Part Four: The Rear End
Moving under the truck, it was time to change out some other vital fluids. After looking at the fuel filter, I could only imagine the last time the rear differential was serviced. There is really not much to this job, and it turned out to be more messy than difficult. I opted to use Royal Purple for the rest of the fluids, because my editor did some dyno-testing in a previous issue and got a 5 hp gain by just changing the oil. I picked up a new gasket and a tube of RTV sealant to complete the job.
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1. Before opening anything, I decided to clean off the 15-plus years of crud from the diff. | 
2. I started at the bottom, removing bolts around the diff cover until the fluid started draining out. Once it was done trickling out, I cleaned the cover and gave it a fresh coat of paint. |
3. I spread a small bead of RTV on the gasket to help hold it in place and to improve the seal. | 
4. Once the cover was reinstalled, I fed in almost two bottles of the Royal Purple Max-Gear 75-90. Max-Gear is designed to provide protection to heavily loaded gears with a blend of synthetic oils and Royal Purple's proprietary Synslide additive. All viscosities of Max-Gear are formulated with hypoid friction modifiers, which are necessary for use in clutch- or cone-type differentials. So, if you have a posi, no additional additives will be necessary. | 
5. You know the rearend is full when it starts trickling out of the fill hole. |
Part Five: Engine Oil
The engine oil and filter were next. According to Fra, the Tough Guard oil filter, which offers a 99 precent multi-pass efficiency, uses a combination synthetic glass and cellulose taht provides exceptional filtration for the life of the filter. Royal Purple's 10W-30 is made with the same blend of synthetic oils and the Synslide additive. I also picked up a new drain plug and oil cap.
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1. Before I installed the new Fram filter, I filled it with some oil and smeared a light coat on the O-ring. | 
2. Before filling up the crankcase, I installed the new drain plug with the new washer, which should help prevent any leaks, from here anyway. |
Sport Truck Tech Tip
Some Fresh Air!
While I was under there, I decided to swap out the O2 sensor I got from Bosch. The O2 sensor is the primary measurement device for the fuel control computer in the truck to know if the engine is too rich or too lean. Because I had fuel problems, I decided to put in a new one for safety's sake. The new unit already has antiseize compound on the threads, so all I had to do was thread it in, tighten it up, and plug it in. Before you start the truck for the first time after installing a new O2 sensor, turn the key on to the run position for about 10 to 15 seconds to let the sensor heat up and burn off any contaminants.