Particulates Clogging Fluid Flow
If your transmission overheats, is old, or is starting to deteriorate for any reason, then there’s a good chance that you have particulates in your fluid, clogging up the valve body or the fluid lines. The best prevention is to change the fluid and the transmission filter regularly. If you drop the (tranny) pan for some reason and find particulates, make sure to get a new filter, flush as much of the fluid as you can, and either clean out or replace the cooler(s).
Too Much Force
Transmissions sometimes break simply due to being overpowered by the engine. If you have a modified engine, then you might possibly be producing too much power for your tranny. Long-term damage can be worn-out clutches, but they can also suffer instantaneous input shaft, intermediate shaft, and/or output shaft failures.
Input shafts, intermediate shafts, and output shafts can all be broken in a transmission with too much force. The broken shaft you’re looking at here is the intermediate shaft out of our Dodge project truck. Notice that this shaft has had its lube holes enlarged to feed more oil to the overdrive gearset. While this can be good, it also has the potential for creating a weak point in the shaft if you’re running extremely high horsepower numbers. Stock shafts usually do not break until you start getting into the 350hp range.
You can order these shafts in 4130 chromoly or in 300M, but they are very expensive. There are also some billet drums available to further strengthen your pack.
Low Roller Clutches
The low roller clutches in the rear end of the transmission case are splined and pressed into the back of the case. And unfortunately they can sometimes spin. If this happens, you’ll either need to get a new case or use a retrofit bolt-in low roller clutch (which is a readily available and often-used item). Obviously the bolt-in retrofit is the easiest way to go.
The overdrive gearset with its overdrive clutches and planetary can sometimes fail due to a lack of lube. The best way to prevent it is to enlarge the lube circuit to allow more fluid to flow to it.