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Old 03-28-2007, 08:56 PM   #1
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International DTA 360 Downshifting Hard

I've got a 1992 International with a DTA 360, an Allison AT545 tranny and when coming to a stop it really downshifts hard into the lower gears.

It really seems to run well overall. It's got a solid, steady idle, the engine runs smooth and the tranny shifts smoothly into gear but really dowshifts hard when returning back to 2nd and 1st gear.

The guy I bought from told me that it' supposed to shift like that but I don't buy it. I can't think of any reason why it would be normal to downshift so hard.

Any advice/insight would be much appreciated.

Thanks!

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Old 03-28-2007, 09:09 PM   #2
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I don't know about others, but my AT545 downshifts surprisingly firmly as well, most noticeably into 2nd and 1st gears. I think it's just the nature of the beast. The logical reason for it would be longevity. By downshifting (and upshifting) firmly the clutches aren't given a chance to slip or have multiple clutch packs engaged at the same time, even temporarily. I would liken it to a shift kit or the two/haul mode in modern pickup trannies that delay up shifts and speed up downshifts as well as upping line pressure to give firm shifts.
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Old 03-28-2007, 09:17 PM   #3
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Allison auto trans

This maker of auto trans is the best. If possible got to a school district, big trans repair shop or a large truck equiptment shop and talk to a repair person. Ask them to take a quick ride with you. You must go to any place with your bus. It will be warm and ready to shift.
The part that ordinarily controls shifts are the trans valve body and the modulator. Get some information and discover the modulator location. This part is available and not tooo expensive. I believe the modulator is held in position by a snap ring, and not difficult to change.
Next check the fluid level and color. The oil should be cherry red and not smell burned. Some old units not serviced very oftain have brown oil and the filter can collapse internally. Every few years, it is good to check and change the internal frilter inside the oil pan. Many small Allison trans do not have an external spin off filter. External filters and trans temp guage are good and valuable.. Frank
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Old 03-28-2007, 09:23 PM   #4
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This may lean slightly off subject, but since you mentioned it: My bus came with a trans temp gauge, but over the course of the 700 mile trip to bring the bus home it barely moved. Is that normal or should it warm up a little more?
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Old 03-28-2007, 09:34 PM   #5
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What's the bottom number on the gauge? Depending on sending unit location I would imagine 200 to be a pretty typical number. If the tranny cooler is integral to the radiator your temp will likely be about the same as the engine temp after a while.
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Old 03-28-2007, 09:41 PM   #6
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I have a different motor, but the same tranny. Mine downshifts kind of hard into the lower gears as well. It doesn't seem to be a problem though. It shifts fine all the time.
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Old 03-28-2007, 09:51 PM   #7
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Just to stay on thread here my tranny downshifts a little hard too, but I don't think there's any problem. I've driven buses where the tranny was about to go out and everything felt loose on them. I know nothing about trannies, but when I worked for a big school district the last several years I probably drove 30 or 40 different buses in a year. Every bus felt a little different. Some made groaning noises when they shifted which didn't sound healthy to me.

The temp gauge: I have no idea what the bottom number is. I'll check tomorrow. I spent the first 200 miles trying to decipher what the gauge was for
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Old 03-29-2007, 12:48 AM   #8
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My (former) 545 downshifted hard also. I think Experience explained it well.
But you should also investigate the overall condition of your transmission, and
its need for servicing, yes. My shop manager says KEEP THE FLUID CLEAN!

Just had the tranny in my pickup rebuilt for trailer towing. Oh yeah buddy!
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