Almost 2 years of my waiting time has come to end finally. Yes, here you go.
In simple terms an overdrive is the final/cruising gear. It reduces the power output by lowering the gear ratio. The overdrive mechanism increases fuel efficiency, and saves strain on the transmission and the drive train.
Warn has developed a overdrive for Jeeps, It is a very old design that has been around for decades. The same has been bought over by Saturn Company then ATV Mfg. started rebuilding it or producing the same for the niche market.
The Warn overdrive is a simple 2 speed gearbox that mates to the Jeep's transfer case and provides a 25% drop in engine rpm when engaged. Instead of creating the final gear as overdrive, the Warn overdrive model introduced new gear ratio between each gears. Hence a transmission in which the highest gear ratio is less than a one-to-one ratio. This means the drive shaft turns faster than the engine crankshaft. The overdrive feature saves fuel and, because the engine runs slower, engine wear and noise are reduced.
What I have got is the same Warn Design reproduced by ATV Mfg. for Mahindra Jeep transmission/transfer case specification. What makes the Mahindra Jeep different from its American cousins is that of Tooth and Spline counts in the transfer case, hence the regular or used Warn Overdrives will not fit directly into Mahindra Jeeps. Herm Till ford reproduced the gear with 29tooth and 15 spline count to suite the Mahindra Jeeps. The same is what I have got and going to be placed into my Jeep.
Instead of the normal 5speed gearbox with overdrive that provides an additional gear to rotate faster than the engine(crankshaft) RPM, The warn overdrive actually sits on the PTO port of Dana/Spicer T-19 transfer case and takes the input from transfer case main gear shaft and converts into different gearing ration and sends it back to the actual transmission. Because of this particular model, the warn model overdrive can introduce as much as double the number of existing transmission gears.
Currently my Jeep equipped with KMT-90 4 forward and 1 Reverse transmission, hence I'm running the Jeep with 10 gearing ratios including the 4 wheel drive Low mode. By installing the Warn Overdrive I will get 20nos of gearing ratio that will enable to choose huge range of gearing ratio according to my need.
The moment I enable the Overdrive all the gear ratio will be on the higher side, hence going to give me a smoother noiseless ride. Whenever I need to do Offroad the overdrive will be temporarily disabled by pulling the Overdrive lever back to the driver side position. Practically the overdrive will be left in engaged mode all the time as most of the time the jeep is driven on the road.
Now I will let the pictures talk about what are the items came with the Herm Tillford supplied overdrive baggage.
Come back to this space to see more on the installation side, then comes the actual driving experience part.
The actual speed change figures for ball back engine RPM figures will be made available after completion of the calculation. Just for your information, here is the formula to calculate the speed
