Help! big brakes without splash shield = no brakes in the rain!!!

Yes, happened with me on my C6 Vette with a front BBK.

 

Put on drilled rotors or pump the pedal once before braking to remove the water. Pad compound won't do anything.

 

What exactly happens and what is your set-up?

 

I had slotted rotors, cold they worked fine, but the first heavy rain I almost rear ended a car at the light. Not even Stoptech had a good answer as to why. Pedal was mushy too, but in the dry the pedal was hard and the Stoptechs very responsive.

 

On the street I tend to avoid overly aggressive pads for their lack of initial bite, particularly in rain or extreme cold (the later being a particular concern for a more northern climate).

As a sanity check I would swap to proper street pads to make sure its not simply a hard compound + rain + cold issue.

If it persists, a more extensive work up of the braking system is in order.

 

Water gets on the rotors and push the pads back so you have to pump them once or twice to clear the water and push the pads back out to the rotor - that's why they feel soft. Drilled rotors help by not allowing the water to have an unbroken surface to build up on (and is really the only reason for drilled rotors). Pads really won't make a difference other than helping with cold performance, but if they are otherwise ok in the cold a change won't do much for rain performance. You have to either keep the water off the rotors or use rotors made for the rain. Or, get in the habit of tapping the brakes every so often in the rain to keep the pads out and rotors clear.

 

I started doing this and they were much better but still soft in heavy rain.

 

If you have good pedal, it does sound like a heat/compound issue unlike how Todd described his, which sounds more like water getting trapped on the rotor and pushing the pads back. I'm not sure what your pad options are for that application but there should be something more street oriented that would work better.

 

Lots of modern cars do not have splash shields nor do the rotors have holes or slots. In fact I think the 308 was the last Ferrari equipped with splash shields. I'll tell you what most do have though, brake ducts, the most efficient way to route a constant supply of water to your rotors and pads ever devised.



Your problem is not water. The problem is the pads you are using.

 

If that is true why doesn't it happen on any of my cars or any of my clients cars or any of the other tens of thousands of Ferrari's Porsches, etc,etc,etc on the road with drilled rotors. It that was true DOT would have banned them years ago.

I don't doubt he has a brake problem but its not rain and its not drilled rotors.

 

Chris,

You are totally manual now and removed all the ABS plumbing?

 

ABS in a 308?

 

Thought he had a 355? So which is it?

Opps read the set-up did not look at pics. Was on my phone

So chris,

Did martin calculate the master cyclinder sizing to be matched with piston caliper size for those calipers.

 

I was saying the drilled rotors help the problem, not hurt it.

Your clients probably never drive their cars in the rain, it's happened to me on my stock bmw. The bmw it was due to worn rotors that had a lip on the edge holding water in. It feels exactly like pad knockback. Have any of your clients experienced that or is that not real, either?

If the pedal goes soft, it's not the pads, it's the pads getting pushed back into the caliper. If you have a firm pedal, then the pads are too cold and can't build heat quickly enough in the rain. The pad pushback is worse with floating rotors, which a lot of these big brake kits have and not a lot of stock cars have.

If you look at the new bmw and Mercedes, they have a system that pre loads the pads in the wet to combat the issue. If it wasn't a real issue, why would they bother?

 

I have never experienced this problem and frequently race in the rain. Something else is going on as my cars have no splash shields and if anything duct work that would help bring moisture in. In fact, on the ACR-X we added water jets in the brake ducts to better cool the brakes. I've also never experienced this on the street.

 

And I only ever experienced it in a street car, go figure. I have dealt with pad knockback before on a couple of cars and it felt exactly the same, which is why I relayed my experience - the soft pedal is the symptom that says it's not the pads. In the other situation where the pedal is firm but the brakes don't work for a few seconds definitely sounds like the pads, though.

 

Nobody drives their cars in the rain???? Oh come on.

 

As these threads develop we get more to the story. There is so much that has not been told. For example, what about bed-in procedure? How much track use? What pad compound? Oems design for a reason. Owners cherry pick what sounds like a good idea with incomplete engineering and single datapoint testing. I think Chris is lucky to find this problem in a non-urgent way. So few of us drive to the limits even on a track that testing is nearly always incomplete.

When the brake engineers at Stoptech designed the SCCA T1 racing brake kit on my Corvette it took empirical calculation on paper, manufacture of multiple caliper set-ups, and a day of private on track testing of many sets of calipers by their test driver in my car before we had a working prototype. The process was not easy or quick and that was with professional team of 1/2 dozen guys doing it.

I would not be surprised if there are multiple holes in your set-up where an unforseen change in operating conditions is outside your operational range.

Pad knock back is not the whole story here. Pad knockback does happen more with full floating rotors, more with flexing calipers, less pistons in calipers, more with flexing uprights, more with flexing mounting brackets, more with poor wheel bearings, more with suspension lack of rigidity. Race calipers solve a lot of that with anti-knockback springs in the calipers. So you got new tech on a decades old design and some pad knockback could conspire just because the suspension might not be up to F50 brakes while car was designed for somewhere around 200 RWHP. But more to the story needs to be told. For example 99% of rotor hat combos sold for streetcars are not floating but actually fixed. What does chris have? Racer's use full floating typically 10-20 thous. So the more float the more "potential" knockback. You could take up the slack as many racers do before a braking point but Chris has done that with poor results. It contributes to pedal feel, modulation, and braking performance depending on knockback severity.

 

Yours sounds like a pad issue contrary to my initial post, where Todd's sounds like something else due to the soft pedal. I didn't pay attention to the weaker initial bite when cold, which will get worse when wet as it'll take longer to get heat in. If you had good initial bite in the cold then it'd be a head scratcher. What pads are available for your setup?

 

Knockback can be all kinds of issues, from warped rotors, to worn bearings, to flex in uprights over bumps (e.g. at Road America the curbs are violent enough to knock pads back). I suppose water could knock pads back, but I've never experienced that and knockback is not simply a lack of brake force; the pedal will travel farther and be softer at first or may even need to be pumped up. If you are applying a firm pedal and the car still does not slow, that is odd and I'd attribute it more to cold pads that need heat for a good friction coefficient than water, per se.