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Old 03-08-2016, 08:54 AM   #11
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Beyond achieving the desired ratio, there are a number of other considerations when swapping rear axles.

Weight rating:
It has to at least match the recipient vehicles GVAW

Overall Width: It's gotta fit (pretty obvious)

Width of spring perches:
)a little less obvious, but important) they can be relocated but it's not all that easy ( I know...I had to move mine)

Shock or air bag location:
(if it has any) here again they can be relocated but will involve more work, time & $$$

Tire/Wheel size:
Ideally the same as what is on your vehicle (otherwise, you change them all)

Lug bolt pattern: Here again, unless the wheels on the donor match your existing patterns, figure on spending mo money to get them all the same or having different wheels front and rear ( which spare to carry?...room for two?)

These are just a few of the things I recall having to deal with while searching for highway gearing on my old rig. Of course if you can find the ratio you need as just a ring & pinion set...the other issues take care of themselves.

Best of luck and anyone else with thoughts on axle swaps...please chime in.
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Old 03-08-2016, 09:20 AM   #12
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Quote:
Originally Posted by dgorila1 View Post
How hard would it be to get an axle from an over the road truck from a salvage yard and swap it for the stock axle? Are there any huge hurdles that would have to be overcome or that would prevent this from being done?
Basically what Tango mentions. It most certainly can be done, but unless the current original axle has issues other than ratio, the only real reason to change out housings would be personal preference for some reason. Gears are pretty easy. You can change out the gear head with no real special tools, or the gear set, but would require some special tools and knowledge.

Changing out the whole axle housing, can be done, but requires a lot of measuring and fitting.
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Old 03-08-2016, 11:17 AM   #13
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Changing out the gears is easy peasy with a motorcycle jack to help pop it in there. Our bus started with miserable 6.11 ratio and went 47mph tops. Got a 4.78 for a good price from a guy on skoolie, now we get about 60mph.
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Old 03-08-2016, 11:33 AM   #14
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I did a check - a '95 MCI had a 4.11 - they are a highway bus...but it didn't show the gearing in the transmission.
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Old 03-08-2016, 11:36 AM   #15
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One of the very few questions I asked before bidding on my bus was what the rear axle ratio was. They told me 4.44 and I got excited! I get about 63mph out of a forty footer with 195 hp. Does pretty well in the mountains, too.
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Old 03-08-2016, 01:34 PM   #16
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Now there's an issue that I hadn't considered before. Are the rear axles on a rear engine bus of the same basic configuration as that of a conventional (front engine and driveshaft) setup? Come to think of it, does a rear engine bus have a driveshaft? Here I'd been assuming that it was an integrated setup like a front engine front wheel drive car, and I have no reason to make that assumption. (You know what happens....)

Looking at it from the outside as I am now, and with the usual amount of teenaged screwing around with cars under my belt, I would be more scared of swapping axles than raising a roof. The only thing I'd consider would be a new-gearset-same-punkin situation.
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Old 03-08-2016, 01:58 PM   #17
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Buses with rear engines have a driveshaft. They can be very short with short being defined as less than 36" which includes a slip joint.

The differentials on rear engine buses are generally identical to any other differential except they are mounted in a mirror image so that a right turning engine will turn the wheels in the correct direction. If it isn't installed mirror image you will have one forward gear and lots of gears in reverse.

The advantages of swapping a complete assembly is you can upgrade to better brakes. Most Type 'D' RE buses have 9" rear brakes. But some lighter duty buses have as small as 7" rear brakes while some heavy duty buses have as large as 13" rear brakes.

The nice thing about newer buses that have been built in the last few years is that an IC bus uses standard IHC medium duty truck parts, a Thomas bus uses standard Freightliner medium duty truck parts, and a Blue Bird uses standard Volvo medium duty truck parts. Going to a junk yard and finding something that will be a bolt in swap is relatively easy. A Rockwell Meritor axle under a bus with 10-hole hub piloted wheels is basically the same thing as a Rockwell Meritor axle under a truck with 10-hole hub piloted wheels. For that matter you could upgrade to an air suspension if you don't have one already.

You may actually discover it is easier to swap a whole assembly than trying to swap out the gears in the pumpkin.
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Old 03-08-2016, 02:07 PM   #18
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Yeah I can see the mirror image thing; the driveshaft attaches to the diff at the rear, not the front. Thanks for the answer! I won't be so scared of it anymore. I'm sure I could figure out backfitting the pneumatics for air ride; would I have to weld fittings to the frame?

And, by "newer buses that have been built in the last few years" do you mean 15 year old buses that come up for auction? Or newer than that? Thanks in advance -
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Old 03-08-2016, 03:09 PM   #19
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I have seen MCI's cruising at 80 mph, and per drivers, they get 9-11 mpg!
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Old 03-08-2016, 11:35 PM   #20
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Quote:
Originally Posted by pengyou View Post
I did a check - a '95 MCI had a 4.11 - they are a highway bus...but it didn't show the gearing in the transmission.
Find out what transmission make and model and google it. If it's an MCI with an automatic, it'll be an allison more than likely. Detroit Allison would be a contact to find info.
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