Newbie with Epic Plans

[Ronnie]

Originally Posted by Sehnsucht

Cheese Wagon brings up a good point that got me to thinking... Admittedly I'm not speaking from personal experience with REs but it almost seems counterintuitive that when the suspension flexes the driveshaft exerts an almost opposite force than the axle's torque rod and this itself could suggest REs may be prone to an excessive wear on the pinion seal. Whereas every other god-fearing rear wheel drive vehicle in the world has the driveshaft and the torque rod (if equipped) on the leading side of the axle, a rear engine bus does not. This would suggest that as the suspension compresses under load weight or rough travel the axle is driven both upwards and rearwards corresponding to the arch of the torque rod yet it's this upwards and rearwards action that essentially drives the axle into the driveshaft, forcing it to contract as well as the U-joints to adjust to the varying angle. And given that of the variety of school bus formats the RE has the shortest possible driveshaft, that means any axle movement has less distance in terms of driveshaft length to absorb the contraction.

I'm not suggesting REs have a design flaw, I'm just really enjoying this topic! Even if no one else is getting anything from it I certainly am!

The driveshaft does have a slip joint to allow for and aft movement. The pinion bearings are what would be taking the load. The oil seal goes for the ride, meaning no load is on it. The driveshaft I have seen on rear engine buses are about 2ft long.

[CHEESE_WAGON]

At least the OP isn't a reddidiot or quora flunky...

The stupid... It burns...

[CHEESE_WAGON]

Originally Posted by Ronnie

The driveshaft does have a slip joint to allow for and aft movement. The pinion bearings are what would be taking the load. The oil seal goes for the ride, meaning no load is on it. The driveshaft I have seen on rear engine buses are about 2ft long.

Perhaps the seal is under no stress from this, but what about the sloshing and slinging of fluid toward the rear as the bus moves forward (remember, route buses spend 95% of their time accelerating from a stop). Gallons of heavy gear oil against a what, nylon, neoprene, rope seal?

The force of that momentum has got to work on a seal when oriented in this fashion, especially if the axle isn't really designed much different than a conventional FE / RWD. I certainly don't think the seal would be any different. Maybe I'm off base here, but it certainly begs the question.

And what about the slop in the pinion bearing allowing the shaft to wallow out against the seal over time? Yet another idea that should be explored here.

[Sehnsucht]

"It's a Jeep thing..."

I never gave a moment's thought to driveshafts until I had a Jeep Wrangler at which point I learned way too much about these seemingly innocuous components, especially when you go to lift the suspension. In some ways there are similarities between the front axle of a 4WD Jeep and our rear engine bus... The rear input axle, the short driveshaft... These factors introduce challenges that no doubt the manufacturer had to consider and hopefully address or rule out as practical considerations in order to build a reliable vehicle. Of course as mentioned it could be they only cared that it last long enough to survive the warranty and not their problem after that but given the sheer number of units out there and this is only the first time I can recall this particular issue I would theorize it isn't a prevalent issue. I just get too in my own head about stuff like this.

So for the OP, don't let all this focus on the pinion seal be validation of that as the source of the leak. Rather, just suggest it to the mechanic who is on-site as a potential source of the issue and let them determine if it is or isn't because their eyes are the only ones seeing the problem first-hand. The rest of us are just cobbling together our own pieces of knowledge and experience but with an impressive amount of depth into this topic. As I said, I'm personally enjoying it from an academic perspective but I don't want to forget we're trying to help the OP diagnose an issue.

[Ronnie]

Originally Posted by CHEESE_WAGON

Perhaps the seal is under no stress from this, but what about the sloshing and slinging of fluid toward the rear as the bus moves forward (remember, route buses spend 95% of their time accelerating from a stop). Gallons of heavy gear oil against a what, nylon, neoprene, rope seal?

The force of that momentum has got to work on a seal when oriented in this fashion, especially if the axle isn't really designed much different than a conventional FE / RWD. I certainly don't think the seal would be any different. Maybe I'm off base here, but it certainly begs the question.

And what about the slop in the pinion bearing allowing the shaft to wallow out against the seal over time? Yet another idea that should be explored here.

