Help determine my HJ61 gearing and advise on re-gear options

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TLink FJ60

TLink FJ60

10 Year
Joined
May 1, 2012
Threads
18
Messages
115
Location
Nashville, TN
I bought my 1989 HJ61 (12H-T/H55F) about a year ago thinking it would have 3.73 or 4.11 gearing. I get on trails occasionally, but mainly I'm driving to backcountry camping destinations. So I want highway cruising to be reasonable on fuel mileage and engine wear. I noticed right away it revs higher than my US FJ60 (which has 3.73 gears), so I assumed I had 4.11 gearing. It wasn't until being frustrated with the revs and slow speed on a recent 500 mile road trip that I decided to try and figure out what gearing I actually have. I'm running 265/75R16 BFG ATKO > according to manufacturer they have 31.6" diameter. In 4th gear trying to keep the tach in at 2000rpm I'm going about 41mph according to GPS. Please check my math...

41 mph > (41 * 5280)/60 = 3608 ft/min
31.6" dia tires > Tire circumference = (31.6 * 3.14)/12 = 8.27 ft.
Tire revs = 3608/8.27 = 436.35 rpm

Gear Ratio = engine-rpm / tire-rpm > 2000 / 436.35 = 4.58

Conclusion: I have 4.56 gears.

1. Please let me know if you agree or disagree with my assessment. There is certainly room for error in my method: tire diameter compression under vehicle weight, accuracy of reading tach, bad math, other factors? If I have 4.56 gears, does that mean a PO swapped them? I'm not aware 4.56 was ever stock in a 60 series. The HJ61 was imported from Japan in December 2014.

2. Should I re-gear and to what ratio (3.73)? How do I go about it. It might be worth mentioning that it is a right-hand-drive, so finding a swap could be difficult (I actually don't know how different RHD axles are). I'm in Tennessee.
 
How about bigger tyres?

Another way of determining what gears you've got is to jack up a rear tire and count how many revs the driveshaft spins with one rev of the wheel.

AFAIK, 4:56 was never offered by Toyota.

The attached chart is referenced at 65 mph.

image.webp
 
Last edited:
Thanks. Nice table. I don't think I want to wind my engine high enough to get 65mph in 4th gear.

If I'm running 41mph at 2000rpm, that's equivalent to 65mph at 3170 [ (65/41)*2000=3170 ]. My tires are between 31 & 32. The column in which 3170 falls in between 31" & 32" tires is 4.56. That seems consistent with my above calculations.

Good idea on the counting drive shaft revs for 1 tire rev. I'll try that when the sun is shining.

I know many folks would mitigate with bigger tires. I prefer the look and height of mine and like the fuel saving benefits of turning lighter tires.
 
It might have aftermarket gears .. if that the case 4.56 it's way to hi for what you are doing and tires you have .. so yes 3.73 would make more sense in your application ..

Even tho if you go to 3.73 your 12H-T ( if healthy and assuming yes ) have enough to move 33" with no problems .. giving you better HW speed vs rpm operative range..
 
Support rear axle on jack stands. Both sides, put a chalk mark on both tires and the ground, put another chalk mark on the drive shaft flange and one on the diff. Rotate both rear tires together while counting drive shaft revolutions. If it goes around 4.5 times = 4.56 4.1 times = 4.10 3.75 times = 3.73 ect...

You can use chalk on your tire (and a level or plumb bob) to find the exact distance traveled for 1 tire rotation to do the math accurately.

There are many charts and calculators on Google.

FJ60 had 3.73 FJ62 had 4.10 either should fit as well as 80 series ect... I have 3.73 in my FJ60 1HZ-T

H55F gear ratios as follows;

First 4.843:1

Second 2.619:1

Third 1.516:1

Fourth 1:1

Fifth 0.845:1

Reverse 4.8
 
BJ60, HJ60 and HJ61 w/5 spd w/stock diff gear = 3.70 ring/pinion ratio
 
Not always 3.73, some came 4.11 stock. You can confirm the ratio by rotating the driveshaft/tire, but the ratio is also in the axle code on the firewall data plate.
 
Contrasting tire and axle rotations seems like the most accurate measure so I did that. Basically for 1 tire rotation I get just over 4 axle rotations...so that means I have 4.10 (or 4.11 ?) gears - not 4.56. Apparently reading the tach and assuming actual travel distance relative to tire height has some amount of error - not too surprised there.

So I have 4.10 or 4.11 gears. How hard is it to re-gear to 3.70? I know squat about the inside of the axle. Is that job something I should for sure have a shop do for me? Or should I just wait until I can find someone who wants to swap? If I use a shop - do they need to have specific TLC experience or is any shop with general 4x4 experience gonna be okay? Thanks.
 
SteveJackson said:
Not always 3.73, some came 4.11 stock. You can confirm the ratio by rotating the driveshaft/tire, but the ratio is also in the axle code on the firewall data plate.
Click to expand...

Firewall Data plate says K082. I think that means 9" 4.11 from a quick search I did.
 
David*BJ70 said:
If all H55F and t-case gear ratio are all the same, what is the stock tire size for an HJ61 with stock 4.11 ring/pinion ratio ?

Is your 265/75R16 + GPS match your speedometer ?
Click to expand...

Speedometer and GPS are really close with the 265/75R16s. I'm gonna check it again tonight when I go out. I don't know what the stock size is, but it must be close to what I have.
 
I think you're either going to be geared too tall or too short with those tires with 3:70 or 4:10.

The only way to get out of that hell is to get bigger tires with the gears you've got or 245s or 30" tires with 3:70s.

265s are an awkward size.

I'm driving 31s with a H55F and 3:70 gears and I think it's geared too tall. 265s are virtually the same size as 31s.
 
... well probably the speedometer driven gear in the t-casse are different from 3.70 to 4.11 ring/pinion ratio ...
 
Output Shaft said:
I think you're either going to be geared too tall or too short with those tires with 3:70 or 4:10.

The only way to get out of that hell is to get bigger tires with the gears you've got or 245s or 30" tires with 3:70s.

265s are an awkward size.

I'm driving 31s with a H55F and 3:70 gears and I think it's geared too tall. 265s are virtually the same size as 31s.
Click to expand...

Output Shaft, do you think 3.70 will be too tall even with a 12HT diesel? I have an FJ60 (owned for 18 years) with 31x10.50s, H55F, and stock 3.73 - and it really does just fine. The 12HT is stronger than the 2F. Seems like I'll do well with 31+" tires.
 
My BJ74 is H55/4.11 with 285/75/16 (33 inch) tires. A real 65 mph is around 2,500 rpm in 5th.

A JDM HJ61 stock should be 4.11.
 
TLink FJ60 said:
Output Shaft, do you think 3.70 will be too tall even with a 12HT diesel?
Click to expand...

Well since you are familiar/happy with a FJ60 w 3:70 gears, H55F and 31" tires, and you know the torque range of the 12HT, It seems like that would be a good choice.

Hey!
I just thought of something....

Why not just swap out the FJ60 3rd member (rear only) into your HJ61 and go for a test drive. See how you like it.
You could swap it easily. No big deal. You could swap it out, test drive and swap it back in a weekend. So no downtime if one of them is your dd.

That's what I would do.

If you decide to do that, report back here. I'm sure a lot of guys would be curious how it drives.
 
If the 61 is cable-locked it would be a bit more challenging.
 
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