How are you cooling your brakes?

#1

Brake_Cooling.JPG640x602

I just went thru a set of front rotors in 4 weeks, call it 7 hard track hours, and the same moderate. That doesn’t seem too good for a set of rotors. What’s different about the new set up is that I put in a brake cooling system. But maybe the system I chose is causing assymetrical cooling and causing cracks. The rotors are getting tossed, by a shop with decent race experience, because the surface cracking is really bad, even tho there’s decent thickness left.

Do you agree that my rotors should have lasted longer?
What are you guys doing about brake cooling?
What do you think of the 2 systems pictured?

I couldn’t find a photo of my brake cooling system, but it’s the one that directs the airflow entirely at the side of the rotor. It’s the low cost solution available and it’s sold by one of our sponsors. It strikes me that the side of the rotor is the worst possible solution for cooling. Not only is there little surface area, but it would mean completely assymetical cooling for the pair of rotors.

The top system in the photo, is the most elaborate alternative that I’ve found and covers much of the rotor. It looks like it would give the most symmetrical cooling. But I’ve not seen it installed on anyone’s cars, and I’ve not heard any comments on it. Maybe it’s the best solution, or maybe assymetrical cooling isn’t my problem at all and I’m on a wild goose chase. And elaborate solutions to non-problems just cause more problems.

The bottom brake cooling system in the photo is widely available and a couple of us use it. It has part of the air “port” blocked, which directs some airflow down in between the rotors.

What say you?

#2

Most people are running cooling sytems just like the ones pictured. I personally run the gruvenparts.com backing plates. Personally, I don’t think there’s too much difference between them all. Rotors are definitely throwaway items on these cars, but they’re also cheap. They make good 6th place trophy stands to boot. I typically get about 4 weekends out of a set. The idea is that the backing plates keep the brakes cool to prevent fading. The longevity of the parts is a by product of the process.

I think if you search you will find a thread from a while ago talking about the different backing plate designs, costs, and whatnot. If you want tons more info, search bf.c on the topic. Pages and pages of non-empirical-data-based ultimatums :lol:

#3

Craig is spot-on with his comments. Most of the systems I’ve seen, from the high-end to budget solutions, attempt to direct the air towards the center vanes, at least as a goal. How directly they route and how much air ‘spills’ out along the way is another matter.

A system that just dumps air at the inboard side of the rotor face seems like it’s not doing much good.

Having said all that, 4 weekends of hard use isn’t beyond reason for rotor life. You might also think about your driving style. The length of time the brakes are engaged has a huge amount to do with heat buildup and resulting issues.

Shorter, harder braking is generally the way to go vs. longer, softer. I think we all know that, but it’s one of those bad habits that’s easy to creep back into.

#4

I have the Factory 3 brake duct kit and am more than happy with it.

A lot of rotor life has to do with your braking technique. I’ve got over 9 weekends on my rotors and they still have lot of life left in them.

#5

I think that the Factory3 kit is similar to the bottom one pictured, which is better then mine. I note that no one seems to like the top cooling kit pictured.

Re. braking technique and braking harder and shorter. I know that’s true, but that doesn’t mean I’m doing it. On fast turns I’m working on going in faster then I’m comfortable with. On slow turns I’m working on getting my speed down sufficiently. And doing both perfectly time after time. When I’m working on those issues I brake kinda slowly and methodically. I figure that once I’m better and nailing the optimum entry speed, turn-in, etc. precisely, then I’ll work on doing it accompanied by brief threshold braking.

And I’m also experimenting with different pads, trailbraking, I have a mushy brake pedal blah blah excuse blah.

How much surface cracking is acceptable? Maybe the shop got over-excited.

#6

Any crack that doesn’t extent from edge to edge is fine.

Here is a picture of Mr. Junky’s brake cooling system tip (which I have to trim from time to time as they melt - $2/ft from Home Depot) and a picture of a unacceptable rotor crack.

All the crack failures I have seen on Mr. Junky are on the outer rotor surface so maybe there is a good reason to try to cool the outer rotor as well as the inner rotor.

#7

Went to the shop this morning where the car too often lives. I noted that my outside front brake pads are wearing twice as fast as my inside pads. Note in the origonal post I described how my brake cooling backing plates direct air only at the inside rotor. So the hot rotor is eating pads on both sides of the car. Is my assymetrical brake cooling solution a plausible explanation for assymetrical pad wear? What are other possible causes?

Rotor wear, the issue that started this thread. I looked at the rotors that the shop said were badly cracked. They got over excited…It’s only surface cracking. I certainly wasted everyone’s time on that issue.

#8

Sticky piston or guide pins?

#9

edavidson wrote:

I dunno. Both wheels show the same wear pattern. And I’m not sure how a sticky piston or worn guide pins could cause the outside pads to wear so much faster then the inside pads.

Accepting the fact, that I really don’t know chit, if the wear pattern was one of “leading edge wears, trailing edge doesn’t” then I’d be more inclined to be suspicious of the piston or guide pins.

#10

I think 4 weekends for a set of rotots is about right. I usually go through 2 sets a year. Probably a set every 3 race weekends.

#11

I can’t help but notice that no one is commenting on the orange cooling system pictured at the top of the thread. Is a system that completely encloses the rotor a good idea?

#12

I hadn’t noticed that, but if the lip on the outside of the piece covers up the vanes on the outer circumference of the rotor, that seems like a really bad plan. The air comes into the center of the rotor and travels through the rotors and is expelled along the outer edge. Why would you want to block the flow for air to expel?

