Gear ratio

[judaspriest75]

So I just found out that my rear end is going out in my 1984 f150 with a 300 i6 4.9L and I'm going to change out the whole rear end axle and everything and I was wondering what the highest gear ratio I could put in it. For good gas mileage purposes only, well that and I'm tired of going 5 mph in first gear.

[RhinoZ24]

You can go as high as you want that'll fit in the differential housing. For good mileage however, I would stay anywhere from 3.15-3.31, 3.55 at the most. What size is the rear end?

[judaspriest75]

Honestly I don't know I think somewhere around 4:10

[termi]

I've always thought 3:73's were a good mpg/acceleration trade off in my opinion .I don't think you have 4:10's, if its stock at least

[judaspriest75]

I don't think it's stock. And it's pretty low gears

[RhinoZ24]

I meant size of the rear end, sorry lol. As in my '05 has 3.55's but the size of the rear end is 8.8"

[termi]

I don't think it's stock. And it's pretty low gears

Oh, well if it is 4:10's, a swap to 3:73s might be what your looking for. Go too high and you'll hate it cuz you'll have like zero acceleration lol

[judaspriest75]

Would 3:50, 3:00, or 2:75 word and if so, what would be the highest ratio?

[RhinoZ24]

Are you replacing the whole axle or just the gears?

[judaspriest75]

I might just go ahead and replace the whole axle maybe but it's whatever I would be able to do in the next 5 months Till I enlist in the army

[RhinoZ24]

Gears would be faster and cheaper, as long as the rest of the axle is in good condition. In that case you can fit almost any gear in to it as long as its from a similar model year. It depends on the size of the rear end to, not just the ratio. For instance my '05 has a 3.55 gear ratio and the size is 8.8", they also offered a 9" rear end during the same year. Find out the size of your rear end and that'll help you figure out what ratio you can fit in there.

[judaspriest75]

I believe it is 9" but I'll probably double check tomorrow but what would be higher, the 2:75, 3:00, or 3:50?

[RhinoZ24]

The higher the number, the higher the ratio and the more power (torque) you'll get. The lower the number though, and the less power but more MPG's you'll get.

[judaspriest75]

Oh lol. Gear ratio is the only thing that confuses me all the time

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So if I have a lower gear ratio would I be able to go faster or is it if I have a higher gear ratio?

[RhinoZ24]

It's all good, and it's kind of a middle ground thing. Too high of a gear ratio and you'll have a lot of torque but be putting extra strain on the engine to get up to speed, slowing you down basically. Too low of a ratio and you won't have enough torque to get you up and going fast enough. You gotta find the happy medium.

[termi]

The higher the number, the higher the ratio and the more power (torque) you'll get. The lower the number though, and the less power but more MPG's you'll get.

Your right and all, but aint it the higher the number the lower the gear and vice versa?

[RhinoZ24]

Idk, its kinda confusing lol. But the higher the gear ratio number, the more teeth the bigger gear has compared to the smaller gear. At the moment the technical names for these gears elude me lol.

[5.0Flareside]

If you don't know which rear end it is look. If there is a bolt on cover on the rear, its a 8.8" if not 9". Both were available those years if I'm not mistaken

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Idk, its kinda confusing lol. But the higher the gear ratio number, the more teeth the bigger gear has compared to the smaller gear. At the moment the technical names for these gears elude me lol.

Ring and pinion

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[RhinoZ24]

If you don't know which rear end it is look. If there is a bolt on cover on the rear, its a 8.8" if not 9". Both were available those years if I'm not mistaken

Sent from my Droid Maxx on Tapatalk

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Ring and pinion

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There we go, I almost said rack and pinion lol. I knew that didn't sound right because that's for power steering.