Grinding in the 5th
 

OK, so couple of weeks ago I have changed the transmission oil and diff oil. What can I say, a lot of stuff in there!

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So, I have changed it to Motul Gear 300 GL4/5 75W90 in Transmission and 75W90 GL5 Royal Purple in the Diff. It was all good and fine until about a week in, I have started to hear a grinding noise coming from what I am thinking it might be the transmission but it very well come from the diff in the following conditions:
1. cold - first 5-10 minutes of driving
2. In the 5th
3. When I drive with a 60-65 km/h (34-40 mph)
4. Sometimes when I decelerate.

It usually goes away in about 10-15 minutes.

What do you guys think it might be?

I think it's a loose synchro , I've had this problem for about 25k miles now. Besides the weird feeling when I downshift to 5th I can't say anything bad about the drivetrain. Changed out the transmission and diff fluid to motul about 10k ago ... did nothing for me

All common. Run Pentosin MTF2 in the tranny. Keep the RP in the diff. Shift harder and faster. It will all equalize in the end.

I have Motul in the Diff and MTL in the box which made it much better. I found with Gear 300 in the box initially it was certainly stiffer (after a few weeks) and may have been noisier. All of the aftermarket rear trans mounts (Perrin, Kartboy, TRD) seem to lift the rear of the box a bit as well which may contribute NVH as well as their additional stiffness.

Check for clutch drag. A dragging clutch can kill your transmission within only a few shifts as the synchros are fragile. It doesn’t matter what they are made of or if they are double or triple synchro, they will be ruined if the clutch drags, period.

http://www.jackstransmissions.com/pa...kills-synchros