As for your uneven pad wear, sticky pistons and/or sticky guide pins seem like the most likely cause. My first guess is guide pins, because the piston pushes on the inside pad, but the caliper housing pushes on the outside pad. The pins are what allow the housing to move side-to-side. If the pins are sticky, causing the caliper housing to not want to return to a neutral position, so to speak, then the outside pad might be dragging on the pad during times that the brakes are not in use.

If you have Girling calipers, you can get OEM bushing replacements, and if you have ATE, the brass guide pins are probably the way to go.

#13

Chuck - my setup is similar to picture #1 - but that lip does not cover the outer veins. It leaves not much clearance between the rotor and the plate, but that is as designed. Seems to work just fine, which leads to the next question…

You guys are saying 4 or so weekends and it is time for rotors… how do you know? Are you checking thickness of the rotor? Is it because of cracks?

I am changing my rotors out this weekend for the same reason I am changing out control arms - preventive maintenance. After 2 years and 25 30 minute sessions, I thought it was time. I have gone through 3 sets of pads - no cracks or grove around the edge. And my technique sucks - I brake like the car is a limo!

How do you know?

#14

ctbimmer wrote:

[quote]I hadn’t noticed that, but if the lip on the outside of the piece covers up the vanes on the outer circumference of the rotor, that seems like a really bad plan. The air comes into the center of the rotor and travels through the rotors and is expelled along the outer edge. Why would you want to block the flow for air to expel?

[/quote]

I think that only 2/3rds of the rotor is encased by the backing plate assembly. So I think that the concept is that high pressure hits the front of the spinning rotors, travels thru the vanes and out the other side. But if the vanes are designed to pump air from the hub to the outer radius of the rotors, then there’s going to be conflicting air flows. I also note that the design would appear to nicely ensure airflow past much of the rotor outside surface. So all rotor surfaces are exposed to air flow. I may have only got a B in “Heat Transfer” 20yrs ago, but I did learn that intuition can lead me astray. There’s got to be some data out there where folks put brake cooling designs thru rigorous tests.

On the downside, the orange backing plates might make it hard to quickly check brake pad thickness.

Just for clarity, I’m not disparaging the design that Chuck sells. My perception is that most folks are using his or similar. I bought my backing plates before I figured out this Chuck’s were better.

#15

I would bet that the lip meets the backside of the rotor at the outer edge, not that it overlaps the rotor where the vanes expel air. I have ones similar to those on my e30 M3 and the whole intent is to guide air to the center of the backside of the rotor so the flow goes in there and out the vanes - i.e. cooling is from inside of the rotor by air passing through the vanes, not one face or the other.
cheers,
bruce

Ranger wrote:

#16

jblack wrote:

Cracks. Go with your gut/level of precaution.

In case anyone’s unaware (like I was the first two or three times), if the rotor cracks (severely/all the way through), it can cause vibration. Much like out of balance wheels and tires. Fortunately, I haven’t let it get to the point of exploding.

#17

Thanks Craig. I’m going to inspect the heck out of those rotors when I get them off.

#18

I will pass on the knowledge of my more esteemed colleagues (The Reverend and JP) regarding how one knows when to replace rotors that aren’t cracked. There are two ways:

  1. The pads typically don’t cover the entire rotor and will thus leave a raised lip at the perimeter as the rotor gets worn down. A pronounced lip is one sign that new rotors are needed soon.

  2. There’s a half-round grove (usually rusted) between where the rotor fits over the hub and the shiny silver braking surface. Once the rotor has worn so that it is flush with the bottom of this groove (i.e. the groove is basically gone), then it’s time for new rotors.

Sasha

#19

I looked hard this morning at how my rotor backing plates orient the 3" air ducts. These are the same backing plates that I’ve been bitching about for a week. I needed to better understand Chuck’s comment about the rotor pumping air from it’s inner radius to the rotor’s perimeter.

I could see how the rotor was designed such that air is able to get inside of it near the hub, from the rear. And I could also see how my much lamented backing plates kinda directed air towards the inside hub-rear. And I figure that directing air at the vanes at the hub ought to be about a little more effective as directing air at the vanes at the rotor’s perimeter. And that’s another problem.

The vanes are straight, so they don’t pump air well. They just churn and centripetal force pushes some air thru. If they were helical, they could pump air efficiently from the inside radius to the outer perimeter.

In the absence of test data, all we have is guesses. Maybe directing air at the rotor’s hub area is as good/better as directing it at the outer perimeter, or maybe not. Heat Transfer may be a little tricky but fluid dynamics is worse. So trying to intuit convection cooling is a bastard. Maybe my backing plates suck or maybe they are fine and I should quit whining about them. Maybe assymetical heat hosed my outer brake pads, or maybe it’s a caliper problem. Maybe it would be easier to figure out women. And who is that in Rev Alonzo’s Avatar?

I’m going to swap out front calipers and see if my brake pad wear becomes symmetrical. This cooling issue has deteriorated into a mass of guesswork, so one variable at a time.

Later Edit. Pelican has an artical in “101 Projects” that says that the vanes pump air from the outside perimeter to the inside, not vice-versa as I described above. But that would only work with helical vanes. Straight vanes will barely pump and air flow will go out, not in. But understanding the direction of air flow is still important because the direction your rotors are pumping air, assuming helical vanes, needs to synch with the location of your brake ducts. If helical vanes are pumping air out of the rotor at the hub, there’d be no sense and directing cold air at the same site.

Later later edit: You guys were trying to point this out to me, but I was too stupid to see it. The Orange backing plate does not enclose the rotor. Both systems do largely the same thing. The question remains how well they direct air towards the hub, instead of towards the rotor’s outside perimeter.

#20

research what pro teams have done on their racecars. The e30 M3 is the most similar to our cars in a lot of ways.
bruce