Hey guys,

For the past 3months I had a problem on my 6mt 2003 g35 coupe. I'm thinking it's the synchros, but it just seems strange.

When I for example drive at either 20mph or 80mph, any speed really. With the clutch in, rpms being at 800. Just idling... I have the clutch fully pressed in and I shift from 4th to 3rd... This is all while the engine is idling at no point do I let go off the clutch... It grinds/thumps...


I mean why would it thump/grind, act strange when It's at such low rpm. Otherwise it doesn't grind.. unless I'm redlining 2nd gear and shift fast to 3rd... if it shift slow it does not grind....



Thanks

 

Worn synchros, old fluid makes it worse, if it's been more than the recommended service interval of 30k miles then change the fluid. It will not eliminate the problem but it can make it less noticeable. Mine is just starting to show signs of worn synchros as well (2006 with the newer CD009) it's basically how a manual transmission "wears out". It will get progressively worse over time until you get sick of it and dump in a new or rebuilt tranny.

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You should verify proper clutch DISENGAGEMENT however. Jack up the vehicle, start the engine, depress the clutch, use the brakes to stop rear tire rotation. Let go of the brakes while still holding the clutch and you should have zero rear tire rotation.

If your tires do slowly beging to rotate then you have a clutch not fully disengaging, either from a worn clutch master cylinder, slave cylinder, or air in the line (rarely from worn clutch lines).

 

Sounds like the 4th gear synchros to me as well. Either drive around it or replace the transmission with a bulletproof CD009. I've got an early trans as well and at 118k I'm starting to grind into 6th unless I granny shift but so far all the real gears catch no problems.
EDIT: Beat me to it!

 

Lol that CD009 is definitely not bulletproof but it does take longer to show symptoms of wear.

 

Ahh ok my bad, the only reason I said that is I've heard of LS swaps and TT builds using stock CD009s with no problems but I had no idea about longevity

 

Well it can handle a metric ***ton of torque stock, something in the range of nearly 1000lbs but it will still wear out.