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On Tuesday, February 20, I took my car to Rearend Specialties in Santa Clara to have them install FMS 3.73 gears and an FMS balanced aluminum driveshaft. This was appointment #2, as I had to reschedule the first due to being unexpectedly snowed in during my Reno get-away weekend.

Rearend Specialties was recommended to me from the guys at 98cobra.com and I was very pleased with the service I received from them. My ride was not able to pick me up, so the guys there put my car in first so that I could just wait for them to finish. The total job took about 1.5 hours. They also installed my new driveshaft free of charge. They said that they had to drop the driveshaft anyway, so they would just put in the new one. That saved me a bit of wrenching - thanks!

The only thing that didn't go as scheduled was the carrier bearings (pictured above). When they were swapping out the gears, they noticed that one of the carrier bearings was chunked up. They advised me that they should both be replaced. I am not sure why one would get hammered, but sure enough, it was.

When I left, I noticed a difference right away. The car seemed to drive and shift much smoother than before - not sure why. Also, I noticed that my speedometer was reading a bit high. This will be fixed next time I have a dyno tune done. I think the new driveshaft had a lot to do with the smoothness. There is a 500 mile break-in period, and after that I will be able to see how much of a difference there is off the line. I can't wait!

Below is the recommended break-in schedule for gears. The copy was taken from a paper given to me by Rearend Specialties.

REAREND SPECIALTIES -
IMPORTANT DIFFERENTIAL CARE
AND BREAK-IN INFORMATION

NEW GEAR BREAK-IN: All new gear sets require a break-in period to prevent damage from overheating. After driving the first 15 to 20 miles, stop and let the differential cool before proceeding. Limit freeway speeds to under 55mph. Go easy on it. RS Warranty also requires at least 500 miles before towing. RS recommends towing for very short distances (less than 15 miles) and letting the differential cool before continuing during the first 45 towing miles. This may seem unnecessary but it is very easy to damage the differential by loading it before the gear set is completely broken in. RS also recommends changing the oil after the first 500 miles. This will remove any metal particles or phosphorus coating that has come from the new gear set.

The greatest damage results when a new ring & pinion has been run for several miles during the first 500 miles when the oil is very hot. Any heavy use or overloading at this time will cause irreparable damage to the gear that will not be warranted by RS.

OVERLOADING NEW GEAR-SETS WILL CAUSE THE GEAR OIL TO BREAK DOWN AND THE RING & PINION WILL FAIL...OR MELT!

POSITRACTIONS
Positraction chatter is normal for limited slip and positraction differentials. Both rear tires must measure the same height from the ground to the top of the wheel in order for the differential to function properly without premature wear. Limited slip additive or friction modifier for limited slip differentials must be used with the oil to reduce positraction chatter.

DETROIT LOCKERS
Detroit Locker locking differentials will bang and clunk during normal operation. Both rear tires must measure the same height from the ground to the top of the wheel in order for a locking differential to function properly.

GEAR NOISE
Richmond Gear and other aftermarket (non OEM) gears are designed primarily for strength and may be noisy. The noise is especially inherent in vans and quiet passenger cars.

This information was reproduced without the permission of Rearend Specialties. Hopefully, they won't care :-)

Rearend Specialties
1040 Di Giulio Ave #350
Santa Clara, Ca 95050
Phone: 408.988.3619
Fax: 408.988.1105