No brakes in the rain, I have no rotor backing plates

[heliolps2]

I have 76 911S thats been Modified ,I use to live in sunny SoCal, now I live in the east coast I never noticed the problem before, but like I said I didn't see that much rain in Cal, I had taken the backing plate off when I upgraded the brakes to 993TT up front and 965 turbo calipers with 930 rotors in the rear, I also upgraded to G50 , so i have 89 Carrera pedal assembly ,booster and 19mm m/c ( hope this weekend upgrading to the turbo m/c 23.8mm one) I also have brake ducting to the rotors !

Last week end I did a 1600 mile round trip in the car and got in a 4 hour down pour in TN, it was raining so bad that it was blinding , When I went to use the brakes I had none, if I held the pedal down after few seconds, then they would start to work.

Do I have to reinstall the back plates to protect the rotors from all that water or what ?

thanks , if any body can help

Helio

[uwanna]

I see you have widebody fenders on your car. Do you have relatively large spacers on your wheels to fill out the fenders? I observed the same "wet braking" dilemma you had after going wide body and using large wheel spacers on my car. With the large spacers, the brake rotors are no longer "inside" the wheel, were they are somewhat protected from the intense water flow of a rain storm. The rotors on my car are right out in the open where they receive all the water. The rotors being out in the open are probably benefited cooling wise when it's dry outside, but definitely a liability when it's raining. Also removing the backing plates probably doesn't help either. Anyway, that's my evaluation, and my experience. I somewhat mitigated the "wet braking" problem by adding drilled rotors to my car (I had been told that either slotted or drilled rotors would "let the water out quicker")

[KTL]

Yes the splash shields are the main contributor to your problem. I've noticed this on my 911 and also on my E39 M5 BMW.

What brake pads are you using? If you have sporty track pads that need some heat, that will be a contributor as well.

Lastly, the master cylinder swap should be high on your to-do list. The bigger master will reduce the pedal throw and you'll be able to modulate the brakes better.

[trak ratt]

I would have thought the problem was more pad related than anything else.

[uwanna]

Originally Posted by trak ratt

I would have thought the problem was more pad related than anything else.

Don't know about that, never had a wet braking problem till I added the big wheel spacers. Just sayin!

[Elombard]

Hmm try blocking off the ducts with some tape or something, that may be enough. If your ducts collected a big slug of water that would do weird things. The backing plates will contribute but I bet the ducts let a lot of the water in.

[heliolps2]

thanks guys,

I have two sets of wheels ,these wheels use spacers, and a set that does not use spacers and I have the same problem, I'll try taping closed the duct and what it does.I'm using Textar pads OEM supplier from our host front and rears, and Padgid sports on the track ,

I tossed my backing plates years ago , does any one have an extra set that I can get ?

thanks
Helio

[trak ratt]

Originally Posted by heliolps2

... I tossed my backing plates years ago , does any one have an extra set that I can get ?

thanks
Helio

U know I do...

[Grady Clay]

Helio,

This is what engineering is all about – compromise.

When new, your 911 was Porsche’s best engineering compromise between a safe and suitable street car that will tolerate (but still not immune from) driving in hard rain and ‘deep’ water and a relatively suitable (compared to most automobiles) track car, right off the showroom.

You have made engineering decisions that have moved the car away from that streetable compromise and toward more of a dry-weather track car.
If you look at a 911 prepared for a rain 24-hours of Le Mans, it is very different from yours.
Racers almost never have the wheels cantilevered outboard.
For rain, the air ducts are usually removed or taped off.
Critical are slotted rotors or otherwise a system that ‘wipes’ the rotors.
Softer and more slotted pads are used.
Most important, the driver expects to lightly apply (left foot) the brakes to wipe the surface just prior to serious braking (at the end of the Mulsanne Straight).


Looking at your issues:
Probably foremost is having the front wheels offset allowing the brakes to be in the ‘open air’, not shrouded by the wheels.
A close second may be the air ducts not blocked off.

I can’t tell from the picture if there are cross-drilled or slotted rotors but those will help wipe water off and give it somewhere to go.
Think of this as similar to using grooved (treaded) ‘rain’ tires compared to ‘slicks’.
Clearly, hard track pads are not suitable in the rain.

