Knowledge needed
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Fleet Mechanic
Joined: Nov 2022
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How can I check my 91'?
Logistics Pro
Joined: Aug 2010
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From: Chillicothe
The 3.55s and 31s driving in 4th gear with my m5od got me the same mpg at 65 as it did in 5th at 65. It was a test I tried a few years ago to see if I would lose mpg going to 4.10s. The rpms in 4th at 65 with 3.55s is the almost identical rpms as 5th with 4.10s. This is because as you give the truck a better mechanical advantage with better gears, the engine has to work less to keep it moving. So even though your rpms are a little higher, your manifold vacuum is higher because the load on the engine is lower.
Thread Starter
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Fleet Mechanic
Joined: Nov 2022
Posts: 1,697
Likes: 416
How much highway driving do you do? And how fast? Ill give you a fun fact.
The 3.55s and 31s driving in 4th gear with my m5od got me the same mpg at 65 as it did in 5th at 65. It was a test I tried a few years ago to see if I would lose mpg going to 4.10s. The rpms in 4th at 65 with 3.55s is the almost identical rpms as 5th with 4.10s. This is because as you give the truck a better mechanical advantage with better gears, the engine has to work less to keep it moving. So even though your rpms are a little higher, your manifold vacuum is higher because the load on the engine is lower.
The 3.55s and 31s driving in 4th gear with my m5od got me the same mpg at 65 as it did in 5th at 65. It was a test I tried a few years ago to see if I would lose mpg going to 4.10s. The rpms in 4th at 65 with 3.55s is the almost identical rpms as 5th with 4.10s. This is because as you give the truck a better mechanical advantage with better gears, the engine has to work less to keep it moving. So even though your rpms are a little higher, your manifold vacuum is higher because the load on the engine is lower.
I've never done gears before, but it can't be too hard, maybe I'll have to throw some 4.10s in there this summer, any good brands? Nothing ridiculously expensive.
Lead Driver
Joined: May 2011
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Hmm that sounds actually pretty good for me, I do mostly town driving, some highway, but also plenty of inner woods driving, don't plan on freeway too much, if at all.
I've never done gears before, but it can't be too hard, maybe I'll have to throw some 4.10s in there this summer, any good brands? Nothing ridiculously expensive.
I've never done gears before, but it can't be too hard, maybe I'll have to throw some 4.10s in there this summer, any good brands? Nothing ridiculously expensive.
Lead Driver
Joined: Jun 2021
Posts: 5,221
Likes: 805
jokes aside, 3.55 - 4.10 is my vote
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Logistics Pro
Joined: Aug 2010
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From: Chillicothe
I would watch some videos on how to set it up. Also check junkyards and marketplace for whole rearends. If you could score a rear that already has a 4.10 it is as easy as rolling the old assembly out and the new used one back in place.
Hotshot
Joined: Sep 2001
Posts: 11,958
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Whatever you get DO NOT get a body lift. That is janky junk. Bumpers don't line up, fan shroud doesn't line up, shifter linkage and brake lines etc may not be long enough.
I would suggest a leveling kit or just leveling coils and 32 11.50s. Then 4.10 minimum gearing with a 5.0.
It is not easy to find a rear end with better than 3.55 because 4.10 was only offered in F150s for the Lightning and the F250 F350 trucks.
If it is a daily then just keep it with 31 10.50s. Best solution.
Setting up a rear gear set is not something the average shade tree mechanic can do. But if you research how to do it, you may decide that it is something you want to do I did mine and it wasn't too bad.
I would suggest a leveling kit or just leveling coils and 32 11.50s. Then 4.10 minimum gearing with a 5.0.
It is not easy to find a rear end with better than 3.55 because 4.10 was only offered in F150s for the Lightning and the F250 F350 trucks.
If it is a daily then just keep it with 31 10.50s. Best solution.
Setting up a rear gear set is not something the average shade tree mechanic can do. But if you research how to do it, you may decide that it is something you want to do I did mine and it wasn't too bad.
Logistics Pro
Joined: Aug 2010
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From: Chillicothe
Well while they are not super common, saying the only f150s to get 4.10s were Lightnings is wrong. Car-part website shows a f150 front diffs with 4 09 gears. Which is the correct ratio for a 4.10 rear. Hell I even had one at one point but didn't swap it in as a friend needed it for his daily that was a factory 4.10 truck.
Lead Driver
Joined: Jun 2021
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Well while they are not super common, saying the only f150s to get 4.10s were Lightnings is wrong. Car-part website shows a f150 front diffs with 4 09 gears. Which is the correct ratio for a 4.10 rear. Hell I even had one at one point but didn't swap it in as a friend needed it for his daily that was a factory 4.10 truck.
Logistics Pro
Joined: Aug 2010
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From: Chillicothe
I'm either putting a 3.08 ( already have ready to swap)in my nova to replace the 3.73 or trading the th350 for a 200-4r( need to find) so I can cruise at 70 and not be screaming.
Lead Driver
Joined: May 2011
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Ever heard of a "laycock OD"? It's a gear vendor before gear vendor was gear vendor. Manual trans volvos in the 80s had them from the factory....reason i bring it up; I've found them in junkyards over the years, and have gotten them for anywhere from 80 - cost of a jy trans. Might be worth shopping around for one, all parts for them can still be bought from gear vendor, they're basically identical.
