{"product_id":"synchrotech-l15b-transmission-synchro-master-rebuild-kit-17-20-civic-si","title":"Synchrotech L15B Transmission Synchro Master Rebuild Kit","description":"\u003cul\u003e\n\u003cli\u003eReplacement Synchros for L15B Transmission \u003c\/li\u003e\n\u003cli\u003eComplete Rebuild Kit with Seals, Sleeves, Bearings, and Springs \u003c\/li\u003e\n\u003cli\u003eCompatible with 10th Gen Civic Si\/EX-T \u003c\/li\u003e\n\u003cli\u003eInspect Hubs Before Ordering \u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003c!-- split --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli\u003e\u003ca class=\"active\" href=\"#Description\"\u003eDescription\u003c\/a\u003e\u003c\/li\u003e\n \u003cli\u003e\u003ca href=\"#VehicleFitment\"\u003eVehicle Fitment\u003c\/a\u003e\u003c\/li\u003e \u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\n\n\u003cli class=\"active\" id=\"Description\"\u003e\n\u003ch3\u003eSynchrotech L15B Synchro Master Rebuild Kit - 2016-2020 Honda Civic EX-T \u0026amp; Si\u003c\/h3\u003e\n\n\u003cp\u003eThe 10th gen Si is a genuinely good car, and it's now old enough and driven hard enough that transmissions are starting to need attention. If yours grinds going into a gear, this is the complete fix: synchros, 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.\u003c\/p\u003e\n\n\u003ch4\u003eYes, These Wear Out Too\u003c\/h4\u003e\n\n\u003cp\u003eWorth addressing, because people don't expect synchro problems on a car this recent.\u003c\/p\u003e\n\n\u003cp\u003eThe 10th gen Si is a car people shift hard. It's a turbo four with a good gearbox and an owner base that uses it, which means these transmissions accumulate aggressive shifts faster than a commuter would. Add a tune, more boost, or track days and the loads go up further.\u003c\/p\u003e\n\n\u003cp\u003eSo a grinding L15B isn't a sign something went wrong. It's a sign the car got used the way it was built to be used, and now the synchros want replacing.\u003c\/p\u003e\n\n\u003ch4\u003eHow To Tell Your Synchros Are Done\u003c\/h4\u003e\n\n\u003cp\u003eA few reliable signs, and one test worth running.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eIt grinds into one specific gear.\u003c\/strong\u003e If everything shifts clean except third, that's third gear's synchro. Isolated grinding almost always means an isolated problem.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eDownshifts are worse than upshifts.\u003c\/strong\u003e 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eIt's getting worse.\u003c\/strong\u003e Wear starts as slight notchiness and progresses to metal-on-metal grinding you feel in your hand.\u003c\/p\u003e\n\n\u003cp\u003eOne 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 than pulling a transmission.\u003c\/p\u003e\n\n\u003ch4\u003eCarbon Or Brass?\u003c\/h4\u003e\n\n\u003cp\u003eBoth fix a grinding transmission. They suit different cars.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eBrass (SYN125B)\u003c\/strong\u003e is the OEM-style material and the right pick if the Si is your daily. It restores factory shift feel, it's proven, and it costs less. If you're refreshing the car and want it back to how it felt new, start here.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCarbon (SYN125)\u003c\/strong\u003e 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 over time. If you're tuned, running boost, or seeing track days, this is the one.\u003c\/p\u003e\n\n\u003cp\u003eStraight talk on one point: carbon shifts better, but don't expect dramatically longer life than brass. You're paying for how it engages.\u003c\/p\u003e\n\n\u003ch4\u003eCheck Your Hubs Before You Order\u003c\/h4\u003e\n\n\u003cp\u003eThe 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 one.\u003c\/p\u003e\n\n\u003cp\u003eThis kit includes new 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.\u003c\/p\u003e\n\n\u003ch4\u003eWhat's In The Kit\u003c\/h4\u003e\n\n\u003cul\u003e\n    \u003cli\u003eSynchros for every gear (carbon or brass, your choice)\u003c\/li\u003e\n    \u003cli\u003eSynchro springs\u003c\/li\u003e\n    \u003cli\u003eSlider sleeves\u003c\/li\u003e\n    \u003cli\u003eBearings\u003c\/li\u003e\n    \u003cli\u003eSeals\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eThat's a complete rebuild rather than a partial one. Everything that wears is covered, which is the point of a master kit versus replacing one synchro and going back in a year for the next.\u003c\/p\u003e\n\n\u003ch4\u003eWorth Doing Once\u003c\/h4\u003e\n\n\u003cp\u003eGetting into the 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.\u003c\/p\u003e\n\n\u003cp\u003eSo while it's open, inspect everything and replace what's genuinely past spec rather than what you assumed was bad. That's how you close it up once and get the shift you were after instead of doing this again next year.\u003c\/p\u003e\n\n\u003ch4\u003eFitment\u003c\/h4\u003e\n\n\u003cp\u003e2016-2020 Honda Civic EX-T and Si (L15B)\u003c\/p\u003e\n\n\u003cp\u003eCarbon: SYN125\u003cbr\u003eBrass: SYN125B\u003c\/p\u003e\n\n\u003ch4\u003eWho Should Run This Kit\u003c\/h4\u003e\n\n\u003cp\u003eThis is for the 10th gen owner whose transmission has started grinding and who wants it fixed properly, and for the builder refreshing a gearbox on a car that's making more than it did stock. Inspect your hubs, pick brass or carbon based on how you actually drive, and get your shifts back.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFits:\u003c\/strong\u003e 2016-2020 Honda Civic EX-T and Si (L15B). \u003cstrong\u003ePart numbers:\u003c\/strong\u003e SYN125 (carbon), SYN125B (brass). \u003cstrong\u003eMaterials:\u003c\/strong\u003e brass (OEM-style) or Synchrotech Pro Series carbon composite. \u003cstrong\u003eIncludes:\u003c\/strong\u003e synchros, springs, sleeves, bearings, and seals.\u003c\/p\u003e\n\u003c\/li\u003e\n\n \n\u003cli id=\"VehicleFitment\"\u003e\n \u003cp\u003e2016-2020 Honda Civic EX-T\u003cbr\u003e2017-2020 Honda Civic Si\u003cbr\u003e\u003cbr\u003e\u003c\/p\u003e \n\u003c\/li\u003e\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\u003c\/ul\u003e\n","brand":"Synchrotech Transmissions","offers":[{"title":"Carbon","offer_id":46745643188258,"sku":"SYN-MK-SYN125","price":808.45,"currency_code":"USD","in_stock":false},{"title":"Brass","offer_id":46745643221026,"sku":"SYN-MK-SYN125B","price":750.7,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/2218\/5701\/files\/SYN-MK-SYN125_698d.png?v=1788291895","url":"https:\/\/www.hybrid-racing.com\/products\/synchrotech-l15b-transmission-synchro-master-rebuild-kit-17-20-civic-si","provider":"Hybrid Racing","version":"1.0","type":"link"}