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In scenarios where the left rear wheel moves into the mudguard and the right rear wheel moves down the projections of the lower links causes the drive shaft to bend pushing the flange into the tank guard. E.g. traversing ruts could cause such scenarios.
I have a close eye on these dents, but it looks like that it really only causes these dents in the metal tank guard while the integrity of the tank itself is not compromised.
With all the experience over the last years my preferred maintenance strategy is now:
The 5,000 km interval has also the advantage, that it comes together with tyre rotation, LSD torque check and adjustment of the rear hand brakes. For these works I put the car on stands anyway, which allows me to turn the drive shafts to get the grease nipples in a position that allows to attach the grease gun. Without having the car on stands this can be a tricky undertaking.
I know it is not ideal, but I fill the joints till I can recognize a small amount of grease coming out of the seal - not ideal for the seal, but I prefer a filled joint with a possible slightly reduced seal life span over the risk of a seizing joint that could cause much more damage to the linked parts, e.g. to the LSD.
There is something “strange” that may indicate that Hyundai responded to this problem: the newer rear propeller shafts have a small aperture on the opposite site of the grease nipple - the old ones didn’t have this hole.
When asking the dealership about the reason I couldn’t get a satisfying answer, but I assume that it is considered to relief the pressure from the seal: now the slip joint can be filled till the grease comes through this hole - leaves the seal intact, but allows water and dust to get in, so IMO not an ideal solution.
I was tempted to seal this hole with a tape, but it could also be considered to facilitate a better response of the slip joint to required movements. Without the hole pressure equalization / air exchange happens via the seal, which is again not ideal for the seal and a new, tight seal could even cause an unwanted dampening effect resulting in drive shaft vibration.
Terracan owners with a suspension lift might find some serious dents in the metal tank guard. It is caused by the flange of the rear propeller shaft.
Hyundai Service Passport states a 30,000 km interval for “cleaning, re-tightening and lubricating” the propeller shafts. This might be ok for the 3 uni joints (1 for the front propeller shaft, 2 for the rear propeller shaft), but - IMO - not for the slip joint of the rear propeller shaft.
The slip joint loses a lot of grease when working hard, and once out of grease it can seize. A seized propeller shaft can hardly respond to the suspension travel, or only by bending; this will cause vibrations and abnormal wear and tear for the LSD.
A lot of the earlier LSD issues (“diff shudder”) might be caused by lack of drive shaft lubrication.
When I started to check the items on the service passport list, I also found - long after the first 30,000 km inspection - a drive shaft nipple in an awkward position that wouldn’t have allow to attach a grease gun. I assume that for the Hyundai mechanics used to service passenger cars a propeller shaft that needs to be greased was a some kind strange animal.
Later the slip joint needed a grease filling in more and more shorter intervals, at the end every 5,000 km as the seal couldn’t hold the grease any longer. Luckily I got the drive shaft replaced under warranty due to this issue.
Greasing of the uni joins and the slip joint bears a risk. Too much grease that gets squeezed against and under the seals can destroy them.
But what is the best way to recognize when it is enough?