M5OD-R1 advice

[sgtsandman]

It depends on the design of the transmission. I've seen transmissions that use gear oil, ones that used modified 5W-30 motor oil, and of course ones that use some form of ATF. Me personally, I prefer to use something compatible with what is supposed to be in the transmission if not what the manufacturer specifies. To each their own on straying from that. I don't pay your bills.

 

[PetroleumJunkie412]

Had really good luck with MT90 in my FM146. YMMV.

 

[Ranger-Roush]

Do not do this.

GL-5 rated gear lube will eat the synchros in your transmission over time. It happens because there is a chemical reaction between sulpur/phosphorus and the bronze synchronizer rings in your transmission. A thousand miles is probably no big deal but you need to drain it and refill with ATF or anything other than gear lube, run it a week or so, and change the fluid again to flush out the remaining gear lube.

GL-4 rated gear lube is OK to use in the older TK and FM transmissions made in the 80's but NOT the M5OD manual trans in our trucks.

I'm not sure where you heard that it's OK to do this but it's simply NOT... you might as well be changing your oil with brake fluid too.

While i appreciate the input, your analogy is off by a long shot. I have a 96 ranger that i replaced the ATF with gear lube almost 10 years ago when the truck had somewhere around 100K miles. It now has 218K miles on it with no issues and shifts flawlessly. Now i put 75w90 in that truck which has a lower sulfur and phosphors content than the 75w140, and is not a viscous so i will replace it with that this weekend.
Now with that said i would like to point out the only reason to replace the ATF with gear lube is to remedy a transmission with worn out syncros, like i said after replacing the clutch, slave, throw out bearing, pilot bearing, and master it still shifted hard. The gear lube has a significantly higher dynamic coefficient of friction (compared to ATF) which significantly reduces the "free -wheeling torque" of the input shaft when the clutch is depressed which in turn makes it significantly easier to make a gear change. If you were at a cross roads to either rebuild or replace you transmission, you could try this. It has worked great for me, i'm sure it has an impact on the gas mileage, but it sure beats spending the money on parts, and again, what do you have to loose if your syncros are already worn out.

 

[racsan]

Ive ran pennzoil syncromesh fluid in mine before. when I first got my 94 the trans was low on fluid and had gear oil in it, I didnt have any atf on hand and wanted to change it right away. I used 303 tractor hydraulic oil. Didnt leave it in long, maybe a month then replaced with the pennzoil stuff. havent had any issues with it. When I had got a rebuilt M5OD for my previous truck (the 93 4x4) there was a tag on the transmission that said to use 5w30 synthetic engine oil. I thought that was strange but did it anyhow. Drove it another 100K + miles, it never did like to downshift- had to pause between gears downshifting and “blip” the gas pedal, going up through the gears was fine. Had a hurst shifter on it and the same hurst is in the truck im driving now. Its well worth the money. Way back in my younger days I had a jeep CJ-7, 4 speed. Like a fool I thought gear oil was better in a manual transmission than atf. I drained it and put in 80w90. well you couldn’t hardly shift it after that once winter came and then the transmission was horribly noisy. I put atf back it but transmission was permanently damaged. sold it for the payoff amount of the loan. (it was too damn cold for me in the winter anyhow) . Now yes there are transmissions that do use gear oil ( back in the day creeper 1st 4-speeds come to mind) , but you can do damage by running the wrong oil.

 

[Shran]

While i appreciate the input, your analogy is off by a long shot. I have a 96 ranger that i replaced the ATF with gear lube almost 10 years ago when the truck had somewhere around 100K miles. It now has 218K miles on it with no issues and shifts flawlessly. Now i put 75w90 in that truck which has a lower sulfur and phosphors content than the 75w140, and is not a viscous so i will replace it with that this weekend.
Now with that said i would like to point out the only reason to replace the ATF with gear lube is to remedy a transmission with worn out syncros, like i said after replacing the clutch, slave, throw out bearing, pilot bearing, and master it still shifted hard. The gear lube has a significantly higher dynamic coefficient of friction (compared to ATF) which significantly reduces the "free -wheeling torque" of the input shaft when the clutch is depressed which in turn makes it significantly easier to make a gear change. If you were at a cross roads to either rebuild or replace you transmission, you could try this. It has worked great for me, i'm sure it has an impact on the gas mileage, but it sure beats spending the money on parts, and again, what do you have to loose if your syncros are already worn out.

My analogy may be off a little but the point remains: GL-5 spec gear lube is specifically formulated for a purpose and it says NOT manual transmissions with copper or bronze synchros. I dump generic 80w90 in my old 4 speeds, the synchros in those are steel, it will not hurt them. On that same note, the old TK and FM Ranger transmissions call for GL-4 which has significantly less sulphur and phosphorus additives and is safe (but my god, they do not shift easy when it's cold!) I imagine that the gear lubes you have been using are GL-5 rated... it is quite hard to find GL-4 fluid.

The solution for worn parts, rather than a rebuild, is an engine oil heavier than ATF, IMO. It has nothing in it that will harm anything and will do exactly like you refer to - make up for loose, worn parts. ATF is just about at water consistency at operating temp - something like 10w-40 or 15w-40 or even 20w-50 could work well. As I said earlier, I had excellent luck with 5w-30 in one instance.

I am all for trying new lubes and stuff if it works better but I also don't want to see someone with little mechanical knowledge dump the wrong oil into a nice, low mileage trans and ruin it because they read this thread.