Carbon Fiber Blockers - what lube


Registered User
I recently rebuilt my M5R2 with the new carbon fiber blocker rings, a brand new 2nd gear and a good used 1-2 slider ring among other items. I used AC Delco synchromesh with the friction modifier included. I was surprised that the bottle listed it as 75W-80. Also surprised that it smelled just like gear lube - I don't recall the older GM synchromesh smelling like that.

I've put about 500 miles on the car since rebuild and haven't even tried a speed shift. Just drove like normal, letting it break in. A couple months ago I got in the car and literally drove 10 miles across town. Under normal shifting I got a grind on two occasions while going into 2nd gear. WTF?? I wasn't even remotely trying to speed was around 4500 rpm too.

I think this fluid isn't working out, but I have no clue what to try next. And I have little hope that I could actually shift this thing anywhere near my peak HP rpm which is 6600.

Do I try straight up ATF? Anyone got experience with these blockers? Hate to grind my stuff away while trying to figure out what fluid it wants.



Registered User
According to this article, regarding Tremec transmissions....

.... they say to use a non-detergent ATF Dexron 3. And they say specifically that if you have upgraded all carbon synchros, then you do not want to run heavier fluid and again recommend just running a quality name brand ATF DEX3 fluid. I don't know how to tell if something has detergents - so I'm just going with some Valvoline Dex/Merc 3. Can get a gallon jug for $25.


SCCoA Member
I have to run regular dex 3 in my t56 with carbon fiber blocker rings. I put some shaefers synthetic dex 3 equivalent in it and it didn't like it at all ive had to change it twice.

Scott Long

Registered User
I would try the Dex III as 75w80 is really thick stuff. Hopefully it helps since you have new blocker rings you shouldn't be getting any grinding with a proper fluid. I can't remember what we put in mine but it shifted good, just notchy on the 1-2 which I disliked and has had me wanting to swap it for an AOD if I ever race the car again.