If the hf2av uses 3 gears to drive the output shaft in high range, how does the underdrive kit work? (2 Viewers)

[rc51kid]

Back in town and catching up here gents. I still don't have a resolute answer on when to use the aftermarket idler assembly. What we do know is the gears themselves can have a bit of additional noise, levels seem to vary based on age of install and perhaps additional factors such as tires, roof racks, etc. I've heard from at least two that have the idler gear/shaft and didn't notice any difference in noise or more appropriately they still have a bit of noise. Hardly scientific I know I still need to have a minute to dig through the gears and determine if this is ideal for the under-drive or the over-drive sets, it simply can't be ideal for both any more than the stock gears work for both. I pinged a friend overseas that has been selling/using these overdrive/underdrive gears in builds for more than a decade, he wasn't even aware there was an aftermarket idler gear outside of stock applications.

More pics of the gears fwiw (still coated with cosmoline

View attachment 1874082

View attachment 1874083

I might be interested in trying this out. I am planning to do transfer case rebuild with gears this spring. I have a set of marlin low range gears already. I will be getting a spare case. I just emailed you guys a few days ago about price and availability of lower high range gears. My email is dana@aplace4us.com. You guys just emailed back yesterday i think. My plan is to rebuild the case with all new OEM parts form Onur. Can you send me a price on this gear also?

 

[rc51kid]

Lower low range gears only..

I could be wrong...i am a lot according to my wife. But i think the issue being discussed here is with the lower high range gear.

 

[Shoredreamer]

But, in true Mud form, this thread implies a problem or deficiency where none has been documented other than some alleged noise that has only been reported by a few.

Per my experience, with these low range gears from Japan, not China, noise levels are actually lower than before. I used a transfer case from my wrecked 94 that was always quieter than the one that was in my 93 (similar miles) when I bought it.

A good sound deadening material and new insulation, which many do anyway, including myself, should be enough to block any extra decibels perceived by delicate ears.

Opinions and empirical data is all over the chart so, is there an actual problem, or is Mud just bored? Not once has anyone, including my wife who has ridden on long road trips with me in my 80 with these gears, ever commented “what’s that noise”?

In fact, recently a co-worker and I drove my rig 2000 mostly all highway miles and he was astonished at how quiet it was with 37” trXus Mud terrains.

I have my proverbial bucket of popcorn ready to see where this one goes.

The noise most people are talking about on the thread are with the high range underdrive and/or overdrive case gears, not the low range gears. The low range 3:1 HF2A gears DO actually change the gear diameters in the case corresponding with the change in tooth count. The Underdrive and Overdrive modified case gears change tooth count but DON’T change diameter. I actually have a bigger change in gear noise in my low range gears though after my regear not my underdrive gears, so riddle me this!
Stock lowgears above
3:1 TG gears below

stock high gears right
Sumo UD gears left

 

[Shoredreamer]

Also found a cool video that seems like it pertains directly to the topic of gear mesh, cutting and shape, but it’s way over my head in comprehension. Enjoy

 

[baldilocks]

I could be wrong...i am a lot according to my wife. But i think the issue being discussed here is with the lower high range gear.

Yes, you win. But mud sensitivity is on the rise nonetheless. The ole salty dogs are fewer and fewer and web wheeling is becoming an actual pastime. I’m assuming those who say these gears are too noisy never drove a wide open fj40 with mud tires down the highway all day in 100 degree heat in order to get to the mountain and on the trail.

After market R&P sets usually make more noise than oem sets too. I know mine do. Should I call Just Differentisls and demand a resolution?

 

[baldilocks]

The noise most people are talking about on the thread are with the high range underdrive and/or overdrive case gears, not the low range gears. The low range 3:1 HF2A gears DO actually change the gear diameters in the case corresponding with the change in tooth count. The Underdrive and Overdrive modified case gears change tooth count but DON’T change diameter. I actually have a bigger change in gear noise in my low range gears though after my regear not my underdrive gears, so riddle me this!
Stock lowgears above
3:1 TG gears belowView attachment 1875264stock high gears right
Sumo UD gears leftView attachment 1875265

Have you ever run a vehicle that has an NP208 T-case? It uses planetary gears for the low range reduction and you talk about noisy. It is what it is but people are no longer what they was.

 

[DanMedeiros]

i would argue that @Shoredreamer wheels more than 98% of the posters on MUD FWIW. So cut him some slack AND... he is building this case for me!

 

[Shoredreamer]

i would argue that @Shoredreamer wheels more than 98% of the posters on MUD FWIW. So cut him some slack AND... he is building this case for me!

Haha! Slow down there Dan, plus you should be sweet talkin’ @cruiseroutfit to get that idler gear not me

 

[Shoredreamer]

Have you ever run a vehicle that has an NP208 T-case? It uses planetary gears for the low range reduction and you talk about noisy. It is what it is but people are no longer what they was.

Have not. But my god, I do have screaming kids in the truck most of the time so hearing some beefy gear noises from below is music to my ears!

 

[rc51kid]

It sounds to me like there is two aspects to this discussion. One is about the possible noise from the gears. The other question is about how do we get a gearing change from a gear that is the same diameter but with more teeth. Can anyone that has installed these verify with engine rpm and a GPS that there is a 10% difference in speed?

