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EMF Rockwell Pinion Brake How-To

2 - 3/8x 1 1/2 grade 8 bolts are used to fasten the caliper to the caliper mount.

They should be inserted through the caliper then the mount. This will prevent excess bolt stem from draging on the face of the rotor. They need to be put through tthe caliper prior to sliding the caliper over the rotor.

The three bolts that hold the caliper mount to the housing are 1/2 x 1 3/4 inch long grade 8 bolts. They will replace the shorter stock ones. One washer will be placed between the caiper mount and the axle housing for proper spacing of the caliper in relation to the rotor.

The above and below pictures are the incorrect way of installing the caliper mount. The washers were not used between the mount and housing as is required for proper centering of the caliper.

notice the rotor is mounted behind the flange and not on the face of the flange. We chose to mount it like this incase the flange bolts break. Mounting this way will retain the rotor and not allow it to fly off. If the pinion nut breaks the rotor will still be attached to the drive shaft aso not allowing it to frisbee into a crowd.

placing the caliper over the rotor with the mounting bolts already inserted into the caliper

The washers properly placed between the caliper mount and housing giving the .110 extra clearance needed to center the rotor.

notice the rotor is centered equally between the two pads.

What the assembly should look like once installed

The steel rotor is made so the center circle will fit over the flange in place of the pinion dust shield. It may be a tight fit but can be pressed on by tightening the flange/drive shaft bolts. 

A little info on pinion brakes. 

These are the MTRA rules straight from the rule book.


- All vehicles must be equipped with foot operated hydraulic brakes in good working
order. The brakes must be able to stop the vehicle in its own length at 10 MPH (16 kmph)

- If your vehicle does not have lockers, wheel brakes are recommended.

- Rubber tired vehicles must be equipped with dual braking systems consisting of
two master cylinders with one bra dividual lines running to the front
and rear brakes.

- Driveline brake rotors must be steel billet only. A minimum of three tabs 120
degrees apart, are required to keep the rotor from moving. Tabs are not required if
rotor is mounted on the driveshaft side of the pinion. (Steel billet rotors are solid with
no webbing or fins )

- Vehicles equipped with driveline brakes are required to have the front brake
assembly mounted on the front differential. The rear can be mounted on the transfer

These are the rules the monster trucks must follow. They were created over 30 years of putting on events. Many accidents happened and many failures. These are the rules that prevent bad things from happening to drivers, track officials, camera men and the audience. They help lesson the chance of death, injury and lawsuits. As long as the promoter of the event and its officials are dilligent with safety and gross negligence can't be proven, everyone including the sport is safe from slimey lawyers and stupid people. 

Normal questions I get after I show people the rules

Q - What does this have to do with my selection of pinion brakes? I'm a monster truck. I'm only going to run mud or trail ride. 

A- The rules were made to protect life.

An example : You run toyota calipers and rotors for pinion brakes. Your buddy does the same thing and recomended it as a cheap easy solution. You're now on the trail after wheeling most the day. Climbing hills and decending down the back sides of them. Driving through holes and the odd creek. Now you come across a mud hole that you're going to play in . Your son and friends jump out to watch. As you're revving your motor and spinning the wheels you feel a vibration. You get out and your son is lying on the ground with half his head missing. Nobody knows what happened. Turns out the cast rotor you were running fractured in the last hole you drove through. It flew apart and killed your child.

It's a horrible example. But the only one I can think of to make people stop and think before using cast rotors.

Q- Why is cast bad? 

A- Cast breaks or fractures. It's ridged and brittle and It can fly into pieces. 

Properties of steel are great formability and durability, it has good tensile and yield strength and good thermal conductivity

Q- Why can cars use cast rotors? 

A - Wheel brakes used on cars or trucks rotate after the crown and pinion. They travel at much lower rpms. On a 2 1/2 ton diff 6.72 rpm less, on a planetary 15 - 30 rpm less. That means at 3000 rpm 
the rotor on a pinion brake spins 3000rpm a wheel brake rotor would only be spinning at 446 rpm. 

If a crack developes at 446 rpm you'll feel it in the pedal before too much happens. 
At 3000 rpm a crack in a cast disc has a chance of shattering because of the velosity.
The heat that a pinion brake creates is also problem for a cast rotor. The high rpms along with the full power of the drive train working against the pads will make the rotor so hot it will glow. Somthing you might see on a wheel brake but only at high speeds or if you're hauling a heavy load. With the added harshness of cold mud or water being thrown on the boiling rotor only increases the potential of cracks. Steel is just better suited for high then cold heat shocking. 

Q -why can't I just use regular brake pads? 

A - Normal pads can't handle the heat and fade out providing poor braking. They lose the ability to grip on the hot rotor. Special compounds are made for such applications and need to be used in pinion brake aplications.

AN example : PolyMatrix 7112 "E" compound has immediate cold response and a smooth rising torque curve over a wide temperature range. "E" provides steady control during burn-outs and staging, with immediate response and fade free performance.