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1992 F150

Discussion in 'Engine, Transmission/Axle & Driveline/Axle' started by Austin106, Feb 25, 2018.

  1. Austin106

    Austin106 New Member

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    Hey all! I recently purchased a new to me 1992 Ford F-150. 302 engine, 5 speed manual trans. So I’m looking to change the rearend to drop my rpms when driving on the highway. I think it has a 3.55 rearend. The whole truck is completely stock. So what I’m asking is..... What would you guys recommend? It’s sitting on the stock 15 inch tires.

    Picture of truck is my profile picture
  2. Action

    Action Moderator Staff Member Respected Member

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    What is the engine RPM now at 60 in high gear?

    The considerations would be if there is any load that the truck will be doing.

    Larger diameter wheel/tires will do the same thing.

    The axle ratios offered to do the job you are looking for would likely be 3.08 and 2.73. Going there will reduce the power available and decrease the load capacity. 4X4 will be more difficult because you would be doing the font and rear.

    What is the GVW now?
    What body style?
    Or post first 7 digits of VIN
    >>>>>>>>>>Action
  3. Austin106

    Austin106 New Member

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    E70C5705-954B-4E69-85AB-FFAB35E6062A.jpeg Engine rpm is around 2350-2400 I think. The truck doesn’t have a tachometer for now. All I know is it sounds to be a little high for my liking the truck does not used for any loads. My new job requires me to go out of town for work and it’s a lot of highway driving. I want to avoid putting larger tires on because I like the rim and tire combo I have lol. Truck is not 4x4.im not sure the gvw. But buddy style is the 92-96

    The first 7 of vin is 1FTEF15
    Last 7 of vin is LA51749
    Last edited by a moderator: Feb 25, 2018
  4. Action

    Action Moderator Staff Member Respected Member

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    Based on the first 7 of the VIN ....
    The truck has a GVWR between 6001 and 7000 pounds based on the brake system. On the driver's door post or door there will be a sticker. In the lower left will be Type GVW. under that will be F15 ..... 3 or 4 or 5. My guess is 4

    If you change the rear axle ratio to a smaller number you will reduce the load capacity of the truck. Putting much if a load in the truck will likely damage the transmission or the engine.

    If the RPM drops much lower than 2200 to 2000 you may never be able to sustain high gear as the engine will lug down. You might want to get a tach and take an actual measurement to be sure.

    Also you might want to verify the actual rear axle ratio. Not just guess at 3.55

    Lets look at the trade off;
    If you do make the change let's say you get 2 more miles to the gallon. Actually that is a big amount in the engineering world! About a 13% gain based on a rated MPG of 15 MPG.* If fuel costs you $2.50 a gallon and you drive 15,000 miles a year.
    In a year you will have bought 1000 gallons of fuel and paid $2500.
    At 17MPG driving the same distance and cost for fuel.
    In a year you will have bought 882.35 gallons of fuel and paid $2205.88

    The difference is $294.12
    If the rear axle change costs $500, (and you did the labor) your break even is somewhere in the second year. (However you are out some labor) If you have some one do it for you, expect double or triple the costs. Which pushes the break even point beyond year two or year three.

    So is it worth it? Or would you do this to have the experience?

    *BTW used vehicles rarely get the MPG that the vehicle got when new. Increasing fuel economy would be keeping tires pumped up and the vehicle well maintained. I stress well be cause the average car owner is lacking in some maintenance on their vehicles. One just has to view a few threads on this forum to see that. And ni the part of the country you are operating the fuel economy will be less just because the environment is NOT well suited for good economy.

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  5. Action

    Action Moderator Staff Member Respected Member

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    FYI

    https://www.fueleconomy.gov/feg/download.shtml

    >>>>>>>>>>>>Action
  6. Austin106

    Austin106 New Member

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    Thanks Action! I appreciate the insight. I will be putting a tach in my truck when I get the money.
  7. Austin106

    Austin106 New Member

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    Hey guys. So I never did change rear ended but I did get a new trans for my truck. Now I put the new one in. Go to put drive shaft on... but the output shaft is bigger than my original trans. I’m looking for a drive shaft so I’m hoping someone can tell where I need to measure my original drive shaft.. unless someone knows off the top of their head the length of it?? Would be greatly appreciated
  8. Action

    Action Moderator Staff Member Respected Member

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    You will need to have a drive line made for the truck.
    ZephyrEFI just had a drive line made in this thread.
    http://www.fordforumsonline.com/threads/zephyr-build.26041/page-2#post-176041
    You might message him to understand was is involved.

    Ford has a lot of combinations of drive lines for all of the power train options.

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