Paul: I am inexperienced on buses right now (I am a newbie), but I do have an engineering degree, and I have worked on vehicle and machinery drivetrains in the past, so let me take a stab at it, and maybe other smarter, more experienced people can correct any errors I might make.

The bus weighs 45,000 pounds and the maximum grade is 25%.

A 25% grade converts 25% of the bus's weight to rearward force when climbing, so that means a rearward force of 25% of 45,000 pounds = 11,250 pounds.

This dwarfs the force required to accelerate the bus from zero mph to say 5 or 10 mph (anything faster would be unsafe on a steep hill!). So, basically the question is can the combination of engine and gearing produce more than 11,250 pounds force.

You don't say what model of Allison, but 1st gear is going to be at LEAST a 3.0 multiplier of torque. (1st gear in any Allison specs I have seen has always been greater than 3.0).

You don't say what rear axle ratio is on the bus, but let's assume the WORST probable case, which would be ,maybe 2.75 if someone REALLY misgeared it.

I don't have a dyno charty for an 8V92T in front of me, and the dyno chart would not go low enough in rpm anyway (they commonly stop at 1200 ro 1000 rpm), but any turbocharged 8V92 has to make at LEAST 1000 ft lb of torque even at low rpm (the torque converter will ensure that you have at elast SOME rpm to work with!). Do NOT assume you will have the PEAK (published) torque at low rpm. The torque curve falls off BOTH at higher and lower rpm than at the peak troque rpm.

So, I am seeing at LEAST 1000 ft lb x 3.0 transmission mutliplication x 2.75 axle multiplication = 8250 ft lb of torque at the wheels.

If you axle ratio is actually say 3.7 and your transmission 1st gear is actually 3.69 (like mine is), you might have as much as 1000 x 3.7 x 3.69 = 13,700 ft lb. of torque at the wheels.

You didn't give you wheel and tire size, but I'm going to assume just about the worst you might have: 11R24.5 with a diameter of 43 inches.

That means your 8250 to 13,700 ft lb of torque converts to somewhere between 4600 to 8100 pounds force at the intersection of the wheels with the driveway. (Froce available = torque divided by RADIUS of the tire in FEET (not inches).

Since you need 11,250 pounds of force, it looks on the surface like you will NOT be able to climb the 25% grade.

Now, you DO have a torque converter. And a torque converter is specifically designed to multiply torque from a dead start, and can mulitply it by up to about a factor of 3. So, theoretically, that torque converter can multiply your force at the wheel by up to 3 tims, which woudl give you 25,000 to 41,000 pounds of force - which IS enough to make the climb. Theoretically.

However, having the torwue converter multiply torque to get a bus GOING froma dead stop to where 1st gear can take over on its own is one thing. To expect the troque converter to work in that manner for almost 4/10 of a mile is going to generate a TERRIFIC amount of heat. I would be worried about the torque converter and transmission fluid overheating and failing. And, if it fails part way up a 25% or 16% hill, you are in serious trouble.

That's my first reason for advising against trying this.

Secondly, I don't think I would WANT to try to climb that steep a grade in a 45,000 pound bus even if I COULD. Way too dangerous, and a HUGE load on the entire drivetrain, let alone the torque converter.

Plus, once you get to the gravel, I doubt you can apply enough torque, even if you had it, to move the bus - the tires would likely spin instead, because that would be easier than "lifting" the bus.

The switchback on a hill that steep would also just be INVITING a tipover, and buses ARE pretty high.

Finally, I definitely would NOT want to back the bus down that hill. I regard that as very dangerous given the turns required.

I am assuming you are asking a serious question, and that this is not some sort of joke posting . . .

Jim G