolled out from the factory (car was already on the streets of Finland in the beginning of June 2000). After that (do not know the date of change) Porsche changed the yaw-rate sensor which is a critical part in the system.
The part number for new "rate of turn sensor" is 996.606.145.00 and it can be only combined with the newer hydraulic unit 996.355.955.58 (there has been two previous units with same part number ending .51 and .57. The previous rate of turn sensor was 996.606.147.00 and they look different.
PM me if further instructions are needed as I have some handy files available.
Cooling is very important in all brake related issues. I am very sure proper cooling helps even in this problem. However, I tried both Motul and Castrol racing fluid along with Cup ducts and still had the problem. Perhaps that was not enough but I think it should be.
Last edited by Kaizu; 03-01-2010 at 07:10 AM.
#54
Just another note on this, I can definitely 100% for sure confirm that dis-connecting the pre-charge pump kills the PSM completely, however still leaves a fully functional ABS system to drive with.
Also, when plugging the connector back in, there are no active failure codes in the car and the PSM and ABS warning lights are off (and the system is back on) - could be good to know for those who don't have a code reset tool.
Additionally, driving a full two days with the pre-charge pump disconnected, on 265 fronts and 315 rears, hot day as well, I had absolutely zero braking problems this time. The car could also slip and slide in any way I wanted to with no interference from any type of "core" PSM.
Thx Speedfreak again for the input.
ANOTHER NOTE: This above, does not suggest the final solution of the OP issue reg a brake problem on Nurburgring.
Last edited by MrWhite; 04-03-2010 at 05:22 PM.
#55
...but at high speeds the GT3 calipers work fantanstic compared with OEM and ABS locks as OEM.
I am thinking to upgrade the rear ones.....has someone some info abbout? ..is it worth?
#56
Just another note on this, I can definitely 100% for sure confirm that dis-connecting the pre-charge pump kills the PSM completely, however still leaves a fully functional ABS system to drive with.
Also, when plugging the connector back in, there are no active failure codes in the car and the PSM and ABS warning lights are off (and the system is back on) - could be good to know for those who don't have a code reset tool.
Additionally, driving a full two days with the pre-charge pump disconnected, on 265 fronts and 315 rears, hot day as well, I had absolutely zero braking problems this time. The car could also slip and slide in any way I wanted to with no interference from any type of "core" PSM.
Thx Speedfreak again for the input.
ANOTHER NOTE: This above, does not suggest the final solution of the OP issue reg a brake problem on Nurburgring.
Also, when plugging the connector back in, there are no active failure codes in the car and the PSM and ABS warning lights are off (and the system is back on) - could be good to know for those who don't have a code reset tool.
Additionally, driving a full two days with the pre-charge pump disconnected, on 265 fronts and 315 rears, hot day as well, I had absolutely zero braking problems this time. The car could also slip and slide in any way I wanted to with no interference from any type of "core" PSM.
Thx Speedfreak again for the input.
ANOTHER NOTE: This above, does not suggest the final solution of the OP issue reg a brake problem on Nurburgring.
#57
Great info for those who are heavily tracking their Turbo. I experienced this PSM issue on our shop car at Roebling Road last weekend. 2001 Turbo, around 550hp, rwd. PSM was "off" the entire time, but would come on abruptly mid corner with trail braking or light brake application.
I pulled the PSM relay as pictured in Speedfreak's post on page 3 and I'm pretty confident that this is the fix based on what I'm reading here and elsewhere.
I pulled the PSM relay as pictured in Speedfreak's post on page 3 and I'm pretty confident that this is the fix based on what I'm reading here and elsewhere.
#58
I get the brake fluid level light on track, unless the fluid level is precisely at the tip of the arrow marked MAX. It seems that even a mm over or under eventually lights it up. It also occasionally triggers the red WARNING about brake system failure. Students riding in the car sometimes get a little edgy when they see it, and I just flip the lever off and keep going.
I once had a lockup under heavy braking at Turn 14 at Road America, but that was because I had hosed up the alignment and the steering angle sensor was off, so the PSM turned itself off.
The fact that you get yours under light braking does suggest a stuck piston somewhere.
Jon
I once had a lockup under heavy braking at Turn 14 at Road America, but that was because I had hosed up the alignment and the steering angle sensor was off, so the PSM turned itself off.
The fact that you get yours under light braking does suggest a stuck piston somewhere.
Jon
Last edited by pwdrhound; 09-14-2011 at 08:27 PM.
#59
Finally pulled the plug (literally)! Since I had my last alignment done with a little more aggressive settings, my PSM sometimes kicked in when taking sharp turns with higher then average speed. I tried switching off the PSM but it still came in once awhile. I finally pulled the plug as stated on page 3 (picture). You do get the PSM OFF warning light + the dashboard warning (which can be turnned off). So far, the car is driving fine.