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Old 07-04-2016, 11:11 AM   #11
Mini-Skoolie
 
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Hello Turf
You did look a little relieved to be over the pass when I saw you the other day.
I think power trains and gearing are somewhat of a trade-off my bus pulls the pass fine but will only run 60 on the flat. A re-gear is out of the question for me because I will be around the continental divide a lot and it is not an easy task with a RE bus. So I just have to live with slower highway travel.
Soon I will be retired and travel will not be rushed so the only problem will be the people behind me that are still trying to get somewhere in a hurry.
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Old 07-04-2016, 11:18 AM   #12
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Not sure what size tires you are running, but going larger in diameter will get you a few more MPH. You can determine just how many by using the calculator below...(the one at the bottom especially)...

Engine RPM Calculator
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Old 07-04-2016, 11:42 AM   #13
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Tango
You hit the nail on the head, the rear stock size tires were replaced with low profile tires by the school system (for whatever reason?).
I have a deal in the works with a truck tire dealer he has use for the low profile tires they run them on some flatbed trailers to reduce load height.
I am anxious to get this completed he will match the two front tires and spare (Michelins) with 1 more to put on rear, and new tires on front. Then I will just have to go for a run to find out how the speed will change.
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Old 07-04-2016, 11:43 AM   #14
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pulling up the pass was tough. if anything, i need more power, and a transmission that wont slip under more power. i remember that peak torque is at lower rpm's, so i try an ease off the pedal and go slow. the incline was steep and long and a few times the trans gives away and slips.

not sure if it was my head or for real, but the next 100 miles of so it just felt like i was a pulling an anchor. after a fuel stop, the truck felt normal again.

i dont think the motor/trans would push bigger tires. i have 11x22.5's now. i am considering a flush and fill of the transmission.
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Old 07-04-2016, 12:04 PM   #15
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the pass is steep frequently we see a motor home broke down and being towed back down, or a pickup with large camper. most of the time the radiator is steaming or the transmission has lost a large amount of fluid on the road. Sounds like a good idea to service the transmission.
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Old 07-04-2016, 12:13 PM   #16
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Originally Posted by crawler View Post
the pass is steep frequently we see a motor home broke down and being towed back down, or a pickup with large camper. most of the time the radiator is steaming or the transmission has lost a large amount of fluid on the road. Sounds like a good idea to service the transmission.

as much as I like the good old AT545.. I surely would NOT want one on a steep pass..

transmission fluid can and DOES boil...

lugging a transmission WILL get it hot... by lugging it i mean running it against the stall speed RPM of the UNLOCKED converter and the differential between converter shell speed and transmission inpiut shaft is high... you will make TONS of heat..

a Lock-up transmission like an MT643 or the allison 1000,2000,3000 is a MUST in the serious passes...

as is a transmission cooler... just servicing the transmission wont prevent it from over-heating.. and all it takes is ONCE with the fluid 250 degrees and that transmission will cook...

servicing it will not hurt it.. but also make sure its ready to run a mountain climb like that... an external fan-forced cooler and a trans temp gauge at the very least..

-Christopher
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Old 07-04-2016, 12:32 PM   #17
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I am totally on board with Chris. A temp gauge & plenty of cooler area are critical to tranny survival. It is also worth checking factory specs to see if any of the newer synthetic fluids are compatible as they handle heat much better than the older non-syn types.

Below is yet another temp/mileage chart worth reviewing if you have any doubts about tranny temps and fluid serviceability. It is consistent with Allison's own numbers for "conventional fluid". The syns are a bit better.

Hayden - Transmission and Engine Oil Coolers
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Old 07-05-2016, 12:33 AM   #18
Mini-Skoolie
 
Join Date: Jun 2015
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yes I like the mt643 with the large cooling system I have not experienced any high engine or transmission temperature's while pulling any of the passes. The auto-chains are also nice if you have to go when chain law is on.
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Old 07-05-2016, 07:26 AM   #19
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Originally Posted by Tango View Post
I am totally on board with Chris. A temp gauge & plenty of cooler area are critical to tranny survival. It is also worth checking factory specs to see if any of the newer synthetic fluids are compatible as they handle heat much better than the older non-syn types.

Below is yet another temp/mileage chart worth reviewing if you have any doubts about tranny temps and fluid serviceability. It is consistent with Allison's own numbers for "conventional fluid". The syns are a bit better.

Hayden - Transmission and Engine Oil Coolers
can I run syn in my AT545?

I swear i read somewhere that the front pump in the AT545 cant build pressure properly with the syn fluids lower overall viscosity.. of course now i cant find what I was reading..

-Christopher
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Old 07-05-2016, 07:52 AM   #20
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can I run syn in my AT545?
Over on School Bus Fleet, there's a discussion about synth in an AT-545. You can, as long as its on Allison's approved list, and used with the right filters, including internal.
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