80 Series Underdrive high range gears and 3:1 low range gears

OTRAMM

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Got to install both sets of transfer case gears on an 80 series a few weeks ago. The 3:1 low range gears I'd done before the under drive high range gears were a new one. The 10% under drive was nice for offsetting larger tires on the highway and the 3:1 gave it some nice low end.
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MTKID

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Would that high range gear also fit the 98’ case as well? Did it require modifying the case? Are you offering the set yet, yourself? Q’s, q’s, q’s!
 

OTRAMM

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I'm not sure if it will work in a 98 case. I'll do some checking. The high range gears didn't require any case mods. I get the gears through Cruiser Brothers. I'm one of their resellers/installers.
 

MTKID

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Good info. Thanks! I’m eager to see if some has done this in a 100 yet.
 

GW Nugget

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If you have the 3 to 1 gears along with the 10% underdrive gears does that compound together in low? What is the final drive?
 

OTRAMM

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They don't compound. It's one or the other. Final drive depends on axle ratio and transmission ratio as well.
 

GW Nugget

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Well maybe the word compound is used incorrectly be me?
In this thread that I've read since posting this question I have learned the 10% UD does effect the 3to1 gears.
It changes it from a 3.1 to a 3.3 final.
You're spot on, with any change to the high-range ratio, you are proportionally changing the low range ratio as well.
Final T-Case Gearing Chart with different options, whipped this up quick so feel free to check my math.
View attachment 1613583
Gear Chart pic.JPG
 
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OTRAMM

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Hmm, maybe. The way the shift hub works I always thought it was either, or. I've never actually counted the output revolutions to see though.
 

HDJdreams

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The 1.1 gears for “high” range affects both high and low range by changing the input ratio from the motor. Only possible because of the offset of both driveshafts. Land Rover transfercases used to come from factory with 1.2 and 1.4 input gears. It effectively does the same thing as changing axle gears. @cruiseroutfit has a thread on these that explains in detail.

I have 1.1 with “34s” (285/75R17). I was shocked at how noisy they are. (Turns out the gear cutter cheated by only providing 2 of the 3 gears).

I had my transfer case rebuilt and both 1.1 and 3.1 gears installed. The 1.1 gears are definitely audible above 30 mph, mine get louder with speed. Since I have to travel on 75-80 mph (actual speed limit) Interstate to go anywhere, the gear noise REALLY bothers me. I compare the the noise to mud tires but higher pitch and next to the driver so it’s more intrusive.

I have another FZJ80 also on 34s (34x10.5R17) and stock transfercase. So every few days I get a reminder of the baseline. There is definite noise and honesty I don’t notice a difference going up hills and all around driving. 1.1 just doesn’t really make a difference. I wish I would have kept the stock high range gears and saved up for 4.88 instead.

If you don’t mind mud tires on the highway, the gears likely won’t bother you.
 

MTKID

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The 1.1 gears for “high” range affects both high and low range by changing the input ratio from the motor. Only possible because of the offset of both driveshafts. Land Rover transfercases used to come from factory with 1.2 and 1.4 input gears. It effectively does the same thing as changing axle gears. @cruiseroutfit has a thread on these that explains in detail.

I have 1.1 with “34s” (285/75R17). I was shocked at how noisy they are. (Turns out the gear cutter cheated by only providing 2 of the 3 gears).

I had my transfer case rebuilt and both 1.1 and 3.1 gears installed. The 1.1 gears are definitely audible above 30 mph, mine get louder with speed. Since I have to travel on 75-80 mph (actual speed limit) Interstate to go anywhere, the gear noise REALLY bothers me. I compare the the noise to mud tires but higher pitch and next to the driver so it’s more intrusive.

I have another FZJ80 also on 34s (34x10.5R17) and stock transfercase. So every few days I get a reminder of the baseline. There is definite noise and honesty I don’t notice a difference going up hills and all around driving. 1.1 just doesn’t really make a difference. I wish I would have kept the stock high range gears and saved up for 4.88 instead.

If you don’t mind mud tires on the highway, the gears likely won’t bother you.
What would something like this do for these gears? Would this service have any effect on noise or just longevity & heat? Pricing says $150-$350 which seems reasonable to me if it actually reduces noise by even a small amount.

 

OTRAMM

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What would something like this do for these gears? Would this service have any effect on noise or just longevity & heat? Pricing says $150-$350 which seems reasonable to me if it actually reduces noise by even a small amount.


In this case I don't think that it would help. The issue is that you're running a new gear against a used gear. The mesh patterns aren't going to be quite the same and that's where you'l get the noise.
 
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I ordered them through Cruiser Brothers. They know the what fits what😁
@OTRAMM are those terrain tamer boxes in the first picture the high range underdrive? I can call them and order them but I need to give them the correct part numbers

I assume the sumo gear box is the low range reduction gears as well?
 

OTRAMM

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I don't remember which was which. They'll know what you need and get you all set up.
 

Road Apple

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OTRAMM...how are you liking the gears offroad and highway?

Did you replace 1 or 2 gears for the 1.1 overdrive? How is your noise level at highway speeds?

If you had it to do over again, would you re-gear the diffs and skip the 1.1 overdrive gears?
 

OTRAMM

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This was on a customer's truck not mine. I didn't notice any noise over the mud terrains on the highway but I have heard reports of noise from them. This is the route I'm planning to go on my 80 when I get around to hearing.
 
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