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I owned a 2005 Infinit G35 and it has a manual transmission. At some point something strange was happening in regards to shifting.

Example: When in first gear, if I revved the engine to 3000RPM and shifting into 2nd, it would slightly grind. If I revved the engine highter to say 4500RPM, and then tried to shift into 2nd but not forcing it, at some point as the RPM's came down it would go into 2nd no problem.

So I then took my car for an oil change at the dealership, and the mechanic took the car out for a drive and when I got the car back everything was fine. They didn't even mention what they did, but whatever they did it wasn't anything elaborate since they didn't charge me and it didn't take any longer that a routine oil change (2 hours maybe since it is a dealership).

Anyhow, what possibly could the issue have been?

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    "it was a manual" is it still or now auto? – Solar Mike Jul 11 '18 at 15:37
  • @SolarMike I don't own the car anymore, hence the past tense. Never understood what happened. – cool breeze Jul 11 '18 at 16:21
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Sounds like they probably just changed the transmission fluid.

I own an '06 G35 with the same transmission, and they are known for being somewhat notch-y with the wrong weight or old transmission fluid, especially getting into 2nd gear when the fluid is cold. The reason it would easily slip in as the engine RPMs dropped is because the engine and transmission eventually reached the same speed, at which point the transmission wouldn't have needed synchros to mesh/engage the gears.

Side note: '03-'04 G35's with the "CD008" manual transmissions had major issues with the synchros, to the point that many owners had their transmissions replaced under warranty due to grinding into 5th and 6th gears after as little as 20k miles. These issues were fixed with the CD009 transmission that came in the '05-'06 cars.

  • Maybe the just topped it up? b/c they didn't charge me for it. But if it was low the engine light would have come on. Thanks for the insights! – cool breeze Jul 11 '18 at 16:55
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    AFAIK there is no transmission low oil warning light - the oil warning light is for engine oil pressure... – Solar Mike Jul 11 '18 at 17:10
  • Correct, there is no low tranny oil light, and if it was low fluid you probably would have noticed the problem in other gears as well. It's also possible they adjusted your clutch pedal if it wasn't fully disengaging the clutch, but again you would have noticed that in other gears. I can't think of any other relatively quick/easy things they could have done that would have changed anything about the gear engagement. – MooseLucifer Jul 11 '18 at 17:24
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I don't know about the G35 but some manual transmission cars have cables in the gear shift mechanism instead of "stiff" mechanical links. Over time the cables can stretch slightly, and the "gate" which the gear lever moves in prevents the gears in the box aligning perfectly.

Sometimes the symptoms are temperature dependent - i.e. the gears shift easily when starting from cold but the problems start when the engine gets hot - or vice versa.

If the garage spotted this on a test drive, it's a very quick job to adjust the cables, so they might have done it "for free" (especially if they charge rip-off prices for the oil change, and want you to be a repeat customer because of the "good service" you got!)

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