Putting 10w-30 oil in a R154 Transmission

Bru · 12-02-2010, 07:50 PM

OK, it may sound like heresy but I was fed up with my sticky first to second gear and hard down shifting into second on turning a corner with my R154 transmission. I tried Mobile 1 and also Moroso Gear climbing oil and even added half a can of STP oil treatment with no improvement. I was thinking about trying some Red Line or that Ford gear oil that Mazda people rave about but they want huge money for that just like the Moroso oil. I called the local speed shop and he recommended using plain old 10w-30 motor oil which is what he used at the track. I went ahead and got some Castrol GTX 10w-30 and put it in. Castrol also makes that Ford gear oil that's available in Europe under their own name. All I can say is it's much better. I took a 190 mile road trip with no problems. Shifts are much better especially when cold and even downshifting into second gear turning a corner is better. I don't know what the long-term ramifications of using this oil is but I was ready to chuck the transmission anyway. It's a lower mile transmission at around 100K. The car has 251K with a engine rebuild at 238 K. To talk about oils for a minute, the GL designation in gear oil stands for Gear Lubricant. GL-5 oil has twice the sulfur compounds of a GL-4 oil. The sulfur compounds are necessary for a hypoid gear differential and are not needed in a transmission and they tend to attack the bronze synchronizers anyway. In doing some research online I found out that Mopar is going to a thinner oil for standard transmissions to solve shifting issues. The Supra manual specifies 75w-90 GL-4 or 5 gear oil in the manual transmussion. All I can say is Castrol GTX 10w-30 motor oil works better for me.
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I rebuilt the transmission in 2014 with new synchros and bearings from driftmotion and Redline oil.
None of the old synchros or roller bearings were out of spec but the new components made a difference.
R154 transmissions are knotchy at best. That didn't change. No problems downshifting into 2nd while turning a corner now or noticing a difference after warming up. The 10W-30 thing was a last ditch effort. Don't try it unless you are out of options.

907mge · 12-02-2010, 09:11 PM

I would think 10w30 would be way too thin. I don't know though. The weight of the oil is usually choosen based on the way it was machined, but maybe yours is just gettin worn out and the clearances are getting larger. My friend runs royal purple in his r154 and I run it in my celica's 6spd. It seems to have made a difference in the feel of the shifting. I also have found alot of people like the redline light weight gear oil alot.

12-02-2010, 07:50 PM	#1
Bru Bone Stock w Upgrades ;-) Join Date: Apr 2010 Location: Tampa Bay Posts: 202	Putting 10w-30 oil in a R154 Transmission OK, it may sound like heresy but I was fed up with my sticky first to second gear and hard down shifting into second on turning a corner with my R154 transmission. I tried Mobile 1 and also Moroso Gear climbing oil and even added half a can of STP oil treatment with no improvement. I was thinking about trying some Red Line or that Ford gear oil that Mazda people rave about but they want huge money for that just like the Moroso oil. I called the local speed shop and he recommended using plain old 10w-30 motor oil which is what he used at the track. I went ahead and got some Castrol GTX 10w-30 and put it in. Castrol also makes that Ford gear oil that's available in Europe under their own name. All I can say is it's much better. I took a 190 mile road trip with no problems. Shifts are much better especially when cold and even downshifting into second gear turning a corner is better. I don't know what the long-term ramifications of using this oil is but I was ready to chuck the transmission anyway. It's a lower mile transmission at around 100K. The car has 251K with a engine rebuild at 238 K. To talk about oils for a minute, the GL designation in gear oil stands for Gear Lubricant. GL-5 oil has twice the sulfur compounds of a GL-4 oil. The sulfur compounds are necessary for a hypoid gear differential and are not needed in a transmission and they tend to attack the bronze synchronizers anyway. In doing some research online I found out that Mopar is going to a thinner oil for standard transmissions to solve shifting issues. The Supra manual specifies 75w-90 GL-4 or 5 gear oil in the manual transmussion. All I can say is Castrol GTX 10w-30 motor oil works better for me. ------------------------------------------------------------------- I rebuilt the transmission in 2014 with new synchros and bearings from driftmotion and Redline oil. None of the old synchros or roller bearings were out of spec but the new components made a difference. R154 transmissions are knotchy at best. That didn't change. No problems downshifting into 2nd while turning a corner now or noticing a difference after warming up. The 10W-30 thing was a last ditch effort. Don't try it unless you are out of options. Last edited by Bru; 04-15-2016 at 11:43 PM.

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12-02-2010, 09:11 PM	#2
907mge 20psi boost Join Date: Dec 2009 Location: Harrisburg Posts: 759	I would think 10w30 would be way too thin. I don't know though. The weight of the oil is usually choosen based on the way it was machined, but maybe yours is just gettin worn out and the clearances are getting larger. My friend runs royal purple in his r154 and I run it in my celica's 6spd. It seems to have made a difference in the feel of the shifting. I also have found alot of people like the redline light weight gear oil alot.