Model S/X: LDU problems (the large rear motor) — seal leak and failure

Summary

The large rear drive unit (LDU) on early Model S/X is prone to coolant leaks through the seal on the rotor shaft. Coolant ingress into the stator/inverter degrades insulation, causes noise ("milling/grinding"), insulation faults and ultimately full failure.

Diagnosis

• Fogging / coolant traces around the speed sensor / rotor exit.
• Foreign "buzzing/milling" noise of growing volume.
• Insulation faults, power limits.

What to do

1. Diagnostics: remove the speed sensor and check for coolant; measure insulation.
2. Repair (options):
   • Replace / repair the LDU as an assembly.
   • Bypass/Delete the rotor cooling (out of warranty): re-routes the loop, eliminating the weak seal.
   • Stator/bearing repair, flushing, inverter restoration if needed.

Prevention

• Regularly check for leaks; at the first signs — don't delay.
• Watch coolant level/cleanliness, don't overheat the drive.

What it costs in Belarus

• Early stage (leak without serious consequences): ≈ $1 000–2 000.
• Repair with disassembly, drying/rewinding and bearings: ≈ $2 500–5 500.
• LDU replacement / reman: ≈ $5 500–7 000.

Links

• TMC: overview of LDU/RDU coolant leak issues — https://teslamotorsclub.com/tmc/threads/early-ms-ldu-rdu-coolant-leakage-current-state-of-affairs.327284/
• Revolt Systems on the "coolant bypass" — https://revoltsystems.com/tesla-large-drive-unit-ldu-coolant-bypass-kit-the-achilles-seal-fix/
• Gruber Motors on the consequences of a leak — https://www.youtube.com/watch?v=zBEtkGHdKwU
• Repair pricing example — https://elmob.us/tesla-ldu-coolant-leak-repair