Zipper’s manufactures the strongest transmission door for Big Twin 5 speed transmissions. This double row ball bearing design provides more shaft support than any other product on the market!
This door is the ideal choice for any high performance or hard core racing application.
These doors will give you:
Improved shifting
Less frictional losses
Added Support for durability in large power output applications
Machined from 6061 billet - available in either aluminum or black powder coated finish, includes double row bearings, spacers and shaft nuts for assembly.
Manufactured, with pride, in the USA!
In high output applications, we’ve seen the primary bearing race on 1985-2007 models that is pressed onto the main shaft walk in to the main drive gear and damage it, requiring expensive repairs. This unit replaces the two-piece H-D® bearing with a single sealed unit, similar to the earlier model bearing used successfully for years. Requires the seal listed below for wet applications. Fits all 1985-2006 Big Twins; requires # 872-527 seal and original equipment bearing and race removal.
The ‘Zip-Rack’ is a fully assembled shaft and gear set that has been treated with our famous back-cut service. We start with a full set of new Andrews gears and shafts. The engagement dogs are carefully machined to the proper rake and depth by Zipper’s for positive engagement, eliminating missed shifts at high RPM. The gears and shafts are assembled with new thrust washers and bearings, then installed on a billet door.
Big Twin models are assembled using our billet transmission door specially machined to include super-strong double-row ball bearings which minimize shaft flex while providing the best support and strength possible. Machined billet or black powder coat finish.
This trap door can be used as a heavy duty stock replacement or as a rigid backbone for drag racing and high output 4 speed alternator-equipped Sportsters®. Includes a heavy-duty, double-row mainshaft bearing for extra strength and stability for the clutch and shafts. The double-row bearing greatly reduces the clutch shell rocking that occurs under power - which leads to damaged alternator rotor magnets and stators when contact between the two is made. It is a direct bolt-on replacement and includes mounting hardware and countershaft bearing. Made in USA.
CNC machined from 7075-T6 billet aluminum, our door strengthens this critical area and provides rigid support for the transmission shafts. Includes grade 8 mounting hardware, shift drum bushing, main and countershaft ball bearings and circlips installed for your convenience. Made in USA.
