Differential or Transfer Case Ratio? (1 Viewer)

[Tonito]

Hello friendly people ,

i am considering to change the final drive ratio on my 1989 BJ70 (3B-II, H55F, FF LSD rear) to suit it better to the 33's i am running. It runs kind of okay with the 4.11 differential ratio without carrying anything, but we are planing a trip around the Balkans next october. With that comes some camping gear, probably a roof top tent etc. - a lot of weight for my little N/A shorty.
Next thing is the TÜV here in germany. Actually i run my cruiser illegaly with these large tires until an engineer aproves it. For that the overall ratio should be close to OE spec (205/80R16 with 4.11) and the speedo must run correctly.

On my search for 4.56 gears i stumbled upon the sumo gears kit to change the transfer case gearing.
They say the low range changes to 4:1 and the high range is also 10% lower. Using a gear ratio calculator the final gear with that 10% will be around 4.52:1. So both options would compensate for the 33's. Diff gearing is cheaper. Transfer case gearing gives the 4:1 crawl ratio.

The cruiser is just my weekend ride for mild wheeling in the dirt, the mud and fun in general (no rocks). The trip planed is my first "overland" thing.

Which option would you prefer?

thanks

 

[KennyBob]

I don't have any first hand knowledge, unfortunately. But, I have read here on mud in the 80 section that people have reported an increase of noise from some t-case gears. Sucks because I was seriously considering them in my '91 80 (less work). Hopefully someone will comment with real world experience.

 

[MyCruiserisaHogBeast]

My BJ74 is on 33s with factory gearing and I get around just fine, although I’m not heavy. We’ll see what happens when I load it up with a rack, roof top tent, bumpers, ect. I’m a huge fan of gearing and I find it acceptable right now.

I am actually in the process of getting a case ready to go in 4:1 gears and 10% reduction, but I’m going to 35s. For me this is the best compromise between highway gearing and crawl ratio. I have cable lockers and I’ve decided to just leave the diffs alone, just swapping in some 30 spline shafts.

I have heard that there is often noise associated with 4:1 gears. I have a bunch of Dynamat I’m going to plaster the hump and floors with at some point to minimize it, but in the end I’m not too concerned about it.

 

[Tonito]

Hm ... seems to be no topic of interest for most of the 70 owners!?

@MyCruiserisaHogBeast:
Maybe you can keep us informed about how quiet the gears are and if it is a suitable way to change the final gear ratio.

 

[JuanJ]

Hello,

70 Series' differentials can handle 33 inch tires rather well, even more so if they are skinny (pizza cutters.) Very few vehicles today can handle such tires from factory without modifications.

For peace of mind you can change gears to 4.56:1.

As for transfer gear ratio upgrade, aside from the noise it may reduce your top speed.

I would change axle gears to 4.56:1, install pizza cutters and leave the transfer case alone.





Juan

 

[MyCruiserisaHogBeast]

Hm ... seems to be no topic of interest for most of the 70 owners!?

@MyCruiserisaHogBeast:
Maybe you can keep us informed about how quiet the gears are and if it is a suitable way to change the final gear ratio.

I plan on it! I likely won't get to it until Spring but I'll definitely post. I need to do a build thread on this thing anyway...

 

[Tonito]

70 Series' differentials can handle 33 inch tires rather well, even more so if they are skinny (pizza cutters.) Very few vehicles today can handle such tires from factory without modifications.

For peace of mind you can change gears to 4.56:1.

As for transfer gear ratio upgrade, aside from the noise it may reduce your top speed.

I would change axle gears to 4.56:1, install pizza cutters and leave the transfer case alone.

My BJ70 runs okay with the 33s - actually they are 285/75R16s or 32.8" on 80s steelies - but I would like it to be more responsive to the throttle (without adding a turbo). There is some grunt missing on steeper sections on the highway (reminder: I live in Germany, you are kind of stuck in the right lane/behind a semi truck, if your car is not able to pick up some speed in a few seconds). Currently it is able to maintain a speed of 60mph/100kmh and go up to 120kmh/75mph on ground level and with a lot of run-up. If the road is getting steeper the speed may go down to 90kmh/55mph with no way of picking up more speed without shifting into 4th gear.

