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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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 Posted: Mon Nov 26, 2018 6:48 pm Post subject: Help Please - Traction Control Cutting In When Not Required
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Hi Guys
Please help. Last week I fitted some new rear tyres which are Falken in the standard size same as removed but obviously not N rated. I had seen mixed reviews but thought I would try them. They have been on a week now so 500 miles and pressures are correct.
The issue I have is the traction light comes on and the power cuts or the brakes cut in when not require. Typically this happens on a bend when at steady speed or when slowing down into a bend. Strange thing is when accelerating out of bends it does not happen.
Any thoughts on what to try should I increase or decrease pressures? Should I get new front tyres to match the Falkens or should I just get some continentals like I had before?
Or could it be something else like a damaged or failed sensor or component?
Cheers
Winny
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Robertb
Long Beach
Joined: 01 Sep 2003
Posts: 6771
Location: South Oxfordshire
2002 Porsche 996 Carrera 4S
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| Posted: Mon Nov 26, 2018 7:29 pm Post subject:
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I had a BMW 330 on which I changed the rear tyres only... it handled dreadfully afterwards, much like you describe, improved after a while when the tyres were properly worn in.
It could be the difference in tread depth giving odd wheel speed sensor readings.
What is the tread depth on the front?
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"911- the guilt-free supercar"
Current: 2003 C4S Coupe, seal/black
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The return of Marty Wild
Barcelona
Joined: 04 Nov 2016
Posts: 1277
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| Posted: Mon Nov 26, 2018 7:39 pm Post subject:
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Off topic - Is that a sneaky bit of Beachy Head I spy?!
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Life's too short for cr4ppy cars, keep it German!
Cayman S 987.1
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deMort
Zolder
Joined: 21 Mar 2015
Posts: 5951
Location: Brighton
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| Posted: Mon Nov 26, 2018 7:53 pm Post subject:
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I would start by getting an Indy to do a steering angle calibration ..
After that we are into the rotational difference between tyres .. ie the fronts might need changeing .
Basically the car thinks its starting to slide , it can only measure this by the rotation of the tyres .. if not N rated then you are out of specs but that shouldn,t make a huge difference .. its a bigger problem to have an N rated and a non N rated on the same axle .
Either ways .. steering angle sensor calibration first then we go from there .
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Now At An Indy.
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alex yates
Le Mans
Joined: 06 Mar 2014
Posts: 15273
Location: The Ribble Valley, Lancashire
2000 Porsche 996 Carrera 4
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| Posted: Mon Nov 26, 2018 8:14 pm Post subject:
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Broken reluctor ring.
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2000 Manual 996 C4 Arctic Silver Convertible
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alex yates
Le Mans
Joined: 06 Mar 2014
Posts: 15273
Location: The Ribble Valley, Lancashire
2000 Porsche 996 Carrera 4
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| Posted: Mon Nov 26, 2018 8:23 pm Post subject:
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Is your speedo giving a reasonable reading or is it a fair way out? Also, is it one sided that the braking is on or front/rear? You can tell by feeling the discs after its done it. One (or a pair) will be a lot hotter
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2000 Manual 996 C4 Arctic Silver Convertible
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alex yates
Le Mans
Joined: 06 Mar 2014
Posts: 15273
Location: The Ribble Valley, Lancashire
2000 Porsche 996 Carrera 4
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| Posted: Mon Nov 26, 2018 8:24 pm Post subject:
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I can't see it being tyre related so long as the tyre sizes are correct.
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2000 Manual 996 C4 Arctic Silver Convertible
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Mon Nov 26, 2018 8:44 pm Post subject:
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Thanks for the quick response
Front tyres are 3-3.5mm continental contact sport 5s non n rated. Just checked the pressures all consistently down 2-3 psi but would be expected with recent temp drop
By chance it is going into Parr tomorrow for a 12k service would that include scanning for codes? And would a steering calibration cost much while it is in there?
Yes that is beachy head.
Cheers
Winny
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Mon Nov 26, 2018 8:56 pm Post subject:
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Thanks Alex
Speedo seems accurate. There is no odd braking but will check wheel temps when I get to work tomorrow.
Could it be the front diff? I have noticed it it seems stiff (tyres judder) when pulling away from cold in the morning but it goes within 20 seconds of driving this has also started to happen post tyre change last week.
Cheers
Winny
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alex yates
Le Mans
Joined: 06 Mar 2014
Posts: 15273
Location: The Ribble Valley, Lancashire
2000 Porsche 996 Carrera 4
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| Posted: Mon Nov 26, 2018 8:58 pm Post subject:
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I thought you said the brakes cut in when not required?
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2000 Manual 996 C4 Arctic Silver Convertible
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Johnd52
Montreal
Joined: 06 Oct 2014
Posts: 521
Location: North Yorkshire
2011 Porsche Cayman 987
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| Posted: Mon Nov 26, 2018 9:43 pm Post subject:
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I am sure Demort is right re the steering angle sensor needing a reset. Parr can do this easily. The judder you experience may also be related to the steering, with the back wheel now having more grip and pushing the front a bit more. Is this mainly when cold, low speed with some lock on?
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2015 Cayman GTS. No more PDK but still red.
