SL-C Pedals, Master Cylinders and Reservoirs

Reservoirs

Chamber Master Clyinder Capacity (oz)
Left Rear Brakes 6.3
Middle Front Brakes 9.8
Right Clutch 4.0

The kit included three separate Wilwood reservoirs with push-on barbs. I decided to upgrade them to a three-chamber Tilton reservoir with -4 AN fittings. The three reservoirs have different capacities so it makes sense to assign the largest to the most critical function and the smallest to the least critical.

Qty. Part Number Description Price Ext. Price
1 72-576 Tilton 3-Chamber Plastic Reservoir $135.15 $135.15 
8 3490-04-FOOT 910 PTFE Lined -4 AN Aramid Braided Lightweight Racing Hose (Per Foot) $14.98 $119.84
3 3481-04-000 811 Straight Aluminum -4 AN Hose End  $13.99 $41.97
9 3481-04-090 811 90-degree Aluminum -4 AN Hose End  $23.99 $215.91
3 FBM5071 Aeroquip -4 AN Straight Bulkhead Fitting $4.47 $13.41
2 FBM5099 Aeroquip -4 AN Bulkhead Nuts (Pair) $1.79 $3.58
2   1/4"-20 x 3 1/2" button head bolt    
2   1/4" Stainless Lock Nut    
4   1/4" Stainless Flat Washer    

The 3-1/2" bolts were used to mount the reservoir. They were cut down to about 3-1/4" to better fit.

MASTER CYLINDERS

The Willwood master cylinders that came with the kit were nice, but I didn't like that the reservoir connection points were plastic pieces held in place by an o-ring which then connected to the hose via a standard hose clamp. So I decided to upgrade to Tilton master clyinders which resulted in the need for yet more parts.

Qty. Part Number Description Unit Price Ext. Price
2 76-750 Tilton 3/4" 76-Series Master Cylinder $106.25 $212.50
1 76-875 Tilton 7/8" 76-Series Master Cylinder $106.25 $106.25
3 FBM5051 Aeroquip Straight, Male -4 AN to Male -4 AN Aluminum Coupler Black $2.97 $8.91
1 FBM3513 Aeroquip -4 AN Aluminum Crush Washer (Set of 5) $10.97 $10.97
3 RS.2000M Race Spec 0-2000psig Pressure Transducer $170.00 $510.00
3 FBM2719 Aeroquip Straight, -3 AN Male to 1/8" NPT Female Steel Fitting $12.07  $36.31

Pedals

Qty. Part Number Description Unit Price
1 72-792 Tilton Drive-By-WireThrottle Linkage System $123.25
1 TP8LH Jenvey Dynamics TP8LH P&G Contactless Throttle Position Sensor - LH $160.00

The kit came with a beautiful set of Tilton 72-603 pedals. As you'd expect from a premium racing pedal assembly they are well engineered and massively configurable. The latter being a bit of an issue as the instructions merely state that "pedal position is highly dependent on the driver's preference" and you're looking at bunch of parts on the bench.

The first step is to mount the pedals. The brake pedal is wider than the gas and clutch pedals -- makes sense as the most important thing in any car is stopping. Each pedal can be installed in one of two orientations that provide different mechanical ratios. I wasn't sure which I would prefer so I just picked one. In addition each pedal can be installed in one of two bolt positions which will change the height by 1/2". Since I have small feet, I chose the shorter option -- don't go there, small feet means small shoes and that the body can expend resources growing other appendages. In any event all of these settings will be easy to change even when the pedals are mounted in the car.

The next step was to determine how the pedals should be positioned. With a 1,000 HP motor in a very light car you want the throttle pedal throw to be as long as possible, so I adjusted the min and max limits accordingly.

