Changed from stock to Amsoil gear oil...short grind now from 6-5
 

Not sure if this is a common issue or what, but I just changed the transmission oil in my FRS (around 14k miles) from the stock stuff to Amsoil 75W-90 gear oil, and ever since I've noticed a small/short grind going from 6th gear to 5th gear. Just curious if anyone has noticed this before, or might be able to offer an explanation or (hopefully) a solution? Seems to happen more if I shift quickly from 6th to 5th than if I make the shift more slowly/gradually. It doesn't happen in any other gear, and it doesn't happen during the 5-6 upshift...only 6th to 5th (even 6th to 4th is normal). Absolutely no noise and no grinding...shifting is smooth in every other situation.

Which specific Amsoil? It looks like the Amsoil 75w90s are only GL-5 - they say it can be used in rear axles that require GL4 but that's probably because axles don't have synchros.

Sounds like you should just try a different gear oil, I'm sure you're aware of the usual suspects.

I run the Amsoil 75-90 in my gearbox. The oil is not the problem. Spec for the twins is GL3, the Amsoil sythetic 75W-90 gear oil is GL4, which is a higher spec with more anti-wear additives and is designed for synchronized gearboxes.

What works for one person does not mean that it will work for another. These things don't come off the line completely identical to each other.

It may not be the oil, could be driving it differently or possibly just miraculous timing. Still doesn't mean it isn't just because it works in your car.

I didn't say it should work for everyone since it works for me.
What I said was that it's not the oil - in response to you suggesting it was the oil.
I agree there are many factors that figure into this scenario. My first thought would not be the oil, however.

I'm thinking now it may have been heat...I had been driving around "spiritedly" before I saw this. I tried it again today during lunch and didn't notice a grind...this was, however, at street speed (45mph) and not freeway speed where I noticed it before, so who knows. I'll check the bottle when I get home to verify it's GL-4...I bought some other GL-4 stuff at the parts store on my lunch just in case it's not. I have a road trip coming up in 2 days, so I need to make sure I don't have the wrong oil in there!

I'm running Amsoil in my gearbox (and my engine) and have experienced less 'notchiness' other than the very first cold shifts in the morning. Feels more fluid in general and my experience is that it was worth the upgrade.

+1!

FWIW, Amsoil Manual Transmission & Transaxle Gear Lube (MTG) 75W-90 is GL4.
Amsoil Severe Gear 75W-90 (SVG) is GL-5.
Amsoil Long Life Synthetic 75W-90 (FGR) is also GL-5.

+1 for me.

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@CaptainSlow Hi there, I did experience the same when I swapped fluid to Amsoil 75w90. There were no grinds at lower speed, but felt grinds from 6th to 5th gear at highway speed. I ended up switching to Redline 75w80 (Product image shows MTL in Amazon) and everything was very smooth. I know people have different opinions on 75w80, MT-90, MT-85 but I think all should work fine since they're all GL-4.

I had a low rpm chatter (like when the AC would kick in and the RPM would drop due to compressor) when I ran Amsoil Gear Oil. I switched to Redline MT-90 and it's awesome. Silky smooth shifts and no chatter.. ever. Highly recommend it!

FWIW I'm using Miller's Motorsport CRX 75W90 NT gear oil in my trans and diff, no noises or grinding and around 14 track days, just nice, smooth shifts. It incorporates Nanotechnology additive chemistry to significantly reduce internal frictional and power losses and outperforms other gear oils and other leading gear oils in several categories.

Here's an article from Race Car Engineering about Miller's gear oil: http://performanceracingoils.com/PDF..._the_Gears.pdf