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Rear end gear swap out #45388 04/11/2002 2:18 AM
Joined: Mar 2002 Posts: 8 alabama E eugene55 Member
eugene55 Member E Joined: Mar 2002 Posts: 8 alabama	I am wanting to swap out the gears (3.9) in my original :confused: 55-1st series. It is a daily driver and I need the ability to travel over 45mph on occasion. I have located gears (3.36) from a later model chevy. Any idea how much difference I would see changing from 3.9 to 3.36? Would the diference be worth the trouble of swapping? What would be better? Any ideas welcomed.

Re: Rear end gear swap out #45389 04/11/2002 2:46 AM
Joined: Feb 2001 Posts: 92 Hillsboro, MO, USA B bluebird Wrench Fetcher
bluebird Wrench Fetcher B Joined: Feb 2001 Posts: 92 Hillsboro, MO, USA	Your best option is to go to GearZone and download their Autodyne Calc. It is pretty good and you can modify all sorts of measures, Gear ratios, speeds, etc. and get the RPM for that config. Whats down in the well comes up in the bucket, so watch who's KoolAid you drink.

Re: Rear end gear swap out #45390 04/11/2002 3:42 AM
Joined: Feb 2001 Posts: 1,096 Canterbury , NewZealand D Dusty 'Bolter
Dusty 'Bolter D Joined: Feb 2001 Posts: 1,096 Canterbury , NewZealand	Eugene55 , firstly , your 3.9 gears will enable you to run 55mph easy cruise , asuming your engine is ok . Here is the formula you can use to see what alternate gear sets will do for your RPM. MPH = 0.01136 X RPM X tyre circumference in feet ---------------------------------------------- Gear ratio X Diff ratio e.g. 750 x 16 tyre @ 31'' tall = 8.11 ft circum. MPH = 0.01136 X 2500 X 8.11 ------------------------ 1 x 3.9 = 59.05 mph top gear speed you change the variables to suit your tyre size and diff ratio options .

Re: Rear end gear swap out #45391 04/11/2002 4:51 AM
Joined: Mar 2000 Posts: 73 Rio Linda, Ca. 95673 R Rick Rickard Wrench Fetcher
Rick Rickard Wrench Fetcher R Joined: Mar 2000 Posts: 73 Rio Linda, Ca. 95673	Here is a site that has a calculator http://www.ring-pinion.com/calculators.html . Rick

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