HF2A Sumo overdrive/underdrive transfer gears not adding up? (1 Viewer)

[paz12ht]

Posted this over in the 80 section but thought I'd add it here as well since the gears are also available for the 100/105 (I've fitted them to a 105)-

Anyone else installed a set of Sumo overdrive (not underdrive) gears to their transfer case and have seen some real world results (as in like for like setup only difference being the gears), exactly how many RPM did you drop at 60mph/100kmh and what is your drive train setup (auto, manual, diff ratio etc so i can do the math)?

I've fitted a set to mine and honestly i don't think they've made much difference, claims are allegedly 9-10% overdrive from stock 1:1 gears which should equal to around 200rpm drop at 60mph/100kph with my stock 4.3 diffs and 5 speed H151F but i think I'm lucky to have dropped 50rpm?

Also interested in the underdrive versions if fitted and if they've added up and done as claimed as well?

 

[JunkCrzr89]

@cruiseroutfit

 

[cruiseroutfit]

Assuming you fitted the overdrive gears, you simply can't have not gotten the RPM reduction. Tooth count and ratio are exact science, there isn't any room for variance.

The overdrive gears will net you exactly 8.8% OD

Math here:

 

[paz12ht]

Assuming you fitted the overdrive gears, you simply can't have not gotten the RPM reduction. Tooth count and ratio are exact science, there isn't any room for variance.

The overdrive gears will net you exactly 8.8% OD

Math here:

..................

@cruiseroutfit

Hi Kurt, thanks for your reply.

Yes i did fit the Sumo overdrive transfer gears to my HF2A (though to be clear to everyone not sourced from you) and no unfortunately they have not given me the RPM reduction as you mention (tested using GPS for speed and running checks between dash tacho and hand held lazer on harmonic balancer to confirm dash is reading accurately etc).

Again yes totally agree with your math as per your table (is actually what swayed me to search for and purchase the gears here in Australia) but only if we're talking all gears with full teeth of the exact same size (which then in turn will affect each total gear overall diameter when adding or subtracting teeth)!

The way the Sumo gears are designed so as to retain virtually the exact same size gear diameter as stock (required so as the factory idler can be retain which is in between the two supplied Sumo gears) but to fudge the tooth shape etc to add 1x tooth and subtract 2x teeth (so as they will mesh) unfortunately cannot (and will not) ever make a difference to the actual overall ratio you end up with these gears when actually driven (as all gears are still near physically the exact same size diameter as stock gears!).

Unfortunately i will admit i went into these gears a bit green as I'd never had a HF2A apart before, yes i should have done some more research and actually sat down and thought about it some more but anyway, guess it's lesson learnt (albeit an expensive one).

Regards.

 

[JunkCrzr89]

The way the Sumo gears are designed so as to retain virtually the exact same size gear diameter as stock (required so as the factory idler can be retain which is in between the two supplied Sumo gears) but to fudge the tooth shape etc to add 1x tooth and subtract 2x teeth (so as they will mesh) unfortunately cannot (and will not) ever make a difference to the actual overall ratio you end up with these gears when actually driven (as all gears are still near physically the exact same size diameter as stock gears!).

Not true. Ever seen 4.10 vs 4.56 vs 4.88 gears for a 9.5” diff? Same concept applies to the t/case gears.

 

[cruiseroutfit]

Not true. Ever seen 4.10 vs 4.56 vs 4.88 gears for a 9.5” diff? Same concept applies to the t/case gears.

x2

The diameter of the gear is irrelevant outside of actual fit with the other gears. The tooth count is exact science and will absolutely result in the reduction the math indicates. We too have installed many and tested RPM’s at speed, etc... we get the exact result the math says we will.

I would be very interested to know your tooth counts!

 

[paz12ht]

Not true. Ever seen 4.10 vs 4.56 vs 4.88 gears for a 9.5” diff? Same concept applies to the t/case gears.

Nope never have had the chance to line all three C&Ps up at the same time (or had the need to) but, i have spent the money on the transfer gears (and other parts needed for swap), i have taken the time to install them and i have done the actual physical testing on them as well as double check to ensure it (rpm etc) is correct.

Prior to gears install FZJ105, H151F box, HF2A stock transfer, 4.3 diffs, 285/75/16 @ 100 km/h equals 2400rpm, Sumo transfer gears installed @ 100 km/h equals 2350rpm, where's my other 150rpm vanished to?

