I've had a few thoughts about tranny fluid this morning. See if what I'm thinking makes sense.

The inside of the tranny has several types of materials. Steel gears & hard parts, one bronze ring (reverse), and some sort of fiber material that is on the synchronizer blocker rings. My focus is on the synchro blocker rings and their purpose.

The blocker rings have a friction surface on them - much like a small clutch disc. This friction surface rubs against its (steel) partner, and performs the 'synchronizing' action. On the later trannies, this friction surface looks like really tight steel wool (I'm just describing the look). On the earlier trannies (like my '98), it really looks like a pad, but it has grooves / cuts in it. I've *heard* that the earlier tranny blocker ring pad surfaces were a "paper" variant (and not a "carbon fiber" like the later ones), but I'm not sure.

Now, back to the friction surface. If you're using a fluid that is too 'slippery', the blocker pad may not be able to effectively mate up to its smooth steel partner, and your transmission will feel notchy - you'll feel the blocker grab first, and then feel the gear grab next (as you're easing it in to gear).

Likewise, if your fluid isn't up to snuff, I could conceive that you could actually 'glaze' these blocker ring pads, thereby removing their synchronizing ability - and end up with a notchy, hard to shift tranny as well.

The reason I am thinking about this... I've been using the cheap tranny fluid (any old Dexron III ATF I could find - Coastal, AAmco, etc) in my T56. And it's the notchiest one I've ever driven. I did rebuild it with new blocker rings last year, and I have changed the fluid frequently (every few months of driving), but I am starting to wonder if the fluid was either (a) too slippery, or (b) I glazed the pads.

I have a freshly rebuilt T56 sitting in the garage right now (my spare). I am going to put it in this week, but will now be using GM Synchromesh fluid. Apparently the SM fluid is formulated to provide the correct amount of 'slippery, yet grabby' mix of additives for the blocker pads, with proper formulation for the bronze parts.

If anyone wants to see the actual difference between the earlier and later style synchro blocker ring pads, I could post them up tonight.

Does this make sense?

Andrew

 

For that reason I run 1 bottle of GM limited slip additive in my tranny...

Seems to really help the high-rpm shifting

 

I've always run the Honda ATF tranny fluid, and never had any problems (over 100k now ) nor needed rebuilds (knock on wood). I tried mobil 1 atf once (synthetic) and drained it out within 10 miles (notchy).

Chris

 

There has been talk of GM Synchromesh being bad for 98-00 transmissions. Others swear by it. What is the deal?

 

The difference between the earlier and later trannies is the material that the blocker ring pads are made of. The difference is VERY obvious when you have 2 rings side by side. The earlier material (which looks like a dense pad with square cuts in it) is very different from the later material (which looks like pressed steel wool).

Perhaps the synchromesh doesn't play with the earlier pad material as well. I don't know, but it would make sense. And perhaps the cheaper Dexron III ATF's don't play with the later pads as well. I'd be tempted to just drain my current tranny and swap in some Synchromesh, but I've got the fresh tranny ready to go, and I want some good times at the Shootout.

 

I talked to ELCO Chevrolet, and the guy said he has never heard of a problem with GM Synchromesh in these transmissions.

 

There is at least one person on corvetteforum running Synchromesh in a '00. I'm going to try it in my '99, if I screw it up so be it.

Eric

 

I have Synchromesh in my 99.