Let's Talk Track Brakes Options

[jdogg]

OK, so I've had my car for almost 6 years now, and it has been through a LOT of changes over those years...It started as a stock class 2.0 AXer, then to street prepared, the to SM2 with the addition of the -6. I had done a smattering of track events over those years, primarily focusing on AX, but last fall the track bug bit and bit hard!! I've done about 8 of 'em since October last year, and just can't get enough.
But this brings me to my question(s)/issues. As my driving is improving, I find I am being much harder on the car (a good thing), but some issues are coming to light, most notably the brakes.
I have the much hyped 914club billet hubs on my car, utilizing M calipers, SC vented (not cross drilled) rotors, Carbotech XP10 racing pads, brand new 19mm MC, etc. The brakes work very well...once the pads get some heat in them they will stick your eyeballs to the windshield with no fade issues. The issue I am having with this set up is the pedal softening and the travel growing after a couple sessions. At first I suspected the MC, so I replaced it...then after bleeding the system and leaving it under pressure with my power bleeder, I noticed some fluid seepage around the RF caliper. The calipers were rebuilt last fall and have about 8 track weekends on them, but I went and got a new rebuild kit and rebuilt it. I thought that maybe that was a potential source of air and a possible reason for the pedal travel issues.
I spent the past weekend at Carolina Motorsports Park (CMP) in lovely east bumfuck middle of nowhere no cell service one stoplight Kershaw, SC. A very challenging layout, tight and technical, and very hard on equipment with a lot of hard braking zones, so I figured it was the perfect venue to test out my brand new MC and freshly rebuilt caliper and see if I could keep a pedal all day long. After session 2 on Saturday the pedal travel had indeed moved again. So I bled the brakes (heel and toe with a low brake pedal is nearly impossible) and the pedal came right back where it needed to be. I resigned myself to the fact that I was just going to have to bleed 'em every two sessions. Well, it was successful, uneventful rest of the weekend with plenty of bleeding (although it was hot, really fucking hot...103 on Sunday with lots of humidity). Fast forward to Monday night when I go to unload the car from the trailer....no brakes!!! WTF?!?!
Seem I have blown the left front caliper out now too, and this one leaked fluid all over the damn place....

So does everyone need to bleed their brakes that often to keep a firm - high pedal? Is rebuilding calipers every 2 or 3 events whether they need it or not going to need to become a regular maintenance item? Is there a better way?

[914forme]

Not an issue I am aware of, you got other issues, find them.

Couple of thoughts or ideas, seems you listed you front brakes while they are the highest used items in braking, the rears do have function otherwise we would not have them and save weight. Are you sure your rears are doing anything or at least the proper amount of braking?

Have you checked the calpier temps? Have you checked for run out on hte rotors? Have you checked you hard and softlines?

I run many a auto-x events and never had to rebuld the calipers. Crewed a PCA J-class racer never rebuilt the calipers there either. But if you are overheating them, even though you don't notice fluid boiling, you could be higher than you think. Temp paint or strips are a wise investment to help track down possible problems.

My beat is you ar over using your fronts, heating them to the point of rubber degragation and feeling the pain. I would add a insulator beween the the pads and the piston, help keep the seals alive a little longer. And then add rear bias to help easy the burdent a little.

Depending on how they are setup the rears might not be producing enough heat to allow the pads to build working temperature, and function properly. One trick I use in clases that did not allow bias adjustments was to run different compounds front and rear. Works better than you think.

[drew365]

I have a similar brake setup to yours. Yes a soft pedal is a recurring problem. Yes I bleed them after every event and sometimes during the event. No, I haven't had a problem with blowing out calipers.

[ptb]

What brake fluid are you using and do you have any air ducting to cool the brakes? On my '87 911 (fat pig at 2,800 lbs) I can cook the brakes at a high brake track like Gingerman but be ok at Mid-Ohio. I use Motul 600 with Porterfiled P-4 pads and have 993 ducts mounted to my front A-arms. The biggest improvement was getting rid of the Super Blue brake fluid and using Motul 600. The next step would be Castrol SPX at $80/quart

[Dave_Darling]

I think you mean SRF?

There is a recent discussion on the Bird's racing board by 911 guys about this. Consensus seems to be: Put heat-resistant shims (someone mentioned Titanium??) between the pad and caliper. Switch to SRF. Duct air to the rotors. And even then, you may have to rebuild the brakes annually...

--DD

[jhadler]

You mention a lot of the setup you have, but nothing about fluid. Make sure you've got GOOD fluid in there. All of the best brake gear in the world isn't gonna last if you're using poor brake fluid. And no, not all brake fluid is the same.

