Heavy Truck Automatic Trans.

Where I live the road is on a gentle hill, and is a thirty MPH zone. A few heavy trucks like refuse, oil, and dump, go by occasionally. I can't help but notice their auto transmissions shifting up and down fairly frequently. The town's newest Fire truck has an auto with push button controls on the dash. SOP when we got it was hit D and then down arrow to keep it out of high unless going on main road above 45 MPH. With change of chief this procedure was abandoned by many drivers. I did it when I drove but not many others. When riding in back, returning from one call, I counted twenty two shifts in about two miles. I told management that I thought that it was supposed to be programmed to not go into high unless you hit the "up arrow" button. Does anyone know about this? This has got to be hard on transmissions.

I agree with you. An Allison transmission is nice fcr certain applications, but if it not used correctly it can be very hard on a transmission. It would be better to downshift and keep a steady force on the transmission and the engine RPM's up.

Those transmissions have so many safeguards built in, that it almost takes a act of congress to tear 'em up.

That's why you are hearing all the shifting going on. The thing is just protecting itself.

Allan

The company I worked for bought 5 Chevy semi-tractors with ALLISON automatic trans. One never made it out of town with a load( trans gave out 5 miles from terminal) in less than a year all of them were replaced with 5 speed manual trans.They were 4 speed autos. with two speed axles. You would start out in low axle and let trans.go through all gears and shift into high axle in around 45 MPH. You can't split shift with an auto trans. you have to wait until you came to a stop befor dropping back to low axle.

Is it an allison automatic or an auto shift gear
type?

My last loboy tractor, a Peterbuilt 378 had an Allison auto in it. Nicest operating trans I ever used and not one problem with it. When in conditions you speak of or city driving you would simply lock it so it would only upshift to the gear selected...3rd.
My driver wasn't to keen on the auto as it seemed to be not manly enough. After driving it for a year a motor mount broke and the truck wound up in the shop for a week. I rented an IH with a 13 speed and after a few long days He started asking when his truck would be coming back!

Every Fire Dept vehicle we have is auto. Allison autos, that is. My particular engine goes at 72k. Been very dependable. Getting a new FD vehicle with a standard is almost a thing of the past (unless a specialty) and considering most rookies have never driven anything bigger than their Honda- it may be for the best. We're pushing 12k runs a year and the pumps are rarely in for tranny's/jakes- more likely brakes here.

I hate auto transmissions and I hate driving them... but that is fairly normal for an Allison. Keep your right boot firmly planted on the floor and that takes care of most of the shifting... or lock it in a low enough gear.
I don't think they're bad in terms of reliability. I just dislike driving them. I dislike the traction control on the new trucks. I hate the crew minders that they have tied into the seat belts... and a lot of other stupid things that are tied into NFPA 1901. But that's the way it is.
On the other hand... most people today can't effectively drive a truck with a standard transmission anyway. Even of our guys that do drive the old 5+2 and the 6 speed... some are pretty crude with them.

Rod

When I owned the bus company I had only one manual - for me. I hate those Allisons slushbuckets but they are durable. The drivers would get in them and ram their foot through the floor and I never had to worry. They were always eager to drive mine as a sub, but after hearing them grinding a mile away and "forgetting" to shift the two speed that rarely happened. It just seems like unless you were raised on the farm or on heavy vehicles you can't multitask enough to do all of that shifting, listen to the engine, watch all 4 mirrors, and catch the CB if you need to. Forget trying to keep 40 people warm enough or cool enough.

On the farm the only automatics are on the cars and pickup. They don't even put a manual in the pickup with the engine I wanted. Man how things change. I don't even have a tractor with hydro if you don't count the riding mower.

I've got a '97 Freightliner FL106 with a Series 50 Detroit and a MD3060P Allison. I do alot of both city, and highway driving and the only time I have a problem with mine doing the up and down shifting is on a highway with alot of hills, with the cruise control set. The rest of the time it shifts up and down pretty much like I'd be doing it myself if it was a manual. That said, being a service truck I run at what would basically be considered fully loaded all the time. As such the engine is always pulling and rarely idling along like it would with a lighter weight truck.

As far as the trucks your talking about, and it being hard on the transmission, it sounds to me like their transmissions are doing exxactly what they are designed to do. By that I mean they are keeping the engine running in it's 'sweet spot' to enable them to get the best fuel mileage possible. Although you can't really tell it every automatic transmission, regardless of it's application is doing the same thing. The difference between the trucks and the cars is with the trucks the sweet spot is usually alot smaller than the cars, and with the size of the vehicles/engines/transmissions/loads involved, it's alot easier to tell that there is a shift going on than it is with a smaller vehicle because you can really hear the change in tone of the engine as it revs or slows down.

As far as effecting the life expectancy, my truck had nearly 450,000 miles on it when the transmission went out. In my case the only reason it went out was a leak in the oil cooler put antifreeze in the transmission oil. Unfortunately ethalene glycol mixed with the the oil will cause the fiber on the clutch discs to release from their metal backing plates. Even at that, I changed the cooler, flushed the system and refilled it with fresh transmission fluid. At the time I did that instead of going ahead and getting it rebuilt like everyone told me to do because I was too busy to take the truck down for a week. I wound up making it another year before I finally had to go into the transmission and get it rebuilt.