Pg 2 - Converting FV into Formula First

Disc Brakes and Wheels
Front Discs: Standard VW (Ghia) disc brakes are mandated by the rules. You have wheel mounting options when buying disc brake kits:
1. Buy them pre drilled with the 4 X 130 mm VW wheel bolt pattern
2. Buy them blank with no holes for studs and build a jig for drilling them to your wheel’s bolt pattern.
3. Buy them pre drilled for the 4x 4” standard Formula First pattern ready to screw in 1/2 –20 full thread bolts.

Option number one is the cheapest and option three is the most expensive. The difference will be in the cost of the wheels. Wheels using the VW bolt pattern are typically a few dollars more that a standard 4 X 4” mini stock steel wheel. Competitors use both, but the clear majority of Formula First cars use the 4 X 4” wheels. The advantage to that is if you are at the track and bend a wheel, you can always find a spare wheel from a fellow competitor.

Rear Discs: The rear discs are the same diameter, swept area as the fronts and use the same VW (Ghia) calipers. Rear disc kits come with the same wheel mounting options as listed above. Most kits will supply you with everything you need to change your rear drums to rear discs. You get discs, calipers with pads installed, caliper mounting brackets that take place of your old backing plates and two small spacers called swing axle bearing retainer shims (See: Adjusting Rear Wheel Bearing Axial Clearance) that take up the space between the bearings and the forged retainer. The caliper mounts are found in both stamped steel plate and aluminum castings.

Adjusting Rear Wheel Bearing Axial Clearance
In our quest to update VW drum brake technology to a touch more modern disc set up, we find a few “bumps” in the project that may need attention.

Before we get into the fixes, it is important to understand the function of the components.
The original rear wheel bearing system and drum brakes function with a very small amount of axial “float” in the bearings. This float is needed as the bearing retainer also bolts/compresses the drum brake backing plate to the rear axle housing and acts to accept brake torque. With the use of drum brakes, the amount of float is less critical and will not affect braking capacity as the drum moves in/out under cornering loads. The Germans are pretty picky about holding nice close fits/tolerances, so the original float is very small and rarely noticeable.

Now, we come along and bolt up our newer disc brake technology onto something it was never designed to have and a few troubles can show up. The common issue is that the manufactures of these kits build in plenty of bearing axial clearance to ensure the bearing retainer fully compresses down on the caliper bracket. The problem for us is that as cornering loads are applied, the increased axial bearing float allows the rotor to push the brake pads back. The next time the brakes are applied, the pedal has that much farther to be depressed to compensate for the increase in brake pad travel. It took a while to find this out, as it is not typically seen with the car stationary in the paddock.

The simple way to check if this needs adjustment can be done anywhere in this fashion. Pump the brake pedal to get maximum pedal height. Next, push very strongly side-to-side on the roll bar to simulate cornering load. Depress the brake pedal again and note any increase in travel. If the rear bearing float is too much, the applied pedal height change will be dramatic. By design, the bearing float must be present and some variation in pedal travel (1/4” or so) can be measured, but typically not noticed by the driver. The point of un-acceptability is typically when pedal travel is described as “it goes to the floor on the first pump, but then it’s OK”.

Now that we understand our problem, the solution is relatively easy. The rear axle bearing float needs to be minimized while maintaining sufficient compression on the caliper bracket. There are two ways to accomplish this. One method is to shim the bearing to the correct/desired float. The other method is the way we have done all of our cars to date, by machining the bearing retainer cap to size. Some of the disc kits come with various thickness bearing shims and will function just fine. I have preferred to machine the caps in order to get the correct float.

The best way to measure float with the components un-assembled is with a depth micrometer. One of the dimensions you will need is the height of the installed bearing in the axle housing from the edge of the caliper bracket (bolted down). The other is the depth of bearing retainer. The objective is to establish bearing float (bearing height smaller than retainer depth) of .005” minimum to.010” maximum. This will minimize rotor float and still maintain a good compression of the caliper bracket. For machining, we use a lathe to trim the flange end of the retainer.

Once correct bearing float has been established, here are a few helpful tips for re-assembly. Make sure the bearing retainer threads in the rear axle housing are chased (10 x 1.5). Most axles are used and the last few threads are filled with years of rust and could give false torque indications. Use Loctite on the retainer bolts and torque them to 65 ft lbs. Also, do not use the thin spacer washer that comes with the rear axle seal kit. They were a replacement for the original oil seal failure cup that would keep gear oil off the brake shoes if the seal started to leak. We don’t need it and the quality of the current ones will only give you trouble by collapsing under the rear axle nut torque forces as they are not hardened.

