1980 F150 gear question

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Jun 14, 2015 | 02:36 AM

Troy_455

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1980 F150 gear question

Hey guys I finally got this truck on the highway today. I couldn't believe how high rpms I had to be at for highway speed. For estimating about 65mph, speedo isn't currently working just keeping up with traffic, it was over 3k. The axle code is 14 so it should be 3.00 gears and I have a c6 trans. I'm thinking maybe my grandpa (PO) may have changed the gears since he towed all over the country. Just wondering what other people are seeing for highway rpms.

Jun 14, 2015 | 06:13 AM

Ken Blythen

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From: New Zealand

Quote:

Originally Posted by Troy_455

I'm thinking maybe my grandpa (PO) may have changed the gears since he towed all over the country.

You haven't mentioned your tires, but assuming 28", & allowing a bit for C6 converter slippage, you would be at about 2600 rpm with 3.00 gearing; 3.54 gears would put you just over 3000.

Depending on how heavy his loads were, he may well have regeared. What is your engine?

Jun 14, 2015 | 12:31 PM

Troy_455

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The tires are 235/75/15 so 28.9 inches. I'm thinking he must have regeared. Anyone know how big of tires can fit under these trucks at factory height?

Jun 14, 2015 | 03:30 PM

Franklin2

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Quote:

Originally Posted by Troy_455

The tires are 235/75/15 so 28.9 inches. I'm thinking he must have regeared. Anyone know how big of tires can fit under these trucks at factory height?

If you have stock rims and 4x4, 31x10.5x15 will fit with a little rubbing on the radius arm at full lock in the parking lot, and a little bit of rubbing in the rear with a full load of wood on it when you hit a bump.

Aftermarket rims will stop the rubbing in the front.