{"product_id":"jspm-close-ratio-gearset-for-tr4-tr6-gearbox","title":"JSPM Close Ratio Gearset for TR4-TR6 gearbox","description":"\u003cp\u003e\u003cspan\u003eJSPM Close Ratio Gearset for Triumph TR4 - TR6 gearbox. (gearbox not inlcuded) \u003c\/span\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cspan\u003eUsing an early (pre-1973) gearbox: 1st:  3.14 \/ 2nd: 1.63 \/ 3rd: 1.24 \/ 4th: 1 \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eUsing a late (1973-on) gearbox: 1st: 2.99 \/ 2nd: 1.71 \/ 3rd: 1.29 \/ 4th: 1 \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eFirst gear ratio remains as stock, making it much easier to move around the paddock and grid vs the tall first gear that was used in the “Sprint” gearset. \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eSubtle changes to the 1st \/ 2nd \/ 3rd ratios can be made if an early or late gearbox is used as the starting point. \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eThe second gear is designed to use the late, one piece steel top hat bushing, along with the thicker, less failure prone 2nd gear thrust washer.\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eOn the synchro mating surface, I have reduced the undercut at the gear, and also reduced the end chamfer.  This increases the contact area to the synchro ring, for maximum friction.  \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan\u003eWith the increased diameter of 2nd gear (on the laygear), a small amount of material must be removed from the support bridge for the reverse idler shaft to allow for clearance.\u003c\/span\u003e\u003cspan\u003e\u003c\/span\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan\u003eA small amount of thickness has been added to the layshaft gears to simplify the process of adjusting the laygear endfloat to the minimum spec.  \u003c\/span\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cspan\u003eIn the past, a custom distance piece was required in some cases to achieve endfloat at the minimum end of spec.  \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan\u003eWith this new design, the standard distance piece will need to be machined shorter during setup to adjust endfloat.  \u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan\u003eThis is a simple manual lathe operation.  For anyone who does not have access to this capability, we could easily handle this by mail. \u003c\/span\u003e\u003cspan\u003e\u003c\/span\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"JSPM Parts","offers":[{"title":"Default Title","offer_id":47249304584370,"sku":null,"price":1400.0,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0765\/0902\/0338\/files\/Screenshot2026-03-31102107.jpg?v=1774966905","url":"https:\/\/jspmparts.com\/products\/jspm-close-ratio-gearset-for-tr4-tr6-gearbox","provider":"JSPM Parts","version":"1.0","type":"link"}