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6MT 1st gear possible synchro issue


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I'm looking to buy a 2008 LGT with the 6MT, a little over 100k miles. The owner mentioned that when rolling to a stop, sometimes when he downshifts to first there's a grind. I personally didn't experience that when I drove it, nothing stuck out in particular. Compared to the WRX and the BRZ's 6MT, it seemed a lot smoother, didn't have to shift as much and less notchy.


I looked around online and I found two possible options but a lot of conflicting information.


  1. Replace fluids with cocktails/ never replace fluids because it will kill the transmission
    I'm a little skeptical about both, I don't think simply fluids will fix synchros but then again I don't see the logic behind never replacing fluids.
  2. 6mt is finicky, cannot simply replace synchros/ 6mt is bulletproof vs 5mt
    I don't see why the 6mt needs to always be replaced and can't simply have one synchro fixed? Also, where is this myth that the 6mt is bulletproof coming from?


Thanks for helping out a LGT noob.

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The popular fluid cocktails are usually to help ease an already failing transmission. The thought behind not replacing fluid is more popular with automatic transmissions, with the thought being that doing a flush after a lot of miles may dislodge debris/sludge and clog up the valve body. Not saying I agree, just stating what I've heard. Regardless, this does not apply to a MT, and changing fluid is an important part of regular maintenance.


The 6MT is considered more robust that the 5MT, but I wouldn't say it's bullet-proof.


If the only issue with the trans is the possible slight grind going into first while rolling I wouldn't worry about it personally. In a given month I can count on one hand the number of times I shift to first while still rolling. Double-clutching helps a lot. The majority of the time you shift into first will be from a stop, so if it shifts fine and the other gears are okay I wouldn't worry.

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I was talking about the popular cocktails being a band-aid. Changing out old fluid with a quality oil (Extra-S, Motul 300, etc) will go a long way.


If you buy a used vehicle, complete fluid swap should be right new the top of the list, after thorough brake system inspection. I'm talking all fluids. Brakes, engine, coolant, trans, differential, power steering, and clutch (although clutch is probably the least important). Unless you bought from a source you trust and have records indicating these things have been done recently.


Keep in mind at 100k you will be needing to replace the timing belt and water pump very soon.

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