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justin's Avatar
 
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Front brakes locking up in the rain,

If I hit the brakes a little hard,about the same pressure as stopping on a dry road,they lock up and I start to slide,and I can't turn,until I let off the brakes,just the front wheels,not the back,it is very dangerous,what can be causing this? I have good pads up front,and factory rotors. Tires are pretty new Toyo FZ4's, I checked the air pressure and it's all good. I just started noticing it doing this.
TIA
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Old 10-09-2003, 12:19 AM
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You did not say anything about your rear pads. If they are different than your front pads, that is what you'd should expect. Are your tires the same. You don't say this in your post.
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Old 10-09-2003, 02:49 AM
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The probable cause is that it is a rear wheel drive car,no traction control,no abs.....944 is,for me,difficult to drive under rainy conditions....Last day,with a heavy rain squall,i had great difficulties maintaining direction...

Just be very carefull and soft.

Well you have a 911T and a 928....just the little collection i would like to have,you bast*** :P

The problem is only with the 944?
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Old 10-09-2003, 02:56 AM
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Yeah, thinking about it, if your front pads are good, and something was wrong with the back, the effect would be the fronts locking as you have described. Better check the back brakes and start deducing from there.
Old 10-09-2003, 06:06 AM
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I had a very similar reoccurring problem on my kit car - same tyres all round, correct pressure, good pads, good discs, quality brake fluid / system etc. etc.

After exploring every logical avenue I eventually replaced the front pads despite there being no significant wear, contamination or glazing. Fixed the problem immediately. This happened again about a year later - exactly the same. There was no obvious explaination such as fluid leaking onto the pads or signs of heat build up - it just happened.

Unlike Manute I've never had any problems with the 944 being a poor-handler in the wet. I guess this boils down to the choice of tyres you've selected. A lot of people think that the wider the tyre the better the grip you have in wet conditions. This isn't necessarily so - a 225 might look like it should grip well in the wet but it's only as good as its tread's ability to cut through and shed water - if it does this poorly what your car is actually wearing is a set of water skies and you'll aquaplane / skid

Front tyres always slide first because they're the ones that have the most work to cope with under load. If you can't find an obvious reason for the problem perhaps you might have to reconsider your tyres.

Currently I'm using (secondhand) Yokohoma 195 and they perform great in the wet but drift under hard use in the dry. I've always found Pirelli 215's excellent all-rounders.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

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Last edited by Dark Skies; 10-09-2003 at 07:14 AM..
Old 10-09-2003, 06:55 AM
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To a point, arent' thinner tires generally better in the wet? (more weight on a smaller contact patch)?
Old 10-09-2003, 07:02 AM
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"To a point, arent' thinner tires generally better in the wet? (more weight on a smaller contact patch)?"

That's what I've always been led to believe, although as I understand it the important thing is the surface area to drainage ratio. A 225 slick with no drainage actually doesn't make contact with the road - it's floating on the wet surface because the water isn't being displaced at the point of contact - other than sporadic contact being made due to the uneven surface of the road acting as drainage. The same tyre with a series of thinner contact patches enables the water to be pushed into channels and drained behind itself on rotation.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

"I have only five words for you: From my cold, dead hands."

Last edited by Dark Skies; 10-09-2003 at 07:17 AM..
Old 10-09-2003, 07:13 AM
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Another thing to look at is the balancing valve/oriface between the front and rear. Could be dirty and giving the fronts more pressure than they are supposed to have.
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Old 10-09-2003, 07:53 AM
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My front tyres are a bit worn,maybe that´s why i slip a bit.I have 205 front,225 rear,just the standard measures.

An off topic question for Justin...just for curiosity,what porsche do you prefer of the three you have?
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Old 10-09-2003, 11:03 PM
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Well my front and rear pads are in good shape,as a matter of fact,the back ones are pretty new,I guess I will change the front ones anyway. All my tires are the same size and brand,the front and back pads are different brand though,I never heard of this causing a prob., but I will check. So cal, where is the poporsioning(sp) valve located on this car?
Manute- The 911T is still under construction and the 928 is fun to drive,but it feels heavy,not very nibble feeling like the 944's. If I had to chose between the 944 and the 928,I would chose the 944 for handling and the 928 for a cruiser,Porsche really did their job. Seeing how the 928 is classified as a touring car,I'm not sure what the 944 is classified as.
Thanks everyone for the help on this.
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Old 10-09-2003, 11:33 PM
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Varying brands of pads could imbalance the brakes - some brands are more efficient than others - especially those aimed at the sportier driver. It's certainly worth putting the same brand in the front when you come to replace them for the sake of elimination purposes if nothing else.

Also - new pads require some time to bed in and are more prone to glazing during the first few hundred miles. Is it possible the new rears could have become glazed through harsh braking following installation? That could have set up an imbalance too.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

"I have only five words for you: From my cold, dead hands."
Old 10-10-2003, 05:06 AM
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You can also adjust your driving technique.
If you apply the brakes slower and smoother, more weight transfers to the front of the car, allowing better braking action.
We have lots of rain around Seattle, so we get lots of practice.
Old 10-11-2003, 09:03 AM
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Quote:
Originally posted by Dark Skies

Front tyres always slide first because they're the ones that have the most work to cope with under load. If you can't find an obvious reason for the problem perhaps you might have to reconsider your tyres.
that's actually not true. most passenger cars are sprung so softly that when they brake hard, there is so much weight transfer that the rear usually locks up first
i do agree that most porsches and other sports cars are more likely to lock up the front

it just sounds like you are exceeding your traction budget and need to get larger or grippier rubber
if you pedal modulation changes abruptly along the length of your pedal travel, i would then worry about your brakes but just sounds like you need better tires
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Old 10-11-2003, 02:16 PM
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