Changing differential gear ratio
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Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
Changing differential gear ratio
My Dad has a '96 F-250 PSD with a built up E4OD transmission. The stock gears are 3.55. He pulls an 8000 lb 5th wheel and when running about 60, his engine is running about 1600 RPM. The problem then is running excessive EGT's. He can shift out of overdrive and run the RPM's up around 2200, but this seems excessive for long periods.
My questions are as follows.
What, where and how would we go about changing the rear (and front) axle ratio's. I'd be interested in hearing about good vendors, costs and any advice about changing them out.
Is there a way to calculate what gear ratio's would produce what RPM's at certain speeds? Maybe an online calculator. I'm thinking 3.73's might be good, but 4.10's might be necessary.
Is there a resource somewhere that tells what the transmission ratio's are? This is more for my curiosity. My truck is a 6 sp manual with 3.73's. At 60, I'm running around 1750 RPM's and am wondering if his OD has the same ratio as my OD, thus making a comparison between my truck and his.
Any and all advice and information would be appreciated.
My questions are as follows.
What, where and how would we go about changing the rear (and front) axle ratio's. I'd be interested in hearing about good vendors, costs and any advice about changing them out.
Is there a way to calculate what gear ratio's would produce what RPM's at certain speeds? Maybe an online calculator. I'm thinking 3.73's might be good, but 4.10's might be necessary.
Is there a resource somewhere that tells what the transmission ratio's are? This is more for my curiosity. My truck is a 6 sp manual with 3.73's. At 60, I'm running around 1750 RPM's and am wondering if his OD has the same ratio as my OD, thus making a comparison between my truck and his.
Any and all advice and information would be appreciated.
Post Fiend
Joined: Feb 2007
Posts: 7,191
Likes: 4
From: Blairsville,Ga
according to the owners manual the '96 was available with 3.55 or 4.10 but am sure there are more afrer markt gear ratios for it
4.10 is a good towing gear but will burn more fuel running empty
4.10 is a good towing gear but will burn more fuel running empty
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,734
Likes: 2,661
From: SE Florida
Originally Posted by dchamberlain
when running about 60, his engine is running about 1600 RPM.
The way to calculate this is RPM * new ratio / old ratio.
1600 * 4.10 / 3.55 = 1847.
