rear axle ratio
Thread Starter
|
Senior User
Joined: Jan 2003
Posts: 243
Likes: 0
From: Visalia, CA
rear axle ratio
Hi, just purchased a 64 F100 SB and looking at the ID tag on the door a see a 12 for the axle ratio. Being a 73-79 guy that has a set of shop manuals for the vintage it tells me I have a 3:70 to 1 Would that be what your manuals indicate. The truck is a 292/3 spd. no overdrive. Also assuming that this is must likely a 28 spline 9" instead of a 31. This is an orginal truck, so I dont think anyone has made changes, but you never know!!And Ford used what ever they had toward the tale end of production. 
Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
rear axle ratio
OK with that said what was the stock tire diameter? I was looking to do a gear swap for a set of 3.70's I was under the impression with as low of an RPM that I have at 60 that I have 2.90 or 3.00 in there. But when you factor in tire size that would slow it down too. Weighing my option since I need to buy new skins for my rims when they come in. Krosati what should I be looking for as far as teh stamp goes? I don't remember seeing one last summer when I scrubbed it down.
Last edited by airharley; Jul 23, 2003 at 10:33 PM.
Postmaster
Joined: Nov 2000
Posts: 2,557
Likes: 2
From: Texas
rear axle ratio
My mistake, My ratio is stamped on the flange but I don't think Ford did this from the factory. I think some body else did this at some point. I do still have the tag hanging as well.
The original tire size for 2WD F-100 were either of the following:
Optional 4000 lbs GVW - 6.70-15 2PR (front/rear)
RPM per mile (new tire) 772 at 36 PSI
Standard 5000 lbs GVw - 6.50-16 6PR (front/rear)
RPM per mile (new tire) 700 at 45 PSI
To get a target of 70 mph and rpms at 2500, you will need a ratio of 3.08 and tires diameter of approx. 28.97.
Check out this chart and use the bottom part of the chart to calculate. http://www.csgnetwork.com/multirpmtirecalc.html
The original tire size for 2WD F-100 were either of the following:
Optional 4000 lbs GVW - 6.70-15 2PR (front/rear)
RPM per mile (new tire) 772 at 36 PSI
Standard 5000 lbs GVw - 6.50-16 6PR (front/rear)
RPM per mile (new tire) 700 at 45 PSI
To get a target of 70 mph and rpms at 2500, you will need a ratio of 3.08 and tires diameter of approx. 28.97.
Check out this chart and use the bottom part of the chart to calculate. http://www.csgnetwork.com/multirpmtirecalc.html
Thread
Thread Starter
Forum
Replies
Last Post
Lee250
Clutch, Transmission, Differential, Axle & Transfer Case
3
Jun 14, 2007 09:36 PM
BillWoeb
1999 - 2016 Super Duty
6
Oct 26, 2005 05:27 AM
64_f100_owner
1961 - 1966 F-100 & Larger F-Series Trucks
1
Mar 3, 2004 08:40 AM
jonniekash
1973 - 1979 F-100 & Larger F-Series Trucks
7
Jul 15, 2001 10:29 PM
