Gear Ratio - to change or not to change

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AF Road

AF Road

10 Year
Joined
Aug 26, 2012
Threads
56
Messages
175
Location
Baguio City
Hi fellas, got a 1971 FJ40 which was upgraded to the following:
1. Its now got a 2B diesel Engine from a 1981 BJ40
2. A 4speed tranny also from the same 1981 BJ40
3. 2-3" lift
4. 33" tires

Stock Gear Ratio is the 4:11. Was thinking of changing this. One supplier suggested a 4:88 as an upgrade also since my engine is a non turbo. Another was saying to make it lower i.e. a 3.7 ratio for faster speeds on the highway.

I generally use it in town where the roads are hilly so currently is does struggle to get up a not so steep hill on 2nd so will always have to stick on 1st with the engine noise blaring. I seldom hit the highway but when I do, its usually a 270km drive to another city which now takes 5-6hrs instead of the usual 4 hrs using a modern car.

Not sure which direction to go and wanted to know if any of you have made the change to either one and what were your comments or regrets if any.


Thanks in advance fellas. Pretty much torn between the two suggestions.

AL
 
It all depends on what you really want. If you are running any non-turbo B engine, you're probably not going to want to go higher (3.7 gears), as that will make it even harder for you to climb hills. If you switch to 4.88, you'll have less trouble with hills, but you're 270km drive will take even longer. Sounds to me like you need either a.) more power b.) to decide what you want most to do with your 40 and then make it suitable for that task.

On the other hand, is there a happy medium where it can be highway friendly in high range, but off-road friendly in low-range? I don't know the answer to this yet.
 
JungleBiker said:
It all depends on what you really want. If you are running any non-turbo B engine, you're probably not going to want to go higher (3.7 gears), as that will make it even harder for you to climb hills. If you switch to 4.88, you'll have less trouble with hills, but you're 270km drive will take even longer. Sounds to me like you need either a.) more power b.) to decide what you want most to do with your 40 and then make it suitable for that task.

On the other hand, is there a happy medium where it can be highway friendly in high range, but off-road friendly in low-range? I don't know the answer to this yet.
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Thanks junglebiker. Given the situation, would you just keep it stock at 4.11 or go for the 4.88? Thing is I already bought the kit for the 4.88 change. I can sell it anyway if I keep the 4.11 but tempted to try it out. Is it worth changing? Will the inclined roads (onroad) be that much easier to go on if I went with the 4.88's? What other advantages will there be? Will cabin noise increase with the 4.88's (I guess would be another important factor to consider) ?
 
Sorry I can't help you more AF Road, I haven't started thinking about changing gear ratios in any of my 4x4's yet. My inclination would be to go for more power, though, especially as the 2B only had 93hp to begin with. A turbo kit for a 2B might do nicely for you.
 
The difference of 4:88 to 4:11 is roughly 16%

A comparable 16% decrease in tire diameter, from a 33" tire is a 27.7" tire.

If you put 28" tires on your cruiser with 4:11 gears, that's the same gearing you'll have with 4:88s and 33s (if I did my math right).

Basically you'll be running 500 rpm higher in 4th gear at the same road speed.

That's pretty extreme.

image.webp
 
Output Shaft said:
The difference of 4:88 to 4:11 is roughly 16%

A comparable 16% decrease in tire diameter, from a 33" tire is a 27.7" tire.

If you put 28" tires on your cruiser with 4:11 gears, that's the same gearing you'll have with 4:88s and 33s (if I did my math right).

Basically you'll be running 500 rpm higher in 4th gear at the same road speed.

That's pretty extreme.

View attachment 1213258
Click to expand...


Wasn't the Stock Tire size of an FJ40 28 inches? So 4.56-4.88 ratio with 33" would bring it back more or less to stock performance right?
 
Output Shaft said:
The difference of 4:88 to 4:11 is roughly 16%

A comparable 16% decrease in tire diameter, from a 33" tire is a 27.7" tire.

If you put 28" tires on your cruiser with 4:11 gears, that's the same gearing you'll have with 4:88s and 33s (if I did my math right).

Basically you'll be running 500 rpm higher in 4th gear at the same road speed.

That's pretty extreme.

View attachment 1213258
Click to expand...
Hello, so if I'm reading this right I should put a 3.73 in my 1981 FJ 43 for better highway speeds? I believe I currently have 4.11 gearing. I have 31 inch tires now. I was thinking of swapping up to a 5 speed, but if this solution will ease my rpm's down a little this would be great. Thanks
 
Search the internet for an rpm calculator and compare the various setups you're considering. You'll need to find what the 5th gear reduction is for the h55. Your 4th gear usually is 1:1. Be sure to actually measure your tires. They're typically smaller than advertised. The stk ratio is 3.70, not 3.73.
 
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bernardbar3 said:
Hello, so if I'm reading this right I should put a 3.73 in my 1981 FJ 43 for better highway speeds? I believe I currently have 4.11 gearing. I have 31 inch tires now. I was thinking of swapping up to a 5 speed, but if this solution will ease my rpm's down a little this would be great. Thanks
Click to expand...