Have a look:


The tire size is another thing that bothers me. 33s are a must, it looks silly with 32s (had it on 235/85R16). I love 255/85R16s (had them a couple of years ago) or 33x10.5R15s pizza cutters. But there are way more tires to choose from in 285/75R16.

Using 4.56:1 diff gears or using the transfer case gears with 10% shorter/lower high range is more or less the same on the road (regarding the top speed). But the noise seems to be a thing bothering you all. So i may stick to changing the diff gear ratio to the 4.56s.

greetings

 

[SNLC]

Diff gears play a HUGE role in how a truck feels power wise.

4.56 and 4.88 are pretty common from the factory especially if equipped with a small engine (1PZ, 2LT, 3L). I had a LWB Prado with 4.88’s, a 3L and 31’s and it felt great power wise until you hit the top end and then it just has no more.

Many of these trucks were sent to countries where top speed across the country is 50-65mph. Also mountainous terrain in these said countries. In these places people never complain about power and there is no need for more. Like I say with the right diff gears suited for tour tire size and the low hp engines feel peppy but ya top end is done at 60-65mph.

Cheers

 

[hotgemini]

I run 255/85R16 KM3s (previously KM2s) on my BJ74 (h55f, 4.11, FF). Now obviously I've got the advantage of a turbo, but on the highway I find the gearing to be great, I think I'd find the higher RPM of 4.56 or 4.88 gears pretty tiresome on long distances.

I've also got Marks 4wd transfer case gears, they're 1:1 in high and 3.05:1 in low range (compared to 1.95:1 in low range standard), they're one of the best mods I've done to the truck for offroad capability, so much more control on steep rocky sections (up or downhill).

So my advice is, if it's at all practical, fit a turbo, but if you're into reasonably tough 4wding (particularly in steep stuff, not so much in mud/sand) then I'd go the transfer gear route rather than the diff gearing route.

 

[cruiserpilot]

Being non turbo is the thing here. Low range transfer case gears are really helpful
but for the small percentage of use not cost effective. Go for the differential 4.56:1
as it’s also changeable easily.
My personal recommend since you have over 9 months until October would be to look at
mounting a turbo on it. What are the regulations about that? 3B engines are really tough
and fitting the turbo will be a far better cost effective improvement to performance.

 

[MyCruiserisaHogBeast]

My first mod I recommend to anyone with a four wheel drive is tires+gearing if you're going away from factory. I can't stand an under geared vehicle. That being said I'm currently rolling around on 33s in my BJ74 with stock gears, and I have to say on the street and on dirt roads its really good! It does suffer on the rocks, Land Cruiser low range gearing is too high unless you're sticking with factory tires IMO. It's actually quite content on the highway and cruises at 70 all day long getting fuel economy in the low 20s.

As a previous poster said about his, I also have a turbo which helps immensely.

If you were my customer I would first ask you what your priorities are. Do you need to be able to get over any technical off roading in low range? How much do you value your off road capability vs highway? What's your goal cruising speed? After that, I'd bust out a drive ratio calculator (there are a bunch online) and plug in gearing and speeds and take a look at your RPMs. Being a diesel, it isn't happy at higher RPMs so that limits your options if you're going to keep it happy on the highway. If you were in a gas powered Cruiser I'd just say to go with 4.88s and plan on keeping the speed around 65mph max, but since you've got a diesel, chances are good you're going to be happiest with 4.56s.

As mentioned above, I wouldn't tinker with the T-Case unless you need it to be a low range crawler (something I would never steer you away from) but as it's been mentioned several times, the noise and invasiveness of the install makes it a better option for someone who really wants that additional low range heft.

Good luck!

 

[Tonito]

Well, thank you all for your advise!

I do not want to turn it into a race car. The 60mph range for cruising is fine - with the option to go up to 75 for a short period/overtaking the trucks on the autobahn. As mentioned above, i just miss some power when going uphill and maybe in speeding up in general (to keep up with the traffic).
Running 285/75R16s the RPMs at this speeds will be ...

4.11: 2145@60/2682@75 in 5th gear
4.56: 2380@60/2975@75 in 5th gear

Looks okay to me.

There will be no (or very, very, veeeryyy minor) rock crawling. It is just no big thing here in central europe. Most of the terrain here is woodlands with mud, sometimes a little sand or loose dirt and gravel roads.