 

[HDJdreams]

But mud sensitivity is on the rise nonetheless. The ole salty dogs are fewer and fewer and web wheeling is becoming an actual pastime. I’m assuming those who say these gears are too noisy never drove a wide open fj40 with mud tires down the highway all day in 100 degree heat in order to get to the mountain and on the trail.

After market R&P sets usually make more noise than oem sets too. I know mine do. Should I call Just Differentisls and demand a resolution?

Mud sensitivity...

I HAVE the underdrive high range gears in my rig. I am considering pulling them out because my rig will spend far more time at 65-80 mph than crawling.

If didn’t care about the highway experience, I would ditch 80 series and go back to full size Jeeps, it’s tough and primative like the FJ40, and had a way better power to weight ratio than my 80 and way easier to work on and mod. I gave my 78 Cherokee Chief to my brother when I bought my 80 18 years ago. The few times we wheeled together, the Cherokee would sail through places where the 80 sunk in mud or snow, although the 80 rode way better.

My point is I hope that Mud doesn’t devolve into fiery clashes about off road styles, but focuses on data points based on experience so prospective buyers can make informed choices.

Over the years, I have made some good purchases based Mud recommendations and some that I really regretted.

I am trying to share my experience in a constructive manner.

Before I bought the gears, I read that they were a little noisier but posters generally said they didn’t notice it.

My experience: the 1:1.1s are on par with a set of mud tires on the highway, but higher pitched and get louder with speed. They are definitely noticeable even with mud tires because of the higher frequency and the source being right next to the driver.

Had it been explained to me that way, I might have reconsidered and saved up for 4.88 axle gears.

My point is if a prospective buyer is not a fan of mud tires make on the freeway, it’s likely they won’t like the 1.1s. If they could care less about the noise, then it’s an awesome low cost alternative to regearing axles.

 

[cody c]

It sounds to me like there is two aspects to this discussion. One is about the possible noise from the gears. The other question is about how do we get a gearing change from a gear that is the same diameter but with more teeth. Can anyone that has installed these verify with engine rpm and a GPS that there is a 10% difference in speed?

You should be able to verify by just counting teeth on the gears for the two sets.

Edit: they are in the pictures above they are 9.677% reduction

33 to 33 tooth factory 1:1
31 to 34 aftermarket 1:1.09677

 

[Shoredreamer]

It sounds to me like there is two aspects to this discussion. One is about the possible noise from the gears. The other question is about how do we get a gearing change from a gear that is the same diameter but with more teeth. Can anyone that has installed these verify with engine rpm and a GPS that there is a 10% difference in speed?

If you use the UD gears your actual speed vs registered speed won’t change. It will increase your rpms roughly 10% relative to your speed.

 

[DanMedeiros]

I’m not too worried about the noise. My truck is loud as hell already with a massive RTT and awning sitting on top. I compensated by deleting the actors amp and installing g a big sub, that and lots of knock off dynamat.

I drive in the mountains constantly and need better gearing while rolling on 35s over 7k lbs yet am too cheap to get my diffs regeared

 

[DanMedeiros]

Plus lower low range would be rad. After driving my buddies diesel 70 I am very jealous of his gearing/ engine braking when descending and rocking up on boulders

 

[DanMedeiros]

Yes, you win. But mud sensitivity is on the rise nonetheless. The ole salty dogs are fewer and fewer and web wheeling is becoming an actual pastime. I’m assuming those who say these gears are too noisy never drove a wide open fj40 with mud tires down the highway all day in 100 degree heat in order to get to the mountain and on the trail.

After market R&P sets usually make more noise than oem sets too. I know mine do. Should I call Just Differentisls and demand a resolution?

I hear you about driving a 40 in the highway. I used to drive a 40 on 37s with a Chevy v8. It was like being in a small airplane. All passengers needed a headset and intercom

 

[Willy beamin]

I'm adding the under drive high range gears to my t-case. for those that noise is bothering, have you tried to insulate the sound / deaden it? From a financial standpoint that's less impact on the wallet, especially if you like the performance gains.

 

[nukegoat]

If you use the UD gears your actual speed vs registered speed won’t change. It will increase your rpms roughly 10% relative to your speed.

Right - only downstream gearing of the t case changes that

 

[HDJdreams]

I'm adding the under drive high range gears to my t-case. for those that noise is bothering, have you tried to insulate the sound / deaden it? From a financial standpoint that's less impact on the wallet, especially if you like the performance gains.

Not yet, I have other things to sort out first. We’ll see if the turbo whine (@NLXTACY) drowns it out. (That’s a happier noise )

 

[rc51kid]

You should be able to verify by just counting teeth on the gears for the two sets.

Edit: they are in the pictures above they are 9.677% reduction

33 to 33 tooth factory 1:1
31 to 34 aftermarket 1:1.09677

89

I think that is kind of what is up for debate. Normallywith two gears that have the same tooth profile and shape the number of teeth would directly relate to the diameter of the gear. But that is not really the case here. The teath are different sizes. So I am just trying to see how that all works out. I would figure the diameter of the gears is what really matters at the end of the day. But I don't really know