I have a weird problem, whenever I downshift into 3rd it always seems to grind. The weird thing is that it only does it when I downshift, it upshifts just fine. I have the clutch pushed all the way to the floor and it still does it, it doesn't do it as bad if you very slowly put it into 3rd though. What could be the problem? Thanks in advance.

 

The third gear synchro is probably getting worn. When you upshift, the synchro has to do more work than a downshift, and is therefore more likely tofall short in completingit'sintended purpose.

When upshifting normally the mainshaft is normally and naturally slowing down, the synchros have to do little work to get everything "synchronized". When upshifting, the third gear synchronizer has to increase the speed of the mainshaft and it's associated mass, and more so working against the rotating parts tendency to be slowing down when they need to speed up,this = lots of work.

You can minimize or eliminate this symptom by stopping in neutral for a moment, let the clutch out quickly, speed up th engine to approximately what it would be going if the car was in third, push in the clutch and complete the shift. With practice you can do this quickly and without having to think about it.

The worn synchro probably will not effect the otherwise normal operation of the tranny, nor is it necessarily an indication of a need for a rebuild, if you can live with the symptom.

 

So if I double clutch it won't grind, or it just won't grind as bad?

 

hit and miss. Depends on how good you get at double clutching.

 

Alsoa change of gear oil definitely wont make the situation worse.
One other thing, what is your clutch adjustment like? I've in the past as the clutch wears down, it needs adjusting to ensure its completely disenging when the pedal is depressed. Same thing with a hydralic clutch master cylinder leak.

 

I just replaced my clutch about a month ago. I never thought about changing the gear oil, I'll try to do that tomorrow if I have time.

 

It depends on how good you get at it....

Chances are with practice you wont grind it very often... If you get really good, you wont need synchros at all...

 

Would rev-matching do the same thing?

 

Yes... I would probably do this in your situation, but I didn't want to confuse the issue....

 

True, but I've heard that this places a LOT ofstress on the syncros, at least the ones that still work.