Another 62 gearing question

[Rockrawler]

I have just spent a lot of time reading through searches, but MOST of what I found was for guys running 60's with manual trannys. I'm specifically looking for info on gearing the FJ62 with gas motor and auto tranny with a 33" BFG AT. It seems like a 4.56 would be the obvious choice but want verification from those running my combo before I plunk down the ducketts for gears and required labor. I will then be selling the 4.10's

SO: FJ62/Autotrans/33" BFG's = 4.56 or 4.88?

 

[CSA]

I HATED 33s and 4.10s on my 62. I went with 4.56s, which, as you already know, bring you to about as close to stock gearing as you are going to get. 4.88s would be much too low for a daily driven rig.

 

[Rockrawler]

good to know, do the 4.56's make it feel like a little more or little less power? I have 31's right now & it feels kinda like a dog off the line & uphills suck badly unless I take it out of overdrive & then its just marginal. I need to do a valve adjustment next & set the timing, sure that will help a bit too.

 

[CSA]

A lot of what you describe is general 62 dogishness. It's heavy rig with only about 150 hp on its best day. The 4.56s definitely helped in the around town power department and on hills. On the highway, I wish it was geared a smidge taller. The 4.10s and 33s were sweet on the highway (once the rig was up to speed).

 

[Moody]

I run 4.88's and 33x10.50 bfg's. I went to the 4.88's because I knew that I eventually wanted to go up to 35's. I am happy with it, but it wasn't as big of a help as I had anticipated...still pretty slow overall, but there was a difference. I can still go 75 on the freeway(TOP speed) and it does okay, RPM's are ~2700

-Roger

 

[Rockrawler]

I'll never go 35's, if I went bigger I'd SOA and go 37's, but eventually want to go to a 4BT someday also

 

[overhanger]

I HATED 33s and 4.10s on my 62. I went with 4.56s, which, as you already know, bring you to about as close to stock gearing as you are going to get. 4.88s would be much too low for a daily driven rig.

I run 4.88s with 33s for the road and find them to be perfectly satisfactory. 70 mph at 2500 rpm which, I think, is damn close to stock tires with the stock 4.11 diffs. 4.10 is what later 80s had.

 

[CSA]

I run 4.88s with 33s for the road and find them to be perfectly satisfactory. 70 mph at 2500 rpm which, I think, is damn close to stock tires with the stock 4.11 diffs. 4.10 is what later 80s had.

Some folks might enjoy 4.88 gears and 33" tires, but my main point is that 4.56 gears are as close to stock gearing as one is going to get running 33" tires and significantly closer to stock gearing than 4.88 gears. 62s came equipped with 235/75R15 tires, which are approximately 29" inches in diameter. 33x10.50 BFG AT TAs are approximately 32.7" when new. Thus, 33s are approximately 12% taller than the 235/75R15s. Whereas 4.56 gears are approximately 10% lower than 4.11 gears, 4.88 gears are approximately 16% lower than 4.11 gears. Thus, 4.56 gears do, in fact, bring the truck closer to stock gearing with 33s than 4.88 gears.

 

[Rockrawler]

But is keeping it closer to stock when its a boat anchor to begin with a good thing? Wouldnt overgearing a tad be beneficial for a loaded rig (4 people+gear or groceries) if there's only 4% difference from stock?

 

[overhanger]

Speaking of facts, my speedometer and odometer are both dead on correct with the 33s and 4.88s. 4% difference, as Rockcrawler notes, isn't really that great of a difference.

 

[jefferson-mo]

Hey Rock keep me in mind when you sell the old gears...........I'm gonna want 4.11s

Thanks



back to our regularly scheduled program...........

 

[meluhha]

Hey Rock keep me in mind when you sell the old gears...........I'm gonna want 4.11s...

I think I beat you to it...

Matt

 

[Moby]

Going from a 28" tire to a 33" tire is about an 18% change. Unless I've done my math wrong 4.88 gearing with 33s will put you as close to stock as you can get. Going from a 28" tire to a 31" tire is about an 11% change. 4.56s will therefore get you as close to stock as you can get with 31s.

I run 4.56s with 31s and am very happy. Power doesn't change when you change your gear ratios - the RPM band that the engine is operating in for the same speed changes. On the highway with the lockup clutch in on the converter my RPMs were too low between 55 and 70. Getting the engine back into it's stock rpm range between 55 and 70 helped my truck a lot.

 

[overhanger]

Moby, you are correct about the 28" stock tire size rather than CSA's 29" figure. CSA, rerun your calcs based on the original 225/75/15 28" tire height and see what the figures tell you.
Moby, you also have impeccable taste in dogs, if that is your Golden in the avatar.

 

[overhanger]

CSA, do you have an FSM or the little owners manual that came with the truck? Original stock tire size is listed as 225/75/15 in either of those manuals. A 28" tall tire.

62s came with 235/75R15s, which are approximately 29" in diameter. A BFG AT KO in that size is exactly 29" in diameter, according to BFG. A 31x10.5x15 AT KO is 30.7" inches in diameter, according to BFG. The difference between a 29" tire and a 30.7" tire is aproximately 6%. While it is true that 4.56 gears (approximately 10% lower than 4.11 gears) get you closer to stock gearing with 31s than 4.11 gears, 4.56 gears with 33s get you much closer.

 

[CSA]

CSA, do you have an FSM or the little owners manual that came with the truck? Original stock tire size is listed as 225/75/15 in either of those manuals. A 28" tall tire.

I have both and I also checked the VIN tag. You guys are correct. The stock size is 225/75R15. When I ran my initial calcs, was using BFG's website to get the tire specs. BFG spec'd a 235/75R15 for a 62, which is incorrect.

 

[Rockrawler]

Hey Rock keep me in mind when you sell the old gears...........I'm gonna want 4.11s

Thanks



back to our regularly scheduled program...........

Yeah, you got beat on the gears... now I gotta refuse the 4.56's and find some 4.88's - shoulda waited! Before I do does anyone want a smokin deal on the one of the last sets of Precision 4.56's in the country? I'll sell them at my cost...

 

[Jan-78FJ40]

I think this really depends on how the truck is used.
On the 60 (turbo diesel with 5 speed) I have I run 33s, and the 4.11s are too high for my taste, so I'll put 3.73s in. This truck is mostly used for long distance expedition type travel, and with the 4.11s it just revs too high on the highway.

I think that 33s and 4.88s will be extremely low geared, certainly appropriate for rock crawling, but terrible for highway travel.
j

 

[Rockrawler]

I disagree - with a gas motor underpowered vehicle, it should be ideal

I think this really depends on how the truck is used.
On the 60 (turbo diesel with 5 speed) I have I run 33s, and the 4.11s are too high for my taste, so I'll put 3.73s in. This truck is mostly used for long distance expedition type travel, and with the 4.11s it just revs too high on the highway.

I think that 33s and 4.88s will be extremely low geared, certainly appropriate for rock crawling, but terrible for highway travel.
j

 

[jefferson-mo]

I think I beat you to it...

Matt

GIT-R-DONE


That's cool.......I wanted to get complete axles anyway and refurb them and do an easy axle swap.......