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Problem running neo synthetic in transmission

I changed the transmission fluid to neo-synthetic 75W-90 HD recently. Drained and filled to spec. However, after dropping the car to do a test drive it was intermittently difficult or impossible to put the car into 1st, 2nd, 5th, or reverse. I took the car around the block to run through the gears and still had problems shifting. Sometimes I could shift through the gears easily. Other times it felt like I was moving the shifter through molasses. And sometimes I was completely locked out. I found that I could go from 3 then 2 then 1 when stopped when I was locked out of 1st and 2nd. When I was locked out of 5th I would have to come to a complete stop to get it back. It felt like the synchros were shot but I knew it had to be related to the fluid change. 3 and 4 always worked.

Wanting to rule out the fluid I changed to Redline MT-90. After some initial difficulty shifting to 1,2,5,R I noticed that the side to side movement of the shifter freed up and gear selection became easy again. 5th gear took the longest to get back after the fluid change. I was locked out of it for a couple drives intermittently.

I did quite a bit of research on transmission fluids and I haven’t seen anyone else with this issue. What was odd to me was how the lever was binding up left to right. I believe that’s why it was difficult to get the car into gear (hanging up on the synchros?) and grinding occasionally. Has anyone else run into this issue before?

1993 Rx7 with 113,000 miles
Transmission may have been replaced at 90,000 but records are somewhat unclear.

I ran Red Line in my car for years with no issues. After switching to Neo, I noticed that the car was a bit more difficult to shift when it was cold. Once it warmed up, shifting seemed better than with the Red Line.

Just did mine and drive in 20 degree weather fine. Love it since my grind in second and third is gone now.

I've run Redline for years, recently started running Idemitsu. The Idemitsu has been great, no complaints.

That's really odd about the Neo!

Dale

I currently have NEO in my car. Previously ran Redline. Both worked well but NEO cool/cold performance is like Adam described...a little notchy (especially 1/2) but improves noticeably when it warms up a little.
Before you change fluid again, wait until it warms up a bit. And if you haven't recently, pull the shifter and check to make sure all your shifter bushings are good. And be sure to grease the ball-pivot and lower bushing before re-submerging in the gear oil bath.

I guess I'm the odd man out here cause I switched from redline to royal purple and I've noticed smoother engagement and more ease with shifting. I will admit that shifting is a bit notchy when its cold but it does warm up quickly.

Well, I'll chime in here I guess. I switched to Neo-synthetic 75W-90 HD way back in 1997. Twenty-five thousand miles later that oil is still in there. :eek:
So, after 25k miles of mostly club driving events and several track events I've had no problems except; no quick shifting allowed until the transmission fluid is warmed up, otherwise 2nd gear will crunch. But, that problem has been with the car since it literally rolled off John Hine Mazda's showroom floor. Before settling on Neo I had tried Red Line, and Royal Purple. For my transmission the Neo was the least crunchy when cold.

Quote:

Originally Posted by Sgtblue (Post 12263218)

When I switched to redline all the shifting issues ceased after a couple drives. The shifter bushings were replaced and ball-pivot greased prior to changing the fluid. The difficulty shifting only happened when the fluid was changed. I don't know what type or brand of fluid was in the trans previously but perhaps there was some sort of reaction between it and the neo-synthetic.

Quote:

Originally Posted by mdp (Post 12263266)

That was my hope when choosing Neo. Perhaps the residual old fluid and Neo reacted in a way to bind up the side to side movement of the shifter. So far MT-90 is working well and I haven't had any further issues or notchiness since changing.

anyone using or recommends the magic Motorcraft trans fluid that is so loved in Miata, S2k, RX8 and other clubs?

For years I ran Red Line MT90 with good results.
Then I got some Pettit Rev-O-Max trans oil from a friend to try out.
Hot shifting was about the same to maybe slightly better.
It was cold driving that it showed it was better. The REv-O-Max is easier and quicker to shift.
I have been using it now for about 10 years.

I've run into the same problem when i installed the wrong weight transmission lube before 75-140W when it called for 75-90W it was shocking how much the trans hated it.

neo synth.. other than the notchy cold start up its smoother once warm than any that ive used to date...