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Discussion Starter · #1 · (Edited)
In the next couple of weeks, my SC's projected to complete the 1500 mile period, and I'd like to swap out the transfer case and rear diff fluids because I messed up and went over 110 mph in the first 200 miles while the gears were still getting broken in, and that must have generated quite some heat and possibly burned the fluids especially in the rear diff (or not if no power was sent to the rear drive assembly at high speeds, I wasn't paying attention to the power distribution infogram).

1992


interestingly both use the same fluid.
If I remember correctly, the HTRAC SC has open rear diff, so no friction modifier required there (and no harm done if the fluid already contains)

The question is the transfer case, it seems like we have a lockable center diff, and if that diff is clutch-type, does it need additional friction modifier when changing the fluid with synthetic gear oil that contains some form of friction modifier already?
One example of such gear oil is

1993
 

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it seems like we have a lockable center diff,
IDK, from reviews on the Tucson HTRAC folks seem to say the "locking center diff" isn't actually a diff but a "request" to the HTRAC software to split the power front/back. Some testing done by some youtubers showed the Tucson HTRAC still sending power to the front wheels only (before sending to the rear) with the "center diff" locked. With that said I have no clue how it really works and if the "locking center diff" is actually a locking center diff 馃し鈥嶁檪锔
 

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motorcycle nut here...friction modifiers (i.e. motor oil designed to improve gas mileage) is a big no-no in MC engines...the wet clutches get coated with friction reducing "stuff" and start to slip....I use M/C specific oil or diesel engine oil in my 2 wheel toys....I've used Redline two stroke oil in my vintage bikes...the brand is well known and makes good stuff...it's GL-5 rated and the book calls for that spec. ...so I wouldn't worry if you use it in both "cases" the clutches must be designed to work with that spec.

Amsoil makes some good stuff and has a full line of Differential oils...I believe they all meet GL-5 ( check the spec sheet)

the only chemical that I add to ENGINE oil in new engines is a Zinc additive ...they ( OIl formulators) don't use it anymore as it affects the catalytic converter...usually for the first 1000 miles then I don't add it after that ...here's some info on Zinc:

here's the stuff I buy:

hth
 

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Discussion Starter · #5 ·
IDK, from reviews on the Tucson HTRAC folks seem to say the "locking center diff" isn't actually a diff but a "request" to the HTRAC software to split the power front/back. Some testing done by some youtubers showed the Tucson HTRAC still sending power to the front wheels only (before sending to the rear) with the "center diff" locked. With that said I have no clue how it really works and if the "locking center diff" is actually a locking center diff 馃し鈥嶁檪锔
yeah, without actually finding out the exact transfer case supplier and model, it's hard to tell what mechanism used.
It seems that Hyundai uses the term HTRAC loosely because they have Genesis using some sealed non-serviceable transfer case and call it HTRAC, and the SC has serviceable transfer case so they must be of different transfer cases and quite possibly different suppliers
 

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Discussion Starter · #6 ·
motorcycle nut here...friction modifiers (i.e. motor oil designed to improve gas mileage) is a big no-no in MC engines...the wet clutches get coated with friction reducing "stuff" and start to slip....I use M/C specific oil or diesel engine oil in my 2 wheel toys....I've used Redline two stroke oil in my vintage bikes...the brand is well known and makes good stuff...it's GL-5 rated and the book calls for that spec. ...so I wouldn't worry if you use it in both "cases" the clutches must be designed to work with that spec.

Amsoil makes some good stuff and has a full line of Differential oils...I believe they all meet GL-5 ( check the spec sheet)

the only chemical that I add to ENGINE oil in new engines is a Zinc additive ...they ( OIl formulators) don't use it anymore as it affects the catalytic converter...usually for the first 1000 miles then I don't add it after that ...here's some info on Zinc:

here's the stuff I buy:

hth
interesting read after researching on AMSOIL, I think 75w90 actually would work slightly better in hot climate

 

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While under warranty I would use the exact fluid spec Hyundai recommends. I've read before (somewhere) that you don't want to mix GL-4 and GL-5 gear oils, that is about my limit of knowledge on the subject.

With that said 75W-90 wouldn't be a bad idea if you are really loading up the rear diff. I guess it depends how much power gets transferred to the rear, so this might be more important for those off roading since above 37 MPH the SC switches to auto or part time AWD.
 

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Discussion Starter · #8 · (Edited by Moderator)
With that said 75W-90 wouldn't be a bad idea if you are really loading up the rear diff. I guess it depends how much power gets transferred to the rear, so this might be more important for those off roading since above 37 MPH the SC switches to auto or part time AWD.
You're right, power is not being sent to the rear at all at high speeds.
So what exactly does it mean then? the propeller shaft just won't spin? but the rear wheels are still being dragged along by the road force and do they still spin the the gears in the rear diff in pure FWD situation?

