Rear End Change
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Freshman User
Joined: Oct 2000
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Rear End Change
This weekend I replaced my 3.00 rear end with a 3.50 rear end. Works great, launches like a rocket. Now I have to adjust the speedometer. Any one know where to get the gears and how extensive it is to change?
Thanks
fred
Thanks
fred
Junior User
Joined: Feb 2001
Posts: 60
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Rear End Change
Tell me more! I've been wanting to do the swap for a while now. What engine/trans are you running? I have 360/C6, and it is slow off the line. It pulls hard from 30-50 in 1st, and to 90 in 2nd. I want it to pull hard from start to 60. My truck is my daily driver, so I don't want to go too far. I have been contemplating between 3.50 and 3.70 (or 3.73).
The other train of thought is that I didn't know anything when I had my engine rebuilt 10 yrs ago, and the guy may have put too much cam in it. According to what I have read here, if I rebuilt my engine to a 390 (or stroked it to a 410!), the 3.00 rear end would be just fine. Any opinions?
The other train of thought is that I didn't know anything when I had my engine rebuilt 10 yrs ago, and the guy may have put too much cam in it. According to what I have read here, if I rebuilt my engine to a 390 (or stroked it to a 410!), the 3.00 rear end would be just fine. Any opinions?
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
Rear End Change
Matt, go ahead with the 3.70 rear, just get a higher limit on your gas card, you'll need it. You should be able to get it down to about 6-8 mpg. But just think of the great fun you will be having. 
John
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John
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66F100s Rule
In the cool still quite of night you can hear chevies rusting away.
Posting Guru
Joined: Oct 1999
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From: yes
Rear End Change
I have 4.11's and get 10.5mpg with a low compression 360 and a double pumper carb., so you should get 10 at least if your engine is in proper tune. As far as a proper gear for the speedo, try checking wrecking yards and U-Pull-It's for a truck with the same rearend gears as yours. Then steal the spedometer cable and put it in yours, this assumes that the gear that governs how the speedo reads is the driven gear on the spedometer cable instead of the drive gear in the transmission.
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Joined: Mar 2001
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Rear End Change
I have a 1979 f-250 with a 300-6 and a (I think) 3.75 rear end.
I don't care so much for acceleration but would like better mpg.
Does anyone have a set of 3.0 gears they would like to sell or swap?
jon_ran(No Email Addresses In Posts!)
I don't care so much for acceleration but would like better mpg.
Does anyone have a set of 3.0 gears they would like to sell or swap?
jon_ran(No Email Addresses In Posts!)
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
Rear End Change
My My My, Al Gore did win Fla. and resides at 1600 Penn. ave. 
John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page
[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group
66F100s Rule
In the cool still quite of night you can hear chevies rusting away.
John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page
[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group
66F100s Rule
In the cool still quite of night you can hear chevies rusting away.
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Freshman User
Joined: Oct 2000
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Rear End Change
I have a 300 with Offenhauser manifold, Holley 390, Comp cam 260, Ported/polished head 1.94/1.60 valves, Fisher balancer, MSD ignition, Dynomax headers. The 3.50 rear end changed the performance dramatically. I would not go any lower. It has great launching power. I problably dropped 10 mph for the same RPM so for instance if you are at 50 mph at 2000rpm you'll now be 40 mph.
I've read the other responses and I feel 3.70 would kill your gas mileage. Hope that helps
I've read the other responses and I feel 3.70 would kill your gas mileage. Hope that helps
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From: Hutto 20 mi. above Austin USA
Rear End Change
How many horses do you think you're pumping out with that setup?
Did the balancer make a big improvement in the rev department? What is the advanced duration on that cam, and does it sound stock or like it's got something big?
Thanks alot...
Chris
1982 F100 Flareside
300 I-6 SROD 4speed
MSD6AL, 8.5mm S/C Wires
Blaster 2F Coil
Blue & Silver
Did the balancer make a big improvement in the rev department? What is the advanced duration on that cam, and does it sound stock or like it's got something big?
Thanks alot...
Chris
1982 F100 Flareside
300 I-6 SROD 4speed
MSD6AL, 8.5mm S/C Wires
Blaster 2F Coil
Blue & Silver
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