Dang.! Their pushing 1000 hp on a stock ZF? Yeah, I would say that would be an offset. You’re definitely generating some heat at the point! LoL..

Yeah that 3rd gear is mean. It pulls! I think my case was the AWD, 2+ ton, and a pretty decent pull that got it a bit flustered.

Yep - the stress (force) is provided by the motor. Whether the vehicle accelerates quickly or slowly doesn't matter. The force applied to the drivetrain is the same.


Takeaway: if you took your motor/tranny and swapped it into, say, an E46 chassis, the transmission would be under the same amount of stress, but the vehicle would accelerate a lot faster.

But that defies physics. We’re talking about acceleration, let use the same math and apply it to de-acceleration.

At a speed of 100 mph, it will take longer to stop, put more stress, and create more heat to stop a E53 vs a E46 if the exact same braking system was in both vehicles.

So how can the reverse math be any different? If from a stop to 100 mph, how can it NOT induce more stress, and creat more heat than an E46 with the exact same gearbox?

You said yourself, that the E46 would accelerate faster. That means less stress (heat), and fuel (heat) to propel the E46 vs the E53 to 100 mph.

The weight is definitely a factor. Right?

You are confusing stress (force per unit area) and work (energy).

You are right that the E53 has more kinetic energy at a given speed than an E46, and requires more work (fuel) to get it up to that speed. But if the motor is the same, then the force on the transmission and drivetrain is the same. It has to be applied longer, but the force is the same.

You are right that there will be more heat added to the transmission, differential, u-joints, etc. But heat is not stress, and those things typically don't get so hot that they break. They absorb a very small portion of the work transmitter through them.

Stress is a force divided by an area (it has the same units as pressure, such as pounds per square inch). Heat is not stress, heat is heat.

Think of it this way: let's say you tie a rope to your X5, which weighs 4,600 lbs, and try to pull it. Let's say you can pull with a force of 100 lbs. You pull until your car is traveling at 10 mph. You are completely exhausted, but the rope has experienced no more than 100 lbs of force.

Now tie the rope to your neighbor's sweet Lotus Elise, which weighs 1,980lbs. You pull on it with a force of 100 lbs. The Lotus accelerates to 10 mph a lot faster, and you are not very worn out. But the rope never experiences more than 100 lbs of force. The transmission is the rope. It is exactly the same.

More to the point, a totally different synchro from the one that the pull was done in is not going to experience wear.

I'd bet that this was an adrenaline missed shift. I've been there. Also, once the fun is over, you're out of rhythm a little bit.

Edit: And by "missed," I don't mean wrong gear. I just mean clutch pedal / shifter interplay not entirely in sync. With the longish travel of both the shifter and the clutch pedal, it's easy to do.

No I don’t believe there is damage, I very lightly attempted to put it into 4th, and come down in speed. There was a very light audible. It shifted fine thereafter.

I wasn’t trying to hit 4th. I put the clutch in held it for a few, went to neutral, and then made the attempt at 4th. I was a bit surprised with that particular pull though.

I have a DSSR, a short shifter, and 8lb flywheel with a Kevlar clutch, the shifting is light, tight and effortless. It just seemed like she wasn’t thrilled with being pushed quite that hard.

But if I (human drivetrain LoL..)am completely exhausted that means, I am experiencing more stress. The power still has to flow from the muscles to the limbs, etc.

The rope is static, the gearbox is not. So you have torque + weight affecting all of the rotational mass.

Like I said, you are the engine in this scenario, and the rope is the transmission. The engine does more work (i.e. uses more fuel) but the transmission does not see any more stress.

The last statement you made is not true. Think of it this way, let's say Happy's engine makes 300 lbft of peak torque. If you took your tranny off the car, shifted it to third gear, then took a pipe wrench and twisted the input shaft with a torque of 300 lbft and held the output shaft so that it could not move, the transmission would be experiencing the same stress as it is in your third gear pull. (There is a very minor amount of heat transferred into the transmission that I am ignoring, because your transmission doesn't care about it in the slightest.)

The greater the mass the more inertia it takes to get it to move. If a 2500 lb. vehicle will move with 100 lbs of force then a 5000lb vehicle will take 200 lbs of force to move it. Also, a transmission has gears it is not like a rope.

Synchros most often fail because clutch is out of adjustment. If you are still hearing the grinding I would adjust the clutch sooner than later. If it is only in one gear it is time to change that one out before you have much more expensive damage. I would think that at 46mph I would think you would want to gear down to second.

E53 M54 Exhaust Headers
 

I am going to respectfully disagree.

Me = 4586(1+0.04+0.0025*10^2) E53

Me = 3241(1+0.04+0.0025*10^2) E46

Me =5916 E53

Me = 4180 E46