Shims. Yeah, a set of shims between the pad and the caliper piston will also help. Some say titanium, but they're probably trying to sell them to you. The difference in thermal conductivity between Titanium and Stainless Steel is pretty small, but the cost difference is HUGE. Have some SS shims made if you really want to go that route.

Also, brake ducts. Brake ducts. Brake ducts. Brake ducts. No one thing you can do will help improve brake longevity at the track than installing brake ducts. Do it.

You may also want to look into properly bleeding the proportioning valve too, as that tends to catch air in the system.

Brake Fluid.... Here's writeup we put on our region Time Trials website about brakes and brake fluid. I think you'll find it pretty thorough and helpful.

http://www.sccatimetrials.org/requirements/brakes.html

-Josh2

[jdogg]

Ok, the question of brake fluid has come up several times...I use ATE Super Blue, and it is always fesh before every event (its GOTTA be fresh as often as I am bleeding 'em, haha!).

Also- no proportioning valve..replaced with a Tee at the -6 conversion. Rear venting clearance set properly also. The car feels very well balanced under threshold braking.

My airdam has ducts molded into it for brake cooling, but I have yet to find suitable hose to run to the calipers. Suggestions?

I'd love to hear from someone else with the mystical 914club billet hub set-up...the clearance from the edge of the rotors to the caliper is very minimal, to the point that there is evidence of occasional rubbing...I suppose that could also be a source of additional heat build-up...Is a regular brake lathe capable of turning down the diameter of the rotor i.e. 13" dia. to 12-7/8" dia.?

These shims that have been alluded to....who makes 'em? Just how thick are they? Is there enough room to stuff them in as well as a brand new fat assed racing brake pad?

[jhadler]

ATE is good, Motul is better, SRF is great.

Brake ducting... Just go to Home Depot and get some flexible dryer hose and some hose clamps and zip ties. Anything you can do to get more air to the brakes will be better than nothing. Ideally, you'd want some nice high temp hose (like you get from racer shops etc.). And, ideally you want to put the air where it'll be the most effective, into the caliper. But honestly, any air is better than no air at all. You'd be surprised how effective it'll be. Just aim the air at the caliper and/or rotor.

If you want to invest in some good mounts for the ducting, take a look at the brake duct mounts that Chris (Tangerine Racing) sells. Pretty nice, and simple too.

As for shims? I wouldn't go that route until you've exhausted all your other options. They're really going to have a pretty low cost/benefit ratio. Yes, they help, but nowhere near as much as ducting will.

-Josh2

[mudfoot76]

+2 on switching to Motul and adding brake ducts.

I was having fade issues on my car during DEs and was looking into fabbing up ducts. Then someone suggested that I lessen my CSOB quotient and try the Motul. Night and day difference. No more fading, even on the hottest of days and I am pushing the car to the fullest (I have the M calipers on front too). I've held back on adding ducts as I don't have the problem anymore.

[jdogg]

Thanks for all the great input and suggestions!!! (IMG:style_emoticons/default/beerchug.gif)

I now have a plan of attack for my next event (not till Sept. 22 VIR-s & VIR-f)

1- rebuild that puking caliper
2- head to the home depot for hose and rig up some sort of cooling deal
3- increase the rotor to caliper clearance ever so slightly
4-Try the bitch out! (IMG:style_emoticons/default/driving.gif)
I just bought 2 new freakin' cans of ATE SUper Blue, so the CSOB in me has me holding off on the Motul 600 for right now, but if that fucker goes soft on me at the track, I may just have to spring for it.

I'll try to remember to post back the results.

Also-
CMP is VERY tough on brakes, any deficiencies you may have will INDEED show up there...I know some folks who refuse to go to that track for that very reason. It is a GREAT 914 track, not too many loooooooooooong straight-aways, and lots of tight stuff!!

[jhadler]

CMP is VERY tough on brakes, any deficiencies you may have will INDEED show up there...I know some folks who refuse to go to that track for that very reason. It is a GREAT 914 track, not too many loooooooooooong straight-aways, and lots of tight stuff!!

Sounds just like our departed Second Creek Raceway. Lot's of transition, more than a couple heavy braking zones, and not a lot of time between them. That, coupled with the altitude makes it a very hard track for brakes. Good fluid and good coolingwill go a long way...

-Josh2

[914forme]

SS Shims, and add some heat sync coumpund to them on the pad side. Or pad compound copper ceramic SS ceramic then ceramic and piston. You want to have fun add a computer style heat sync out the top. As long as you have wheel clearance. You coud add water cooling by shooting water mist at then. You could use the computer heat syncs that are water cooled also.

The J-class racer ran Mid-Ohio, Putnam, IRP, and a few other Robeling Road and Elkhart. All stock, except good fluid, and Ducts on the front. Never had issue, though a stock 2.0L can only push you so fast so the braking zone for others was non existant for us. The front brake coolers where a piece of al pipe with a mount that fit over the rotor with a small air foil built in. I shoud have painted a coke logo onto it cause it looked very simular to a Coke/beer can.

