Hi crynof,I just saw your recent post and yakuza’s reply about the 3-spring and 4-spring clutch discs. I think my recent experience with a Japanese-market Jimny JA11 (F6A, 5MT) may be very relevant to your problem.I had a very similar drivetrain vibration/rattle which I have only recently managed to solve after a long investigation.In my JA11, the symptom occurred only while driving under load, especially when accelerating in the low-to-mid RPM range. It was more noticeable in the higher gears and sounded like a loud rattle/rumbling vibration from around the transmission/transfer case area.The important characteristics were:
- It appeared under acceleration/load.
- It had a clear peak within a particular engine RPM range rather than at a particular vehicle speed.
- It disappeared immediately when I lifted off the throttle.
- It also disappeared immediately when I disengaged the clutch.
- It could not be reproduced by revving the engine while stationary in neutral.
I initially suspected the propeller shafts or transfer case. Over a long period I inspected or replaced the propeller-shaft sliding yoke, universal joints/spiders, transmission and transfer-case mounts, and transmission/transfer oils. None of these eliminated the problem.Eventually I replaced the clutch again.The aftermarket clutch disc fitted when the vibration was present was relatively light and had three damper-spring locations.I replaced it with an AISIN OEM-equivalent clutch. The AISIN driven plate is noticeably heavier and has four damper locations, each with paired/double springs.The result was immediate and very clear:The drivetrain rattle and vibration disappeared completely.No other significant drivetrain change was made at the same time.This is why yakuza’s comment about the 3-spring and 4-spring clutch discs caught my attention.I don’t think the number of springs alone necessarily explains it. Disc mass, spring rate, preload, angular travel and damping characteristics will all affect the torsional behaviour of the engine/clutch/gearbox system.My working explanation is that the aftermarket clutch disc allowed the engine’s cyclic torque fluctuations to excite a torsional resonance in the drivetrain. That rotational oscillation then excited the gearbox backlash, producing the rattle and vibration.Your vibration at around 1800 rpm in 3rd and 4th gear therefore sounds very interesting to me.If your Jimny has ever had its clutch replaced, I would strongly recommend finding out exactly which clutch disc is currently fitted before replacing other drivetrain components.Also, if possible, try this when the vibration occurs: keep the vehicle at approximately the same speed but disengage the clutch. If the vibration disappears immediately, that would be another interesting similarity with my JA11.I hope this helps. I spent a long time looking elsewhere in the drivetrain before discovering that the clutch disc itself was the key.
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