Where is your Cruiser from, and what transmission do you currently have? 3.70 diff gears were stock in U.S. market 40's for your year, so you must have a 'foreign" market 40, or someone has swapped the diff gears before now.

At any rate, I have (stock for my year and market) 3.70 diffs in mine. With 33" tires, I can do 65 mph quite comfortably at about 2450 rpm. I like them. I'm also running an H41 transmission, which gives me a lower 1st gear.
 
Without reading all the posts will simply ask are finding yourself down shifting because the gear you in is out of torque rate and slowing down. In that case I would lower your diff gears. Depending on as it is there is middle gear between 4.10:1 and 4.88:1. That is the 4.56:1 which is rarely mentioned.
 
1911 said:
Where is your Cruiser from, and what transmission do you currently have? 3.70 diff gears were stock in U.S. market 40's for your year, so you must have a 'foreign" market 40, or someone has swapped the diff gears before now.

At any rate, I have (stock for my year and market) 3.70 diffs in mine. With 33" tires, I can do 65 mph quite comfortably at about 2450 rpm. I like them. I'm also running an H41 transmission, which gives me a lower 1st gear.
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Hola Amigo, I'm here in Bogota Colombia. Thanks for the great info. I have 265/65/17 with FJC 17 inch rims (not sure if this is a 31 or 32) I'm a new guy to FJ40 series trucks, and not sure what gears I'm running. I'm assuming it's an H41. On a shake down I was cruising about 100 km's comfortably, but up hills I had to downshift. My thoughts are to get a 5 speed H55F or add a header for more performance. Or do both? I'll be importing this truck when I return to Florida in a few months. Thanks

IMG_1265.webp


IMG_4893.webp
 
bernardbar3 said:
Hola Amigo, I'm here in Bogota Colombia. Thanks for the great info. I have 265/65/17 with FJC 17 inch rims (not sure if this is a 31 or 32) I'm a new guy to FJ40 series trucks, and not sure what gears I'm running. I'm assuming it's an H41. On a shake down I was cruising about 100 km's comfortably, but up hills I had to downshift. My thoughts are to get a 5 speed H55F or add a header for more performance. Or do both? I'll be importing this truck when I return to Florida in a few months. Thanks
Click to expand...

Buenos dias,

I guessed from your avatar photo that you might be in central or south America. Looks like a nice truck; I would love to have a 43 myself.

The good news, is that with the H41, you can go with either larger tires or 3.70 diffs and you will still have a low enough 1st gear to get going easily. Taller tires are definitely cheaper than a new transmission. With a modest lift you can fit 33" tires; with a 4" lift (or trimming the rear quarters - not recommended) you could probably fit 35" tires. Larger tires have the effect raising the final gearing for all transmission gears, but again with the H41 that wouldn't be much of a problem.

The cost of swapping in 3.70 diffs is probably going to be in between new tires and an H55, depending on if you can do the work yourself or not. Like with taller tires, the higher-geared diffs will affect all of the transmission gears.

The cost of installing an H55 will be the highest of the three options. If your 1981 has the factory hand brake on the rear axle instead of the transfer case (not sure for the SA market) then it would relatively simple, though there are some wrinkles such as the shifter cane being moved back (because the new H55's still being sold only come with the FJ60 top cover/plate).

Good luck with your changes and importation in any event.
 
1911 said:
Buenos dias,

I guessed from your avatar photo that you might be in central or south America. Looks like a nice truck; I would love to have a 43 myself.

The good news, is that with the H41, you can go with either larger tires or 3.70 diffs and you will still have a low enough 1st gear to get going easily. Taller tires are definitely cheaper than a new transmission. With a modest lift you can fit 33" tires; with a 4" lift (or trimming the rear quarters - not recommended) you could probably fit 35" tires. Larger tires have the effect raising the final gearing for all transmission gears, but again with the H41 that wouldn't be much of a problem.

The cost of swapping in 3.70 diffs is probably going to be in between new tires and an H55, depending on if you can do the work yourself or not. Like with taller tires, the higher-geared diffs will affect all of the transmission gears.

The cost of installing an H55 will be the highest of the three options. If your 1981 has the factory hand brake on the rear axle instead of the transfer case (not sure for the SA market) then it would relatively simple, though there are some wrinkles such as the shifter cane being moved back (because the new H55's still being sold only come with the FJ60 top cover/plate).

Good luck with your changes and importation in any event.
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Thank you Sir. Great response and now I know what direction in which I need to proceed. I'll go with the taller tires (33's) and a 3.70 diff. My FJ43 does have the factory hand brake on the rear axle.

I bought the truck last Feb and had the fiberglass top removed. I had a shop fabricate an all steel top and rear doors. Then, I had the truck taken apart, repaired, replaced rusty areas, then painted. I've been slowly making progress and it's coming along.

I certainly drank the kool-aid, lol. For me it's a keeper.

I'll keep you posted and thanks.
Bernard.

