Harley 4-Speed Transmission Differences
There have been several versions of Harley's 4-speed gearbox during it's 50 year run, along with different mainshafts, countershafts, gear ratios and bearing variations.
This article covers both ratchet-top and rotary-top 4-speeds, and will help clarify what year and model transmissions and parts will interchange.
For Mainshaft and Countershaft article click here.
********************
A Little History
The first Harley to feature a 4-speed transmission was the 1936 "Sixty-One" EL, soon to be known as the Knucklehead. These early gearboxes are often referred to as Pre-Ratchet Top.
An odd shift pattern was seen in 1939 only, with neutral in between 2nd and 3rd gear. This was unpopular and corrected the following year, and the shift pattern remained 'one down, three up' for the next 46 years.
Ratchet-Top Transmission
Nicknamed for the ratcheting action of it's shifter mechanism, the first 'ratchet top' 4-speed was introduced on 1952 Panheads with the new hand-clutch/foot-shift option.
All 1951 and earlier models were hand-shift.
********************
From 1936 through 1964, all Knucklehead and Panhead transmission parts interchange. This includes cases, internal parts, shifters, and kick covers.
Revised Transmission Case
For 1965, the Panhead's last year, electric start was first offered (as an extra cost option). Cast-on tabs were added to the transmission case for stability, and not all parts interchange with earlier boxes.
These 1965 through late 1979 cases carried OE part # 34701-65A.
********************
FL vs FX Transmission Differences
From 1940 through 1976, Big-Twin 4-speed boxes were essentially the same, until the FX model was introduced in 1970.
Both FL and FX models left the favtory with the same shift pattern - one down, three up. But internally, the difference was the shifter drum for FL models was designed for the shift linkage to be connected to the lower side of the drum.
The FX drum was reversed, so the linkage was also reversed (connects to the top of the drum).
Back in the day, hot-rodders were swapping FL gearboxes to later FX style of shift plate to reverse the shift pattern. With a 'one up, three down', racers could upshift quicker and more solidly by pushing down on the shifter rather than pulling up.
********************
Kick Start Provision
Beginning in 1970, electric-start Shovelhead FL gearboxes had no provision for kick-start gears or kicker pedal. However, these parts can be retrofitted from FX models or earlier FL models.
Late Style Ratchet Tops
Ratchet-top transmissions stayed in use until 1978, with later units having the ratchet lever flipped the opposite way of the early style.
********************
Rotary Top Transmission
Rotary top gearboxes were introduced in 1979, and stayed in use until 1986.
A major difference from earlier units was, the shifter drum was replaced with a flat-plate shifter, similar to a Sportster unit transmission.
This style of transmission has various nicknames, including 'pancake top' and 'washing machine top'.
Ratchet Top vs Rotary Top
In today's used parts market, rotary-top boxes are cheaper and easier to come by, but ratchet tops have a better reputation, with many riders saying it can handle more abuse than the rotary top.
Interchangeability
Because the cases are different, ratchet and rotary lids do not interchange.
Pictured: Transmission case for Rotary-Top 4-Speed
Shift mechanisms and starter drive housings are also different.
V-Twin Mfg makes (or used to make) a Rotary to Ratchet Transmission Top conversion kit for 1979-1984 transmissions.
There have also been aftermarket "uni" cases that would accept either top, but these may not be available.
********************
Throughout it's 50 years of production, the Harley 4-speed transmission saw several different mainshafts and countershafts.
Read: Harley 4-Speed Mainshaft and Countershaft Differences
********************
Shovelhead 4-Speed Rebuild Kit
Buying one of Jims 4 Speed transmission rebuild kits will be much cheaper than ordering individual parts.
********************
4-Speed Gear Set
Andrews Stock Ratio 4-Speed Gear Set for Harley Big-Twin feature 2.60:1 first gear and 1.23:1 third gear.
Proudly Made in the USA.
********************
Replacement Ratchet Lid Assembly
V-Twin Mfg. offers a ratchet top assembly for 1952-1978 Harley FL models.
It is a complete assembled ratchet top assembly unit and replaces OEM 34799-65.
********************
3-Speed with Reverse
If you're mixing/matching cases and parts, be aware that there are 3-speed with reverse boxes out there.
These were seen on 1939 through 1976 FL models with sidecars, and were discontinued in 1978.
********************
Those who believe that a four-speed motorcycle transmission is past it's prime probably doesn't own one. It still does a fine job of spreading the abundant torque of a classic Harley Big-Twin motor. While riding, not much down-shifting is needed to accelerate. Whatever gear you're in, just twist the throttle and go!
********************
Related Articles:
Best Carb For Shovelhead
Harley Forks Identification
Convert Harley To Points Ignition
Remove Harley Sprocket Shaft Bearing
Harley Crankcase Lapping Tool and Usage
Custom Wiring A Motorcycle
