Synchrotech D Series Transmission Synchro Master Rebuild Kit

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

If your D-series grinds going into a gear, the synchros are worn and it isn't going to improve on its own. This Synchrotech master kit is the complete fix: synchros for every forward gear plus the springs, sleeves, bearings, and seals to rebuild it properly while the case is open. Available in brass for a factory-quality rebuild or carbon for a real performance upgrade.

Check Your Speedo Gear Before Anything Else

Here's the thing that determines which kit you need, and it's easier to check than it sounds.

D-series transmissions share a great deal in common with each other. What differs between them is the speedo gear bearing size and color, and that's what separates the variants on this page.

Two things to note when you look:

Color: white or black
Size: 35mm or 40mm

Generally, the DX and LX cars run a white 35mm gear while the EX and Si cars run a black 40mm. But go by what's actually in your transmission rather than by the badge on your car, especially on anything that's been swapped, rebuilt, or assembled from parts over the last thirty years. These cars have been apart more than most.

How To Tell Your Synchros Are Done

A few reliable signs, and one test worth running.

It grinds into one specific gear. If everything shifts clean except second, that's second gear's synchro. Isolated grinding almost always means an isolated problem.

Downshifts are worse than upshifts. The useful one. On an upshift, revs are falling naturally and the synchro gets help. On a downshift it has to drag the clutch disc and input shaft up to speed by itself. If the car upshifts quietly but grinds or refuses on a normal downshift, your synchros are worn.

It's getting worse. Wear starts as slight notchiness and progresses to metal-on-metal grinding you feel in your hand.

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 far cheaper to fix than pulling a transmission.

Carbon Or Brass?

Both fix a grinding transmission. They suit different cars.

Brass is the OEM-style material and the right pick for most street cars. It restores factory shift feel, it's proven, and it costs less. On a D-series that's mostly stock and mostly driven, start here.

Carbon is Synchrotech's Pro Series, using a full carbon composite lining built on carbon-carbon technology originally developed for aerospace. The material acts as a braking element during engagement, stopping the gear faster, which means less grind on high-rpm shifts and less wear on your sleeves and engagement teeth. If you shift hard, run track days, drag race, or have built the engine, this is the one.

Straight talk on one point: carbon shifts better, but don't expect dramatically longer life than brass. You're paying for how it engages.

Check Your Hubs Before You Order

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

This kit includes new slider sleeves, so half of that equation is handled. But inspect your hubs and your engagement teeth before you close it up. Sharp and clean means this kit transforms the shift. Rounded off means you need hubs too, and finding out now is far better than after everything's back together.

What's In The Kit

• 1-5 synchros (carbon or brass, your choice)
• 1-5 synchro springs
• 1-5 slider sleeves
• 5 shaft bearings
• 2 axle seals
• Input seal

Find Your Kit

Select your material and transmission at checkout.

Two Things That Catch People Out

The 1996 changeover. Honda moved from the L3/S20 transmissions to the S40 for 1996, so a 95 and a 96 Civic with the same trim take different kits. Check your year carefully.

Trim doesn't always match reality. The DX/LX versus EX/Si split lines up with the speedo gear on an untouched car, but plenty of these have had transmissions swapped over the decades. Look at the gear itself rather than trusting the badge.

Worth Doing Once

Getting into a D-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 by a wide margin. So while it's open, inspect everything and replace what's genuinely past spec rather than what you assumed was bad.

Who Should Run This Kit

This is for anyone whose D-series has started grinding and who's ready to fix it properly, and for the builder going through a transmission during a swap or a refresh. These cars are thirty-plus years old now and the synchros in them have done a lot of shifting. Check your speedo gear, inspect your hubs, pick brass or carbon based on how you drive, and get your shifts back.

Fits: 1989-1991 Honda Civic, 1992-1995 Civic DX, EX, LX, and Si, 1996-2000 Civic DX, EX, and LX, 2001-2005 Civic DX, EX, and LX. See the table above for the correct kit. Materials: brass (OEM-style) or Synchrotech Pro Series carbon composite. Includes: 1-5 synchros, springs, and slider sleeves, 5 shaft bearings, 2 axle seals, and input seal. Important: select by transmission and speedo gear, not by vehicle trim.