Race 6 Speed Grind Issue - Fluid Recommendation?
#1
Race 6 Speed Grind Issue - Fluid Recommendation?
So I have a 2004 Miata built for NASA ST6. The transmission shifts beautifully except in long races when it gets really hot it then it starts to grind. I have had the same issue with all of the following:
Mix of Redline MTL and MT90
Mix of Redline MTL and Lightweight Shockproof
Ford XT-M5-QS Full Synthetic
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy. I have been considering going to the Redline Heavy Shockproof or 50/50 mix of that and something else.
EDIT - I ended up adding a ton of heat shielding and then straight redline MTL and that seemed to work fine even for long races.
Mix of Redline MTL and MT90
Mix of Redline MTL and Lightweight Shockproof
Ford XT-M5-QS Full Synthetic
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy. I have been considering going to the Redline Heavy Shockproof or 50/50 mix of that and something else.
EDIT - I ended up adding a ton of heat shielding and then straight redline MTL and that seemed to work fine even for long races.
Last edited by Davidss; 10-22-2020 at 12:50 AM.
#3
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I would second the Amsoil MTG. Also might be worth throwing a temp sensor in the 6 speed to watch what it is getting up to. There is a thread with a link to the part number for the fitting required.
#7
For example, we heat wrapped the exhaust around the gearbox area AND rigged up aluminium heat shiedling around/beside the exhaust in the gearbox area to try and help prevent the 6 speed failures we were getting.
It didn't help the failures :( ..... but im pretty confident we reduced heat transfer in the process.
Im not entirely sure after trying all those usually well regarded oils that it is going to simply be a different brand of oil type solution, but hope it is, being the easier one.
#8
So I have a 2004 Miata built for NASA ST6. The transmission shifts beautifully except in long races when it gets really hot it then it starts to grind.
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy.
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy.
Not a points hit so why not?
Both your trans and rear would thank you.
#11
First bandaid would be improving exhaust heat shielding, unless you have done all you can. Second bandaid is fluid type and visocity. Have had better success with Amsoil and Motul for trannies versus Redline. You need a thicker oil.
My experience is that a much thick Motul fluid works better than thick Redline for the weights you would be using. I have heard good things about Amsoil as well, it seems to be sinilar quality to the Motul stuff when I've used it. Transmissions I have used wouldn't shift with thick Redline fluid when not hot
However, thicker transmission fluid is still just a bandaid. I've seen people run simple electric pumps wired to an in cabin switch with an oil cooler just for the transmission. Lack of a thermostat makes it dirt simple. You can run everything in the rear end of the vehicle and improve weight distribution. Even in a poor airflow location for the tranny cooler it will significantly reduce temperatures. Extra oil capacity is always good as well. I've seen people run them in the trunk with a small fan and a port cut out by the license plate.
My experience is that a much thick Motul fluid works better than thick Redline for the weights you would be using. I have heard good things about Amsoil as well, it seems to be sinilar quality to the Motul stuff when I've used it. Transmissions I have used wouldn't shift with thick Redline fluid when not hot
However, thicker transmission fluid is still just a bandaid. I've seen people run simple electric pumps wired to an in cabin switch with an oil cooler just for the transmission. Lack of a thermostat makes it dirt simple. You can run everything in the rear end of the vehicle and improve weight distribution. Even in a poor airflow location for the tranny cooler it will significantly reduce temperatures. Extra oil capacity is always good as well. I've seen people run them in the trunk with a small fan and a port cut out by the license plate.
#12
We have been using Amsoil MTG successfully for about a decade but are now experimenting with Motul 300v in an effort to increase film strength even further.
Redline MTL is fine for daily driven street cars but has nowhere near the viscosity required for any performance he was really. We use empty out for autocross cars that have notchy gearboxes when cold. It's that thin. MT90 only a slight improvement. Heavy shockproof has film strength but does not have very good synchro bite. The Ford synthetic also too thin when it gets hot. Crunchy syncro time.
Redline MTL is fine for daily driven street cars but has nowhere near the viscosity required for any performance he was really. We use empty out for autocross cars that have notchy gearboxes when cold. It's that thin. MT90 only a slight improvement. Heavy shockproof has film strength but does not have very good synchro bite. The Ford synthetic also too thin when it gets hot. Crunchy syncro time.
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#13
So I have a 2004 Miata built for NASA ST6. The transmission shifts beautifully except in long races when it gets really hot it then it starts to grind. I have had the same issue with all of the following:
Mix of Redline MTL and MT90
Mix of Redline MTL and Lightweight Shockproof
Ford XT-M5-QS Full Synthetic
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy. I have been considering going to the Redline Heavy Shockproof or 50/50 mix of that and something else.
Mix of Redline MTL and MT90
Mix of Redline MTL and Lightweight Shockproof
Ford XT-M5-QS Full Synthetic
I tend to think it is a heat issue. Again cold or warm it's great but super hot 30+ minutes into a race it gets grindy. I have been considering going to the Redline Heavy Shockproof or 50/50 mix of that and something else.
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