I would put the brake ‘dust shields’ relatively low on the list.
Given the other conditions (offset, ducts, rotors, pads), reinstalling the shields probably will not have a significant effect.

Finally, I think you were expecting something from your car that it was not capable of performing given the modifications.

I’m glad you and your 911 survived.

Best,
Grady

[heliolps2]

Dave (track ratt) how have you been ? I tried calling you a few time and no answer, My kids are for a few weeks, at the in laws , can I stop by some time ? what day would be good for you and do you ?need any help with any thing ? ya if i can get those from you that would be cool, I may also need to borrow a a cutter also.

Grady great explanation, I get it, awesome thank you sir

Helio

[will hung]

I agree with uwanna and Grady. I went back and forth on whether I wanted to toss my backing plates when I rebuilt my suspension and brakes last winter. Many of the guys in England on Impactbumpers.com deleted theirs with no complaints about wet weather driving, and considering how much more rain they get than here, I figured I would be ok. This is in regards to a 911 SC though. I've driven it many times in the rain and have not had problems, but my system is otherwise stock.

[Flieger]

Originally Posted by trak ratt

I would have thought the problem was more pad related than anything else.

I agree with this. The water will be slug off the rotor very quickly. The issue is more likely the wet pads.

Originally Posted by Elombard

Hmm try blocking off the ducts with some tape or something, that may be enough. If your ducts collected a big slug of water that would do weird things. The backing plates will contribute but I bet the ducts let a lot of the water in.

I second this.

Make sure you have street pads, not race pads, block off the ducts.

The issue is not the spacers in themselves, but rather the offset they create. Your other wheels just have the offset built in to them so you have the same issue with the brakes out in the open.

And Grady is right, as usual. Racers and off roaders know they will have to ride the brakes a little bit before any hard braking to get the brakes to work properly after being soaked with water.

I don't think the dust shields will make any noticable difference for you if you leave everything else as it is.

[heliolps2]

who ever would of thought, I'll have to carry some painters tape for the rainy days , I don't useally drive it in the rain, when doing a long road trip you never know.

Helio

[heliolps2]

Grady your right the rotors hang out in the air with spacers and these wheels,

[Bill Verburg]

I'll be the dissenting voice here, backing plates or lack of them will have very little influence in rain, they are more for gravel, ice, packed snow etc.

MO is that the issue lies w/ your choice of m/c. A 19.05mm m/c w/ 993tt fronts and 965 rears is way too small, 3 issues will arise
1) the rears will be prone to lock up
2 & 3 which are closely related) it will be harder to modulate these brakes because of the longish pedal travel and high force amplification entailed by the very very high slave/master ratio

my advice get a 23.8mm m/c kit

[sundevil64]

I have some backing plates from an 86 carrera that are nice. $35 shipped ! or don't drive in the rain... just kidding.

[trak ratt]

Originally Posted by heliolps2

who ever would of thought, I'll have to carry some painters tape for the rainy days

Seriously, you don't think we could fab some flap covers? Controlled from inside the car of course

[wildcat077]

I scared the crap out of myself driving up to an event last Summer in pouring rain ... went to brake and nothing happened ...
I have 996TT brakes and Pagid pads with front cooling ducts and no backing plate !

Although this was more of a monsoon downpour,no such issues at the track.

Cheers !
Phil

[chrismorse]

I had a very scary experience with my green car. Mintex Xtreme pads do not like to be wet. I did a huge brake upgrade and put these pads on, with no backing plates. Not only were the brakes just not there on initial appication wet, but one side or the other would dry first causing unpredictable pull.

Switched to Pagid R4-s and the problem almost went away, no other changes.

[heliolps2]

Is it really possible that brake pads make that much of a difference in the wet, now that I think about it, the reason I didn't have a problem before and had removed the shieleds back then, I had twin 993 oil coolers in front of the air ducts , now I'm using a center oil cooler and the ducts go to the brakes, so I'll have to make covers for the vents that feed the ducts , and remove them when at the track.

Helio