Well think of it this way if the force of acceleration causes the oil to act on the seal, on a rear engine bus, then the force of braking on a CE or FE bus would do the same. seals do wear out over time regardless and this is for the OP a possibility.

by the way it is not a rope seal, Usually neoprene or EDEM rubber with a spring around it circumference, sometimes with an oil sliinger next to it.

[Mandinee1]

Originally Posted by Sehnsucht

"It's a Jeep thing..."

I never gave a moment's thought to driveshafts until I had a Jeep Wrangler at which point I learned way too much about these seemingly innocuous components, especially when you go to lift the suspension. In some ways there are similarities between the front axle of a 4WD Jeep and our rear engine bus... The rear input axle, the short driveshaft... These factors introduce challenges that no doubt the manufacturer had to consider and hopefully address or rule out as practical considerations in order to build a reliable vehicle. Of course as mentioned it could be they only cared that it last long enough to survive the warranty and not their problem after that but given the sheer number of units out there and this is only the first time I can recall this particular issue I would theorize it isn't a prevalent issue. I just get too in my own head about stuff like this.

So for the OP, don't let all this focus on the pinion seal be validation of that as the source of the leak. Rather, just suggest it to the mechanic who is on-site as a potential source of the issue and let them determine if it is or isn't because their eyes are the only ones seeing the problem first-hand. The rest of us are just cobbling together our own pieces of knowledge and experience but with an impressive amount of depth into this topic. As I said, I'm personally enjoying it from an academic perspective but I don't want to forget we're trying to help the OP diagnose an issue.

Thanks, I am following the knowledge as best as I can. Your direct OP pointers are helpful because so much of it is over my head but I love watching the dialogue anyway. I did speak to the mechanic, who told me if it is the pinion seal
Somewhere between $275-500, but he is going to assess and call me before he does anything. The seller has agreed to a deal
With me but is busy this week so I am waiting on him to get the bus to the shop. Hoping everything stays afloat!!!

[Ronnie]

Seems like things are moving well, good luck with it!

I know we kind of went deep, so hope that at least it gives some insight.

[Sehnsucht]

Originally Posted by Ronnie

Seems like things are moving well, good luck with it!

I know we kind of went deep, so hope that at least it gives some insight.

Agreed, sounds likes it could be easily addressed and make a good deal a great deal!

And I agree we kind of get into things deep which is why I like to circle back to where the OP probably is which is not nearly as deep down the rabbit hole!

[CHEESE_WAGON]

Originally Posted by Sehnsucht

So for the OP, don't let all this focus on the pinion seal be validation of that as the source of the leak. Rather, just suggest it to the mechanic who is on-site as a potential source of the issue and let them determine if it is or isn't because their eyes are the only ones seeing the problem first-hand. The rest of us are just cobbling together our own pieces of knowledge and experience but with an impressive amount of depth into this topic. As I said, I'm personally enjoying it from an academic perspective but I don't want to forget we're trying to help the OP diagnose an issue.

Which is exactly the position I'm taking. I'm confident that is the problem, but I have said that I can make no guarantees because I have not laid eyes on it myself, nor will I until I actually arrive to pick it up for transport, should that come to pass.

Originally Posted by Ronnie

Well think of it this way if the force of acceleration causes the oil to act on the seal, on a rear engine bus, then the force of braking on a CE or FE bus would do the same. seals do wear out over time regardless and this is for the OP a possibility.

by the way it is not a rope seal, Usually neoprene or EDEM rubber with a spring around it circumference, sometimes with an oil siinger next to it.

I am aware that most seals are just that. However, I have seen a few seals that are rope on different applications (mostly engine front main seals). Not knowing the design of every single pinion or differential seal out there, I was offering that on the contingency that some might be.

And you do make a point that all the stop-and-go of a route bus would slosh the gear oil against the pinion seal in an FE / RWD configuration. However, sloshing is only part of my theory. In an FE configuration, the gear oil would also have the inertia and weight of the fluid pushing back against the seal while moving forward. This would not be an issue in an FE/RWD configuration. So there is an added factor there that would not be present in an FE/RWD. Maybe it's small potatoes and there really is no consequence, but it's something to consider.

[Native]

One must also consider the fluid forces due to the gears themself. The video posted earlier makes it very clear that any sloshing due to acceleration or breaking (also an acceleration) is insignificant comared with the fluid forces generated by the gears.