Let's Talk Track Brakes Options

[grantsfo]

I use SC rotors with BMW 320 i calipers in front and SC rotors in back with SC calipers. No ventilation at all. However I have BBS wheels that do a good job of keeping things cool. No fade in longer track sessions. But I dont have much car to slow down. I was having some issues with front rear balance, but I think it was pad issue. I just put new set of Hawk Blues on the front and balance appears to be much better.

[914forme]

Th AJ pieces will work wonders up front, the rears you will still have to build your own. At least I don't know anybody who does them. Fiberglass would be easiy for this. Make a plug out of foam, wrap in foil, lay up your part. Remove foam plug via a destruction method of your choice bond it to the old backing plate. Open up plate for airflow.

Crude design follow.

[jdogg]

Th AJ pieces will work wonders up front, the rears you will still have to build your own. At least I don't know anybody who does them. Fiberglass would be easiy for this. Make a plug out of foam, wrap in foil, lay up your part. Remove foam plug via a destruction method of your choice bond it to the old backing plate. Open up plate for airflow.

Crude design follow.

Where would you grab the fresh air from? A scoop under the car similar to the AJ kit? NACA duct in the quarter panel?

[914forme]

I would NACA the rocker with a screen.

[jdogg]

[attachmentid=127
840]Update....I finished the brake ducting last night. I dug out the splash shields that I had taken off years ago and started (IMG:style_emoticons/default/sawzall-smiley.gif) and (IMG:style_emoticons/default/welder.gif) and came up with this:

[jdogg]

Going to VIR this weekend to test it all out.. Saturday and Sunday on South Course, and Monday on full....3 days of abuse!! I think it is going to be good!!!!

[Eric_Shea]

Get screens on there... you will pickup marbles.

Brant, calling Brant.

Very nice engineering BTW. What size steel for the tubing?

[jdogg]

Get screens on there... you will pickup marbles.

Brant, calling Brant.

Very nice engineering BTW. What size steel for the tubing?

Yep, I am going to figure out something for the screening tonight...don't need to plug those vents with melted rubber and negate the system!


The hose size is 2-1/2" which was dictated by the duct openings molded into the airdam. I used 2-1/2" exhaust tubing that I ovalled out at the splash shield...It was actually a pretty simple project once I examined all the clearance issues and found the best place to run the hose into.I have not road tested it yet, but it appears there should be no clearance/binding issues with suspension movement and with steering..the shields required a little "massaging" once the rotor was on for clearance, so they don't look as pretty now, haha!

[Joe Ricard]

I've been thinking about this a lot. I am fairly sure I will end up ripping something like that off if I hit a cone or have an off road excursion on a track.

I am thinking of running the tube through the inner fender well just above the control arm. Use the fog light grills as the inlet. and then do something like Jdogg did for mounting it to the spindle.

[jdogg]

Joe-
I looked at running it above the arm as well, but short of looping the hose up to the top of the fender and back down to the hub, I couldn't see a way to keep it out of the tire's way at full steering lock.
I've temporarily retired from dodging cones, so I'm not worried about one of them getting under there....but an off road excursion, especially over the gaiters, could indeed inflict some damage...That's why I bought twice as much hose as I needed.....Spares!!

[Joe Ricard]

I also was running into problems with my splitter/ underbelly pan. so no room for hose.

the route I want to take is from inside the trunk.

[race914]

Some relevant pics from the 'turbo build' thread in the garage. You can see the brake cooling tubes in the pics of the front trunk. Really nice work.

[jdogg]

OK...A successful weekend! No cooked calipers, brakes stayed cool and consistent all weekend...1 broken clutch cable cut short Sunday, but an instructor let me try out his SS Camaro....a pig of car, but 380HP makes damn short work of the straightaways....I learned there is very little that is similar between a 3600 LB, 380HP car, and a 2100LB, 140 HP, mid-engine go-kart! Oh, and I fortunately had a spare cable, so Monday was still a go!

BUT I am still experiencing a sinking pedal, and my theory on that is this - in between braking sections, the pads are getting knocked back too far, requiring more pedal travel to get them back into contact with the rotor. I started giving the pedal a pump or two right before braking hard, and that helped immensely, the bute was up high where it needed to be. When the pedal sinks like that, heel and toe is nearly impossible, especially at the threshold...I even knocked the gas pedal loose one time because my foot was so far behind it on the brakes.

Is there any way to limit that knock back? Eric, you mentioned removing the knock back pins altogether...would that help and keep the pads closer to the rotor in between braking zones? This is more of a nuisance than anything else, but it would be nice to not have to pump 'em up every time I need 'em.

[stownsen914]

Is there any way to limit that knock back?

Are you sure your rotors aren't warped? Also, check your wheel bearings. If they have any slop, the wheel can cock back and forth slightly between braking zones, and knock the pads back in the process. Either problem could occur at the front or the rear, but the front would be more likely, I would think. Good luck!

[jdogg]

Is there any way to limit that knock back?

Are you sure your rotors aren't warped? Also, check your wheel bearings. If they have any slop, the wheel can cock back and forth slightly between braking zones, and knock the pads back in the process. Either problem could occur at the front or the rear, but the front would be more likely, I would think. Good luck!

Great suggestions! Bearings are new, no slop. And I would think I would feel a warped rotor, especially under threshold braking...I suppose it would be worth putting a dial indicator on the rotor face and checking it for runout to be sure.

Let's talk some more about the stock 914 rear calipers. It has been a while since I rebuilt them, and I can't remember exactly how everything works back there. I currently have the venting clearance set to .06 (pins and spring clip removed), but have not had a chance to see if that has changed any after being on track. Anyway, I guess that as the pads wear, the adjuster must turn with it forcing the piston out to compensate for pad wear and maintain the venting clearance, right?
So, in a high wear environment, is it possible the adjuster can't keep up with the pad wear?? Of course, all of the preceeding conjecture could be null and void when I pull a wheel and check the clearances....just thinking out loud..

[jdogg]

Oh, and I met one of our members this weekend too, Hal Michaels (HalM) with his black '74 2056 Raby motor car. He unfortunately had some brake problems and had to retire early, but it sure was nice to see another 914 out there!

Look forward to seeing you at some more events, Hal!

[davep]

Well, the outer rear adjuster is locked, so it cannot adjust by itself. I doubt the inner would either. Either the pistons rotate to adjust (doubtful), or they just pull themselves off of the adjuster (seen that on most rear calipers).

My friend with the GT said that he used a larger master cylinder to compensate for this problem, and braced the master to ensure his foot action was not wasted on bending the floor.

Factory racing front calipers I have seen do not have the pins.

[Eric_Shea]

Eric, you mentioned removing the knock back pins altogether...would that help and keep the pads closer to the rotor in between braking zones? This is more of a nuisance than anything else, but it would be nice to not have to pump 'em up every time I need 'em.

The knock back mechanism was designed to knock the pads back "toward" the rotor giving you a higher pedal. Taking them out would have the reverse effect of what you are requiring.

I believe you still have a wee bit of air in the system. With or without knock back pins and mechanisms you should be able to have a tall pedal.

How is your rear venting clearance now? It should be set to .004". In a high wear environment you will need to check this and adjust often. If you were accurate with your .06 vs. .006 then that can be a problem. The pistons will move roughly 2mm with the internal mechanism on the adjuster shaft.

Make sure your venting clearance is set properly so we can be sure your rear calipers are in the game. Also, rebleed the brakes. (IMG:style_emoticons/default/wink.gif)