Cruiser Gearing

[racingjason]

Hello all,

I have been contimplating changing the grearing in my HJ61 and I am looking for opinions. While most people seem to head to lower gears for wheeling, I am looking at moving from 4.11's to 3.70's. The truck has the H55 manual gearbox with 31x10.5 tires. (30.7" dia). My plan is to switch up to 235/85's when we take it overseas in a few years (32" dia). The change of tires results in a 4% decrease in RPM and the gear change adds a furthur 10%. Now, I do tow a trailer and thus far it pulls it quite happily even in the mountains. That being said, my RPM on the highway is 2500 and driving it faster than 60 seems to be pushing the 12HT diesel a little harder than I would like. Is a 10-14% increase in gearing too drastic? I am somewhat limited on choices as I need to keep the trailer and truck tires the same.

Cheers.

 

[eric1115]

I have an H55 and 3.70 gears, and have run 235/85's, and it works very well. I'm at a little over 2k rpm at 60mph, and 2500 at 75mph. The 2F doesn't have the grunt that a 12ht does, so if my gasser can do it I'm sure your diesel can too. I've not done much towing with it, but towing with these gears was not all that pleasant. Again, motor makes all the difference in the world on that. I'm planning to go 4.11 when I go up in tire size from here (my current 265/75/16 is same diameter as my old 236/85/16) to a 255/85/16, but plenty happy with my current setup.

 

[1911]

I have an FJ60 with (stock) 3.70 gears and an H55F and running 31" tires, and it runs great. The lower 1st gear in the H55 offsets the larger tires when starting out, and once you get moving the rubber overdrive in combination with the H55 5th gear works great on the highway. When these tires wear out, I'm going to go to 33" (but I don't tow anything with mine).

 

[racingjason]

Thanks for the opinions guys, I think I will give it a try. I will always have the 4.11's on the shelf should I decide to change back later.

 

[RMP&O]

Where does "overseas" mean?

In most countries the speed limit is much lower then up here in N. America. Most of Central America it is 60 to 80ks per hour, maximum.

 

[lowenbrau]

Hello all,

I have been contimplating changing the grearing in my HJ61 and I am looking for opinions. While most people seem to head to lower gears for wheeling, I am looking at moving from 4.11's to 3.70's. The truck has the H55 manual gearbox with 31x10.5 tires. (30.7" dia). My plan is to switch up to 235/85's when we take it overseas in a few years (32" dia). The change of tires results in a 4% decrease in RPM and the gear change adds a furthur 10%. Now, I do tow a trailer and thus far it pulls it quite happily even in the mountains. That being said, my RPM on the highway is 2500 and driving it faster than 60 seems to be pushing the 12HT diesel a little harder than I would like. Is a 10-14% increase in gearing too drastic? I am somewhat limited on choices as I need to keep the trailer and truck tires the same.

Cheers.

Did you change out the gears to 4.11:1 already? JDM HJ61s with manual transmission usually have 3.7:1 in the diffs from the factory.

For what it's worth, your perception that you are overworking your engine is incorrect. Toyota diesels don't mind the revs. They run them at the rev limiter for 10,000 hours in the mines. If nothing else changes I guarantee your EGTs will go up with the gear change. I think the change is reasonable for driving comfort and fuel mileage though even though it may mean hotter pistons. You could always increase the boost a bit to bring the pyro needle back. Downshifting early on the hills while towing works as well.

 

[racingjason]

Where does "overseas" mean?

In most countries the speed limit is much lower then up here in N. America. Most of Central America it is 60 to 80ks per hour, maximum.

Plan is presently Cape to London however, if things don't settle down in Northern Africa in the next little while we may be looking at South America. In many cases it will be about road conditions rather than posted limits. However, having driven the length of the US twice in the past couple years and thinking about doing it again to go to OvEx this year, I am considering a more highway friendly gear.

Lowenbru, I am pretty sure that they are factory. I was told they were 3.70's when I bought it but when I put a pair of ARB's in a few years ago I found out that they were 4.11's. The speedo is close as well) I understand what you are saying about the engines though ( As a mining engineer I have been in many a HZJ winding its way up a decline) but I have found that the fuel efficiency goes down significantly when the RPM'S get too high; so rather than saying overworked I should say operating past the point of optimal efficiency.