In the bus groups and I have been a member of many I have heard many strange things...
The AT545 is a poor transmission
The DT466 is a poor engine
You can get 70mph out of a schoolbus
Bigger tyres make you go faster
Hydraulic brakes are bad
Let’s take all these myths and lay them to rest.
“The AT545 is a poor transmission”. This is usually accompanied by some claim that the person making the claim had one burn out on them or perhaps more or had some other disaster. The actual fact is rather different. The AT545 is a fine transmission. Mine ran out of transmission fluid which stalled the engine. Rather than restarting the engine after it stalled, I leapt out and checked my fluids. There was no transmission fluid on the dipstick so I called for a tow. Because I did that, I did not damage the transmission so all it needed was a replaced seal and more transmission fluid. I now carry two gallons of spare transmission fluid, just in case. Another claim is that the AT545 cannot be used downhill to slow a vehicle. This is a nonsense claim. All transmission can be used to slow a vehicle going down a hill. Just put it in a lower gear and when speed picks up too much, brake down to the speed you want then let the brake cool while the transmission and engine eases you down the hill. For a steep hill, I suggest slipping the transmission into 1.
“The DT466 is a poor engine”. No - it’s a fine engine. It was designed for hauling plenty weight. It’s not a Ferrari engine and it never will be. This is an excellent engine for towing etc. It’s not for interstate racing. A well maintained DT466 will last for hundreds of thousands if not millions of miles. It has an upper rev limit of 2900 RPM. I have heard other say it maxes at 3000 and others say it can be made to go faster. Sure it can - just like you can put nitrous and high octane fuel in a Ford Escort. It will run fast and furious but will break pretty quickly. It’s intended use is medium speed hauling. It’s an about town hailing engine, not am interstate engine. Leave it governed to 2500RPM and you’ll have a happy engine for years if not decades.
“You can get 70mph out of a schoolbus”. Sure you can but you’re going to burn out that engine and transmission. If you throw it off a bridge I bet you can get it to go even faster than 70mph. Of course when it reaches the bottom, you probably won’t find it still runs. The official specification for a school bus is “Must achieve 55mph” and that’s it. Thus most schoolbusses can do 55mph - on the flat. Uphill it drops to 35 and downhill you can get 70. 70 is not advisable as must busses have F rated tyres. F is 50mph. For reference, here are some tyre speed ratings...
F Up to 50 mph
G Up to 56 mph
J Up to 62 mph
K Up to 68 mph
L Up to 75 mph
Schoolbusses were designed to spend 90% of their life on backroads and dirt tracks at anything up to 45mph. On my daily school runs (I drive a schoolbus) I spend most of my time in housing estates at between 20 and 30mph, depending on the speed signs. I do spend periods of up to 10 minutes at 45mph getting between housing estates on 45mph rural roads. Not once in my day do I need to go over 45mph. That’s not to say that I have not had to on some routes. I drove a route one year that involved two interstates. I used a variety of busses. Some would do 57mph with my foot on the floor. Some would barely do 45mph. They were fine. All the interstate traffic was roaring past me. On the other hand even when I’m in my car and 5 or 10mph over the limit, the vast majority are still screaming past me. Hence I stick to the limit in my car and to whatever the bus will do in a work bus.
If you want a bus that goes faster then honestly you shouldn’t have bought a schoolbus. You know how fast they go from when you were a child. You know the legal limit is 55mph for a schoolbus on a road with a limit of 60mph or faster and 45mph or the actual speed limit (whichever is the lesser) on all slower roads. Souping up your engine is not going to help - it’ll burn through fuel at a horrible rate, will wreck the engine and leave you no better off.
“Bigger tyres make you go faster” or “A higher ratio back axle makes you go faster”. Both of these are disingenuous. They will increase speed on the flat but will negatively impact speed uphill and downhill. Downhill you need the gearing and tyre size to be right in order to control descent correctly. Uphill if your ratio is wrong or your tyres too big, you’re putting way too much strain on the engine.
“Hydraulic brakes are bad”. This is utter nonsense. Cars have hydraulic brakes with hardly any problems. Somebody wrote that their hydraulic line suddenly burst and left them with no brakes on their bus. That is complete nonsense as all hydraulic systems have a cable backup system. It is also indicative of a complete lack of inspections and maintainance going back several years. The cry is “air brakes are safer”. Not really - if an air hose breaks or gets snagged then there’s a sudden release of pressure which means the brakes all come on full instantly which in traffic can have deadly consequences. Air brakes and hydraulic brakes both have their pluses and minuses. It’s like drum versus disk brakes - they’re both equally good. The sole advantage of air brakes is that it’s very simple just to add a couple of hoses and control the brakes on a trailer. With hydraulic there’s a lot of fiddling using ancialiary electrical systems.
So, in conclusion - if your stock schoolbus won’t do what you want to do then sell it and buy something else. For the rest of us that have no desire to race on interstates, guzzling fuel, a schoolbus is just fine.
No comments:
Post a Comment