Basic Info - Rear axles/differential

[Oonrahnjay]

OK, bear with me here - I'm not sure exactly how to word this question.

I'm going to change the rear axle in my bus; as it was built, it has a 5.43:1 rear diff and there's no way to change the gearing inside the axle.  The gearing is *way* wrong for what I need and I need to go to a 4.21 or 4.29:1 diff gearing -- that will make it prefect. 

Most of the axles around (the right size for my bus) are from "convential" trucks; what I mean by this is a truck with the engine up front, then the transmission, and a drive shaft, and the axle with the input/u-joint pointing forward to meet the drive shaft.  But my bus is rear-engine.  If I get an axle that's right for everything else (right width, right weight rating, right suspension and brake part mounts), can I "turn it around backwards" and use it OK?  Or does it have to be an axle expecially made for a rear-engine "pusher configuration" with the drive shaft input coming in from the back?  (The direction of rotation of the input shaft isn't a factor.)

Thanks for considering this basically odd-ball question.   BH  NC USA

[bottomacher]

That normally requires relocation of the spring perches or airbag mounts, fill and drain holes, and brake mounting location. Otherwise, I would think it requires a bunch of measuring and thinking.

[bevans6]

You have to make sure you are driving on the "drive" side of the ring gear, not the "coast" side, although I have heard of people successfully doing this.  So direction of rotation of the input shaft may make a difference.

Brian

[Sean]

...  If I get an axle that's right for everything else (right width, right weight rating, right suspension and brake part mounts), can I "turn it around backwards" and use it OK?  Or does it have to be an axle expecially made for a rear-engine "pusher configuration" with the drive shaft input coming in from the back?  (The direction of rotation of the input shaft isn't a factor.)

If I understand your question to mean can you turn the axle around with what is currently the top of the axle still being on top, so you don't need to relocate brake parts and suspension mounts, then the answer is no -- your bus will go backwards in drive and forwards in reverse.  And the direction of rotation of the input shaft is most certainly a factor; if you could reverse the rotation of the shaft (by, say, getting an engine with the opposite rotation) then you could fix this.

In order to get a truck axle to work on a bus, you need to flip it upside-down.  Some axles can do this, and some can't -- you'll need to check with the axle manufacturer.  At a minimum you will need to relocate some parts, but you also might have to drill and tap a new oil fill hole.

HTH,

-Sean
hgttp://ourodyssey.blogspot.com

[luvrbus]

Lot of outfits out there than cut the center section and replace it with one a different ratio, if you are a good fabricator you can do it yourself not a rocket science,the tube type housings are a snap hard to screw one of those up even for me  

good luck

[Oonrahnjay]

You have to make sure you are driving on the "drive" side of the ring gear, not the "coast" side,  (snip) 

THAT'S the kind of information I wanted to know.  I'll talk to the axle guy about this when I get back from vacation in a couple of weeks.

(Sean)  That's at least one advantage.  My engine turns "backward" from N American engines.  So, actually a NA axle setup that "reverses" things is what I need.  (That's why I said "direction of rotation isn't a issue").  So as long as a particular axle "reverses", and it's "driving the drives side on the ring and pinion", it may be right for what I need.

(Clifford)  The one that's in there now is a "compound" axle.  As part of it turning backward from N American engines, there's actually a pair of gears on each axle shaft that reverses rotation.  It's a little complicated to explain but that's the problem -- the stock axle is complicated, there's no spare parts to change the gearing, and the whole thing is made with the cavities inside it just big enough for the gears that are in there now.  There usually is a way to change most anything mechanical but this complicated thing makes it impractical.

Thanks for the help, folks!  Please keep the ideas coming.    BH  NC USA

[artvonne]

  Just remember that the driveshaft has to come to the axle at the same angle. The ring and pinion work a certain way, the main driving force is meant to go into the face of the teeth. While some have flipped them over for custom racing applications, they do not live as long. In a Bus or heavy vehicle, I would strongly recommend against doing that. Like Clifford says, its not rocket science, you just have some rules to follow.

[Oonrahnjay]

  Just remember that the driveshaft has to come to the axle at the same angle. The ring and pinion work a certain way, the main driving force is meant to go into the face of the teeth. While some have flipped them over for custom racing applications, they do not live as long. In a Bus or heavy vehicle, I would strongly recommend against doing that. Like Clifford says, its not rocket science, you just have some rules to follow.

Thanks, Paul.  Getting the basic info (I come from a car background and pusher engines -- at least with a driveshaft -- are new to me) is finding about those rules.   

[Lee Bradley]

  Just remember that the driveshaft has to come to the axle at the same angle. The ring and pinion work a certain way, the main driving force is meant to go into the face of the teeth. While some have flipped them over for custom racing applications, they do not live as long. In a Bus or heavy vehicle, I would strongly recommend against doing that. Like Clifford says, its not rocket science, you just have some rules to follow.

Flipping the axle over doesn't change the drive force on the teeth. You would have to reverse the pinion rotation to drive on the coast side of the teeth.

[luvrbus]

Like Lee said flipping it doesn't change the gear force turning it around does that is a no no
good luck

[bevans6]

Hypoid gear axles have the pinion coming in below the centerline of the ring gear, in most cases.  The pinion shaft and bearings, not to mention the gear faces, are splash lubed.   What does simply flipping the axle do to the lubrication?  The pinion shaft, bearings and the gear interface will now be way high up over the gear oil level.

Brian

[Oonrahnjay]

There's a company near where I'm working on my bus that an axle rebuilder.  They have just about everything -- with the information and points to consider that you've provided, I have what I need to discuss exactly what I need with them.  Thanks to all.   BH  NC