31 spline has press on bearings with a spacer. 
Gear swap
Thread Starter
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Senior User
Joined: Aug 2017
Posts: 202
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Gear swap
I have a 78 f150 roller 302 eldelbrock intake holley carb, mustang shorty headers and c4 trans
Its not a daily driver.
Currently the truck has 2.75 gears 28 spline. Found a 31 spline 3.25 geared rear end at a good price.
Would that make that much of a diffrence in low end? The truck just have much go on the low end.
Or should I keep looking for 3.50 or 3.70 gears?
Its not a daily driver.
Currently the truck has 2.75 gears 28 spline. Found a 31 spline 3.25 geared rear end at a good price.
Would that make that much of a diffrence in low end? The truck just have much go on the low end.
Or should I keep looking for 3.50 or 3.70 gears?
Laughing Gas
Joined: Oct 2010
Posts: 1,237
Likes: 285
From: Clinton, MS
Making that gear change will give you more grunt off of the line. The size of the rear tires will also make a difference. If both axles are Ford 9 inch rears, you can easily swap the third member and axles without having to swap the whole rear end. Just make sure that the bearings on the axles ends are the same size.
Laughing Gas
Joined: Mar 2003
Posts: 789
Likes: 7
From: Durham, NC
Making that gear change will give you more grunt off of the line. The size of the rear tires will also make a difference. If both axles are Ford 9 inch rears, you can easily swap the third member and axles without having to swap the whole rear end. Just make sure that the bearings on the axles ends are the same size.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 784
From: Simi Valley, CA
The 'slim line' side (differential) bearings are the same for all 9" rear axles (excepting 1970/72 F100 with 9 3/8" ring gear) beginning in 1969 from serial number J30,001:
C9AZ-4221-A bearing (stamped with BIN: LM102949) & C9AZ-4222-A bearing cup (stamped with BIN: LM102910).
1974/79 F100 & 1975/79 F150 with 28 & 31 spline 9" axle shafts. There are TWO different types of axle bearings:
Large ball bearing (D8AZ-1225-C replaced C9AZ-1225-A & C1SZ-1225-A) & tapered roller bearing/seal combination (D4AZ-1225-A).
Pic: Side bearings/cups shown as 4221 & 4222, axle bearing is 1225.
Cargo Master
Joined: Apr 2010
Posts: 2,600
Likes: 64
From: Billings, MT
3.50 is a good compromise gear if you dont have overdrive. I recently changed to 3.50 from 4.10 gears and didn't notice a loss in acceleration or grunt at all, my 408 has plenty of torque though. 3.73 and 3.50 are so close you wont notice a power difference
Senior User
Joined: Oct 2017
Posts: 280
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From: british columbia, canada
Of course you didn,t lose any grunt or acceleration going from 350 to 410, the bigger the # means lower gearing not the other way around. Going from 410 to 350 would slow the truck down off the line, going from 350 to 410 always gives better grunt and acceleration but you lose top speed.
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Laughing Gas
Joined: Mar 2003
Posts: 789
Likes: 7
From: Durham, NC
Contrary to what ND just posted, there are 2 different bearing types to look for. One set of bearings are not tapered and have the seal in the housing ahead of the bearing. The bearings are "permanently" sealed and lubed with grease. The other has tapered bearings that are pressed onto the shaft with a spacer. They have the seal outside the bearings, so they are lubed by the gear oil.
Kevinstang's Ford Nine Inch Differential Page + Scroll half way down
https://www.ford-trucks.com/forums/8...-bearings.html
https://www.ford-trucks.com/forums/1...axle-seal.html
Kevinstang's Ford Nine Inch Differential Page + Scroll half way down
https://www.ford-trucks.com/forums/8...-bearings.html
https://www.ford-trucks.com/forums/1...axle-seal.html
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 784
From: Simi Valley, CA
The thing is, you called the bearings by the wrong name. Side (aka differential) bearings are NOT axle (aka wheel) bearings.
I posted the parts catalog pic so you could see the difference. Go back to post #5 and look at it again.
I've been looking these parts up for in Ford parts catalogs for over 45 years, so I know the
difference.
Laughing Gas
Joined: Mar 2003
Posts: 789
Likes: 7
From: Durham, NC
Open your peepers, I said there were TWO different types of axle bearings.
The thing is, you called the bearings by the wrong name. Side (aka differential) bearings are NOT axle (aka wheel) bearings.
I posted the parts catalog pic so you could see the difference. Go back to post #5 and look at it again.
(sigh)
The thing is, you called the bearings by the wrong name. Side (aka differential) bearings are NOT axle (aka wheel) bearings.
I posted the parts catalog pic so you could see the difference. Go back to post #5 and look at it again.
(sigh)
Thread Starter
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Senior User
Joined: Aug 2017
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Thanks for the input.
I'm trying to be cheap and not have to pay someone to swap the gears. I found some 28 spline 3rd members rebuilt with 3.50 gears for $800. Dont really want to or afford to pay that.
I'm trying to be cheap and not have to pay someone to swap the gears. I found some 28 spline 3rd members rebuilt with 3.50 gears for $800. Dont really want to or afford to pay that.
Cargo Master
Joined: Apr 2010
Posts: 2,600
Likes: 64
From: Billings, MT
Of course you didn,t lose any grunt or acceleration going from 350 to 410, the bigger the # means lower gearing not the other way around. Going from 410 to 350 would slow the truck down off the line, going from 350 to 410 always gives better grunt and acceleration but you lose top speed.
re-read. Went FROM 4.10s TO 3.50s
Elder User
Joined: Jun 2015
Posts: 664
Likes: 2
From: York Pa.
I have a 78 f150 roller 302 eldelbrock intake holley carb, mustang shorty headers and c4 trans
Its not a daily driver.
Currently the truck has 2.75 gears 28 spline. Found a 31 spline 3.25 geared rear end at a good price.
Would that make that much of a diffrence in low end? The truck just have much go on the low end.
Or should I keep looking for 3.50 or 3.70 gears?
Its not a daily driver.
Currently the truck has 2.75 gears 28 spline. Found a 31 spline 3.25 geared rear end at a good price.
Would that make that much of a diffrence in low end? The truck just have much go on the low end.
Or should I keep looking for 3.50 or 3.70 gears?
New User
Joined: Mar 2013
Posts: 1
Likes: 0
77 f100 door adjusting
Are you familiar with how to adjust doors on a 77 f100. I took the door and hinges off to clean an repair. Now I can’t get it back lined up, if you know a way I can get it back line up I will greatly appreciate it.
