how to install a lightweight brake rotor

It's a new buzz word among the aftermarket shops- rotating mass. Sounds like a '72 Cadillac Eldorado.

In this case, the words' terms define objects that turn around- rather spin. Tires are rotating mass. Crankshafts are rotating mass. Brake discs are rotating mass. The focus of this article is the brake disc.

Engineers at Dyno Jet, makers of the SleDyno, taught American Snowmobiler staffers that rotating mass kills track horsepower. Less rotating mass equals more track hp. Brake discs are part of this horsepower loss equation.

This discussion was also carried out with Jerry Mathews, operations manager at Starting Line Products, who agreed rotating mass robs horsepower. Upon his recommendation, SLP and American Snowmobiler, swapped out the stock brake disc for SLP's new Ultra Lite™ Wave Rotor and brake pads on a 2000 700 RMK. Rotor part number is 27-70, pads carry part number 27-20 for this RMK. Ask SLP for specific model specifications.

Here are the steps to complete this task. Consult a shop repair manual- we did. If you are patient, this can be done without removing the rear suspension and track drivers. However, as Mathews says, "This can be a royal pain in the butt if you're in a rush."

1. Remove the exhaust system.

2. Remove the drive belt.

3. Remove the hood (recommended by Polaris).

4. Loosen the track by backing off track pressure from the rear axle. Loosen axle lock nuts from the track tension and alignment bolts. Loosen center axle bolt. Let the suspension relax.

5. Drain the snowmobile's chain case oil by placing a drip pan under the snowmobile's right side, near the exhaust outlet, loosen drain plug and drain oil.

6. Remove chaincase bolts.

7. Remove chaincase cover.

8. Using a pair of needle nose pliers, remove the drive shaft cotter pin and nut.

9. Remove both upper and lower gear nuts only.

10. Loosen chain drive chain adjustment bolt and remove chain tensioner unit.

11. Remove chain.

12. Remove upper and lower gears.

13. Remove the top two brake caliper bolts that secure the caliper carrier bracket to the chaincase and set the caliper aside. Do not disconnect the hydraulic brake line.

14. Remove the three bolts which attach inside chaincase housing to the bulkhead. Remember (according to Polaris' shop manual), the front bolt is through bolt- rear and bottom bolts are carriage bolts. These must be replaced in like manner.

15. Loosen the case and rotate the top side down as much as it will go. This is not easy. With a rubber mallet and pry bars, work the top and bottom until it wedges free. This is where patience comes in force. When doing this, work the case slowly, this will protect the drive shaft seals and chaincase gasket seal.

16. Remove the chaincase gasket and clean.

17. Remove brake rotor seal collar.

18. Remove brake rotor.

19. Install new Ultra Lite™ Wave Rotor. Ensure the rotor rotates with the leading edge- spins toward the sled's front. Imagine a saw blade spinning backwards.

20. Reset the brake rotor collar and seal.

21. With the top brake caliper bolts removed, remove rope guide. Do not disconnect hydraulic brake line.

22. Remove hose clamps from brake coolant line that face the engine.

23. Remove coolant line. Use a catch pan to allow anti-freeze to drain into.

24. Remove brake fluid reservoir cover. Use shop cloths to gather up spills as they occur.

25. Using a large C-clamp vise grip, squeeze on the center of the old pads applying pressure to the caliper piston. This allows the caliper to slide back into the caliper assembly.

26. Lift brake bracket unit.

27. Raise the open end of the brake cooler and pad assembly. This traps the engine coolant in the coolant housing. Plug the cooler and engine hose end opening.

28. Place the new SLP anti-friction brake pads into the caliper housing.

29. Slide the brake unit into its bracket until clips snap into place.

30. Separate pads to install over new disc. For your information, and again to the Polaris repair manual, if the brake unit does not easily slide over the disc the caliper piston is not sufficiently compressed.

31. Install coolant hose clamp onto coolant assembly.

32. Reinstall caliper housing bolts and washers. Torque to repair manual specifications.

33. Ensure brake fluid reservoir is filled to proper capacity.

34. Reinstall chaincase components in reverse order of removal, steps 16 up to 1. Remember, remove/removal means install/reinstall when working backwards.

Be sure to clean the chaincase cover gasket and use gasket sealant to reset it in its groove. Avoid forcing any components - protect bearings and seals. Adjust chain tension to manufacturer specifications. When chaincase is reassembled, fill chaincase with quality oil, in our case we used SLP's chaincase oil.

After this is done, the track needs alignment and tightening. Do the following.

1. Tighten axle bolt.

2. Tighten the rear axle tension bolts, as the track starts to stretch, tighten each the tension bolt turn for turn until proper tension poundage is achieved by using a spring scale, such as one to weigh fish, at a one-inch pull from the hyfax. For best results place the snowmobile rear end on a jackstand and hook the scale on to a track clip at the track's center- equal distance from driver to rear axle.

3. When proper tension is achieved, check alignment by starting the snowmobile and throttling up the motor to spin the track several times.

4. Let track and motor come to stop with applying the brake.

5. Turn off the motor.

6. Approximately six-inches from the rear axle, measure the distance between the track clip and hyfax. Measure both sides. If one side has a narrower measurement, tighten the opposite side tension bolt.

7. Retake the measurements.

8. When equal distances are claimed from track clip to hyfax, lock down the tension bolts.

After the first weekend of riding with this brake rotor, noticeable improvements came in the following: easier brake pull, quicker response from lever to caliper to pads; but more so, a brake rotor that did not heat.

When careening down steep ascents, rotors and pads heat, the test 700 RMK did not experience heat fade as it did with the stock equipment. But for most riders, stock may be OK. However, if you want less rotating mass (weight), or if you are an extreme mountain rider, or one who throttles and brakes a bunch on the trails or on the race course, these are the rotor and brake pads for you.

Don't forget the goal of this rotor is reducing rotating mass- that horse-power thief.

Contact SLP at 208/529-0244.