Hey Guys _______ Just curious about these sets of circumstances, O.K_____. a) you’re in 2WD HIGH doing around 3000 to 3500 RPMs in either first or second_____ b) your in 2WD LOW doing the same RPMs ___c) your in 4WD HIGH doing the same RPMs____ d) your ion 4WD LOW doing the same RPMs____e) in a duel transfer case setup (228, plus 228 Taco) your doing the same RPMs,_____ Which case is most stressful and what part of the drive train is most stressed out? ______ a, b ,c, d or e _____ THANKS BAYRUNNER

 

It's hard to answer that without knowing more...like what is the terrain? Also, the type of transmission will affect driveline stress. Automatics are better at soaking up the various lurches and bumps.

 

If you're on flat ground, the stress on the driveshaft (a convenient place to measure) is the same is all those situations. The stress on the engine would be higher in situation "a". If you're against a rock (not moving but trying to), the stress on the driveshaft will be highest in option "e", but stress on the engine may be lowest. For a given situation, it takes a constant amount of torque/hp to move, no more no less. By changing the tanny/transfer gearing, you lower the amount that the engine needs to provide by making it up by lower gearing. Make sense?

example: driving down a flat road at a constant 30mph with no headwind requires 25ft-lbs torque (an arbitrary number by no means meant to be correct);

If your in 4th gear (t-case in high), the engine needs to produce 25ft-lbs (plus a constant due to frictional losses)

If you're in second gear (2.25 ratio), the engine needs to produce 11.1ft-lbs and the gearing acounts for the rest. Either way, the load on the driveshaft is the same 25ft-lbs.

Only when you're not moving but trying to (like up a rock etc.) does stress increase significantly and may not be constant.

example: you're up against a rock and coaxing the engine to climb it. The engine may reach peak torque (say 150ft-lbs). Now if you're in a low gear and the t-case is in low, the actual torque on the driveshaft could be as high as 1350ft-lbs or higher. The further away from the engine you measure, the higher the stress would be.

Law of Conservation of Energy means that an engine will produce as much hp/torque as needed for a given situation (if it can), no more. Just because you have 200hp@3000rpm doesn't mean that's what your producing all the time at 3000rpm. If you're engine is producing more hp than necessary to maintain speed, you're accelerating, if less then you're decelerating.

 

The weakest part of your driveline is the front CV joints when in 4wd no matter what RPM or gear reduction is doing.

In 2wd the weak point is probably a U joint on the driveshaft. If you have a spool in the rear and 37" or bigger tires eventually an axleshaft or diff gears will break.

Its a qusetion of how worn any given part is. If everything is in good condition and you don't get too crazy with tire size you won't have to worry about driveline breakage at any RPM.

I have a broken tranny bearing and have parked the truck because I don't want to knick or scratch the shafts in my tranny. The bearing failed because it had over 210,000 miles with lots of hard wheeling on it and may have been run without enough oil before I bought it. On steep climbs the oil all sloshes away from the input bearing but when you level out on top it all sloshes back if there is enough oil in there. After 200,000 miles the tranny bearings start to get tired.

This is on an '87 5 speed 22R truck.