Front Helical LSD bolt failure
Cars affected:
Evo 4-6.5
Symptom:
A regular ‘clunking’ noise from the front with every rotation of the wheel but only on full or partial lock. It will ‘clunk’ all the time on
lock regardless of suspension travel. It can affect the left, right or both sides. The symptom is exactly the same as CV joint wear except inspection of the driveshafts will reveal no joint
problems or ‘play’.
To help diagnose the problem, try and stop the car just as it is making the ‘clunking’ noise and then try rocking the car back and forth by hand while holding onto
the suspension, steering and driveshaft components in turn. You should be able to feel the ‘clunk’ only on the driveshaft. The ‘clunk’ can be heard coming from the transfer box if
listened to from underneath the car.
Problem and cure:
This is a problem with the factory fitted Front Helical (Torsen) Limited Slip Differential. The Helical LSD is standard fitment on
RSII’s, optional on the RS and although they were never meant to be fitted, some crept onto the GSR models when the production line ran out of normal open type diffs.
The ‘clunking’
noise occurs because the bolts securing the two halves of the diff start to break or come loose. The ‘clunk’ happens on full or partial lock as that is when the diff is under the most strain
due to torque transfer. Generally no damage will be caused to the diff unless it is left for a long time before it is repaired.
The cure for this is to replace the securing bolts with high
grade items. Replace ALL the bolts even if some remain serviceable.
Note there is very little detail on how to strip the Transfer Box and diffs in the workshop manuals. You can find details
for stripping the Transfer Box in the installation manual for the upgraded Ralliart front LSD which is available here - http://www.poweraxel.com/ralliart/catalogue/pdf/instructions/evo6/cp_lsd.pdf . Also note that there are no official service parts, other than the oil seals, for inside the Transfer Box so the bolts will have to be sourced from a fastener supplier. Four 12.9 grade M8x25mm (or 30mm) Flat Head Countersunk screws are required.
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