Synchrotech Transmissions K Series Gear Set Hub

Synchrotech Synchro Hubs - K20 & K24 (RSX, TSX, Civic Si & More)

The hub is the foundation of the whole synchro assembly, and it's the part people skip. It's splined directly to the transmission shaft and everything else rides on it, so when the hub is worn, nothing you bolt around it will fix your shifting. If you've replaced synchros and the transmission still feels wrong, this is very often why. These are Synchrotech's replacement hubs for K-series transmissions, sold individually per gear set.

Which Part Do You Actually Need?

Three parts, three different symptoms. Match yours before you spend money.

That third one is what brings people to this page. A worn hub means the sleeve can't slide cleanly along its splines anymore, so it binds or cocks slightly instead of moving straight. What you feel is a shifter that moves normally right up to a point and then wants serious effort to finish the shift, or a gear that feels blocked even with the clutch all the way down. It's different from a grind and different from a pop-out, and it's the symptom most likely to get misdiagnosed as something else.

What The Hub Does

Simple job, critical role. The hub is splined to the transmission shaft, so it always spins with the shaft. The sleeve rides on the outside of the hub on those same splines, sliding back and forth to lock in whichever gear you selected, and the synchro springs and keys sit in the hub too. So the hub is what everything else is mounted to and referenced from. If those splines are worn, chewed, or wobbling, every part riding on them is compromised no matter how new it is.

Why This Is The Part That Makes Or Breaks A Rebuild

Here's the advice worth more than anything else on this page. Plenty of people replace their synchros, close the transmission up, and find the shift is barely better than when they started. The reason is almost always worn hubs and sleeves. New carbon synchros on a worn hub are no better than new brass on a worn hub, because the problem was never the friction surface.

So when you have the transmission apart, inspect the hub splines carefully. They should engage smoothly with no binding and no play. If the sleeve wobbles on the hub or drags as you slide it by hand, replace the hub. Doing the synchros and skipping a worn hub is how a rebuild disappoints you.

Sold Per Gear Set

Each hub serves a pair of gears, so a transmission uses three: one for 1st and 2nd, one for 3rd and 4th, and one for 5th and 6th. They're sold individually because wear is rarely even. The 1/2 hub usually takes the worst of it, since first and second see the most aggressive engagement and the most launches. If that's the only one past spec, replace it and leave the others alone.

Fits These K-Series Transmissions

Select the hub matching the gear pair you're replacing.

Do It Once

Getting into a K-series transmission is the expensive part of this job, whether you're paying a shop or spending your own weekend. The parts are the cheap half. So while you're in there, inspect everything, the hubs, the sleeves, the synchros, and the engagement teeth on the gears, and replace what's past spec rather than what you assumed was bad. That's how you close it up once and get the shift you were after.

Who Should Grab A Hub

This is for anyone whose shifter binds or blocks out going into a particular gear, and for the builder going through a transmission who's found a hub with worn or sloppy splines. It's also for the person who already did synchros and didn't get the result they wanted. Fix the foundation and everything riding on it works the way it should.

Fits: K20 and K24 transmissions in the 2002-2006 Acura RSX Type-S and Type R, 2004-2008 Acura TSX, 2013-2015 Acura ILX, 2002-2005 Honda Civic Si and Type R, 2006-2011 Honda Civic Si and Type R, 2012-2015 Honda Civic Si, and 2003-2007 Honda Accord. Sold: individually, per gear set. Coverage: 1st/2nd, 3rd/4th, and 5th/6th, three hubs total per transmission.