Rear gears question
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New User
Joined: Apr 2014
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Rear gears question
So I'm still fairly new to this site so I can't, as of yet, post pictures, but I'll try to describe what I've got. I purchased, a month ago or so, a 1965 F-100 custom cab with a 352 engine, 4-speed manual transmission (kinda makes me feel like I'm driving an old Peterbilt 
). Although my intentions are not to totally restore it to show condition (it will be a working family truck) I do want it to look good and work good. One of the things that I don't really like is the slowness of this truck. I took it to the highway and when I reached 55 the poor engine was screaming to please slow down a bit. So I figure I'll need to replace the rear gears first and foremost. Anyway, enough 
I'd like to know what gear would be best to gain speed to be able to reach freeway speeds (top of 90 or so) without sacrificing too much pulling capacity. And, once the new gears are replaced, that probably will cause my speedometer to give out a false reading, so does anybody know what speedometer gear to get with any given diff gear?
Thanks!
). Although my intentions are not to totally restore it to show condition (it will be a working family truck) I do want it to look good and work good. One of the things that I don't really like is the slowness of this truck. I took it to the highway and when I reached 55 the poor engine was screaming to please slow down a bit. So I figure I'll need to replace the rear gears first and foremost. Anyway, enough I'd like to know what gear would be best to gain speed to be able to reach freeway speeds (top of 90 or so) without sacrificing too much pulling capacity. And, once the new gears are replaced, that probably will cause my speedometer to give out a false reading, so does anybody know what speedometer gear to get with any given diff gear?Thanks!
Senior User
Joined: Dec 2012
Posts: 221
Likes: 2
From: Wildwood, Mo
Gears
Well, the choice of gears will depend on the tire size. MY 1979 Bronco with a 4 speed has 3.00 gears which was the standard gears for the automatic transmission. The 3.50 gears were standard for the 4 speed. Not recommended for towing in the mountains but I have towed quite a lot with it. My 15" wheels only have 29" tall tires. It does just fine on the highway. Hope this helps.
By the way enjoy shifting that synchronized 4 speed. If you drove my 1950 F-3 with the no synchro 4 speed you would appreciate how nice your is to shift. Having to downshift to 3rd on a steep hill with traffic behind is exciting.
By the way enjoy shifting that synchronized 4 speed. If you drove my 1950 F-3 with the no synchro 4 speed you would appreciate how nice your is to shift. Having to downshift to 3rd on a steep hill with traffic behind is exciting.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
All very well and good, but the OP has not mentioned which rear axle his truck has!
1966 F100 could have a 9" without Limited Slip, a Dana 44, Dana 60.2 or Dana 60.3 with Limited Slip.
AXLE code stamped on the Warranty Plate, located on the left door face below the latch.
Speedo DRIVE (on the output shaft) and DRIVEN (at the end of the cable) gears depends on trans type, rear axle ratio and tire size.
1966 F100 could have a 9" without Limited Slip, a Dana 44, Dana 60.2 or Dana 60.3 with Limited Slip.
AXLE code stamped on the Warranty Plate, located on the left door face below the latch.
Speedo DRIVE (on the output shaft) and DRIVEN (at the end of the cable) gears depends on trans type, rear axle ratio and tire size.
Fleet Mechanic
Joined: Oct 2007
Posts: 1,976
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I have 3.25 gears and I have a set of 2.75 gears that I have been thinking about dropping in.
I don't tow but do want to cruise at 70mph on occasion without having to wear earplugs.
I don't tow but do want to cruise at 70mph on occasion without having to wear earplugs.
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Elder User
Joined: Feb 2014
Posts: 713
Likes: 3
From: Florida
Total agreement with ND. Until the transmission final drive, tire size, rear differential (9", Dana, open, limited slip, etc.) engine modifications are known, engine rpm and final drive speeds are only a general recommendation. A truck with 265-70-R16 tires vs. a truck with 35" tires will yield entirely different rpm / speed ability.
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Laughing Gas
Joined: Dec 2010
Posts: 1,091
Likes: 14
From: Tucson, Arizona
Cirrusman - post the data from your driver door warranty plate - assuming it is still there and original - and someone from this site will decode it for you. Then we'll know what gearing your truck came with and how to advise you further. If you're planning on driving as fast as you suggested, you'll certainly want to completely go through your suspension, add disc brakes, and possibly add front and rear sway bars. You might also consider helping your 352 breathe better. Remember, when they built your truck in 1965 Ford never intended it to be driven at the speed your talking about.
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Aug 19, 2009 11:40 AM