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I have a 2007 Pontiac G5 with a 5-speed manual (Getrag F23 if you're curious) and about 145k miles.

This problem has been ongoing for a couple years now but is progressively getting worse.

Sometimes when I shift into first while stopped, like at a traffic signal or stop sign, the gearbox will make a horrible grinding noise. About 50% of the time I encounter the grinding, the car's electronics also freak out - the speedometer shoots up to 70mph or so (mind you, I'm stopped), the stereo will momentarily become louder, and the engine speed will drop then go back to idle. In rare occasions, the car will stall when this happens, though it doesn't lurch forward like it would if I hadn't let off the clutch properly.

Here is a video I captured with my dashcam of it happening: https://youtu.be/7-3PYX9f66U

You can clearly hear the grinding, followed by me having to start the car after it stalls.

I have tried researching this online but have not have not found any solutions. I have also ensured that I am fully depressing the clutch and waiting a couple seconds after doing so to shift.

This does not occur in any other gear, especially while moving (though I have experienced the electrical phenomenon a couple times when shifting into reverse). The clutch and throwout bearing were both replaced about 18k miles ago, but the problem occurred before then and persisted afterwards.

Any help would be much appreciated.

  • This sounds like two problems to me: the electrical woes could be a bad ground related to the neutral safety switch, and the grinding tranny could be a bad synchro, or a problem in clutch hydraulic system, though the latter would usually manifest in other gears as well. – MooseLucifer Jul 28 '16 at 16:42
  • Wouldn't a bad synchro cause problems while moving, not while stopped? – thesammon Jul 29 '16 at 19:04
  • The synchro is only used to match the speeds of the two gears that are engaging (input shaft and 1st gear in this case). Once the gears are engaged, a collar holds them together, and the synchro is just along for the ride. Does pumping the clutch a few times prevent or lessen the grinding? – MooseLucifer Jul 29 '16 at 19:33
  • I haven't noticed a difference. One friend did suggest shifting to 2nd and then 1st while stopped, and I haven't yet had any grinding doing that (though I only just started). – thesammon Jul 30 '16 at 22:53
  • First and second are accessed using the same fork. Engaging second would spin the assembly up to engine speed, reducing the workload on the first gear synchro. Did you replace the tranny fluid at the same time as the clutch? – MooseLucifer Aug 1 '16 at 14:08
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If your transmission is making a grinding noise while the car does not move and with clutch fully depressed it means that there is still torque applied to the transmission. I suspect that either the master cylinder or the hydraulic line are having a fault. It is also possible that the repair work on the clutch/slave cylinder was not done right.

For further diagnosis you could jack up the car, put in the first gear, keep the clutch depressed, start the engine, wait and check if the wheels slowly start turning.

  • Thank you, will give it a try the next chance I get. Any idea why it would be intermittent? – thesammon Jul 21 '16 at 16:40
  • My theory: It is intermittent because the seal in one of the cylinders leaks from time to time – Martin Jul 22 '16 at 15:06

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