Manual transmission oil: anyone else try this yet?

I actually started this back in October after I rebuilt my transmission, I just didn't tell anyone . Now that I have almost 10k miles and seven months on it, I figured I should ask.

So since my Aisin R155F five speed is so so very similar to the Aisin AX5/AX15 trannies used in '90s Jeeps, and Toyota didn't exactly wow me with the longevity of its bearings with their 75w90 gear oil recommendation, I figured I'd try Chrysler's instead. Now that the new synchros have a few miles on them I know it shifts a lot better. Like, almost as well as my old EJ Honda Civic, and that's saying a lot.

Chrysler used to recommend 90W GL3 for those trannies, but since there were so many synchro problems with people mistakenly using GL5 and bad shifting quality in general, they later updated the part number to a widely available oil with similar hot viscosity and no hypoid additives: 10w30 motor oil.

Was just wondering if I was the lone guinea pig or if someone has used it before. Personally I like the idea of $7 per tranny oil change so I don't worry about changing it once a year.

 

I always wondered about this, but was curious how the detergents in normal motor oil would react.

 

You must be doing a ton of miles to need changing every year.

 

What about a high quality oil like royal purple or redline? I wonder if the extra cost of these "premium" oils would offset with longer safe service life.

 

I had redline mt90 in there for 21k miles prior to the rebuild

 

How long is it typically good for?

 

I've owned a Mercedes that used 10w-40 engine oil in it's 4 speed transmission and my F250 used ATF in the transfer case. I've had good results from AmsOil gear oil in my Tacoma.

 

Probably 99% of the vehicles on the road will never have it changed.

 

Chrysler has called for 10W-30 engine oil in manual transmissions for a while...I recall my mother's 1987 Omni spec'd it. (Though my 1985 Charger spec'd ATF.) I know four people with AX15's (three Jeeps, one Dakota) and all use 10W-30. One Jeep has an internally-untouched trans with 230,000 miles.

If (when) I get a Taco, I think the trans will get 10W-30.

 

Update

After 10k miles I drained the oil out of the trans and it looked fine (no surprise there). I think it was thinning a little bit because the shifts were starting to get a little notchy-feeling. That was always the problem in Honda transmissions... some people back in the day did UOAs on the Honda MTF and it would start out new as about 20w, but by 25k miles they were down to about 5w or less. I really wonder if the 75w90 oil that Toyota uses at the factory does this a little too. When I drained it after I bought the truck at 123k miles, the fill/drain plugs really looked like they had never been touched, and on a cold snowy March day with a cold tranny the old stuff drained way, way faster than the MT90 did going in.

Anyways I'm trying Mobil1 0w40 this time, that stuff they make for VW cars. Back to smooth. Feels a little more like the MT90 did, aka slightly lazier shifts, but it doesn't have the warmup time and I can still shift into 1st gear on the move with just a blip of the gas and no effort (like I could do with the 10w30).

Somewhat off topic... I see the new R156 gets a triple cone synchro for 1st gear, think that'll eliminate no-man's land? Well, maybe, maybe not... the new gears are spread even wider than ours. That wouldn't be fun to have to shift out at 5500 if you want 3000 rpm in 2nd gear.