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Old 09-04-2010, 08:37 PM   #1
MAMalody
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Shifting Question

I have a question on downshifting going down hill. At what speed do you consider it no longer safe, to disconnect the overdrive, shift from drive to D2 or D2 to D1? I have a '02 F350 7.3 diesel? For some reason I don't see this in the owners manual.
 
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Old 09-05-2010, 04:36 PM   #2
CORattler
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When beginning to descend a grade, you should be in a gear that will limit your speed to the maximum speed you want to go. During this process the engine/transmission act as a brake. The whole point is to descend at a controlled safe speed where you use your TV/RV brakes minimally to avoid over speeding your engine/transmission. Exhaust brakes are terrific for downhill grades and I highly recommend them.
If you're asking at what speeds can you safely downshift for each gear, I don't have that answer but bad things can happen to your engine/transmission if you downshift above maximum rated speed for the selected gear. It's a good question and one best answered before you need to know the answer.
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Old 09-05-2010, 04:52 PM   #3
awaywego
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Mike your owner manual will give you the downshift speeds. On mine below 55 overdrive to 3rd- below 45 from 3rd to 2nd and below 35 from second to 1st. Just hit the brakes and slow it to below the speed then drop the gear.
On a diesel you need an exhaust brake, or in my case I use a turbo brake to slow the speed with the downshift.
You also need to watch your transmission temp when downshifting to slow your decent. The temp will slowly increase on a long downgrade.
I have a 01 7.3 diesel.
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Old 09-05-2010, 07:40 PM   #4
MAMalody
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Thanks, awaywegom that info is just what I was looking for. I will also double check my owners manual again.
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Old 09-06-2010, 12:09 AM   #5
thor
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if you have a tach in your truck watch the rpms if you downshift watch that you dont redline the tach .if it is close then brake hard for a short time to bring our truck and rpms down if your rpms drop low then you can down shift to the next gear that will bring the rpms up. if they get to high then brake hard to lower them again
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Old 09-06-2010, 01:16 AM   #6
PowellsMonty
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Semis use what ever gear they needed to get up the hill to go down.
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Old 09-06-2010, 07:00 PM   #7
clutch
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If you are going to fast for a down shift your transmission should not shift down until it is safe for it to do so. Even if you move the shift lever. Give it a try with an empty truck on a lonely road. It should not go into first gear at like 50 mph.
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