gearing
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gearing
I'm working on making my '75 c600 rescue fire truck a better daily driver. I figure on this site people won't laugh at me like they do in the general public. You'll need to give me a break on the technical stuff because I'm a carpenter and not a mechanic. Truck has a 360/361 with a 4 speed Allison automatic. The Rockwell rearend has a 0720 gear ratio. No tach in truck, but its screaming at 50 mph. The other issue is that the truck struggles to get up a good hill. Motor is cleaned up and running fairly well, still needs fine tuning. GVW is 21,200 lbs, but full of tools it runs at 15,500 lbs. I may tow a small trailer from time to time, but that will be consistant weight for the most part. I'm considering a different gear ratio ie. 583 or 529. what will this mess up ?
Fleet Mechanic
Joined: May 2005
Posts: 1,575
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From: Puyallup, WA
You really need more than 4 gears. Do you have the lighter duty AT540 that was installed in some of these trucks was intended as a city transmission only. It does not have a wide enough gear spread to do everything properly
You really need a 5 or 6 speed Allison. If not that, then a two speed rear end is a work around.
Taller rear gears raise all the effective gear ratios in the tranny. You may find that first gear is now not low enough if you live in hilly territory.
Just my thoughts.
David
You really need a 5 or 6 speed Allison. If not that, then a two speed rear end is a work around.
Taller rear gears raise all the effective gear ratios in the tranny. You may find that first gear is now not low enough if you live in hilly territory.
Just my thoughts.
David
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