Next I installed the clutch, front brake and rear brake master cylinders. I upgraded the Wilwood master cylinders to Tiltons because I believe the Tiltons are superior and they use a -4 AN fitting for the reservoir feed rather that a rubber hose and barb, and they have an additional -3 AN fitting on the pressure side which will allow me to cleanly install pressure sensors. Interestingly the front brake master cylinder is ¾” and the rear is 7/8". Why? Well during braking a car's momentum shifts forward so more braking is done by the front brakes. So shouldn't the front master cylinder be bigger? Nope, for the same amount of pedal travel the smaller cylinder will generate more pressure.

Next I ensured that the front/back brake bias balance bar was set to 50/50 which means that I actually have front bias because the front cylinder is smaller. Note that I will add a an adjustment knob so that I can change the bias while the car is in  motion. I then positioned the brake pedal so that it was closer to the driver than the throttle to facilitate heal-and-toe shifting. I think it's right, but I won't know for sure until I drive the car. To achieve this I had to cut the threaded shaft on both the front and rear brake master cylinders. As can be seen in the picture to the right, the Jet belt sander does a great job at cleaning up the cuts.

Installation instructions here.

Throttle Linkage & Throttle Position Sensor

Since the car is drive by wire (DBW) I purchased Titlton's throttle linkage kit. Like everything Tilton, it's very well made. However, I had an issue with the lock nut on the max travel stud hitting the bracket. I checked things out multiple times and figured that I could grind the bracket, but that didn't seem right for Tilton quality so I called their tech support and sent them some pictures. They called me back about an hour later. Apparently the holes in the bottom of the bracket are asymmetrical and the shaft had been installed backwards at the factory, thus moving the bracket slightly towards the throttle pedal. The picture on the left shows the asymmetrical bottom and the picture on the right shows the symmetrical top. After taking it apart and reassembling it everything was fine.

The bracket is designed for a Penny & Giles TPS280DP sensor. Apparently it’s a very nice hall effect sensor, tested to 60 million operations, 12-bit resolution, zero signal degradation over the lifetime of the sensor, sealed to withstand high pressure wash-downs (IP69K), dual outputs, etc.

All wonderful, but after spending hours of googling around I found all types of press releases, specs, etc., but no place to buy it online. After sending a bunch of emails to the manufacturer and re-sellers I received one quote: $250.04 and “approximately 6-8 weeks” delivery --  two months, really?

When I asked about the lead time for a replacement in case of failure, they suggested that I buy two! Clearly they forgot to mention that parts of it were made of unobtainium. After posting in the GT40s forum one of the members to me that Jenvey Dynamics white labeled as part number TP8LH. The LH indicates that the throttle value increases in the anti-clock-wise direction which is British for counter-clock-wise. In any event, I found an online retailer in the USA which offered it for $90 less.

Reservoir Connections

The reservoir connections were plumbed with -4 AN couplers and crush washers. The hose and and fittings will be done at a later time.

Pressure Sensors

I replaced the supplied brake pressure switch with three high-end pressure transducers on the font brake, rear brake and clutch master cylinders. This will enable me to log the values and have the MoTec Power Distribution Unit (PDU) take actions based on the pressure. The connection required a special -3 AN Male to 1/8" NPT Female connector into the extra -3 AN port on top of the cylinders. The pressure sensor required a 1-1/16" wrench to tighten, which is the first time that I've used that wrench. Ironic that the tiny pressure sensor required a wrench much larger than all of the manly suspension pieces.

All of this resulted in a very clean installation.

Residual Pressure Valves

Everything in the SL-C is low and the brake master cylinders are no exception. They are mounted below the brake calipers and gravity will cause brake fluid from the calipers to drain back into the master cylinder which causes excessive caliper piston retraction which results in a longer brake pedal stroke. To solve this problem, a residual pressure valve (RPV) is installed. A two-psi RPV is firm enough to prevent fluid from flowing back but not so firm as to extend the caliper piston which would cause the brakes to drag. Since there are two master cylinders (front and rear) two RPVs are needed. The kit came with RPVs, but some builders have had issues with them leaking so I upgraded them to Wilwoods.

Qty. Part Number Description Unit Price Ext. Price
2 260-13783 Wilwood 2lb Residual Pressure Valve with Fitting $19.78 $39.56