Gears grinding after changing from Redline MT-90 to Amsoil GL4

[JB21]

I recently changed clutch and gearoil in my 2ZZ/C64 MR2 and i'm now noticing a lot more gearbox grinding. It was fine at first but over the last few weeks the first thing I noticed was cold grinding 2nd, 3rd and 4th, once hot it was fine. Then on my last track day I noticed a slight grind 5th to 4th at high RPM downshifts. Now the 5th to 4th grind is quite bad, worse the higher RPM downshift.

I now need to change the gearoil again to see if I can get around this issue without rebuilding the box. So do I go back to Redline MT-90 or use something like Redline lightweight shockproof?

[Alex Knight]

I've been using the good stuff for years, Motul 300. I've literally never had a synchro grind on track:

https://www.opieoils.co.uk/p-899-motul-gear-300-75w-90-fully-synthetic-racing-transmission-differential-oil.aspx?variantid=1131

Highly recommended.

[JB21]

I've been using the good stuff for years, Motul 300. I've literally never had a synchro grind on track:

https://www.opieoils.co.uk/p-899-motul-gear-300-75w-90-fully-synthetic-racing-transmission-differential-oil.aspx?variantid=1131

Highly recommended.

This is probably decent for a good condition gearbox, but mine now is defo in need of a rebuild given the abuse its seen over the last 4 years and probably 10+ years previously in the Corolla it was in. This is why I need to try one of this specialty oils.

[Alex Knight]

This is probably decent for a good condition gearbox, but mine now is defo in need of a rebuild given the abuse its seen over the last 4 years and probably 10+ years previously in the Corolla it was in. This is why I need to try one of this specialty oils.

My advice is to not flog a dead horse.

Either get a rebuild, or source another box.

[JB21]

My advice is to not flog a dead horse.

Either get a rebuild, or source another box.

Not really got the time for that currently so I'll be going with the £50 gearoil option and hope it see's me through until the off season.

[Dev]

I feel bad that I recommended this transmission oil and you experienced these problems. It shouldn't happen as there are have been many that use it without any issue and seen an improvement over Redline. I would say the best course of action is going back to the MT90 and see if it improves. It's possible that the new transmission fluid exposed failing synchronizers. 

[JB21]

I feel bad that I recommended this transmission oil and you experienced these problems. It shouldn't happen as there are have been many that use it without any issue and seen an improvement over Redline. I would say the best course of action is going back to the MT90 and see if it improves. It's possible that the new transmission fluid exposed failing synchronizers. 

Dont feel bad Dev, its just one of those things. Ive still got the old MT-90 that came out last so i'm going to try this first to see if it helps, if so i may use a mix of MT-90 and lightweight shockproof.

[mr2garageswindon]

I recently changed clutch and gearoil in my 2ZZ/C64 MR2 and i'm now noticing a lot more gearbox grinding. It was fine at first but over the last few weeks the first thing I noticed was cold grinding 2nd, 3rd and 4th, once hot it was fine. Then on my last track day I noticed a slight grind 5th to 4th at high RPM downshifts. Now the 5th to 4th grind is quite bad, worse the higher RPM downshift.

I now need to change the gearoil again to see if I can get around this issue without rebuilding the box. So do I go back to Redline MT-90 or use something like Redline lightweight shockproof?

Check linkages on gearbox move freely and are not "Holding" it to far sideways pulling against the synchros when in gear.. Just a thought.
Most likely worn gearbox bearings tho.

[JB21]

Aye, will check cables and linkages but given it got progressively worse I think its the syncro/bearing. Only grinds on downshifts 5th to 4th, the higher the RPM the worse the grind. All other gears up and down at 8200rpm is fine.

[Dev]

Where are your filling the transmission. Some people are mistaking filling the transmission using the 10mm hex bolt instead of the 17mm fill bolt and getting half a liter less in the transmission.

[JB21]

Where are your filling the transmission. Some people are mistaking filling the transmission using the 10mm hex bolt instead of the 17mm fill bolt and getting half a liter less in the transmission.

I fill mine from the top bung thing, speed sensor hole maybe?

https://i.postimg.cc/rpwYdyTV/Screenshot-20230509-165428-Samsung-Internet.jpg

For the level i undo the top 17mm fill hole and fill until it drizzles out. It takes around 1.8L.

[Dev]

I fill mine from the top bung thing, speed sensor hole maybe?

https://i.postimg.cc/rpwYdyTV/Screenshot-20230509-165428-Samsung-Internet.jpg

For the level i undo the top 17mm fill hole and fill until it drizzles out. It takes around 1.8L.

That would be fine as long as it drips out of the 17mm fill hole. It's probably because you have an LSD and I have an open diff.  I had to fill 2.3 liters in my C60 transmission.
 There were people filling it at the hex bolt and only got 2 us quarts which was low. 

[KRAMSNEHPETS]

My box is doing exactly the same on my track car....

[ChrisGB]

I found that even in good condition, these boxes will not work so well with oils that are too slippery. I weight from factory fill to MT90 at less than 30,000 miles and the synchros became lazy. Matt Lee changed the oil to a Shell gear oil when I was having a turbo kit fitted. Within a few miles the box was much better!