Let's Talk Track Brakes Options

[jdogg]

One thing I've noticed that hasn't been touched on is the rubbing issue. This is a "Bozo No-No" That's what is cooking your calipers. No, a standard brake lathe will not do it, they're meant to do the sides not the edges. You should find a machine shop with a large enough lathe and mill about 2mm off for clearance. I would also have the rotor cryo'd before or after that so you're not always milling rotors.

Bozo NoNo? Ha, tell me I'm stupid why don't you, haha! I like that.... (IMG:style_emoticons/default/av-943.gif) Anyway, on that topic, what do you think about machining the caliper for clearance instead of the rotors...with the track pads I'm running, I expect to be replacing rotors annually, if not more. Would 2 MM be too much to take out of the spacer/caliper?
Is 2mm enough?

Or maybe I should just say F-it and go with a late model carrera setup....hmmmm, $$$$$$

[davep]

I think 2mm would get you into the bores for the bolts.
Besides, when are the pads with respect to the edge of the rotor?
If the rotor is way outside the pads enough to hit the caliper, then that is too much. You turn the rotor and save: unsprung weight, significant inertia and clearance. That inertia reduces acceleration (robs horsepower) and requires extra braking to scrub off (extra heat in the rotor).

[Eric_Shea]

Bozo NoNo? Ha, tell me I'm stupid why don't you, haha! I like that....

Maybe it's a Midwest thing. Maybe I'm too old. Nobody remembers the "Bozo the Clown" show? And if the kids did anything bad then old Bozo would call them on it saying "That's a Bozo No-No"...??? Nevermind. Suffice to say I wasn't calling you stupid. (IMG:style_emoticons/default/wink.gif) Here's a link to more info than you would possibly want:

http://www.snopes.com/radiotv/tv/bozo.asp

I agree with the Canuck. 2mm would put you into the bolt bores. Get those puppies to stop rubbing and you'll stop most if not all your problems.

If you replace annually then you may not want to cryo. Turning the edge off them shouldn't be more than $40 bucks per year...

[jdogg]

Thanks, guys! I have a plan!

[Eddie914]

Are you overheating the front brakes or the rear brakes?

My 914-6 3.2 is set up with 911 SC brakes, Porterfield R4 pads, ATE Superblue fluid and a manual proportioning valve in place of the stock proportioning valve.

Many on the board indicated that the stock proportioning valve can be eliminated. With the manual proportioning valve set wide open, rear lock-up was quite easy to invoke. I continued to increase the brake bias to the front until rear lock-up was eliminated then added an additional turn to the adjustment knob for a safety margin.

The last couple of events the pedal has softened during the day. When the front brakes were bled, the soft pedal continued. When the REAR brakes were bled the nice hard pedal returned???? What gives? Don't the front brakes always overheat first?

At the last event I used an infrared heat gun (I know ... it's not the best type of instrument to measure temperatures on shiny metal) to compare the front and rear brake temperatures after a track session (followed by a cool down lap). Guess what? The rear brakes were MUCH hotter than the front brakes! 550 degress versus 275 degrees.

The front brake cooling ducts must be working pretty well.

Now it's time to fabricate rear cooling ducts.

Anyone have any ideas for rear ducting?

Eddie

[davep]

Using an IR gun is okay as long as you treat the values as low, and use them for comparative purposes. It sounds like you have your brakes pretty well sorted out. Ducting air to the center of the rotor would likely be the best route, but difficult; the vented rotor acts like a radial fan. I have seen clam-shell devices that duct air into the rotor from the outside.

[Brando]

I second the motion for more cooling - on all 4 wheels. Definitely add some phenolic material between the pads and pistons. What kind of flex lines are you using?

There was a member on one of the pelican or rennlist boards I think who took is brake-dust shields and fabricated ducts into those. It was very cleanly done from aluminum and looked nice. It blew right into the center of the rotor and used 1½" or 2" flex hose from the front valence. Come to think, it was a 944 because it had the brake ducts going through a euro-style bumper with ducts in the fog light holes.

[Eddie914]

Here is a nice setup for rear brake cooling ducts.

(IMG:http://i38.photobucket.com/albums/e143/AlkiBMW/914GT/Tech/79_31162400512.jpg)

Eddie

[914forme]

Nice setup for a 944, 911, VW beatle, Thing, or Ghia! You have to make you own for a 914. The other problem is hte wheel size you are using, 15"s do not leave a lot of room back there. But a simple scoop might be all you need. Use an old dust shield, dril a couple holes, and ad a few pieces of sheet metal to see how it all works out. Or why not use a different set of wheels that have a been designed to pull air through the opening.

Other issues with rear ducts, you need a cover over your inlet, or else you pickup rubber, and gravel all day long, and they don't mix well with brakes either. This is one of the reasons the Boxster lost the lower intake ducts that where on the prototype, sucked too many foreign objects into the intake system.

