Rear End Gearing Question

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Feb 7, 2015 | 01:25 PM

bobo3020

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Rear End Gearing Question

I just purchased a 1955 F100. Here are some specs it is shifting to fast I am doing about 35 and in 3rd gear already. Do you guys have any advice on the gearing that would work better for me?

Rear Axle: Stock 28-spline axles, Ford 9" Rear end, Stock 3.50 Ring-and-Pinion

Engine: Ford 408W- Johnny Olson Built
Cylinder Heads: Eldbrock Victor Jr. Heads
Valve-train: Comp XT305H (.240"/.246" @ .050", .541" intake/.585" lift) Flat Tappet Cam, Comp Pushrods, Scorpion 1.72 Rocker Arms, Black Satin- Ribbed Valve Covers
Induction: Eldbrock Aluminum Intake, Holley 750 Cfm Double Pumper Carburetor with FRP Satin & Ribbed Air Cleaner, Carter Electric Fuel Pump
Ignition and Electrical: MSD 8202, MDS6 6200, Summit 140 Amp Alternator, Custom Wiring Harness
Exhaust: Hedman Headers, 3" SS Tubing, SS Wire Flex with Flowmaster Mufflers
Other Items: March Billet Pulleys, Gibson Aluminum Radiator and Oil Cooler
Transmission: TCI FORD C6 with JW Engineering 3000rpm Stall Converter
Shifter: CPP Column Shifter

Feb 7, 2015 | 02:43 PM

smallello

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From: NW Valley AZ

What size are the tires? If they have a small diameter it will lower the gear ratio. (Numerically higher)
3.50 with a 26 inch tire is not the same as 3.50 with a 30 inch tire.

Feb 7, 2015 | 03:18 PM

bobo3020

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Sorry forgot to post that

Wheels and Tires: American Racing Chrome Smoothie Wheels (15" x 8" front & 15” X 10”rear), with Mickey Thompson (235 x 60ZR front, 275 x 60ZR rear)

Feb 7, 2015 | 03:21 PM

truckeemtnfords

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From: Fallon,NV & Bainbridge OH

That speed and 35mph don't mean anything, it just means it is shiftig to soon. What RPM are you turning? 3.50 gears and just about any tire size should not be a problem.

It sounds to me like it needs the shift points adjusted via the vacuum modulator. With that cam and stall converter I bet you are pulling next to no vacuum due to cam overlap. Either get an adjustable modulator and set it up for your application or take it to a good performance trans shop.

Feb 7, 2015 | 06:12 PM

bobo3020

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I do not have a tach on the truck at the moment. Should I put one in it is wired just not in.

Feb 7, 2015 | 11:21 PM

smallello

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From: NW Valley AZ

Go to this site.

Gear Ratios, RPM and Tire Diameter to MPH with Shift Points Calculator

Plug in the numbers for your ratio/tire size/trans gears. It will return the calculated shift points at mph/rpm.

Feb 9, 2015 | 12:38 PM

Nojive55

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From: KC Kansas metro

I agree with Dave, RPM is needed to complete the equation.

Your tires are approximately28 inches tall and with a 3.5 rear gear, 35 mph would be slightly under 1500 rpm. That is not too bad under lazy acceleration. At WOT your shift point should be much higher.

Chances are your daily driver has an AOD so with the 3.50 and a 1-1 final drive your truck is always going to feel like it needs to shift one more time (but oh what fun!).