Hey guys I am down to just my one RX7 and lately when i go to shift quickly from first to second anywhere above 5k rpms second gear grinds real bad. The car itself only has 67k original miles on it and its a 90 vert so its N/A. There isnt anything other than a K&N drop in done to the car so i know im not making too much power for the tranny.

Do you think it could be a bad syncro or what? its done it ever since i put synthetic fluid in the transmission, could the fluid just be too thin?

 

Yeah, the 2nd gear synchro is wearing out. NA transmissions are notorious for this. What brand / weight of oil are you using? Some are crappier than others.

 

2nd gear syncro for sure. Mine started at about 95k. If you want to try to extend th elife of the tranny you can try Neo Synthetic gear oil and see if that helps. Between all of the good synth gear oils (Royal Purple, Redline, etc.) Neo is the only one that came close to helping mine.

 

Do you notice this problem only when the car is cold?

Weirdly, my first-to-second shift quality also worsened a little when I switched from the previous owner's dino gear oil to Redline MT90. If I try to shift from first to second on a cold morning before the car has fully warmed up, there is a grind unless I double clutch. Once the car is warmed up or on a warm day, it shifts fine. Is synthetic gear oil like Redline more sensitive to temperature? I don't know. (Incidentally, my car and tranny have 39,000 miles on them and I first noticed this issue when I replaced the gear oil at 28K.)

 

MT-90 seems to have that effect when the car's cold.

Royal Purple 75W90 seems to work nicely on the street, cold or warm, but when I came off the track after a hot lapping session, purple smoke was emanating from my shifter.

 

My second gear doesn't grind but is notchy when cold, and gets smooth when the lube heats up. I think it is pretty normal unless you are getting a grind like trying to shift with the clutch engaged.

 

Same thing with my car.

OP- Double clutching helps me. I'm going to try using a better oil in the tranny soon since I just changed the transmission and put up a cheaper oil. The new should help out a lot, so that's what I'd reccomend you to do.

 

How many miles are on the fluid in the tranny right now?

 

The OP has the syncro going as has been stated.
The had shifting when cold was a problem from day one. When the customer complained many dealerships were installing ATF fluid to correct this condition, but I switched immediately to Redline which was an improvemet over the dino gear oil. One can see the resistance of the trans oil when cold, as after starting let the clutch pedal up and listen/watch the rpms decrease, the heavier the oil the more the decrease..

Just an FYI - '89TII purchased new, the trans was rebuilt (syncros) 88,000 miles under warranty, then again at 157,000 (syncros and a couple of bearings) and still going strong today.

 

Before I had my trans rebuilt it would shift fine 1-2 when cold, but as soon as it was up to temp the 1-2 shift would grind. It was especially bad at higher RPM. The trans shop gave me back all my old syncros, and the 2nd & 3rd syncros were pretty much totally toast. I ended up needing new 2nd & 3rd gears as well.

 

i would say as far as how old the fluid is, its prolly right around 5k miles. The car does do it worse when cold, but it always will do it if i trying to shift it quickly. I think im gonna go to a thicker dino fluid to help combat it. I do autocross and road course race it and thats when i first noticed it. I do down shift into second a lot from high RPM's on the road course and it sucks when your coming into a corner and its grinding as your trying to decelerate. I have valvoline synthetic in it with the factory weight also. would you guys recommend i try another synthetic or go to a thicker dino fluid?

 

You have worn out your syncros with your 'road racing' downshifting technique.

Remember, there was a time trannies didn't have syncros and drivers actually did the synchronizing using well practiced technique.

 

My 90 N/A requires either a slow cautious shift or a double clutch. I end up double clutching about half the time I'm going into second. I'm at 139k

 

Double clutching and heel-toe rev matching are difficult, but would totally fix your problem. I still have yet to do it well.

 

I was searching for a thread specifically like this cause I was reading thru the service bulletins
and came across something I had not seen mentioned on the forum before.

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DESCRIPTION

Basically it sounds like shifting into 2nd gear before sufficient warm up can be difficualt due to insufficient clearance between 2nd gear synchronizer ring and the 1-2 clutch hub. They changed the design in April of '91. Recommendation of the bulletin is to replace the parts in question with the new design if you are experiencing this problems and you are running a pre-April 91 Miata or RX-7 non-Turbo.


It's probably not relevant but I imagine something like this would cause where and tear more than normal.

New recommended replacement parts (in line with the post 91 spec)
2nd Synchronizer Ring - M502 17 265C
1-2 Clutch Hub Sleeve - M503 17 262A
1-2 Clutch Hub Set - M505 17 260B

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I hope this is useful and this is not a bad place to post it.