Also, you can all see piano black screen shows dusts very well
 

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You're right, power is not being sent to the rear at all at high speeds.
So what exactly does it mean then? the propeller shaft just won't spin? but the rear wheels are still being dragged along by the road force and do they still spin the the gears in the rear diff in pure FWD situation?
Excellent question. I assume the propeller (drive) shaft isn't spinning and the rear diff is open so the rear wheels can rotate at different speeds while cornering. With no load on them in this (assumed) free spin condition the temps shouldn't build up. I'd love to see some animation showing how HTRAC actually works. Its clearly a FWD system that shifts power to the rear under certain situations, that is totally different then your standard 4X4 system that is RWD but engages a transfer case to route power to the front when engaged. Never owned a 4X4 or AWD so this is all new to me :unsure:
 

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Discussion Starter · #12 ·
Excellent question. I assume the propeller (drive) shaft isn't spinning and the rear diff is open so the rear wheels can rotate at different speeds while cornering. With no load on them in this (assumed) free spin condition the temps shouldn't build up. I'd love to see some animation showing how HTRAC actually works. Its clearly a FWD system that shifts power to the rear under certain situations, that is totally different then your standard 4X4 system that is RWD but engages a transfer case to route power to the front when engaged. Never owned a 4X4 or AWD so this is all new to me :unsure:
In the fall when it's not that hot anymore, I'll spend sometime get a gopro camera underneath and see if i can get some footage of propeller shaft, drives shafts in action and hopefully can reveal some mystery
 

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motorcycle nut here...friction modifiers (i.e. motor oil designed to improve gas mileage) is a big no-no in MC engines...the wet clutches get coated with friction reducing "stuff" and start to slip....I use M/C specific oil or diesel engine oil in my 2 wheel toys....I've used Redline two stroke oil in my vintage bikes...the brand is well known and makes good stuff...it's GL-5 rated and the book calls for that spec. ...so I wouldn't worry if you use it in both "cases" the clutches must be designed to work with that spec.

Amsoil makes some good stuff and has a full line of Differential oils...I believe they all meet GL-5 ( check the spec sheet)

the only chemical that I add to ENGINE oil in new engines is a Zinc additive ...they ( OIl formulators) don't use it anymore as it affects the catalytic converter...usually for the first 1000 miles then I don't add it after that ...here's some info on Zinc:

here's the stuff I buy:

hth
A true motorhead's Nirvana, Thanks for links!
 

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What exactly did you mess up? what kind of damage are you expecting going over 110mph within break in period???




In the next couple of weeks, my SC's projected to complete the 1500 mile period, and I'd like to swap out the transfer case and rear diff fluids because I messed up and went over 110 mph in the first 200 miles while the gears were still getting broken in, and that must have generated quite some heat and possibly burned the fluids especially in the rear diff (or not if no power was sent to the rear drive assembly at high speeds, I wasn't paying attention to the power distribution infogram).

View attachment 1992

interestingly both use the same fluid.
If I remember correctly, the HTRAC SC has open rear diff, so no friction modifier required there (and no harm done if the fluid already contains)

The question is the transfer case, it seems like we have a lockable center diff, and if that diff is clutch-type, does it need additional friction modifier when changing the fluid with synthetic gear oil that contains some form of friction modifier already?
One example of such gear oil is

View attachment 1993
 

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Discussion Starter · #15 ·
What exactly did you mess up? what kind of damage are you expecting going over 110mph within break in period???
Most likely nothing.
I goofed and thought the rear diff was under load, but in fact, whenever the speed is over 37 mph, it's front wheel drive only. So going over 110mph does nothing to the rear diff.

However, I found this in the transfer case service guide:
Font Rectangle Parallel Number Document


It specifies severe driving condition and going over 110mph is one of them.

It's a known fact that the most wear and tear of differential gears, manual transmission, and transfer case gears happen during the break-in period, so going over 110mph if the gears are in fact spinning that fast, the gear oil can reach very high temp because the break-in gear movement generates a lot more heat thus cooking the fluid potentially beyond the designed specs and lose lubricating protection.

But given that at high speeds, it's FWD only, I doubt the transfer case is doing much work at those speeds, and I didn't do 110mph for long, probably less than 10 seconds.
And I plan on swapping the transfer case fluid at 5k miles as well, so even if the fluid was cooked badly during break-in period, I'll have new fluid there to have peace of mind.
 

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I goofed and thought the rear diff was under load, but in fact, whenever the speed is over 37 mph, it's front wheel drive only. So going over 110mph does nothing to the rear diff.
There may not be engine load, but the stub axles, spider gears and bearings are still spinning in the diff. Thus high speed driving is going to generate heat back there even when the rear diff is in free spool.

I believe the drive axle is always spinning but the main drive gear in the rear diff is not engaged unless certain conditions are meet, IE: under 37 MPH in lock mode, front wheels spinning, etc.

This video talks about "auto AWD" which is the system the SC uses, its FWD until RWD is needed. Its clutch based where the ECU varies fluid pressure to engage the clutch packs to control how much power get pushed out to the rear wheels. The description in the service manual confirms this. Interestingly it notes some rear power is used when turning to help steer the vehicle around a corner. Thus the AWD SC should handle better then FWD only models.

 

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Discussion Starter · #17 ·
There may not be engine load, but the stub axles, spider gears and bearings are still spinning in the diff. Thus high speed driving is going to generate heat back there even when the rear diff is in free spool.

I believe the drive axle is always spinning but the main drive gear in the rear diff is not engaged unless certain conditions are meet, IE: under 37 MPH in lock mode, front wheels spinning, etc.
I agree with the rear diff spooling all the time as the vehicle movement that moves the rear wheels will drive the gears
However, there's a coupling component that sits between the rear diff and the propeller shaft. I would imagine its function is to bind or unbind the rear diff to the propeller shaft. If the vehicle is in FWD only mode, I'd say the rear diff and propeller shaft are not "connected"

And on the other side of the propeller shaft is the transfer case. Thanks for that video. If I understand correctly, in FWD only situation, the clutch pads in the transfer case should not engage, thus no power should go to the propeller shaft, and if my above hypothesis regarding the coupling device jammed between the rear diff and the propeller shaft holds true, then the rear wheels should not be able to "turn" the propeller shaft.

I didn't know that SC would send power to the rear when cornering, now I know to test pure FWD mode, I just need to find dry straight line asphalt road traveling at a constant speed that should do, and film the propeller shaft in action, that should reveal the mystery
 
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