How to stop a 911 in the rain

[cmcfaul]

because there is no (little) weight in the front of a 911, in the rain, the fronts lock up WAY before the rears. The physics of a 911 just don't work in the rain with little weight transfer.

So, what's the best rain / snow braking technique?

Doing a threshold brake with the fronts uses very little of the stopping power of the rears (where all the weight it).

Is it better to lock up the fronts (if steerage is not needed) and try to threshold brake the rears (almost impossible to tell when the rears have locked).

Or simply lock up all 4 and release if steerage is needed.

Thanks,

Chris
73 911 E

[Peter Zimmermann]

Sounds to me you've got a tire or shock problem. I've been driving 911s for more than 30 years and have never experienced difficulty stopping them in bad weather.

[304065]

Chris, what Pete says. I have raced many, many times in the rain at Lime Rock and my car is lighter up front than stock (fuel cell, f/g front bumper) and corner balanced, and the brakes work fine. Of course you can lock them if you slam on them, but that's not the way you should brake anyway. . . more like squeeze squeeze SQUEEZE SQUEEZE squeeze which technique will transfer weight forward as the car pitches nose down and the heavy braking begins.

Racing in the rain is fun-- you apply the brakes and turn the wheel and the car understeers THROUGH the dry line (you can feel the polished pavement through the wheel) and onto the rain line beyond where it hooks up and turns in. Disconcerting the first couple dozen times you do it.

Be careful in the rain, it's the other drivers I worry about.

[Jack Olsen]

On my car (also lightened in the front more than the rear) I've never noticed different bias issues in the wet.

I'd bet you've got something else going on.

[cmcfaul]

I don't know. I typically pick up a car length or more in the braking zone and have great balance between front and rear in the dry. In the rain, the front just trys to bite but locks up very easily, with very little pedal pressure and hydroplains. I think I get much shorter stopping distances, in the rain, by pumping until the rears lock, ignoring the fronts.

Maybe it's the tires but I have been driving this car for 30 years and have seen lots of different tires. The tires are 205 16 55's. Biggest rubber I could fit which is still small by modern standards. Again, absolutly no issues in the dry.

Chris
73 911 E

[Paulporsche]

Doesn't the weight transfer toward the front during the braking process? Does it transfer faster if the process is faster, say while threshold braking?

[cmcfaul]

Thats my whole point. If the fronts don't bite (easily hydroplane) there is no weight transfer to the front. They act like skis on a snowmobile.

Chris

73 911 E

[kodioneill]

my fronts were locking up on my 1982 sc. i found that the rear rubber brake lines were plugged. after replacing the lines the brakes work perfect. fronts never lock up no matter how hard i try. when i took off the lines i cut them open and found that they were almost completely plugged.

[Rusty Heap]

YUP, you have brake problems, not rain problems.............mine was doing the same thing (in the wet or the dry, not fun during a track day either).....fronts locks up with little or no brake response from the rear even with new pads new rotors and bled the brakes 3-5 times.........

I put in a new master cylinder. AND OH MY GOD WHAT A DIFFERENCE AND IMPROVEMENT!!!!!!!

If this is regarding your '73, and it's still on its origional master cylinder.........36 years old? I'd replace it.

[cmcfaul]

I replaced the master cylinder a couple years ago. Rebuilt all the calipers a couple times over the last few years. On the second set of SS brake lines in the front (3rd set of brake lines since birth). The rears are SS but I don't recall when I replaced them. Easy enough to do.

Ok will replace all the brake lines again and see if there is any difference. Though the front calipers are bigger than the rears (bigger piston) with less weight up there. I still think it's the nature of the beast not a mechanical malfunction.

Will see.

Thanks all,

Chris
73 911 E

[Rusty Heap]

Don't know if you're interested but I have the complete braking system (short of a master cylinder) for sale off my 1982SC I'm parting out.

Front / Rear Calipers recently rebuilt, like new front rotors and metal master pads all around, SS brake lines front and back.

All still on the car but I'll pull them if you're interested in any/all of it. It might help you out?

PM me with an email address and I'll send photos.

[kodioneill]

Originally Posted by cmcfaul

I replaced the master cylinder a couple years ago. Rebuilt all the calipers a couple times over the last few years. On the second set of SS brake lines in the front (3rd set of brake lines since birth). The rears are SS but I don't recall when I replaced them. Easy enough to do.

Ok will replace all the brake lines again and see if there is any difference. Though the front calipers are bigger than the rears (bigger piston) with less weight up there. I still think it's the nature of the beast not a mechanical malfunction.

Will see.

Thanks all,

Chris
73 911 E

the brake system in the front is larger because the front does 70% of the braking.

[Jack Olsen]

The fronts don't have less weight on them during braking. The front wheels do most of the stopping work, wet or dry. If your fronts are locking up and hydroplaning, the rears will, too, unless the fronts are locking up at the very first moment of braking.

Is this happening only in straight-line braking, or when (if) you're trail braking?

I wouldn't jump to replace parts until you understand where the failure is. You sound like you've got a lot of experience and know the car well. In your shoes, I'd do some testing in a parking lot with a spotter, preferably with a video camera, to see how the fronts are locking up relative to the rears in the dry. If the opportunity presents itself, I'd do the same thing when the parking lot is wet and compare the two videos.

[old man neri]

If you are 'hydroplaning' then it is a tire problem. Either it's a bad tire, it's bald, or you are using the wrong pressure.

[lucittm]

What is the date code on your tires? Porsche says if your tires are more than 6 years old, replace them. I know that some of our cars don't get a lot of mileage and the tires get hard over the years. This could be a contributing factor.

Mark