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08-18-2020, 02:22 PM | #1 |
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3.78 vs 3.54 rear end and speedometer/miles
I have to replace ring gear in my roadster. Presently it is stock which I think is 3.78. If I put in a 3.54 gear & pinion, how will this change the mph and odometer reading ? Thanks, Bill
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08-18-2020, 02:53 PM | #2 | |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
Quote:
With the 3.54 gears, your speedo will read about 6% too low. When your speedo says '50', you would be doing about '53'. Last edited by 1930-Pickup; 08-18-2020 at 02:59 PM. |
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08-18-2020, 02:54 PM | #3 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
I run 3:54 in two cars and it seems to give about 6-7 MPH more with the same RPM. You will need to change the speedometer drive gear in the cap on the torque tube. All the parts houses have them listed.
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08-18-2020, 05:35 PM | #4 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
Buy the correct speedometer gear for the 3.54. I think Bratton's has them. Get the whole assembly, don't buy the new gear for your housing.
Charlie Stephens |
08-18-2020, 05:38 PM | #5 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
Charlie - Why? I changed the gear for my 3.54 and it is fairly accurate.
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08-18-2020, 05:40 PM | #6 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
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08-18-2020, 05:54 PM | #7 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
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08-19-2020, 07:09 AM | #8 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
thank you for the info. Bll
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08-19-2020, 08:01 AM | #9 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
A 3.54! One of the best things I ever did! Rebuilding the rear is a PITA, however it's worth it. If you live in a flat area and have a strong engine, you can go to a 3.27. I am in a very hilly area, so I played it safe and went for the 3.54. The amazing thing is, it climbs the hills around here better than the old 3.78. My engine mods are just a head cut .040 and a "B" carb with a bored out manifold. Yes, there's some improvement, but no one would call it a "Hot Rod". It's more of a dream on the highway. I gave up nothing and gained on all counts. Yes, By all means do it. Be sure to follow Tom Endy's tutorials on Rebuilding ford differentials. It's not a simple process!
Terry Last edited by Terry, NJ; 08-19-2020 at 08:15 AM. |
08-19-2020, 06:37 PM | #10 | |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
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08-19-2020, 07:55 PM | #11 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
I look at it from a different perspective 26%od with a 3.78 or a 3.54 at crusing speed of 62 mph? The 3.54 drops engine rpm down 130 from the 3.78..from 2130 to 2000 or so..better effciency,no lugging..
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08-19-2020, 08:06 PM | #12 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
My late 30 pickup also had a 4.11 in it and had a shop put in 3.54. Rebuilt engine standard head. Nice to now be able to keep up with other club members at 45 mph without the engine at really high revs. Good power for hills, max top speed is 55 mph. I do not drive highway speeds so this is OK with me.
From what I've read people who drive highway speeds run a Mitchell with 3.78 rear end. Do not remember which ratio Mitchell most run. |
08-19-2020, 09:01 PM | #13 | |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
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08-19-2020, 09:58 PM | #14 | |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
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Terry |
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08-19-2020, 10:28 PM | #15 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
You can find Borg Warner overdrives for that kind of money..
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08-20-2020, 12:21 AM | #16 | |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
Quote:
Are you saying, go with an O/D with 3.78, go with an O/D with 3.54 or just go with the 3.54? Thanks
__________________
Ruth "Sometimes you really DO need to read the whole thread" |
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08-20-2020, 08:53 AM | #17 |
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Re: 3.78 vs 3.54 rear end and speedometer/miles
The gain from rpm reduction at freeway speed.OD/3.78 or OD/3.54..at 62mph OD 3.54 the rpm is 130 less and at the bottom of the torque range..makes it a little more pleasant to drive.700 bucks (Terry's cost for a 3.54 upgrade) more pleasant? that's debatable.
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