Piston Slap: Synchromech-ity

Longtime TTAC Commentator dolo54 asks:

You mentioned using GM syncromesh in your recent Piston Slap article. I have a 91300zx (NA) that has a very typical problem for the model. The syncro for the 5th to 4th gear change is worn (they were made out of too soft a metal until the 95 transmission). I use the recommended Red Line MT-90 transmission oil, which helped quite a bit. But I still get a bit of a grind unless I double clutch the downshift. I’m wondering if I could use this synchromesh safely. I’ve read that you can use a more slippery oil to cure the problem in the short term, but it increases wear and in a short time the syncro will be gone completely (great for a sleazy salesman I suppose). How does synchromesh work and would it speed damage to an already worn syncro?

Sajeev answers:

We have a saying here in Texas: pour some sawdust in the tranny and that shit’ll clear right up. Or not.

Now let’s get serious. Unlike the Red Line oil(CHECK) used in your transmission, Synchromesh is a mix of oil and additives. After a little Internet research, people are guessing that Synchromesh is made of 5w30 non-detergent oil with friction modifiers and an EP additive, which supposedly works well under “extreme pressures.” Sounds about right to me.

I’ve seen Synchromesh’s trio of unique properties fix an early 1990s Maxima gearbox that (formerly) needed granny shifting on the 1-2 upshift. Considering the chance that “EP” additives can cushion a fragile 4-5 synchro, your Z might follow the Maxima’s lead. So if you have $150 to spare, give it a shot: buy Synchromesh and save some cash for new Red Line if it fails. Or save your current Red Line in leftover Milk jugs if it is relatively new and clean.

[Send your technical queries to mehta@ttac.com]