Another thing to note on the above picture, the brake bolts have no provision for locking. Now maybe he used lock-tite GREEN! buts I doubt it. You hang around motorcycle, Kart, and aviation folks a lot, you learn we auto-racers take a lazy approach to bolting and securing stuff.

[alpha434]

BBS still sells wheel fans, I know of no other company that still does. It was a 80's fad that was somehow forgotten. Those bastards.

Anyway, you could also probably make some, and your front wheels would benefit as well as the rears. Or have them made. Plus they have an aero-advantage, albeit small. Search for pictures of the Shell 962. It had them. I also saw that a german 914 setup for racing had them. It was the picture with 30 914s or however many on one car trailer. * old picture, if anyone remembers the post...

The wheel fans act centrifugally to suck air out from under the body and past the brakes.

[914forme]

Yep, I have seen 80s vettes use Corvair fans in the wheels with welded adapters.

Don't the turbo twists have a fan function also???? I could be wrong on that.

Or do it like NASCAR and just toss tones of duct work at it.

[jdogg]

OK...quick update..I had the rotors cut down at the machine shop, and rebuilt the offending caliper. The next move is ducting some air down there, which brings up this question.....Where to send the air. Is it best to aim it at the center of the rotor(at the hub) and let it radiate out the venting, or should it be directed right at the caliper? It appears from Eddie's picture that sending it to the center of the rotor is the deal, and is the direction I am leaning....Opinions???


I do believe the seal failure was indeed caused by excessive heat...the dust seals were completely toast, and the piston seals felt a little hardened when I removed them..Hopefully these latest changes will cure my braking ails, will know for sure in about 2 weeks.

Also- Thanks out to Eric Shea for sending me some much needed pieces....I am sure he has much better things to do with his time than send me o-rings, bolts and a rear adjuster, but he came through as if it were nothing!

[race914]

You want to cool the rotors.

Several vendors offer cooling 'kits' similar to this pic



or you can go with the 'clam shell' approach

[Eric_Shea]

Glad to help! (IMG:style_emoticons/default/wink.gif)

For your situation... go with the AJ kit pictured above. Or - Try an event with what you've done. A rotor rubbing on a caliper will kill it in short order. I'd be willing to bet you're good to go now.

[jdogg]

I am going to rig something up similar to that AJ kit RACE914 posted above...my spoiler has ducts in it already, I just need to run some hose and direct the air to the proper place....I may dig out my splash shields that were removed long ago to see if there is a neat way use those to duct some air in there...

[DanT]

Ran 2 days at Laguna Seca this weekend and had absolutely no brake problems.
M calipers with vented rotors up front with Porterfield Rs4 pads.
Front 914-4 calipers in rear with stock pads. No proportioning valve, just a T.

no fade, good pedal feel for 20-30 min sessions on Friday.

Saturday was Cherry's Jubilee. We give hot laps to hot rodders for charity.

3 hard laps, come into hot grid, unload one rider and get another, for another 3 hot laps. This is very hard on the brakes, since you never get to do a cool down lap, and the brakes begin to heat sink after several rounds.

again no problems with fade or pedal feel.
I have just a stock style LE front air dam. No additional brake cooling.

I would bet your brake heating is/was due to your dragging caliper/rotor. (IMG:style_emoticons/default/smile.gif)

[Joe Ricard]

I had a lapping day with an LE air dam. no problems with Stock solid front rotors. R4 pads.

Next event with cow catcher air dam I smoked the brakes to a pretty blue.

Air flow is EVERYTING.

[DanT]

I had a lapping day with an LE air dam. no problems with Stock solid front rotors. R4 pads.

Next event with cow catcher air dam I smoked the brakes to a pretty blue.

Air flow is EVERYTING.

yes, on my 2.7L RS motored 914-6 I had a GT style air dam and had to make sure the ducting was hooked up to cool the 4 piston JFZ calipers.

[jhadler]

yes, on my 2.7L RS motored 914-6 I had a GT style air dam and had to make sure the ducting was hooked up to cool the 4 piston JFZ calipers.

Dan, how and where did you setup the oil cooler with that air dam. I have one, still on the shelf , and could not find a cooler that would fit in that opening.

-Josh2

[DanT]

yes, on my 2.7L RS motored 914-6 I had a GT style air dam and had to make sure the ducting was hooked up to cool the 4 piston JFZ calipers.

Dan, how and where did you setup the oil cooler with that air dam. I have one, still on the shelf , and could not find a cooler that would fit in that opening.

-Josh2

Josh,
it was a 19 row Mocal, I don't remember the details though, since it was about 11 years ago.
worked great, never had a heat problem even with big motor. All stainless lines all the way front to back with aeroquip fittings, used a carrera thermostat mounted in the rear near the motor.
If I remember correctly the cooler was mounted to the air dam...I can do some checking on that and get back to you.