IMG_0426.webp
 
1911 said:
Where is your Cruiser from, and what transmission do you currently have? 3.70 diff gears were stock in U.S. market 40's for your year, so you must have a 'foreign" market 40, or someone has swapped the diff gears before now.

At any rate, I have (stock for my year and market) 3.70 diffs in mine. With 33" tires, I can do 65 mph quite comfortably at about 2450 rpm. I like them. I'm also running an H41 transmission, which gives me a lower 1st gear.
Click to expand...
Great timing on this thread, as I’m having similar thoughts myself. After a long hiatus, I’m back with a new to me South American 1982 FJ43 (H41, 3.70 diffs, stock 2F). Still sitting on my project 1971 FJ40 as well.

IMG_0100.webp


Re: the 43: I’ve spent some time searching, and running the numbers with a trans/gear calculator, and I’m tempted to swap in some freshly rebuilt 4.10 axles I already have instead of messing around with these leaking, unknown history, clearly bad brakes and drum brake front axles.

With the H41, 4.10 gears and 235/85-16 tires I’ll be right at 2820 rpm @ 65mph. Serviceable for sure, though higher than the 2510 rpm I’d have with 3.70s.

That said, I do have a H55 sitting in deep storage, which would drop rpms substantially, to around 2400 @ 65mph and 2580 @ 70mph all in 5th gear.

Am I silly for swapping out the 3.70 axles? Is there some factor I haven’t considered? It all seems super clear to me: swap to the 4.10s, it’ll drive fine and down the road that H55 will give me back the lower rpms and then some. The only sacrifice seems to be crawl ratio, if I abandon the H41.

I really just want to use the brand new axles I have readily available, and be on the road faster. @1911, your rig seems similar, am I thinking about this right?

 
mdsims said:
Great timing on this thread, as I’m having similar thoughts myself. After a long hiatus, I’m back with a new to me South American 1982 FJ43 (H41, 3.70 diffs, stock 2F). Still sitting on my project 1971 FJ40 as well.

View attachment 3632207

Re: the 43: I’ve spent some time searching, and running the numbers with a trans/gear calculator, and I’m tempted to swap in some freshly rebuilt 4.10 axles I already have instead of messing around with these leaking, unknown history, clearly bad brakes and drum brake front axles.

With the H41, 4.10 gears and 235/85-16 tires I’ll be right at 2820 rpm @ 65mph. Serviceable for sure, though higher than the 2510 rpm I’d have with 3.70s.

That said, I do have a H55 sitting in deep storage, which would drop rpms substantially, to around 2400 @ 65mph and 2580 @ 70mph all in 5th gear.

Am I silly for swapping out the 3.70 axles? Is there some factor I haven’t considered? It all seems super clear to me: swap to the 4.10s, it’ll drive fine and down the road that H55 will give me back the lower rpms and then some. The only sacrifice seems to be crawl ratio, if I abandon the H41.

I really just want to use the brand new axles I have readily available, and be on the road faster. @1911, your rig seems similar, am I thinking about this right?

Click to expand...

Congrats on the 43; I love that mid-wheel base.

You're ahead of the game by using that gear ratio calculator - it's the same one I use. I like it, because it has most Toyota transmissions already in the database as choices in the drop-down menus, and even has a "Toyota 4.0 conversion" menu choice that works for Orion transfer cases.

I would say your axle/differential gear choices would ideally be driven by what you want to do with this truck - if you're going to drive it much on the highway, the 3.70 diffs are really nice to have. If it's mostly going to be a trail rig, then the lower-geared options would be better.

The only thing I would point out in your transmission selection is that the H55 also has a pretty low 1st gear at 4.84:1, almost as low as the H41 1st which is 5.30:1, so you wouldn't be giving up much crawl ratio to go that way. To use the H55, you're going to have to re-do your parking brake, but you probably already knew that. If you can get a U.S. market late 40 rear axle, it will have the parking brake built in to the axle, but it will still be 3.70 gears.

I built mine (3.70 axles, H41, Orion transfer, and 33" tires) as a compromise that I can both drive it all day on the highway to get to good trail areas, then still have a capable trail rig when I get there. As I mentioned earlier, 65 mph at 2450 rpm for my truck is very comfortable, and 75 mph is easily doable if needed.
But I get your other considerations as well. I have disc brakes on all four wheels and consider that to be a significant upgrade for daily driving also. It's great that parts for these old trucks are still available enough to give you many options.

All best wishes for your modifications in any event. It's a beautiful truck.
 
Thanks. In many ways, I got lucky with this one: late 82 build so I have the transmission cross-member, split case, hand brake and rear parking brake axle, power steering. The 5 speed swap will be a breeze.

I’d be kidding myself if I didn’t acknowledge most of my driving will be paved roads and visits to jobsites. But leaning toward swapping in the 4.10 axles anyway. These are well built, powder coated housings, FJ62 front brakes and pumpkins, all new hardware and Beale lines. Can always swap in FJ60 differentials later I suppose.

I’ll have to dig into the front end a bit more after life settles down in the next month or so.
 
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