Best rear end ratio?

Clutch, transmission, rear axle

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takehikes
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Best rear end ratio?

Postby takehikes » Mon Oct 02, 2017 11:26 am

I have a 68 F100 short bed flareside with a 240-6, 3 speed manual and a 3.70 rear end.
I have zero chance of ever towing so would like to have a better rear gear for highway cruising.
Suggestions on what number would be best?
Its my daily driver and used out on open road on occasion but when I do I'd like it to not spin so tight.
1968 F100 SWB Flareside, 240-6, 3 speed, 3.70 rear, bone stock and rust free.

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sargentrs
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Re: Best rear end ratio?

Postby sargentrs » Mon Oct 02, 2017 1:29 pm

As long as you're not interested in burnouts, a 3.00 - 3.25 has worked well for me.
Randy
1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: viewtopic.php?f=22&t=59995 Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
1964 Ford Fairlane 500. 289/Cruise-O-Matic, A/C, P/S.

takehikes
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Re: Best rear end ratio?

Postby takehikes » Mon Oct 02, 2017 3:28 pm

I was thinking a 3.00 or 3.25 as I read about a Galaxie of the same vintage with an automatic in it (and a 240-6) that drov ejust fine. Its a big pig of a car so I figured performance ought to be OK>
1968 F100 SWB Flareside, 240-6, 3 speed, 3.70 rear, bone stock and rust free.

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sargentrs
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Re: Best rear end ratio?

Postby sargentrs » Mon Oct 02, 2017 5:58 pm

My Fairlane (289/auto) came with a 3.00 and I replaced it with a 3.25. Made just enough difference to make driving more enjoyable. My truck started with 3.00's and I upped her to 3.89's. Really woke her up out of the gate but she was screaming at 65 mph. Going back in 3.00's for more highway driveability and top end.
Randy
1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: viewtopic.php?f=22&t=59995 Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
1964 Ford Fairlane 500. 289/Cruise-O-Matic, A/C, P/S.

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jzjames
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Re: Best rear end ratio?

Postby jzjames » Tue Oct 03, 2017 12:11 pm

For your sb flareside I wouldn't go less than 3.50, but I think the 3.70 is better. That is unless you're going to do major drivetrain modifications for a more modern type of ride.

For in-town driving and occasional highway, wouldn't you rather have the power to wheel around and accelerate?

I considered changing differential on mine w 300-I6 but glad I didn't. My highway driving is at 60-65 mph but I can chug out of a stop light and beat new cars. :D
And with the Offenhauser intake, efi exh. manifolds and 2bbl Ford carb, its ''awake" enough for me.

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Re: Best rear end ratio?

Postby Red Mercury » Tue Oct 03, 2017 8:42 pm

I have a 67 Mercury 100 with a 240, 3 speed manual and 3.70 gearing. The truck has been in the family since new and always had terrible gas mileage--low teens. I changed the gears to 3.00 and found that the little 240 just didn't have enough power to run those gears for my liking. I then went to a 3.25 gear set. Even the 3.25's require a little bit of riding the clutch to get it rolling and it lacks power on the highway. The truck will not hold speed on a steep hill. Passing another vehicle takes some time & distance. Gas mileage improved by approximately 3 MPG. I am going to put the 3.70's back into the truck. Every 240, 3 speed manual truck that I have seen came with 3.70 gears and I now understand that Ford did that because it was the best match for the 240.

On another note, my father had a 69 F100 302, C4 automatic with 3.25 gears (factory) and it was much better. Much more drivable. I attribute that to the 302/auto combination. Mileage was much better at just under 20 MPG.

takehikes
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Re: Best rear end ratio?

Postby takehikes » Wed Oct 04, 2017 8:42 am

thats the kind of info I wanted. Since I am not going to modify the engine at all I'll stay with the 3.70's and deal with the noise and MPG.
I know if I modify the engine and drop a 5 speed in it that it will be a much better combination but I am trying like heck to keep the truck as stock as possible as its a virtually unmolested rust free 68.
1968 F100 SWB Flareside, 240-6, 3 speed, 3.70 rear, bone stock and rust free.


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