 

[paz12ht]

x2

The diameter of the gear is irrelevant outside of actual fit with the other gears. The tooth count is exact science and will absolutely result in the reduction the math indicates. We too have installed many and tested RPM’s at speed, etc... we get the exact result the math says we will.

I would be very interested to know your tooth counts!

Kurt pics of the exact gears as i installed (btw i also required the Sumo intermediate shaft as gears would not fit in my box without it!).

Unfortunately I cannot agree with you as far as the diameter of the gears being irrelevant (this I did not really realise until I actually owned them and was in the midst of installing) at the end of the day a 35" tire is always going to travel a longer distance than a 33" is for the same amount of revolutions, that is exact science and gears are imo, no different.

Regards.

 

[cruisermatt]

Unfortunately I cannot agree with you as far as the diameter of the gears being irrelevant (this I did not really realise until I actually owned them and was in the midst of installing) at the end of the day a 35" tire is always going to travel a longer distance than a 33" is for the same amount of revolutions, that is exact science and gears are imo, no different.

You’re joking right?

 

[JunkCrzr89]

Prior to gears install FZJ105, H151F box, HF2A stock transfer, 4.3 diffs, 285/75/16 @ 100 km/h equals 2400rpm, Sumo transfer gears installed @ 100 km/h equals 2350rpm, where's my other 150rpm vanished to?

Sounds like you don’t understand the difference between overdrive and underdrive high range gears. You installed overdrive gears and expect them to function as underdrive gears!

 

[cruisermatt]

GPS verified speed difference at same RPM ?

 

[cruiseroutfit]

Kurt pics of the exact gears as i installed (btw i also required the Sumo intermediate shaft as gears would not fit in my box without it!).

Unfortunately I cannot agree with you as far as the diameter of the gears being irrelevant (this I did not really realise until I actually owned them and was in the midst of installing) at the end of the day a 35" tire is always going to travel a longer distance than a 33" is for the same amount of revolutions, that is exact science and gears are imo, no different.

Gears do not engage face to face on their outside diameter, their interface is tooth to tooth. I’m sorry, I’m not going to be swayed here. You’re literally trying to convince me that gear ratios (actual tooth numbers/tooth numbers) are no longer valid unless we take into consideration their diameters (which has never had any ratio relevance). Furthermore, you’re disputing the results that tens of thousands of others have had with these overdrive and underdrive T-gears over the decades.

Fwiw, your tooth counts 34/31 do match the Overdrive gear set. I’m sorry but I can only suspect your testing methods/memory for pre and post rpm/speed. These gears have not been sold as a placebo for decades

 

[nukegoat]

Kurt pics of the exact gears as i installed (btw i also required the Sumo intermediate shaft as gears would not fit in my box without it!).

Unfortunately I cannot agree with you as far as the diameter of the gears being irrelevant (this I did not really realise until I actually owned them and was in the midst of installing) at the end of the day a 35" tire is always going to travel a longer distance than a 33" is for the same amount of revolutions, that is exact science and gears are imo, no different.

Regards.

View attachment 2722201

View attachment 2722202

LOL

 

[ramangain]

Prior to gears install FZJ105, H151F box, HF2A stock transfer, 4.3 diffs, 285/75/16 @ 100 km/h equals 2400rpm, Sumo transfer gears installed @ 100 km/h equals 2350rpm, where's my other 150rpm vanished to?

May I suggest double checking all of yor math and assumptions?

 

[paz12ht]

So my post/thread was asking for people who have actually installed these exact same gears and for those same people to give me their opinion or some actual real time results they've received.

Instead I get people (apart from Kurt who has a vested interest) who have never fitted these gears (I assume as they've really not added any intelligent feedback) prefer to question my actual real time results and triple checked calculations, good work gentlemen

For something that allegedly has been sold for decades in the "tens of thousands" there doesn't seem to be too many people offering up their realtime feedback?

 

[cruiseroutfit]

So my post/thread was asking for people who have actually installed these exact same gears and for those same people to give me their opinion or some actual real time results they've received.

Instead I get people (apart from Kurt who has a vested interest) who have never fitted these gears (I assume as they've really not added any intelligent feedback) prefer to question my actual real time results and triple checked calculations, good work gentlemen

For something that allegedly has been sold for decades in the "tens of thousands" there doesn't seem to be too many people offering up their realtime feedback?

