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Unread 11-09-2016, 05:30 PM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default Re: Vorshlag Budget TT Build: Project DANGER ZONE

Project Update for November 9th, 2016: On this, the day after an historic election, I think we need a distraction. Let's talk about race cars - welcome to the #DangerZone!

A lot has happened to our C4 Corvette since my last post. We developed a custom dual Tilton master cylinder brake setup to replace the constantly failing stock masters and booster. Then we tested that at an HPDE event and it worked flawlessly. Then we prepped the car for paint and off it went to my buddy Shiloh's shop. Afterwards the car came back SO beautiful we felt obligated to spruce up a few other things. Long story short - its now too pretty for me to own and race anymore, so the car is For Sale. Read below to catch up!


After four rebuilt OEM brake master cylinders failed on this car we were out of patience with the stock parts. These were not lasting a weekend and the failure mode was pretty abrupt: one lap you solid had brakes, then on some random corner the pedal would go to the floor and you had nothing. Bleeding wouldn't help a bit. Luckily none of these failures led to a crash - so far.

Jason had been wanting to make a brake solution to fix a situation just like this for years. This would replace the stock bake master cylinder and brake booster. As I have mentioned in the past the stock booster is PLASTIC on the C4 and they fail regularly as well (this car already had one rebuilt unit installed).

Real race cars tend to not use vacuum assist brakes or OEM stepped bore master cylinders. For safety and tune-ability they use two separate master cylinders, which can vary in bore size, and tend to use them with new pedal(s), either hung from above or from below.

Racing dual aftermarket master cylinder setups are almost always setup with one master cylinder for the front and one for the rear, plumbed independently for safety. A "balance bar" can then be employed to adjust the brake balance from front to rear quickly - literally by pressing on one master cylinder more than the other, via a lever at the brake actuator rod.

Race cars with manual transmissions (which is most) will often also replace the clutch pedal and master cylinder at the same time, so there are 2 pedal/3 master mounting kits you can buy. And if the brake and clutch master cylinders are hard to access (on the floor or under the dash) for fluid checks/refills, the fluid reservoirs are often remote mounted elsewhere, like above.

The trick in mounting these into an OEM chassis is having something to mount them to - usually top hung pedals are mounted to a roll cage tube, and bottom hung are mounted off the floor. Those both take lots of time to mount and brace. Sometimes you can mount the brake masters and new pedals right to the firewall, but usually they still need some support from a roll cage. We have done dual masters all 3 ways.

There are complete "pedal box" kits you can order, sometimes even for a specific car. Most race cars with gutted interiors and roll cages are built using generic pedal kits, like the Tilton above. Mounting top mounted or "hung" pedals from a roll cage tube is a good bit of work, and there is still a lot of factory wiring behind the dash panel on this car (it has all of the working gauges). Floor mounted pedal boxes are slightly more common.

These are the parts we sourced - the Tilton MCs, Tilton balance bar, Tilton remote knob, and the pedal multiplier

The main issue we had was that the factory floor on the C4 is too narrow and is somewhat weak (fiberglass) and the firewall isn't really open to adding in more mounting holes (fiberglass), but the OEM brake booster opening is fairly strong - see below at left.

We also didn't want to replace the stock pedals because, well, that's a bunch of work that is very difficult to un-do. We wanted to test a theory so a bolt-on solution that uses factory mounting holes was preferred - if this didn't work we could just put another new brake master and booster back on.

The solution (above) we came up with is a setup that has a CNC billet aluminum bracket / mount that bolts to the OEM booster mounting holes at the firewall. This way we could keep the OEM brake pedal arm and bracket. No cutting, no fabrication to the car at all, purely a bolt-on assembly. This firewall bracket has a pedal multiplier setup built inside that changes the pedal effort for the now manual brakes. This make the brakes have more of an OEM-like amount of brake pedal travel. We might never make another one for a C4, but this would be a good test for an idea for other, more relevant cars that might need this solution.

Forward of this billet firewall bracket are four studs that hold a steel bracket, to which the two Tilton master cylinders are mounted. In between the pedal multiplier and the masters goes the actuator rod and balance bar. This leads to a dial on the dash to adjust front to rear bias on the fly.

It took some tricky machining on our CNC mill to make the main billet aluminum part, but we wanted some new challenges for our machines. Jason made this piece in 3 CNC setups and mounted the pedal multiplier to the main pivot.

Ryan built the steel bracket that the two Tilton master cylinders mount to from a CAD drawing. Then all of this was bolted together into this assembly shown below. He then made a custom actuator rod that connected to the factory brake pedal under the dash. The rest of the pedal assembly was left stock. This was done to make this a bolt-in upgrade.

Once installed on the car we had to find a place to mount the 1995 Corvette ECM, which normally goes on a bracket near the brake booster. The solution is shown above, which unfortunately hides some of the sexy machined bits in this new, dual MC manual brake setup.

We did not want to chuck out the ABS system so we plumbed the return lines from the ABS pump into a Y-fitting that fed back to both master cylinders. This allowed us to keep the ABS functional.

The Tilton balance bar adjustment knob was mounted to an aluminum panel on the dash that also holds the Traction Control switch (it defaults to off now). We initially tested this new setup on the street, and quickly changed master cylinder bore diameters to get more braking force. Even using the best hydraulic ratio formulas you often have some trial and error - we were close, but needed one more iteration. The pedal effort is firmer than before (no vacuum assist) but the pedal travel is perfect and heel-toe is still easy. We then needed to test the car on track to prove it...


During this brake master upgrade period we also made some other small changes to the Corvette, to make it more reliable on track as well as to clear up any TTC class legality questions.

Earlier in the year, as we were fighting brake master cylinder issues that we couldn't diagnose easily, we threw some hastily made brake duct inlets and backing plates on the front of the car. That was when we briefly ran the car in TT2 class, which has no aero restrictions. The easy place to add the brake cooling air inlets was under the front nose. Because this is not exactly a good high pressure spot I decided on some vertical panels (see above) on the outside of these 3" round vents, to keep air from spilling away laterally from the inlets.

After some discussion with two different NASA race directors it was felt this vertical plane we added was in "a grey area" that could be protested, and someone could argue this deflector as a "canard" or "air dam". No, these didn't provide any downforce, and actually probably added a little lift, but they look like canards and the NASA rule book doesn't define terms like "canard"... its all up to the rules maker or protest judge to interpret the rules however they see fit. So to remove any doubt, we redesigned these brake duct inlets and removed the potential brake cooling "canards".

These plastic NACA ducts had an identical 3" hose connection and they were, in fact, much easier to install than the work needed to fabricate the "canards" and and brake duct inlets we had used before. Are they as effective? Hard to say without some very detailed testing, but these were deemed TTC legal without any doubt (or points) by the same race directors, so they went on.

A fire proof Nomex shift boot and aluminum mounting base were then added. We use this Joe's Racing shift boot kit on many builds, dating all the way back to our Alpha E36 LS1 car back in 2006. This boot goes over the old rubber transmission tunnel boot that was now 25 years old. This Nomex boot added a layer of noise, exhaust, and fire sealing to the stock transmission tunnel.

continued below

Last edited by Fair!; 11-09-2016 at 07:05 PM.
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