School or public trans. or other

[EastCoastCB]

Understanding Axle Ratios | Medium Duty Work Truck Info

for serious school bus-based towing...

[RoadRanger2015]

Thanks EastCoastCB, that was a very informative article. I can understand the ratio's better. The 4.10 would be very nice. How much does it cost to change ratio's on a used RE bus? What was your experience?

[EastCoastCB]

I prefer FE buses and that's what I have. Ratios are the same regardless.
Price on swapping is in the 1000-1500 range, roughly.

[Tango]

Below again is a tool that helps base gearing decisions on real data. You can play "what if" with virtually any combination before you spend any money.

Any change to the rear axle, tranny or tire size will alter the actual final drive ratio going to the ground. If you know a given engines power & torque curve you can gear to optimize it to your needs. But remember...what is perfect for a long haul highway cruiser is not what you need for something like a heavy load short run hauler. So, no matter what you wind up with, it will be a compromise. But if correctly balanced, one that will be appropriate to your usage.

Engine RPM Calculator

[nat_ster]

Changing ratios in rear engine buses is more limited due to the reverse ring gear.

In a front engine bus, you can use a gear set from any medium duty truck with the same rear axle.

However, in a rear engine bus, it uses a special revers ring gear, and flipped rear axle housing not used on anything but rear engine buses.

So if there are 1000 gear sets available for the front engine bus, there will only be a few available for the rear engine bus, as the parts can only come from another rear engine bus.

I have never seen a rear engine bus around here with higher than 4.78. Most are 5.38.

This can change with geographic region due to the way the buses were ordered.

Also the Thomas rear engine buses are made superior in my opinion.
Much stronger rear frames, engine bay is laid out better, larger air cleaner, bigger retarder, and 6th gear unlocked on the ones with the MD3060.

Nat

[Kubla]

4.10 will get you 78 mph at 2700 rpm or about 65 at 2100 rpm if you have a mt643 or any other direct drive lock up tranny. With an at545 you are looking at about 67 at 2700 rpm due to slippage

[RoadRanger2015]

I do not expect to hit 78. I can live with 68, but don't want to expect too much. I assume that, the lower the rpm, the better. How low can one go with the proper configuration?

The Thomas RE models seem to have what I am looking for. Now it's time to find one in decent shape.

[EastCoastCB]

How much weight you looking to pull?

[RoadRanger2015]

I am considering towing about 14,000 lbs. But that range should give me something to work with. I appreciate you interest and assistance.

[EastCoastCB]

I don't think a RE bus is going to be the best choice for pulling that much.
It depends on how the rear frame is built. You'd almost certainly be exceeding the GVWR of most school buses though. My empty shell weighs nearly 18k on the scales and my Gross is 33k. With any kind of conversion and pulling 14k I'd be well beyond maxed out.

[nat_ster]

Originally Posted by EastCoastCB

I don't think a RE bus is going to be the best choice for pulling that much.
It depends on how the rear frame is built. You'd almost certainly be exceeding the GVWR of most school buses though. My empty shell weighs nearly 18k on the scales and my Gross is 33k. With any kind of conversion and pulling 14k I'd be well beyond maxed out.

A RE bus will pull and handle large towing needs far better than any front engine bus.

Before giving this kind of advice, you need to look into the engine bay of about 25 RE buses.

Not all RE buses use sub frames. Not all that do use sub frames are built the same.

The Thomas RE's are built well. The subframes are more than enough to tow 20,000 pounds.

Understand towing before giving advice. If he is towing 14,000 pounds, his hitch weight is still only going to be what the hitch can handle. Anything up to a 5000 pound hitch weight will be no issue for a Thomas RE.

Over on pirate 4x4, guys extend medium duty truck frames all the time. The same principles they use are the ones used by the bus manufactures. The sub frame runs back along the full frame at minimum 3 feet.

The sub frame on ALL RE's runs past the rear axle. So the subframe and the full frame are both taking the weight.

On my 96 RE Bluebird, the subframe runs 6 feet past the rear axle, looking towards the front. Subframe is sleeved inside the full frame, and is the same height and thickness as the full frame.

Most Thomas's use a drop frame. It is still full size rails, overlapped onto the full size frame.

Also, RE buses have less rear overhang. This equals less leverage on the rear frame when towing, and less swing when turning. Most FE buses have too much rear swing for a standard length tongue trailer. The tongue needs to be the same length as the rear overhang of the bus. Most bumper pull trailers are sized for a pickup truck to pull them.

Remember, I have 400 buses to look at daily. Our bus driving season just started again. Last year I was driving a dog nose. This year I drive a 03 Thomas ISB Cummins 8.3 at 250hp, MD3060 with the 6th gear unlocked.

I love this bus.



Nat

[RoadRanger2015]

My CDL may compensate for that legal aspect, but I just want to be sure it will be possible and safe.

[RoadRanger2015]

Thanks Nat. You reflect my thinking. And the RE Thomas' that I have seen should do the trick. Yet, as of now the motors in most of them seem to be a bit too small for my desires. That 8.3 would be ideal with the right tranny. I have a bit of time before I jump on a used bus. Still many questions to answer and much more research to do.

Thanks for the feedback.

[EastCoastCB]

I understand towing, Nat.

RE bus-


FE bus-

[family wagon]

Come on Nat, you're getting a little carried away with the details..

Not all RE setups have their engine cradle/sub-frame extending forward beyond or even to the rear axle. Although my Blue Bird is a rare duck with its transit instead of school body, it's an example of one RE in which the engine frame does not go that far. Instead, the engine frame is mounted lower than the main frame and overlaps only about 3 feet. It stops nearly four feet short of the rear axle, and it doesn't even sleeve inside the main frame. The main frame is C profile turned inward, and the engine frame is C profile turned outward so that the webs of the C's are bolted together. I don't imagine there are many buses like mine out there, and so I dare guess it's the same chassis as one of their other models.. All-American, maybe? (pictures of mine are included in the towing thread EastCoastCB linked to earlier.)

I anticipate towing nearly 10k with mine, but the 1000-ish pounds of tongue weight does concern me a little because it's in addition to an already heavy 8.3 engine and tranny. I don't have any idea at what point all this tail weight unloads the front axle enough to be questionable. Who knows; I may end up finding a way to flat-tow or dolly my full-size van instead of using a full trailer.

Oh.. and your '03 Thomas has an ISC engine, not ISB. The 8.3 liter was always a C series engine. (I know, it was probably just a typo.. but still!)

The point about rear overhang/swing is a good one. I towed a 12k dump trailer with my FE bus just a couple times. I remember it was pretty tricky baking up that rig to unload the trailer at the landfill. It was still national school bus yellow at that point, and the bewildered and perplexed expressions from onlookers were priceless!

[Kubla]

if you are going to tow 14k pounds, you will need something more robust than either the AT545 or MT643 and you will need to install a tranny cooler on whatever you get

[RoadRanger2015]

I am getting the notion that towing 14k will be pretty cumbersome and costly. There certainly is a possibility to scale back on the weight. What would be reasonable expectations?

[EastCoastCB]

On a RE bus- flat towing a car or pickup.

[RoadRanger2015]

Thanks. I was hoping for more. Like hauling a small machine/wood shop.

[EastCoastCB]

Anything is possible, especially if fabricating is an option.
For real towing, I'd be looking for a short full size conventional or FE flatnose with a beefy engine/transmission. A short FE transit style school bus has a very tight turning radius and would likely be my first choice.