Synchrotech K Series Transmission Synchro Master Rebuild Kit

Synchrotech K-Series Synchro Master Rebuild Kit - Carbon or Brass

If your K-series grinds going into a gear, you've probably already made peace with it. You slow the shift down, you baby third, you double clutch without thinking about it. That's a worn synchro, and it doesn't get better on its own. This Synchrotech master kit is the complete fix, every synchro your transmission uses plus the springs, bearings, sleeves, and seals to do the job properly while it's apart. It's available in brass for a factory-quality rebuild or Synchrotech carbon for a genuine performance upgrade.

What A Synchro Actually Does

Worth understanding before you spend money, because it explains why the fix is what it is. Your transmission uses a synchromesh system, and the synchro is the friction ring at the heart of it. When you shift, the gear you're selecting is spinning at a different speed than the shaft it needs to lock onto. The synchro grabs that gear and drags it to matching speed in a fraction of a second, so the teeth mesh cleanly instead of colliding. When that friction surface wears down, the synchromesh can't do its job fast enough anymore, and the teeth clash. That's the grind you hear.

How To Tell Yours Are Bad

A few reliable signs, and one genuinely useful test.

It grinds going into one specific gear. This is the classic. If everything shifts clean except third, that's third gear's synchro. Isolated grinding almost always means an isolated synchro rather than a transmission-wide problem.

Downshifts are worse than upshifts. This is the test worth running. On an upshift, engine revs are falling naturally and the synchro gets help. On a downshift, the synchro has to drag the clutch disc and input shaft up to a much higher speed all by itself. So if your car upshifts quietly but grinds, fights, or flat refuses on a normal downshift, your synchros are the problem.

It's getting worse. Synchro wear starts as slight notchiness or a light click through the shifter and progresses to metal-on-metal grinding you feel in your palm. If it's worse this month than it was last month, that's the pattern.

You're forcing gears or it pops out. Having to push harder than you used to, or a gear that won't stay in, both point the same direction.

One honest note: grinding can also come from a clutch that isn't fully disengaging or from low or wrong transmission fluid. Rule those out first, they're a lot cheaper to fix than pulling the transmission.

Carbon Or Brass? Here's How To Choose

Both fix a grinding transmission. They suit different cars.

Brass is the OEM-style material and the right call for most street cars. It restores factory shift feel, it's proven over decades, and it costs less. If you're refreshing a daily driver or a mostly stock car, start here and don't overthink it.

Carbon is Synchrotech's Pro Series, and it's a genuinely different thing from OEM brass or the spray-coated and woven-fabric carbon synchros out there. These use a full carbon composite lining built on carbon-carbon technology originally developed for aerospace, and the material acts as a braking element during engagement. It stops the gear faster, which means less grind on high-rpm shifts and less wear on your sleeves and engagement teeth over time. If you're shifting hard, running track days, drag racing, or making real power, this is the one.

We'll be straight about one thing: Synchrotech carbon shifts better, but don't buy it expecting dramatically longer life than brass. You're paying for how it engages, not for extra mileage.

Check Your Hubs And Sleeves Before You Order

The most important advice on this page, and the thing most listings skip. Synchros work against your hubs and sleeves, and if those are worn, new synchros of any material won't fix your shifting. New carbon on chewed-up hubs is no better than new brass on chewed-up hubs.

So open the transmission and inspect before you buy. Look at the engagement teeth, the sleeves, and the hubs. If they're sharp and clean, a synchro kit will transform the shift. If they're rounded off or damaged, budget for those parts too, because otherwise you'll do all this work and be disappointed. Synchrotech makes hardened steel sleeves and hubs if you need them.

Worth Doing Once

Getting into a K-series transmission is most of the work on this job, so the parts are the smaller part of the equation. That's the argument for a master kit over replacing a single synchro: you're already in there, the labor is spent either way, and a one-gear fix means doing it all again when the next one goes. Whether you're paying a shop or spending your own weekend, do it once and do it completely.

What's In The Master Kit

• Synchros for every gear your transmission uses
• Synchro springs
• Bearings
• Sleeves
• Seals

The kit matches your transmission, so a 6-speed application gets six gears' worth and a 5-speed gets five plus reverse. Everything that wears in there is covered, which is the whole point of a master kit.

Pick The Right Variant, This Is The Critical Part

Read this carefully, because K-series transmissions use different synchro designs and the kits are not interchangeable. The difference is cone count, meaning how many friction surfaces each synchro uses. More cones means more friction area and more synchronizing capacity, and Honda used different designs across the lineup and even across model years of the same car.

That's why the RSX Type-S is split into two different kits by year. An 02-04 and an 05-06 are not the same inside. Find your car below:

If you're not certain which design your transmission uses, check the transmission code on the case before ordering. Getting this wrong means parts that won't work in a job that takes real effort to get into.

Who Should Run This Kit

This is for anyone whose K-series has started grinding and who's ready to fix it properly rather than driving around it. Refreshing a high-mileage transmission, building a gearbox during a swap, or upgrading a car that gets shifted hard, this is the complete synchro package. Inspect your hubs and sleeves, pick brass or carbon based on how you actually drive, match your variant carefully, and get your shifts back.

Fits: K20 and K24 transmissions, see the variant table above. Materials: brass (OEM-style) or Synchrotech Pro Series carbon composite. Includes: synchros, springs, bearings, sleeves, and seals. Coverage: all forward gears, plus reverse on 5-speed applications. Important: select the variant matching your exact model, year, and synchro cone design.