Shimano Dura Ace PD-7300 pedals

The first road bike I purchased was a second hand Batavus Professional team bike, equipped with Shimano Dura Ace.
Dura Ace was (and is) Shimano’s top end component group, but especially in the late 1970s, early 1980s, Campagnolo was considered to be the absolute No. 1.
Besides this subjective image thing, it was also what I experienced myself. Campagnolo Record had better surface quality, better bearings and sealing, higher quality hardware, better materials and design details like cast components instead of pressed sheet steel (e.g. brake lever brackets). So, it lasted longer, was easier to maintain, less rattling, better appearance.
So, bit by bit, I was replacing the Dura Ace components by Record.
When Shimano entered the pro road scene at the end of the 1970s, the company, the people around it and the teams using the stuff were not taken seriously. Flandria, IJsboerke and Cilo must have suffered from it.
With this background, it may be easy to understand why the market didn’t embrace the new AX series, when introduced it in 1980. The reputation of Shimano was not that good (“bad, cheap Japanese stuff”) and the difference with traditional bike components was too big. The traditional bike world was not ready to understand the benefits of new technologies. AX series offered many new things: one key release (everything with a 5mm Allen key), cassette hub, Uniglide, Dyna-Drive, aerodynamics and several others.
When it comes to Shimano AX parts, I cannot speak from my own experience. I understood what Shimano claimed and admitted that there could be some advantages, but didn’t believe that the differences were deciding. And soon, rumours were spread, that the new Shimano gruppos were having serious quality issues. Parapull brakes were not powerful enough, rear mechs weren’t working well or snapped and “there was also something with Dyna-Drive cranks and pedals.
I ‘m still not sure what the problems were, despite my 9 years experience at Shimano. Broken cranks, broken pedals, worn bearings: I don’t know.
A fact is, that especially tall people, thus heavy, were using DD pedals. One of the benefits was, that the base of the riders’ foot was level with the pedal axle and the saddle could be lowered by approx. 1.5 cm. Koga Miyata even changed the geometry of their road race frames by keeping the length and the angles, but lowering the top tube.
Anyway, Shimano AX series died soon and so did some of its features like Dyna-Drive and the whole aero thing. What remained were the brake cables with internal cable routing and freehub and cassette.
What were Shimano’s objectives with Dyna-Drive?
In the first place, by bringing the riders foot closer to the pedal axle, the biomechanics were improved. Less energy was wasted to keep the feet stable on the pedals. Like Shimano said, a bit like walking of flat shoes instead of high heels.
Besides that, the whole low profile design of pedal and crank fitted nicely in the total picture of aerodynamics of the AX series.
Because of the low centre of gravity, the pedals should always hang in the right position with the toe clips up and the pedals body down, so no hassle to get the foot into the clips.
Instead of an axle that supported the whole pedal body, Shimano used a very short axle with a very large diameter. The axle and bearings wear completely at the side of the pedal and partly in the crank arms. Instead of the standard 9/16” fitting, Shimano used 1” to offer enough strength, stiffness and bearing durability. But somewhere they failed…
In each pedal I counted 30 pcs 3/32” balls. I think the correct placement is 14 pcs on the inside and 16 pcs at the outside, near the pedal body. On one side the balls must be placed on the axle stubble and not in the bearing cup, otherwise it cannot be assembled.
The bearing cannot be countered in the normal way. There’s a screw for a 5 mm Allen key that can be reached from the side of the pedal body. That screw counters the bearing.
Shimano DD pedals are not the first with this “drop-spindle” design. Similar constructions were used in the 19th century and in the 1950s .

See also: Speedplay Bicycle Pedal History Museum

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