New Life for Old Shifters

 

 

 

 

Johnson Engineering
100 Blake Road
Denver, IA 50622
(319)984-9298
(319)984-9299 fax
info@twistgear.net

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June 3, 2003

Twist That Early 5-Speed Into A Smooth, Modern Performer!

When Harley made the move from four to five-speeds in 1984-85, it began a process that wouldn't be finalized until 1991, with the transition to a splined output shaft to replace the keyed taper shaft that was prone to breakage.

Converting your 1985-1991 five-speed to a modern day TwistGear/WideGear setup is easier than you think.

Adapting TwistGear and WideGear to Older 5-speeds

Both TwistGear and our new WideGear 30mm extension are easily retrofitted to 1985-1990 BT 5-speeds, resulting in major increases in reliability, performance, and comfort. Harley-Davidson's 5-speed, introduced in 1984-85, retained the traditional key and tapered shaft design joining the clutch hub to the transmission. The key tended to shear, usually in direct relation to available horsepower and torque, the spacer seal was easily damaged during installation, the main shaft bushing was prone to leaking, and servicing required case removal.

In 1991 the splined mainshaft design was introduced, which not only strengthened the drivetrain components significantly, but made servicing the clutch and transmission much easier as well — a definite improvement all the way around. Ball bearings replaced the needle bearing supporting the main gear, while the old style main shaft bushing was converted to needle bearings and sealed with an interior oil seal.

To convert the old style 5-speed, you'll need a splined main shaft and clutch hub, along with your preferred clutch. You'll also need a transmission output sprocket to go with theTwistGear or WideGear kit you're installing. You may also want to invest in a late model trapdoor that can take advantage of the larger bearings used since '98. To the best of our knowledge, the following OEM part numbers can be sourced for the conversion. Other versions are available from the aftermarket.

PART

P/N

clutch hub

37550-98

main shaft
(not required with WideGear)

35042-91

transmission sprocket, 32T

40250-94-A

compensator sprocket, 24T

40269-85

compensator sprocket, 25T

40308-94

clutch shell and sprocket, 37T

37707-94

clutch shell and sprocket, 36T

37707-98

Benefits Include Major Upgrade In Seals And Spacer

Our improved spacer and oil seal are also major improvements that result from upgrading. The old spacer design (see our new, improved version for four-speeds that combines spacer and seal) was wide, with a small, fragile cross-section and minimal lead-in chamfer, creating a lot of difficulty during oil seal installation. Further degrading longevity are the narrow transmission sprocket splines, which generate high spline stress.

The 1994 sprocket upgrade is wider, allowing a large diameter narrow spacer that in turn allows a bigger lead-in chamfer. The end result is reduced spline stress and easier seal installation. Our spacer, included in the TwistGear kit or available separately, has a lead-in chamfer twice that of the 1991 OEM spacer, speeding installation and reducing the potential of installation damage.

Our oil seal design is different as well. All our helical system upgrade - TwistGear, WideGear, and SportGear - kits include our exclusive triple lip oil seal, which can also be purchased separately, as can our alloy spacer. If you're considering an overhaul, now's the perfect time to upgrade both the reliability and performance of that vintage tranny. It's easier than you think, and better than you could imagine.

What About Four Speeds?

As for four-speed frames, there are several manufacturers of "five into four" cases that fit square swingarm frames and accept trapdoor cassettes. Although we haven't tested them, we see no reason why they wouldn't work. Disclaimers usually include having to retro back to a tapered mainshaft, but in order to use TwistGear, you'd do the opposite and fit a splined late model mainshaft, which would also affect the rest of the drivetrain, including the clutch hub.

There's also the issue of shifter linkage and cable routing, but all in all it looks like a relatively easy workaround that can bring modern technology to those old Shovels, Pans, and Knucks. We're currently developing sources for riders who don't want to give up their classic rides in order to benefit from modern five-speed transmission technology.

SportGear™ and TwistGear® are trademarks of Johnson Engineering, Inc. Buell™, Dyna™, and Sportster™ are trademarks of the Harley-Davidson Motor Company. No affiliation with the Harley-Davidson Motor Company is implied or inferred.