The area you are in, look at your Nascar builders for cheap take offs, those guys need to cool brakes way more than you do. And the hand me downs are cheap!!!!!

[jhadler]

SS Shims, and add some heat sync coumpund to them on the pad side.

(IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/blink.gif)

The shims are to reduce the heat transfer, not improve it... The last thing you want to do is add some kind of thermally conductive paste to the system...

You coud add water cooling by shooting water mist at then.

And don't forget to replace your rotors after every race as they will be hideously warped at the end of the day. (IMG:style_emoticons/default/biggrin.gif)

Still, it'd be really cool to make water cooled brakes like the European truck racers do. The front of the car would spout steam every time at the end of the straightaway. Really freak out the competition...

-Josh2

[914forme]

Yes I did say that wrong. Unless he is the compition then I said it just right (IMG:style_emoticons/default/happy11.gif)

[Eric_Shea]

Might want to look for the late model pistons (dished) and remove your knock-back pins. Much more surface area for cooling.

[jdogg]

Might want to look for the late model pistons (dished) and remove your knock-back pins. Much more surface area for cooling.

Eric-
Tell me more...By late model, do you mean late model "m" caliper pistons? How would I know what the hell I was looking at? Are the SC pistons the same size? What are the "knock back pins" ? Do you mean the pins in the caliper that slide into the piston?

[Eric_Shea]

Late model M-Caliper pistons (kinda harder to find in M-Calipers but some had them) or A-Caliper pistons. Yup, they're the same size.

Knock-back pins are the ones that slide into the pistons. By 76 or 77 (I think) ATE had done away with them and went with the later dish or cup style pistons in the same calipers. Knock-back pins are meant to literally knock the pad back toward the rotor offering a high pedal feel. They have been known to be problematic in race cars and many simply remove them or their recepticals.

If you stay with your current pistons and you're racing, you may want to simply remove the mechanism inside the piston (C clip and yank). If you go with the later cup pistons simply snap the pins off with a pair of needle nose pliers.

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.

Do that... get some ducting in there and you'll be a happy camper racer.

[davep]

Cryo'd rotors would be a good idea. The rotor should not be larger in diameter than where the pads touch them (it adds excess weight, and worse increases the inertia).

Possibly part of your problem is not cooling the brakes properly before parking. Cool down laps on the track or off of the track are necessary to get the heat out of the brakes. If you do not do so, a hot rotor will warp, and also cook the piston seals. I have seen dust seals that are totally disintegrated. They probably should not be used. If you use a brake duct to get air into the center of the rotor, then at least use metal ducting; I understand that the vinyl ducting is not even legal for most clothes driers. Second, consider a fan setup to force air through after you park it to ensure an even cool down; I'm not suggesting to build it in, just a little rig to blow air into the scoops. I strongly believe that more damage is done while parked than when on the track.

I have it on good authority (from an endurance racer) that oversize master cylinders are very useful in preventing low pedals. Part of that comes from the pistons being knocked back excessively by the rotor ( thermal expansion, wobble, warp, flex, whatever). He used a 23 mm (back in 1971 to 1973), standard on the GT was the 20mm MC. Also, brace the MC to reduce the floor flex. He never had problems with the "S" or 908 caliper variant.

[alpha434]

You can buy titanium sheet in 99% pure form and make those shims just as easy as the SS. And about as cheap. I've been going to the Denver Art Museum and stealing their construction slag (those fools are using titanium sheet to cover the whole building.)

I see it go up on ebay every so often too.

The problem with shims- and more so with the Ti over stainless, is the way it rattles. It pushes the pads apart a little extra and you lose brake pressure. Bad for coming down the straight and late braking that first turn...

But if you affix the Ti to the brake pad, it doesn't cause a problem. I bend a piece around the pads and through the split in the pads and back up. Works so good, that I run them on my stock 914 on the street.

[alpha434]

I've been doing the water cooled brakes for a while. And I've got a great mechanism, but I need some better electronics. . .

In each wheel, I have a unit, made from a small piece of PVC tube, with a C02 quick change adapter (paintball gear) on one side, and a tube running to a windshield squirter off of some odd year acura integra. That model had a valve that was part of the squirter. I run the wires to the brake pedal. If you hit the brakes, it squirts.

The problem is that I don't want it to squirt EVERY time. Pretty much just when you late brake hard. So I need to add a g-force sensor into the loop or something. If it squirts every time, then you run out of water way too fast.

In the picture in my avatar, the unit is just behind the headlight cover, and you can refill it/change co2 cartridges by removing the black piece.