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9in gears
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Fleet Mechanic
Joined: Oct 2007
Posts: 1,972
Likes: 103
9in gears
Im shopping for a better set of gears for my 64 F100.
The tag says 3.10. ND says thats not possible, but thats what it says.
My speedo is off 17mph. Indicated speed 50mph, actual speed 67mph.
To much to correct with a driven gear change, current gear is 17 teeth..
I suspect the truck had a much steeper gear when new. Its a 292/AT.
I want a 28 spline 3.25 or 3.50 gear. Other than F100/F150s what other vehicles should I look at?
Im tempted to look for an Explorer 8.8, the 9in is overkill for my truck. Its low hp and its not going to do any work as long as I own it.
The tag says 3.10. ND says thats not possible, but thats what it says.
My speedo is off 17mph. Indicated speed 50mph, actual speed 67mph.
To much to correct with a driven gear change, current gear is 17 teeth..
I suspect the truck had a much steeper gear when new. Its a 292/AT.
I want a 28 spline 3.25 or 3.50 gear. Other than F100/F150s what other vehicles should I look at?
Im tempted to look for an Explorer 8.8, the 9in is overkill for my truck. Its low hp and its not going to do any work as long as I own it.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
I see different opinions on testing for ratios, raise one wheel, raise both wheels, but I like something a little different, roll the truck on the ground. 1st get a bud for safety and with the truck on a very level ground (like a garage floor) mark the left rear tire, roll it one complete rotation while counting the rotations of the driveshaft. You can mark it with a Sharpie, piece of tape, you choose.
This will give you the actual count with no possible interruptions. You will need at least 2 teeth different on the speedo gear to get a closer reading.
John
This will give you the actual count with no possible interruptions. You will need at least 2 teeth different on the speedo gear to get a closer reading.
John
Logistics Pro
Joined: May 2015
Posts: 4,463
Likes: 954
From: Tri Cities, TN
Try car-part.com and set the search for distance. You will get back more results using carrier in the search box. Any 28 spline will work. And they are about as common as rocks. I would try to find one that has the correct yoke on it though. I believe Ford used something like 7 different yokes over the years. Changing the yoke isn't a big deal but there is a little more to it than just swapping them out. I would stay away from the 8.8 unless you are into re-engineering the whole backend of your truck. Or you could just have yours rebuilt, that way you get new everything in the ratio you want.
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Any just about any 1960's or 1970's full or mid size car (minus the Granada and Comet). So you are looking for stuff like T birds, Cougars, LTD's, Galaxies Torino's, Mustangs (pre 74), Lincoln's, Mercury Marquis's and Montego's Colony Park wagons, Cougars. You only need the Crown and pinion so axel spline count is not a consideration unless of course you are looking to swap the whole pumpkin. If I remember correctly some of the larger cars and trucks have a 9 3/8" Ring gear. You can identify the 9 3/8" case by the curved top support rib on the case See the Below pic borrowed of the internet. The 9" case rib goes straight across.
The 9 3/8" pumpkin will fit the 9" housing if you cut the clearance notch in it for the larger gear like the 9 3/8" housings have
Once you pull your pumpkin you will know exactly what your gear ratio is as it is stamped on the ring gear. The you can then calculate how high you can go with the driven gears available. Remember the 9" was available with some really high ratios around 2.3:1 I think the ratio your truck had stock was around the 3.89 mark.
The 9 3/8" pumpkin will fit the 9" housing if you cut the clearance notch in it for the larger gear like the 9 3/8" housings have
Once you pull your pumpkin you will know exactly what your gear ratio is as it is stamped on the ring gear. The you can then calculate how high you can go with the driven gears available. Remember the 9" was available with some really high ratios around 2.3:1 I think the ratio your truck had stock was around the 3.89 mark.
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
In the bumpside trucks ('67-'72), the axle code on the warranty tag affixed to the drivers door with a code of "08" would be a 28-spline, open differential with 3.50 gears. A "17" would have 3.25 gears and an "09" would have 3.70 gears. Some '68-'72 Ford F100s came with a Ford 9-3/8" rear end. All of these had 31-spline axles/differentials.
All Bumpside trucks with a Ford 9-inch rear end had a 28-spline differential/28-spline axles. Many of the Dentside ('73-'79) trucks had 31-spline differentials/axles but there were some with 28-splines. All Bullnose ('80-'86) trucks with a 9-inch rear had 31-spline differentials/axles.
