4.10 or 4.56 or in between

[stegomon]

Running a 2.9 with 31s. And an fm146 with 3.73s . In low rang i can not crawl like i want to. I keep stalling out on the more rocky ,hilly trails. Also my truck is a turd in the lower rpm on the road. I think i should regear. But i am not sure what gears I want to use. But i do know I don't want to spend all out doors. Any ideas?

 

[adsm08]

I think a 4.10 ratio will get you back to being close to the factory final drive. Not sure what ratio you can find between 4.10 and 4.56 for a 7.5. I know they had 4.27s in the 8.8s in the early 80s.

 

[Surrey]

For gears we need to know which axles you have, not what tranny...

If you've got an 87, then stock axles woulda been a d28 front/7.5" rear.
If this is the case, you can find 4.10 gears out of a similar-year Ranger or B2 in a junkyard. There seems to be a smaller number of ratios used in these trucks.

If you have a 8.8" rear or d35 front, they are both harder to find 4.10 gears in but no impossible. There just seems to be more ratios available, and the higher ones like 3.27 are much more common than the 4.10s

 

[bobbywalter]

2.9 tired? 373 and 31 usually get along good with manual.

if its that tired 456 gears or a 4.0.

 

[bobbywalter]

410 seem too deep with the 4.0 on the hiway but ok off road with 33-36 in tires in my b2...same 146 trans

 

[Lil-Pony]

Doubler with 4.10s?

 

[PlumCrazy]

4.0, Geared down M5OD, Doubler, 4.10s works flawlessly on 35s for me.

I imagine just a doubler, with 3.73s and 31s would be close to the same overall ratio.

FYI, tranny does make difference...

The OP actually has a lower 1st than both RBV M5OD gearsets.

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[adsm08]

The OP actually has a lower 1st than both RBV M5OD gearsets.

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Barely. We are talking 3.77 vs 3.72. You would have to have rear end gears like that mountain mover dump trucks to notice that difference.

 

[straycat]

MY 2wd 4.0 runs a 4.10 and I run 33x12.5x15 BFG KO tires. Great power and great gas milage. Mines has an automatic trans. Yours should do well with the 4.10 gear with a smaller motor. Ask your 4x4 shop about it. Are you doing the install or having a shop do it?

 

[swynx]

If I remember right the math equation is. Whatever size tire you wanna run multiplied by.12... So (33x.12=3.96) seems to get within ball park for an ok ride. Had an 87 with a 210k 2.9 fm146 and 31s. Floored in 4th it would barely do 80.

my 3.0 1987 Nissan had 4.33s and i never ever used 4 low and first. Could ghost ride the thing on 31s was a great combo for overall performance imo 23 mpg in town

 

[swynx]

After screwing around on the calculator I found that tire size multiplied by .13 gives a ratio closer to what ppl prefer like 3.73 and 29s, 4.10 and 31s, 4.33 and 33s, 4.56 and 35s, 4.88 and 37...

 

[PlumCrazy]

We are running 4.10s on the B2 with a M5OD (4.0 ratios) and 31s, low enough for trails and hill climbs, but its 4.0.

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[Surrey]

I used to run 31s with 3.45 gears and it had no problems keeping speed on the highways.

 

[swynx]

4.0s low end torque is awesome.

 

[swynx]

That 2.9 I had died after only 2 days. Long story short 200$ turned into siezed engine. I'm assuming that had to do with power loss lol