If the hf2av uses 3 gears to drive the output shaft in high range, how does the underdrive kit work? (1 Viewer)

[ThreeEyedBandit]

There is no debate, tooth count on gears directly relate to the ratio. You can't skip teeth.

It looks like they are slightly changing the gear pitch so the can fudge the tooth count from the input to output, all while keeping the pitch diameters close to factory so they still mesh 'properly'.

It is a 'properly' since they are messing with the pitches. And since they are helical that allows them to be quiet(ish) and still jive together(with the mismatch of pitch and PD).

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

 

[TNOverlander]

Interesting, I too have the underdrive high range Sumo gears from Kurt @cruiseroutfit , and I found that they are a little bit noisier (which I was expecting). Mine, however, get quieter as they increase in frequency the faster I go. I have to try a bit harder to hear them on the interstate over my mud tires.

I have factory gears in the differentials, and I don't know what others experiences have been on these axles, but on the Ford 9", I have had three different "professionals" install lower gears in that and all were noiser than than these T case gears. So, be sure to do your research if you decide to change up as you may end up back where you are with more money down the hole.

Of course, the real question is are there quieter and noisier sets transfer cases among different members or are we all just at a different tolerance given our expectations? Not knocking anyone, just saying I've had some loud rear diff gears in the past; so, I feel like my tcase is pretty quiet and others may have similar or opposite experiences.

Also, I agree, the reason I drive the 80 instead of the Jeep J10 I had previously was to enjoy the better street manners, etc. That and I had kids

Mud sensitivity...


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 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.

 

[slow95z]

i know i would see @rc51kid here after our talk yesterday

 

[LC4LIFE]

Well, I have a relatively quite rig with KO2's, and I have both UD and LR gears that I will be installing in the next couple of weeks. I will report back with my findings. Hoping I am not disappointed, but I figure if its noisy that's a good time to load in the sound deadening on the tunnel and floor, which I haven't done yet.

 

[HDJdreams]

I need to sit down with the modified idler and the high range and low range gear sets to verify which it was actually designed for. It simply can't be for both as they have different tooth counts.

@cruiseroutfit Any update as to whether the geometry of the idler was optimized for the underdrive gears or not?

 

[cruiseroutfit]

@cruiseroutfit Any update as to whether the geometry of the idler was optimized for the underdrive gears or not?

Sorry no, I've been in Peru for the Dakar Rally race. Just getting back in the mix here. I'll ne back in the shop today.

 

[HDJdreams]

Sorry no, I've been in Peru for the Dakar Rally race. Just getting back in the mix here. I'll ne back in the shop today.

That’s the most awesome excuse ever!

 

[cruiseroutfit]

That’s the most awesome excuse ever!

I figured it was a pretty good one

I'll be posting a trip report with a bunch of pics soon!

And I should have time to work with the gear this week after I dig out the snow and dig out the paperwork on my desk.

 

[HDJdreams]

@cruiseroutfit Any word on whether the geometry on the “modified” idler is any different than stock and if it was optimized for 1.1:1 gears?

 

[cruiseroutfit]

@cruiseroutfit Any word on whether the geometry on the “modified” idler is any different than stock and if it was optimized for 1.1:1 gears?

Nope, I've not had a chance/remembered to pull that stuff out and tinker when I'm in the shop. I've been traveling a fair bit which is ironically when I have more time outside of nights/weekends to browse Mud. As with all things Cruiser Outfitters, it's always best to reach out to us via Cruiser Outfitters ie. shoot over an email and I can work on it when I'm at the shop

 

[cruiseroutfit]

PS, since you are accepting of my excuses for being awol from the shop Here is my latest. Been rolling around with these Cruisers (and many more) this last week.

 

[cruiserdan]

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.

This reminded me of a very old, little known noise remedy.

Vehicles built prior to October 1993 had the transfer case shift lever housing hard-mounted to the top on the transmission (mine was one of them). The lever transmits more gear noise into the cabin. That housing was subsequently changed to one that incorporated busings between the lever housing and the transmission case. There was a service bulletin on that and I had mine updated with the new parts sometime in 1994 while it was still under warranty. It made a dramatic difference in gear noise transmitted into the cabin.