Ford passenger cars with a 9-inch rear end generally have longer companion flanges (where the driveshaft attaches to the 3rd member) than the companion flanges on the trucks.
All Bumpside trucks with a Ford 9-inch rear end had a 28-spline differential/28-spline axles. Many of the Dentside ('73-'79) trucks had 31-spline differentials/axles but there were some with 28-splines. All Bullnose ('80-'86) trucks with a 9-inch rear had 31-spline differentials/axles.
Ford passenger cars with a 9-inch rear end generally have longer companion flanges (where the driveshaft attaches to the 3rd member) than the companion flanges on the trucks.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 784
From: Simi Valley, CA
1976/80 Granada/Monarch 9" came with rear disc brakes. This same rear axle with discs used in 1977/80 Lincoln Versailles ("rebadged" Granada).
The 8" was introduced in 1962 Fairlane/Meteor, it looks very similar to the 9."
1966/69 Comet could have an 7 1/4" integral, 8" or 9" rear axle.
Mountain Pass
Joined: Apr 2016
Posts: 144
Likes: 2
From: Skagit County, WA
Do you want a different gear seat or just a correct speedo reading? If it's just the speedo then there is a much easier means to that end: http://www.ebay.com/itm/like/131689402154?lpid=82&chn=ps&ul_noapp=true
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Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
1975/80 Granada/Monarch could have 8" or 9" or the WER integral 8.7" rear axle.
1976/80 Granada/Monarch 9" came with rear disc brakes. This same rear axle with discs used in 1977/80 Lincoln Versailles ("rebadged" Granada).
The 8" was introduced in 1962 Fairlane/Meteor, it looks very similar to the 9."
1966/69 Comet could have an 7 1/4" integral, 8" or 9" rear axle.
1976/80 Granada/Monarch 9" came with rear disc brakes. This same rear axle with discs used in 1977/80 Lincoln Versailles ("rebadged" Granada).
The 8" was introduced in 1962 Fairlane/Meteor, it looks very similar to the 9."
1966/69 Comet could have an 7 1/4" integral, 8" or 9" rear axle.
I think most came with pretty high geared rear ends also. So I just omitted them. Even finding something as steep as 3.5'ish in a car is a tough go unless it is a stang.
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Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
1975/80 Granada/Monarch could have 8" or 9" or the WER integral 8.7" rear axle.
1976/80 Granada/Monarch 9" came with rear disc brakes. This same rear axle with discs used in 1977/80 Lincoln Versailles ("rebadged" Granada).
The 8" was introduced in 1962 Fairlane/Meteor, it looks very similar to the 9."
1966/69 Comet could have an 7 1/4" integral, 8" or 9" rear axle.
1976/80 Granada/Monarch 9" came with rear disc brakes. This same rear axle with discs used in 1977/80 Lincoln Versailles ("rebadged" Granada).
The 8" was introduced in 1962 Fairlane/Meteor, it looks very similar to the 9."
1966/69 Comet could have an 7 1/4" integral, 8" or 9" rear axle.
Thread Starter
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Fleet Mechanic
Joined: Oct 2007
Posts: 1,972
Likes: 103
I may rethink the rear swap. 3.10s should be pretty good behind a healthy engine in a F100.
I guessing my 292 is putting somewhere around 100hp to the wheels, maybe less.
With modern head gaskets Im probably at 7.5:1 compression, AT and the crossover single exhaust. Not a good performance package.
I guessing my 292 is putting somewhere around 100hp to the wheels, maybe less.
With modern head gaskets Im probably at 7.5:1 compression, AT and the crossover single exhaust. Not a good performance package.
Elder User
Joined: Jul 2004
Posts: 700
Likes: 0
From: Fairbanks
I swaped in a set of 3.00 into my 65 f100 with a 240 I did not have any problem going down the road. I ended up putting a set of 3.55's in because the 3.00 was too tall with my overdrive. If I dont use the overdrive 3.00's are great
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
Final drive equivalent is figured by multiplying the overdrive ratio of the transmission by the gear ratio of the rear end.
.68 x 3.55 = 2.41:1.
In overdrive with 3.55:1 rear end gears, it would be as if the rear end had 2.41:1 gears in it.
With an overdrive and 3.00:1 rear end gears, the final drive equivalent would be 2.04:1.
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