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Hello all!

For those with AWD and experience clunking (engaging/disengaging) when making a turn from a complete stop, your wheels are rotating at a different rate of speed. The feedback from the wheel hub speed sensors/encoders are telling the computer this and the rear engages/disengages as if there's loss of traction. From what I've learned, having owned my SFS 2.0T for over 2 years now and a viscous coupler blown (replaced under warranty), I can tell you a few things to look for.

Basic funtionality: The drive shaft from the front differential to the rear differential is rotating full time. The viscous coupler in between the shaft and the rear diff and engages when the computer sends a signal to the actuator between zero and 40 mph. Over time, the internals get sloppy and ultimately fail. I suspect it's like a lovejoy coupler with a rubber boot between the two mating surfaces. Look it up in google images if you're curious. It's my best guess that if my theory is correct, this boot wears out, breaks apart-whatever, and then there's excessive play between the 3 fingers on each side that union. One good high torque engagement and boom, there goes the coupler! Part costs like $750 from the dealer and the parts department told me they always keeps one in stock because they are constantly replacing them. I know this to be the weak link of all 2013, 2014, 2015, 2016, 2017 DM Santa Fe Sport all wheel drive AWD drivetrain. (added for better indexing for search engines)

Bought used 42k miles, and returned to dealer to complain about clunking when making a hard turn 90 degrees from a stop. Nothings wrong they said. Time progressed and around 75k, roads were wet and lost traction when taking off. Boom! I knew it was toast. FWD only. Returned to dealer and confirmed what I knew. Replaced in like 1.5 hours. Warranty deductible of $50 and out the door.

With a fresh viscous coupler, the bumping/clunking I described was no longer happening. Now that my odometer is @ 92k, I'm starting to notice it again. Beware AWD SFS's! Otherwise, great car but put together with plastic pins and everything else plastic. Life cycle could be 30-40k miles depending on driving habits. I'm not easy on mine. Hope this helps somebody! BTW, I have no intention of following up on this thread to answer questions. If you ask, someone else in the community will need to chime in. I did this simply because info is limited and wanted to provide my experience and feedback on this.
1). Hyundai use the vehicle abs as part of the AWD system. This require even brake pad engagement and clean brake fluid.

Warning: Never push caliper piston with dirty brake fluid up into the ABS. This will lockup the ABS valves and cause ABS failure, AWD dysfunction. 14 million people posted on Google, reporting ABS failure after brake job. Do not be 14 million and one statistic reporting ABS failure because old brake fluid was pushed into the ABS unit causing $$$thousands in damage.

Always bleed the brake system 1st before a brake job and 2nd brake bleed after brake job to top the fluid. Always open the brake bleed valve prior to pushing the caliper piston to release the brake pad. Two quarts of Dot 3 fluid (2010-2013 Hyundai’s) cost $12.50 each or $25 USD.

2). Use full synthetic 75w-90 gear oil with friction modifiers for limited slip in front and rear differential. Some AWD Hyundai’s had diff. limited slip. I use Valvoline full synthetic 75W-90 with limited slip friction modifier in both differentials. $17 usd from Walmart.

Warning: Never use regular gear oil in limited slip differential. Regular gear oil will cause the limited slip clutch to permanently lock causing clunking noise going around corners.

Using limited slip friction modifier in regular differential will only make the differential operate more smoothly.

3). Change the Transmission fluid. The clean operation of the automatic transmission seems to affect the fluid coupler. I performed a 4X flush with Valvoline Max-Life full synthetic ATF at $17 per gallon or est $100 USD to get a smooth transmission and smooth fluid coupler electronic engagement. I perform the 1st (4x) ATF flush at 60K and 30K severe maintenance Cycle.

4X drain/fill is, 1st drain/fill 50% clean, 50 mile drive 2nd drain/fill 75% clean, 500 miles drive then 3rd drain/fill 87% clean, 3000 mile (oil change cycle) 4th drain/fill 92% clean ATF, …then severe service maintanence cycle 30K mile ATF drain/flush.

This is how I maintain my 2010 Tucson Ultimate AWD with 80K miles and 2010 Santa Fe GLS AWD with 120K miles. The AWD’s works great and transmission operate smoothly. My daughter just took the Santa Fe up to the Paradise at 11,000 ft on top of Mt. Rainer with no issues and went on logging roads 2-3 hour for camping, …in 100F hot high alt. Weather with air conditioner on full blast and 4 passengers with camping gears!!!
 
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