Once the bearing float is correctly set, the pad push back issue becomes a non-issue and you can fully enjoy the benefits of maintenance free disc brakes in your Formula First.

Rack and Pinion Steering
If you’re use to steering your FV with a TRW VW box you will love rack and pinion. Locating the rack will take some time, but the benefits outweigh the mounting hassles. The main thing to accomplish in the location of the rack is to minimize toe change through the suspension travel. Also, use a higher quality rack. Your driving at high speeds and don’t want to loose steering at a point when you need it most.

Rear Suspension

The rear suspension requires less work than the front suspension but there are things you need to be aware of. On most cars in Formula Vee trim the weight is right at 825lbs. without driver. That same car in Formula First trim weights 850 lbs. without driver. If we figure a 200 lb driver, the Formula First will now need an extra 75 lbs. in ballast to make minimum weight.
Due to extra weight and stiffer rear wheel rates required by the wider tires. The rear spring rate will most likely need to be increased.
Otherwise the FV rear suspension will remain unchanged.

Exhaust system
One good thing is that you will be able to use the existing FV exhaust system. The 1600cc Formula First engine exhaust ports are 1/4" wider per side than the 1200cc engine. In most situations, the exhaust will go on snug the first time. After one our two heat cycles, the pipes will re-fit themselves to the new engine.

Bodywork Modifications
The requirements for bodywork modification will vary depending on the amount of conversion you decide to take on. The rear or tail body would be really minimal. You may need to open up ductwork holes or add oil cooler ductwork. Mid sections should be just the same except that you might have to make cutouts for rack and pinion tie rods. The front or nose, however, might be more of an issue depending if you stick with the original link pin beam or switch to the ball joint beam. The reason for this is the ball joint beam upper tube is one inch higher than the link pin beam. On most cars that have a lot of room up front inside the nose such as D13's and Citations it’s usually no problem. Cars with very small noses like Protoform P-2's you need to do a bit of trimming and maybe fiberglass rearranging because the beam is taller the tubes are farther apart. If you have a car with beam covering wing-lets such as a Protoform or a Laser then these winglets should be cut off or re-spaced. You might even do a new nose if you want a really clean front end. If you just don’t care you can just tape it up with racers tape and get out on the track.

Alignment Settings
Here is some basic chassis setting info that many have found to be a good base line. Over time, these numbers may change. But for now, they will get you in the general area.

Beam Caster (measured across the upper and lower tubes): 2 to 3 degrees (top tube tipped back)
Note: Always set the caster/camber eccentrics to minimize caster with correct camber set. Always set caster/camber before toe.

Front Camber: 3/4 degree negative each side
Front Toe: Zero to 1/32" out
Rear Camber: 1/2 to 3/4 degree negative each side
Rear Droop: Zero to 1/2 degree positive (total)
Rear Toe: Zero to 1/32" in

Tire Pressure Range (Hoosier R60):
Front: 12 to 13 psi cold
Rear: 14 to 15 psi cold

At these settings, your car will be pretty happy. Of course your own settings may be adjusted to whatever fits your liking.

Conclusion
The conversion of a Formula Vee into Formula First will not be as difficult as building you own space shuttle. However, many of the details can be time consuming. It’s best to plan on a least a couple of months of part time work to get the process done right. You don’t want to start converting in May when your first race is in June. Some tasks like bolting on disk brakes are simple. Other jobs like grinding the calipers are more involved but can be simplified by following the procedure we have outlined. Other jobs like mounting the steering rack may take a touch of engineering savvy and above average fabricating skills. If you allow yourself at least three months from start to finish, you will be in great shape. In this article, we have not dwelled on the cost conversion at all because they are too variable. I have heard estimates ranging from $2,500 to $8,000. The lower estimates always come from people who build their own engines. Without a doubt, the engine will be the biggest cost incurred.

SCCA Homologation needs to be planned for as well. You will need to allow about two weeks for this process. Start now and get familiar with the process by downloading the application from the SCCA’s web site and see what needs to be done. The most tedious thing in the process is you will need to take about twenty pictures of your car in a mostly finished state. You either need to print them on a photo printer or get them printed so this can take a few days. One thing they never ask for in the application is pictures of the fuel cell and the fire system. Take pictures of these. The fire system picture should show the gauge that shows a full charge. Also take pictures of the nozzles just in case. If your fuel cell has a manufacturer and date stamp take a picture of that too. Remember not all fuel cells now meet the SCCA’s spec. Stock car units like the Jaz cell are definitely are not allowed. If your car is homologated as FV, it costs nothing to re-homologate as FST. If you want dual homologation as FV and FST it’s about $75- 80 dollars. This is an easy process and the SCCA people are great, but you have to leave plenty of time.

Have fun with converting your new Formula First!