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Mon Nov 26, 2018 10:02 pm Post subject:
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Alex
I'm not sure how the traction control works but yes driving along a bend or going into a roundabout the light comes on and the car starts to jump about I'm not sure if the traction control cuts the power or applies the brakes (or both?) but when braking going into a roundabout if it comes on you do get that on off pulsing from the abs
Braking without a bend the brakes feel fine and the abs stays off
John
The judder seems to be only when cold and only if turning out of a parking space or the drive way. I have had this before but not for a long time and I seem to remember it being a cold thing.
Could his really be tyre related and how / why would a steering sensor suddenly fail following a tyre change? Is it just a coincidence?
Cheers
Winny
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alex yates
Le Mans
Joined: 06 Mar 2014
Posts: 15273
Location: The Ribble Valley, Lancashire
2000 Porsche 996 Carrera 4
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| Posted: Mon Nov 26, 2018 10:07 pm Post subject:
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My money's on a broken reluctor ring. Mine was doing a similar thing. After feeling round each disc (and feeling the heat), the rear RH brake was actuating on its own causing the judder and also when you pressed the brakes, you also had the pulsating. Turned our the rear LH reluctor ring had broken. Was still in position but giving an incorrect speed reading, conning the traction system that the RH rear wheel was travelling a lot faster than the left so applied the brake to slow it down.
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2000 Manual 996 C4 Arctic Silver Convertible
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James M-S
Imola
Joined: 11 Apr 2017
Posts: 817
Location: Derbyshire
2009 Porsche 997 Carrera 2
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| Posted: Mon Nov 26, 2018 11:29 pm Post subject:
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What is the date code on new tyres? Could they be losing grip due to release agent from the mould?
It might happen at lower speed than expected due to low temp and damp roads?
Just a thought. Hopefully parr will resolve it.
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Manual 997.2 c2 :Basalt + gtechniq : H&S + Gundo
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toohey
Monza
Joined: 22 Jan 2009
Posts: 184
Location: Naarfolk
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| Posted: Tue Nov 27, 2018 9:26 am Post subject:
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what size are the front tyres? - i bought some second hand wheels for my car and the front tyres were actually the wrong profile! The larger profile fronts meant that the rears (correct size) were always turning quicker and cause the ECU to back off the ignition timing and all sorts  - changing the fronts when i spotted it made a significant difference to performance and its behaviour......
...... if it's not that and i don't expect it is..... I'm with Alex - check the traction rings....
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Bluebird911
Nürburgring
Joined: 29 May 2010
Posts: 439
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| Posted: Tue Nov 27, 2018 1:56 pm Post subject:
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This does seem a strange one, but a heck of a coincidence with the tyre change if it started playing up at the same time.
I had a similar experience a few years back when the steering angle sensor lost its calibration. Happened a couple of times, so the sensor was replaced.
most of the time it wasn't as dramatic as you describe - I would travel about 200yds while the car carried out diagnostics and calibrations and the ABS light would come on. On occasions when it didn't come on, driving around bends at a range of speeds, I experienced wheel braking / power reduction etc (sometimes quite severe) until the road straightened out and it would settle down again.
Mine is a C4. Alex's suggestion is worth checking out as well.
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Tue Nov 27, 2018 10:36 pm Post subject:
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Thanks for all the help guys
I got the car back from Parr today they could only get it to do this once but I suspect they were not driving fast enough 
Anyway what they did find was odd tyre wear on the front insides and also the bushes on the suspension arms stating to pop out. they suspect this is the cause. I'm about to take the car off the road on 1st December so thinking when I get it out again April I will get new front tyres and maybe do the arms over winter. How hard is it to do the bushes? Is it a complete arm or just the bush? Once done get it setup properly and see what happens.
Cheers
winny
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Martin996RSR
Spa-Francorchamps
Joined: 08 Dec 2016
Posts: 297
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| Posted: Wed Nov 28, 2018 3:54 pm Post subject:
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It's normally done by replacing the whole arm. You can however buy polybushes and just replace the bush, but it's a lot of faff.
I'd be very surprised if the bushes were the cause of the problem. The car's wheel speed measurement system(which is how the ABS and TC systems know when to do something) is where I would start. Alex's reluctor ring suggestion is what I would be looking into first, along with the steering angle calibration.
I've run my car with a nearly bald tyre on one side and a new tyre on the other side of the same axle with no ABS/TC impact whatsoever.
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Wed Nov 28, 2018 9:13 pm Post subject:
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I would be interested in knowing how to check the reluctor rings if it is an easy job.
That said I'm fairly sure Parr are correct with their diagnosis as I have tried the car with the PSM turned off and the front end does let go at the same points where it loses power / slows down with the PSM on. I think it's a combination of minor issues at the front and extra grip at the back.
Guess we will have to wait until April to find out.
Thanks for all your help guys
Winny
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Winny911
Montreal
Joined: 13 Dec 2012
Posts: 512
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| Posted: Wed Nov 28, 2018 9:14 pm Post subject:
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I would be interested in knowing how to check the reluctor rings if it is an easy job.
That said I'm fairly sure Parr are correct with their diagnosis as I have tried the car with the PSM turned off and the front end does let go at the same points where it loses power / slows down with the PSM on. I think it's a combination of minor issues at the front and extra grip at the back.
Guess we will have to wait until April to find out.
Thanks for all your help guys
Winny
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