Post up in the 8x Series section (Edit: looks like you did, I can't guess why no one wants to reply??) and you'll find 100x more feedback. While overdrive/underdrive gears have been available for 6x/7x/8x applications for decades by brands like Sumo, Terrain Tamer, Marks 4WD, Japan offerings, etc... they have only been more recently installed in the 100/470 full-time cases so the sample size is significantly smaller around the globe.

That said, I don't know that one has to have ever installed the gears to agree that the diameter simply won't change the tooth count and resulting ratio.

 

[jLB]

I've fitted a set to mine and honestly i don't think they've made much difference, claims are allegedly 9-10% overdrive from stock 1:1 gears which should equal to around 200rpm drop at 60mph/100kph with my stock 4.3 diffs and 5 speed H151F but i think I'm lucky to have dropped 50rpm?

@cruiseroutfit

Hi Kurt, thanks for your reply.

Yes i did fit the Sumo overdrive transfer gears to my HF2A (though to be clear to everyone not sourced from you) and no unfortunately they have not given me the RPM reduction as you mention (tested using GPS for speed and running checks between dash tacho and hand held lazer on harmonic balancer to confirm dash is reading accurately etc).

Again yes totally agree with your math as per your table (is actually what swayed me to search for and purchase the gears here in Australia) but only if we're talking all gears with full teeth of the exact same size (which then in turn will affect each total gear overall diameter when adding or subtracting teeth)!

The way the Sumo gears are designed so as to retain virtually the exact same size gear diameter as stock (required so as the factory idler can be retain which is in between the two supplied Sumo gears) but to fudge the tooth shape etc to add 1x tooth and subtract 2x teeth (so as they will mesh) unfortunately cannot (and will not) ever make a difference to the actual overall ratio you end up with these gears when actually driven (as all gears are still near physically the exact same size diameter as stock gears!).

Unfortunately i will admit i went into these gears a bit green as I'd never had a HF2A apart before, yes i should have done some more research and actually sat down and thought about it some more but anyway, guess it's lesson learnt (albeit an expensive one).

Regards.

Nope never have had the chance to line all three C&Ps up at the same time (or had the need to) but, i have spent the money on the transfer gears (and other parts needed for swap), i have taken the time to install them and i have done the actual physical testing on them as well as double check to ensure it (rpm etc) is correct.

Prior to gears install FZJ105, H151F box, HF2A stock transfer, 4.3 diffs, 285/75/16 @ 100 km/h equals 2400rpm, Sumo transfer gears installed @ 100 km/h equals 2350rpm, where's my other 150rpm vanished to?

Kurt pics of the exact gears as i installed (btw i also required the Sumo intermediate shaft as gears would not fit in my box without it!).

Unfortunately I cannot agree with you as far as the diameter of the gears being irrelevant (this I did not really realise until I actually owned them and was in the midst of installing) at the end of the day a 35" tire is always going to travel a longer distance than a 33" is for the same amount of revolutions, that is exact science and gears are imo, no different.

Regards.

The flaw in your logic/comparison between gears and tire diameter, and resulting faulty hypothesis, that diameter has something to do with gear ratio, completely misses the fact, that regardless of diameter, a 31 tooth gear travels ~11.61* per tooth, and a 34 tooth gear travels ~10.59* per tooth. Whether I look at it by teeth (34/31) or degrees (11.61*/10.59*) I still get ~1.096 revolutions of the smaller gear for every 1.0 revolutions of the larger gear.

Is it possible that your "before" measurement is/was less accurate than your "after" measurement, or could the before "measurement" be mathematically calculated instead of measured?

I'm curious, with what sounds like stock axle gears, stock transmission, stock gas/petrol engine, and slightly oversize tires, what's the interest in overdrive gears?

 

[paz12ht]

@cruiseroutfit

So my wife tells me I never do this but that cannot be right (pun intended), I shall like to eat humble pie and admit I was indeed wrong (publically)

The calculators I used online, my memory (obviously wrong) and others I spoke to about their rpms, setup etc all pointed to the Sumo gears not doing as supposed however, they are indeed doing exactly what they should be.

I devised a plan that would test them definitively, i've just pulled both tailshafts off transfer, selected 4th gear with transfer in 4wd (CDL) high, rpm measured at crank with laser 1260rpm (+/- a few rpm), rear output shaft 1390 (did more than just once of course at varying rpms).

Again apologies to those that actually took the time to reply with constructive criticism, to the others that just decided to add their two cents with no substance