Gear Vendors...

[NewSkewlHauler]

I thought I had a great idea, until I talked to Gear Vendors. I kind of like what their product would do for RVs and towing, so I called to see if they made a unit for Allison 545s, or 643s for that matter...nope. They said they've looked into it, but they aren't interested in doing anything with those trannys. They have kits or units for the Allisons that go behind the Duramaxes, though.

So my next question is that if Gear Vendors doesn't make an auxillary transmission for Allison, does anyone? I think this type of setup would be a great (albeit expensive) solution to the non-lockup of the 545; you'd have a 3rd over before you'd use the factory overdrive...great for towing, headwinds, and hills. I don't suppose there'd be a way to adapt an aux tranny off a big rig? Are there other (perhaps "better") transmissions to swap into our buses versus the AT545? Perhaps something that Gear Vendors might support? The buses I'm 99.9% certain I'm going to end up with have the 6.6L Brazilian diesel in them...actually, I'll be getting one running bus, then the body of the other one plus the contents of a wrecked camper (eventually)...but I digress. Any thoughts????

Thanks,
Ben.

[The Eggcrate]

I would love to hear an answer to this question! My bus, with the allison 545 needs some added top end speed, and I just can't seem to find a reasonable solution. I don't want to lose the low end of course, because I definitely want to be able to pull the maximum weight. If I could get my hands on a "brownie" intermediate overdrive transmission, that would be awesome, but they definitely don't seem all that common.

[the_experience03]

I think you could do it with a "divorced" aux. tranny, but the cost would be pretty high with driveshaft mods. You'd still be contending with the inefficiencies of the transmission too. You certainly would get more speed and efficiency, but it would be a diminishing returns sort of a thing. There is obviously a lot of room for improvement, but for every 15% more gearing you gain you also might see an additional 5% of slippage in the converter. That's all fine and well because you're still gaining. I would just worry about the heat. The lion's share of heat from an automatic transmission is caused by the shearing of the fluid in the torque converter. As long as you could be conservative I think you'd be fine. Still, only a 15% overdrive (.85:1 ratio) would turn my 4.56's into 3.88's and I'm not sure I could pull those reliably. I still think swapping entire rear ends for a better ratio (offering your current one as a trade, of course) is probably the most cost effective route.

[nearhomeless]

The options would seem to be:
- convert to an Allison 1000 (and likely exceed GVWR ratings)
- use an old "brownie box" turned backwards (like to be something like a 2:1 ratio forwards and a 0.50:1 overdrive the other way, and could well weigh 300-600lbs) I think only certain types of gear cuts work (straight cut?)
- change axle ratio
- get a 2 speed rear end (ie out of a dump truck) with higher normal gears (may be hard to find way faster gears though)
- use higher profile tires (24" rims and such, unlikely to make a huge difference but a few inches is some difference)

I haven't heard of brownie boxes that overdrive really, just underdrive ones. If a 'backwards' brownie box wouldn't work, one going forwards and then using different axle ratios and larger tires might work. What it would cost to adapt i'm not sure, depends whether your tranny was ever used with a brownie box in some other application.

[the_experience03]

I know of a few guys that have flipped transfer cases around like you described. It worked, but it causes some issues. The input shaft is now the output shaft and vice versa. The problem comes with the bearings and sometimes even the shaft size. Input shafts and bearings just aren't designed for all that torque. Compare the input shaft of an automatic to the output shaft and you will see. The other issue is gear thrust. If you flip it around you are actually driving it in reverse of the direction it was designed. Now obviously this happens when they're mounted "correctly" when you put the vehicle in reverse, but that is only for short periods of time. Putting the thrust in reverse COULD cause the case to come apart. Again, the gears are designed to push against one surface and bearing set which is usually substantially stronger. Now you're doing just the opposite. A brownie box is a lot stronger, but I fear the same kinds of problems.

[NewSkewlHauler]

Hmmm...That's about what I thought. Is there a "better" transmission out there that's a reasonable swap for an AT545? I suppose there isn't otherwise someone would have done it. I don't think "my bus" has an issue, but in the event that it does, I'd like to know if there's something else I can do. I also plan to do a lot of towing with the bus. Other than a tranny temp gauge, which it has, and maybe a cooler, what is there anything I can do to increase the longevity and performance of my motor/tranny? Thanks again.

Ben.

[nevrenufhp]

If you're looking to swap out an AT545 or MT643/653, then the best possible replacement would be an MD3060. They have the lockup converter and can come with single(.75) or double overdrive(.65). Some even had a retarder unit, but that's more stuff to hook up. They do have a small "computer" on them, but it's almost fully self contained. On an older, mechanical injected diesel, it just needs a throttle position sensor added to make it work right.

[frank-id]

I have been trying to get the best mph and low crusing speeds for a lot time. One of my favorite buses is a 1990 Int bus with a Blue Bird body. After a lot of thought, I decided to change the final gear ratio from 4:10 to 3:70. The gears were about $600 and not difficult to change. But now, the bus needs more horsepower. With just 180 HP, and trying to maintain 65-70mph, in western USA, the shifting is constant. On the flat roadways, speed and milage are great, but any small hill slows any progress. The bus does tow a Jeep Cherokee for runaround duty. The allison trans are the best way beyond any others. In the near future, my Crown will be getting a Cummins 855 and a Allison 645. This summer is very hot and I'm adding a back porch on my house. I'm 71 years and the time passes too quickly. Frank

[nevrenufhp]

Well Frank, upping the power is as simple as adjusting a screw. There's a few threads that talk about it. Also the link in my signature (the globe on the right) will take you thru it. It's about a 30-40hp jump.
My sister is moving to Twin Falls next month.