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Old 02-18-2021, 10:25 PM   #1
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Join Date: Feb 2021
Location: San Bernardino CA
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Year: 1999
Coachwork: Bluebird
Chassis: TC RE
Engine: 8.3 Cummins MD3060
1999 Bluebird TC2000

Hello! My partner and I are in search for the perfect bus for us and our budget, and I think we've found the one we want, but want more knowledgeable people than myself to tell me if it's a good combination.
It's a 5.9 Cummins 24 valve and Allison AT545.
The owner says that the brakes were replaced less than 5000 miles ago, the batteries were replaced less than a year ago, as well as a transmission rebuild before they bought it for their small business about 4 years ago.
They also said that it was mostly driven on the highway and county roads while in their use, and that it hits the 70mph mark.
So I guess my question for everyone is does this sound like a good engine and transmission combo? And what other mechanical aspects do you look for in a bus?

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Old 02-18-2021, 10:41 PM   #2
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Well...most would say that "perfect bus" and AT545 wouldn't normally go together in the same paragraph. The 545 is pretty decent and they've suffered lots of abuse in many, many buses and other vehicles...while holding up okay. But they do suffer from a lack of full lock-up, which reduces efficiency and they can run hot. I'm not up on the 5.9 engine, and haven't owned one, so I will let others chime in on that.

I will say...it's refreshing to read a post looking for a bus other than a Bluebird with a Cummings 8.3L. I swear someone must have recently written some blog saying that's the only one to buy.
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Old 02-18-2021, 10:47 PM   #3
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Join Date: Feb 2021
Location: San Bernardino CA
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Year: 1999
Coachwork: Bluebird
Chassis: TC RE
Engine: 8.3 Cummins MD3060
My research was showing the same thing, that they're good overall, just have a tendency to run hot when pulling uphill!
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Old 02-18-2021, 10:50 PM   #4
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AT545 is the base trans, no lockup. Not terrible, but not ideal, especially for highway, as they will easily overheat at highway speed. I don't think I'd want to tempt the fates cruising at 70 mph with one. They are more or less meant for low-speed city and rural route buses, not interstate cruising.

And just because it can do 70 doesn't mean it's a good idea. I moved a bus for someone recently that the seller said could do 65... And it could. At the max governed speed of 2600 rpm. And some will say, 'But they wouldn't set the governor there if it couldn't take it'. But that's max safe RPM, doesn't mean it's the optimum sustained CRUISING RPM. Probably not a good idea to run at 2600 rpm for a 10-hour trip.

Also keep in mind that with most, the faster you go, the worse the fuel economy will be. Some buses can get 7-9 or better at 65-70. Others do much worse. Most diesels will be happiest at around 1800-2200 rpm, whatever speed that grants is entirely dependent on the transmission's top gear ratio, the rear axle gear ratio, and the tire size.

Certain 5.9 Cummins are known for what is known as the 'killer dowel pin'. This is an alignment pin to center the timing cover that is known to work loose and ends up in the timing gears, which can trash the engine. I'm not sure if this one is one of those.

Overall, I'm not going to say not to buy it, but I wouldn't buy it for highway driving -- 70 mph is likely to kill that transmission quick. And that's if it's not overspeeding the engine. Cummins are resilient and known for taking a bit more RPM, but if I were a betting man, I'd say this sucker is probably pushing 2500 at 70 mph, and I would never cruise at that RPM with a diesel. More RPM = more heat = more stress. I'd say best scenario would likely be about 58-62 at about 2100-2200 if the gearing allows it (would require axle gearing between 3.90:1 and 4.11:1 with 37 inch tires). The 4th gear ratio of the AT545 is 1.00:1 (output speed is engine speed, basically).

You really need to know three things...

Tire size
Rear axle gear ratio
Optimum engine RPM vs Max RPM

That info, with an MPH / RPM calculator like this one, should give you the safest and best cruising speed for this bus.
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Old 02-18-2021, 10:56 PM   #5
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Join Date: Nov 2014
Location: NM USA KD6WJG
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Year: 1991
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I have had 2 of them over the years and one of them was in a tow truck. I pulled a lot of cars, trucks and class c motorhomes with it. Went over Tehachapi grade and grapevine with it. I installed an extra cooler with electric fans and a temp gauge. Just have to learn how to drive it. Are there better transmissions? Are there better engines? Yes there are. But how much do you want to spend?
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Old 02-18-2021, 11:03 PM   #6
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Quote:
Originally Posted by s2mikon View Post
I have had 2 of them over the years and one of them was in a tow truck. I pulled a lot of cars, trucks and class c motorhomes with it. Went over Tehachapi grade and grapevine with it. I installed an extra cooler with electric fans and a temp gauge. Just have to learn how to drive it. Are there better transmissions? Are there better engines? Yes there are. But how much do you want to spend?
Not to second guess, but are you sure those were AT545s and not a different model? Sounds incredible to me, though a tow truck with a Class C motorhome in tow is probably still lighter than a bus.
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