Come to a complete stop before shifting into reverse and it won't grind.

 

Today I switched it back out to some fresh Syncromesh and the trans is shifting better than it ever has, I think the fluid leaked out some and was low when i bought the truck. I'll leave it like this and see how it does in the long run. I kept the fresh Mercon I drained out- maybe when I buy that classic F100 truck I want I'll clean out the valves with it or something The ATF seems very thin when at the operating temp of the transmission which might explain why when it's not warmed up yet it shifts good until that point. The reverse still grinds even at a complete stop unless it's eased very slowly into reverse, which is fine by me as I'll just be careful

 

It's not possible for reverse to grind if you're at a complete stop. It's likely your clutch isn't fully disengaging, which would also make shifts hard, and make it particularly hard to get into 1st and Reverse

 

Reverse synchro is probably just worn down. Not sure why you changed back to the synchromesh fluid. I guess you know what is better for the transmission than the engineers that recommended Mercon.

 

The synchromesh is likely a bit stickier in consistency, thus it helps with the worn brass to work better. Won't hurt anything. Just a band aide fix.

The size of tire has not much to do with wearing out synchros. It is driving habits.

In any vehicle before the 80's you had to stop completely and then carefully put it in reverse. These transmissions have a synchro in reverse which if you use it too much, wears out, and then you are stuck doing it "the old fashion way".

 

I've run my M5R2 on synthetic 10W-30 motor oil for a few years and it's worked just fine. This wasn't some crazy idea I came up with. There's actually an older Mazda technical document that recommends this fluid precisely.

 

so is it a gallon of ATF fluid or 5 quarts that is needed to fill it up properly ?

 

As much knowledge as this forum has to offer, skip it in favor of bobistheoilguy forums when dealing with lubricants. I've run dino and syn ATF after draining the ATF/gear oil blend the po had in the trans. After digging through MANY threads on bobs forum I tried the cheapest syn MTF and the trans is smoother then it's ever been.

 

Hi,
Just put in a Eagle Sales $1400 M5OD tranny in my 89 F-150 XLT Lariet!

Used Amsoil Syn ATF and it works great!!!

http://eagleenginesales.com/transmissions/

 

My '89 owners manual says refill is 3.8 quarts of MERCON ATF.