This could be why your 94 was quieter.

 

[cruiseroutfit]

This reminded me of a very old, little known noise remedy.

Vehicles built prior to October 1993 had the transfer case shift lever housing hard-mounted to the top on the transmission (mine was one of them). The lever transmits more gear noise into the cabin. That housing was subsequently changed to one that incorporated busings between the lever housing and the transmission case. There was a service bulletin on that and I had mine updated with the new parts sometime in 1994 while it was still under warranty. It made a dramatic difference in gear noise transmitted into the cabin.

This could be why your 94 was quieter.

Thanks for sharing that Dan. I'm going to see if I can find the TSB we discussed in TIS.

 

[cruiseroutfit]

Alright, I had a chance to come up for air today, my travel/training schedule has been crazy busy this spring and spring is crazy here in the shop too. I had a chance to pull down a factory VC variant 8x t-case (thanks @bryson) and do some side by side comparison of the stock 36221-60121 and modified 36221-60121 idler gear. They are in fact the exact same count (39 tooth) however the actual tooth design/shape is slightly different and the overall diameter is slightly smaller on the modified (5.825" vs 5.755"). We have sold several of the modified idlers but they had bearing surface and/or tooth damage on their existing gears so they replaced everything in the case with a new gear (if one were to do our high range gears, our low range gear and the modified idlers, you'd replace all 5 gears). What we still don't know is if the modified idler is better suited for overdrive, under-drive or even just stock gears. The donor case I have is missing an input shaft (had to ship out today for use in a 100 Series) but I have a handful en route and should have them in a few days. From there we can test fit with the UD and OD gears and check the pattern. @Delta VS is prepping to install a set of our high range underdrive gears (TCG9007UDHR) and is willing to test fit the idler in his setup and compare stock versus modified with the stock input gear and the UDHR input gear. He will likely get to it quicker than I can this time of year.

Keep in mind there are not any resellers of these high-range gears recommending use of the modified idler, it simply appears in some application guides as an option. The standard two-gear replacement that we offer has been available out of Japan and Australia for a decade or more from a few different vendors. I'd venture to say there are trucks out there with 100K+ miles on these sets without any reported issue outside of increased gear lash noise in some cases. As I've mentioned before, the noise isn't terribly surprising, we've been dealing with that on low range gears for the 4x/6x/7x for 25 years (Marks gears in a Split-Case for example), that said if there is a way to reduce the noise with the modified gear, of course we will offer that as a solution.

Stock 36221-60121 on left, new modified gear on right

 

[auttiman]

Are these gears that make more noise lower than stock? If so, what is the stock ratio vs the ratio of these?

 

[cruiseroutfit]

Are these gears that make more noise lower than stock? If so, what is the stock ratio vs the ratio of these?

Underdrive (lower) and overdrive (higher), noise is similar between the two.

Ratios can be seen here:

 

[auttiman]

Underdrive (lower) and overdrive (higher), noise is similar between the two.

Ratios can be seen here:

View attachment 1926320

So stock is 2.48:1 and these new gears would be as low as 3.3:1 ???

 

[cruiseroutfit]

So stock is 2.48:1 and these new gears would be as low as 3.3:1 ???

Correct. If you combine the TCG9007HRUD and the TCG900731, low range as indicated will result in 3.317:1. The chart is 100% accurate

 

[SteveL]

Since I am in the planning stages of a 6.2L Gen5 swap into my LX450 I am anxiously waiting on results of the new idler gear. I want to do the 9% overdrive to help out with the final drive ratio since I will have plenty of power available. I plan to keep Displacement on Demand and look to get good fuel mileage. Planning for limited off road, mostly on road use, quiet tires etc.

Anyone else use the OD gears on a V8 swap?

 

[richardlillard1]

Underdrive (lower) and overdrive (higher), noise is similar between the two.

Ratios can be seen here:

View attachment 1926320

Yeah, but what about tire size?