As my conclusion out of this thread: Diff gears is the way to go and the best way to keep it simple/reliable/affordable.

I also purchased two oe cable lockers out of a 60 series (convertet to pneumatic actuators) two or three months ago, so i can prepare them with the 4.56 gears before even opening up the axles (just need the longer spline drive shafts).

My personal recommend since you have over 9 months until October would be to look at
mounting a turbo on it. What are the regulations about that? 3B engines are really tough
and fitting the turbo will be a far better cost effective improvement to performance.

I would love to go the turbo route. And you may be angry if i tell you that i already got one (almost brand new from a Volvo Penta 3,7l engine). I also got another rotary IP (3B-II engine) modified with a larger internals and a boost compensator. Both were happy coincidences and almost cost me nothing. The things that are missing: a stealthy front mounted intercooler (maybe from a jeep jk turbo diesel) and a good manifold (you can not rotate the 3B-II exhaust manifold), but I am not that good in fabricating (yet). Next thing is i measured the compression some time ago. It is not bad, but not great either.
Now there is the "regulations" part. The german TÜV has to approve mods like changing tire sizes or adding turbos to make them legal. It's not impossible but has to be well made and you have to consider things like better brakes too (or find a prove that your brakes are fine, because they are the same in turbo cruisers - actually i changed to 4Runner V6 calipers a while ago - which also has to be approved by itself).
So i want the cruiser in tip top shape, but it is not there yet. For a trip through seven or eight countries i want everything to be just fine - technically and legally - but there is way more to do - stuff like a drawer system, a fold out table, roof rack, fitting the air compressor and tank, fiddling with the electric system, checking everything, rebuild the knuckles (check the birfields and change to the long spline shaft), change the u-joints and rebalance the drive shafts, refurbish some suspension/steering/geometry things to make it less scary to drive (maybe my girlfriend will drive it then), etc. - a lot to do for a lazy guy like me

Again: thank you all very much!

 

[cruiseroutfit]

The good news about Split Transfer Cases as found in the 70 series, there are some great T-Case options now available that weren’t even just five years ago. Marks Gears have been around for many years but these newer gears are quieter and offer additional ratios too!

As you can see there are options for those that want to change high range and low range, as well as options for those that just want to change high range or low range.

 

[fireball]

Kurt,
I am running 35s on my bj74. I want to keep high range the same as it cruises nicely on the highway. Would you recommend the 3.3 or 4.0 low range?

 

[clintnz]

I got the Marks adapters 1.08 / 3.05 gear set a few years back, while the ratios are perfect for my setup they are fairly noisy. Not a big deal in low range or for a mainly offroad truck but it gets annoying on the highway. They've obviously had a few complaints as there is now a disclaimer about this on their website that wasn't there when I ordered mine

I've got 35-36" wheels & 4.1 diffs. The 3.05 low range is perfect for general 4wd, but if you've got much rock crawling in the mix you'd likely want to go lower.

Cheers
Clint

 

[cruiseroutfit]

Kurt,
I am running 35s on my bj74. I want to keep high range the same as it cruises nicely on the highway. Would you recommend the 3.3 or 4.0 low range?

Your only option is 3:1 if you want high range or remain exactly the same. Both the 3.3:1 and 4:1 both change your high range as well (see chart below).

If you can stomach the 8% under drive in high range, the 4:1 would be great paired with 35’s and a 13BT there needs some RPM’s to spin things.

 

[cruiseroutfit]

I got the Marks adapters 1.08 / 3.05 gear set a few years back, while the ratios are perfect for my setup they are fairly noisy. Not a big deal in low range or for a mainly offroad truck but it gets annoying on the highway. They've obviously had a few complaints as there is now a disclaimer about this on their website that wasn't there when I ordered mine

I've got 35-36" wheels & 4.1 diffs. The 3.05 low range is perfect for general 4wd, but if you've got much rock crawling in the mix you'd likely want to go lower.

Cheers
Clint

Just to be clear the Marks are different manufactures and design than the Sumo Japanese kits we offer. We’ve done many Marks over the years including into personal vehicles and they definite were known to have a bit of noise. Any reduction or cheat tooth overdrive/underdeive will have noise imo. Some more than others.