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

[nukegoat]

Since you have 3 gears in a row like oOo then it would seem you have to replace all 3, right? Or does the old idler shaft gear just mesh kinda poorly with the new high range output and input?

 

[nukegoat]

@cruiseroutfit

 

[iptman]

@OTRAMM did a couple videos on installing both high under drive and lower gears. I'm sure he hit somewhere in these.

 

[nukegoat]

I watched part 1. I dont really get how one can replace only the input gear and the output gear and get a different ratio while leaving the idler the same. Seems like you would have to be fudging something to use a different tooth count on the input.

 

[mct75]

With 3 gears, changing the size of two of them would have to move the shaft in the middle closer to the smaller gear, yes?

 

[nukegoat]

With 3 gears, changing the size of two of them would have to move the shaft in the middle closer to the smaller gear, yes?

No. Thats my point. With a smaller effective diameter for the input gear, the location where meshing occurs should be translated. You should make the idler gear bigger in diameter to do so.

 

[mct75]

How does the ratio change if the two gears are the same size then?

 

[ThreeEyedBandit]

By changing the third gear if it isn't the idler gear.

How does the ratio change if the two gears are the same size then?

I'm curious what they are doing here. Possibly changing the gear pitch slightly so the can mess with the tooth count while keeping my the pitch diameter usable?

Curiosity has been peaked with this, definitely fudging is happening.

When I have mine apart guess I'll do some math to see what I can come up with

 

[wv_lx450]

i wondered the same while i was putting mine together but completely forgot to compare the sizes of the new and old. they definitely mesh together with no noticeable space when putting it back together and theres no slack or play at all when spinning the input or output shaft.

 

[Shoredreamer]

Regearing a case right now for a friend. Underdrive gears are same size as stock within 1/8”. They work damn well too!

 

[nukegoat]

So it looks like they are just trying to fudge a different tooth count. I have to imagine this doesnt result in an ideal mesh.

 

[iptman]

By the looks of the picture above the teeth are narrower on the Sumo gears (assuming those are on the right) than the OEM.

 

[cruiseroutfit]

By changing the number of gears by a couple teeth, you accomplish the ratio changes. All the teeth count can be seen at the bottom of the first post here:
YWST: Low Range T-Case Gear Sets for the 1980-2007 Cruisers

 

[nukegoat]

Also given

By changing the number of gears by a couple teeth, you accomplish the ration changes. All the teeth count can be seen at the bottom of the first post here:
YWST: Low Range T-Case Gear Sets for the 1980-2007 Cruisers

Yeah but teeth shape/pitch are a function of a gear pairing - unless youre just messing within the tolerance envelope of a given design you cant just willy nilly change tooth counts on one gear but not the other.

 

[cruiseroutfit]

Also given

Yeah but teeth shape/pitch are a function of a gear pairing - unless youre just messing within the tolerance envelope of a given design you cant just willy nilly change tooth counts on one gear but not the other.

Correct, as you can see from the chart they only move 2/3 gear tooth counts. These gears have now been on the market for a decade+ so the longevity and noise concerns are fairly well documented. As I mentioned we do have a modified idler assembly, it's traditionally recommended when the stock setup has extensive wear or gear noise is untolerable? The manufacture doesn't specify when it should/shouldn't be used. To date we've sold just a few of that idler assembly and I'm still sorting through the exact benefit and application (see discussion in thread I linked)

 

[iptman]

So there is a different idler gear available that would mesh up better and make less gear noise?

 

[HDJdreams]

So there is a different idler gear available that would mesh up better and make less gear noise?

X2

 

[cruiseroutfit]

So there is a different idler gear available that would mesh up better and make less gear noise?

In the event their is noise or an improper mesh. We now have the modified idler. I have not personally installed or tested so I'm still reluctant to make claims on them just yet.

Anyone want a gear set and a modified idler setup?

 

[cruiseroutfit]

Fwiw, pics I took of the modified gear:
Transfer case re-gearing

 

[cruiseroutfit]

Fwiw again, the modified idler with our TCG900731 & TCG9007UDHR
Transfer case re-gearing