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Old 09-04-2019, 04:39 PM   #1
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At545 power it can handle?

We just was the winning bid on a 12 valve Cummins with an at 545. Because the Cummins is typically consider under powered, I plan to change some things with the p-pump,
infection timing,andd injectors. What can an at545 handle? I don't want to slam it with a ton of power all of a sudden right after buying it and blow a transmission.
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Old 09-04-2019, 05:09 PM   #2
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235hp/445 tq.
I'd just focus on longevity. Its gearing that makes speed in a bus, not power output.
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Old 09-04-2019, 08:00 PM   #3
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Keep it maintained with fluid and filter changes and it will last you.
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Old 09-05-2019, 01:42 AM   #4
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... and by all means, keep the transmission COOL!
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Old 09-05-2019, 05:14 AM   #5
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Gonna turn up the power and esp torque? Swap the trans. A big cooler and good maint can increase longevity of the 545, but lots also depends on how heavy your whole setup will be and terrain you plan to traverse.
EC is right, gears play a huge role, but gears to make you go fast on the highway may not be gears you need to climb western mountains.
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Old 09-05-2019, 08:36 AM   #6
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Pretty much any diesel bus with the AT545 is at or over it's rated capacity in stock trim. I imagine that's a big part of why it has a bad reputation in school buses. On the up side, it was cheap as chips and they log a lot of miles of start/stop on 35mph roads.
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Old 09-05-2019, 10:18 AM   #7
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AT545s are actually BETTER route transmissions than MT643s, AD2000s etc..



the lockup units are always locking and unlockin in route service which is tough on alot of components.. (anyone ever feel the surge when a 643 locks up in 3rd gear?)..





many many city busses that ran 24/7. were built with AT545s that would last.. huge trans coolers and also the fact that the converter isnt making Huge heat continuously..


what happens to them on the highway which destroys them.. . esp omn hill climbs..



the bus inherently will slow down on hills.. but the engine speed may stay at max RPM.. the more the difference in input shaft speed vs engine speed makes LOTS of heat and quickly...



same happens if trying to drive the bus fast on flast ground... wind resistance tries to slow the bus down.. engine runs at max RPM.. and you make lots of heat...



I did drive quite a few miles on each of my 2 busses with AT545s that did break.. the 3rd bus still has (and always will) its AT540... tearing apart those broken AT545s, one definitely died from heat stroke... the other appeared to have broken valvebody parts..



as for coolers.. as a reference.. a bus enthusiast gathering I was at a couple weeks ago... a GM Old look that had been re-powered with an 8.2 and an AT545 (a VERY common re-power for those 1950s and 1960s busses).. has a trans cooler bigger thasn the A/C coil on most cars....



dont go out and buy a little cooler at auto-zone and expect to keep your 545 happy.. get one made for cooling a medium duty trans.. and you can keep it happy for a long time



-Christopher
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Old 09-05-2019, 12:12 PM   #8
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I have no personal experience with them but read that they aren't going be a contender for optimal mpg's atall..and also that they dont, or sometimes don't, slow your bus effectively on steep downhill grades. Sounds like a better flatland stop and go transmition to me. That is just hearsay though
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Old 09-05-2019, 12:33 PM   #9
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Don't expect a 545 to hold up to towing either and no lock up means when you go down hill you will be using the big pedal alot more.
The torque rating on them are quite low, alot of light duty (3/4 - 1ton) trucks autos are rated for similar duty.

Adding more power to the 5.9 will only ensure a faster death of the "slush box" (is what I call any automatic). When I was bus shopping I made sure to stay away from the 545s, I went with a MD3060 but there are other good trans, I wanted the built in retarder that is standard on the 3060s so going down hills I don't use the service brakes as much.
I'm going to replumb a radiator from a F350 (NEW) to cool my trans even more, heat should never be a problem using the whole rad to cool the trans, and yeah a fan on it too, not sure where it's going yet but it will happen.
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Old 09-05-2019, 12:40 PM   #10
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Quote:
Originally Posted by PatrickBaptist View Post
When I was bus shopping I made sure to stay away from the 545s, I went with a MD3060 but there are other good trans, I wanted the built in retarder that is standard on the 3060s so going down hills.
Retarder standard on the 3060?

I am fairly certain that it was optional. The two 3060's that I have owned have not had retarders. I wish I had a retarder. My 1st bus had a Jake brake . I miss it.
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