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Tobesetc
Albert Park


Joined: 02 Jun 2014
Posts: 1500
Location: West London, UK


PostPosted: Sun Mar 10, 2019 9:15 am    Post subject: Brake question Reply with quote

993 C4 with standard brakes. Several times I've noticed that the ABS system seems to cut in earlier than I would expect. When braking fairly heavily, the pedal seems to stutter away from you as the brakes are cut in and out to avoid locking up. It isn't that the ABS isn't working, rather that (I feel) it cuts in earlier than I would expect.

This has happened consistently throughout my ownership on whatever old or brand new tyres it's wearing. It's not getting worse. It's not something I notice anywhere near every drive, just when I apply heavy braking, so it's a marginal thing that occurs infrequently. But it's more often than I expect - I guess I'm judging against my experience in other cars, it happens more often than any other car I've driven regularly... but I suppose its the heavier of the sports cars that I've owned, so...

Does not feel like the brakes don't work, just that the ABS is firing a bit "easily" . It's booked into a local (ish) Indy for this to be checked this week.

Does this mean I have to stop wearing my lead diving boots when I drive? Maybe I'm just trying to give myself an excuse to upgrade the brakes - but something tells me that upgrading brakes and leaving the same ABS system in place, isn't going to stop it!

Thoughts?
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Endoman
Barcelona


Joined: 11 Apr 2011
Posts: 1300
Location: Bolton U.K.


PostPosted: Sun Mar 10, 2019 11:03 am    Post subject: Reply with quote

Interesting.
If the car was new to you (which it isn't) I would have suspected brake grabbing, caused by bad discs, pad lift, worn tyres, underinflated tyres, worn suspension bushes/shocks, seized brake piston.
But as you say maybe just your leaden plates of meat.
I only get the abs activating in the usual situations, slippy surface, emergency stops.
I suppose it could be something electrical in the sensor/activation circuit.
The ABS on the 944 never works even on track.Though I've been through the whole system even rebuilt the abs pump which was seized.
Ages ago in an MG Montego (which was shyte) the front brakes would lock at the slightest provocation needless to say I eventually wrote it off againt a lamp post.
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wilsonny
Monza


Joined: 01 Dec 2012
Posts: 177
Location: Cumbria


PostPosted: Mon Mar 11, 2019 8:00 pm    Post subject: Reply with quote

could be heavy feet but sounds like something must be wrong here... on my standard c2, my abs hardly ever comes in even on track... it's only when I've really braked to the point of tyre lock up that it triggers. that's with all new std. Porsche brake bits.
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decgraham
Barcelona


Joined: 17 Sep 2008
Posts: 1292
Location: Spain


PostPosted: Tue Mar 12, 2019 7:38 am    Post subject: Reply with quote

Where I live, there is a very steep hill leading down to the main road. Occasionally my ABS will kick in as the when it rains the road gets very slippery, so just the ABS doing its job when the brakes lock up and the car starts to slip on the road surface. It never cuts in any other time though.

ATB Smile
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alex yates
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 15538
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue Mar 12, 2019 7:44 am    Post subject: Reply with quote

I doubt this has anything to do with either your brakes or your ABS. The ABS is only looking at frequency readings from the sensors. If it sees abnormal patterns it will start working.

Are you running different size rolling radius tyres than standard between front and back?
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alex yates
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 15538
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue Mar 12, 2019 7:47 am    Post subject: Reply with quote

Also, over time do you get any abnormal tyre wear? eg: Does it eat front tyres.

Could also be something to do with your AWD viscous coupling.
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Tobesetc
Albert Park


Joined: 02 Jun 2014
Posts: 1500
Location: West London, UK


PostPosted: Tue Mar 12, 2019 8:18 am    Post subject: Reply with quote

Brand new wheels exactly the same dimensions as RS 18" wheels on brand new Michelin tyres, running on suspension newly adjusted by Centre Gravity and deemed to be working as new.

Did it on the original 17" Cups, did it on hollow TTs with new tyres, does it still. Not often, I must add.
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madalaa
Fuji


Joined: 13 Mar 2008
Posts: 9380
Location: West London

2009 Porsche Boxster 987

PostPosted: Tue Mar 12, 2019 8:40 am    Post subject: Reply with quote

Tobes ........ it very rarely happened on my C4 and in fact I can only remembering it happening on a few occasions when I had to do an emergency stop or when I have failed to slow down quickly enough on a sharp corner up in the mountains of Europe.

It never happened when I tracked the car.

It doesn't seem right to me but I can't give you any explanation for the cause.
 
  
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Tobesetc
Albert Park


Joined: 02 Jun 2014
Posts: 1500
Location: West London, UK


PostPosted: Tue Mar 12, 2019 10:36 am    Post subject: Reply with quote

I'm probably being over picky, as I probably should/could describe the times it happens as emergency or late breaking in damp... maybe I just do that too often! Wink

Going to get it checked out anyway.
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9xxnick
Monza


Joined: 29 Jul 2014
Posts: 161



PostPosted: Thu Mar 14, 2019 9:48 pm    Post subject: Reply with quote

The ABS cuts in to prevent one or more wheel locking up. If one of the four brakes (one per road wheel) is relatively ineffective this could cause the synptoms you are experiencing.

The annual MOT check should however show up any brake imbalance from side to side on each axle, and also tests the effectiveness of front and rear axle brakes separately. So if there's a problem with the brakes it should be identified at the time of the MOT test.

I suppose the other area to check is the tyres. Old, hard and/or not very good quality tyres could lead to reduced grip, especially in the wet, and hence trigger the ABS earlier than expected.
 
  
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Endoman
Barcelona


Joined: 11 Apr 2011
Posts: 1300
Location: Bolton U.K.


PostPosted: Thu Mar 14, 2019 10:02 pm    Post subject: Reply with quote

I think you are just looking for an excuse to go for Big Reds it's cheaper just to paint them Smile
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Tobesetc
Albert Park


Joined: 02 Jun 2014
Posts: 1500
Location: West London, UK


PostPosted: Fri Mar 15, 2019 3:40 pm    Post subject: Reply with quote

Already done the painting... but you have a point that's it's an excuse! Wink
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