Yamaha RD350 No. 9: Shocks, It Was Nothing

The RD350’s rear suspension seemed kind of springy to me, like there was no damping or the shock oil had leaked out. In corners the bike would hit a bump and bounce. Nothing frightening or dangerous but in combination with the front forks needing a rebuild anything less than smooth pavement was a ragged, unsophisticated ride. The RD still wore its original shock absorbers from 1974 so I figured it was time for a replacement set.

I found many options online, prices ranged from $500 to $50. I think we all know what option I took. Look, it’s not that I don’t want a really nice set of shocks it’s just that I’ve had some bad luck with expensive shock absorbers. In a nutshell they didn’t last very long. I mean it’s not like a dirt bike where you need good suspension. I’m using the RD350 on the street, an environment where you hardly need rear suspension at all. I found a set of shocks on ebay that looked similar to the original Yamaha shocks. For $47 shipping included I was willing to take a chance. The shocks arrived in about 3 days.

Out of the box the eBay shocks looked really well made. The chrome was beautiful, the top-mounting boss was cast aluminum and the things even have a plastic sleeve between the shock body and the spring to eliminate squeaking. The original shocks did not have this feature and squeaked a lot. They sounded like an old, rusty gate swinging in the wind when you hit a bump.

Fitment was straightforward except that the original Yamaha shocks had no bushings: the rubber inside the mounts fit directly over the shock studs. I had to press out the steel bushings on the new shock, which was fairly easy using a bench vice and a couple appropriately sized sockets. Instead of black rubber like the originals the new shocks used a material that resembled urethane and may in fact be urethane. It is translucent yellow and looks cool.

With the bushing removed the new shocks fit a bit loose on the mounting studs but not loose enough to fit a bushing. I thought about cutting a strip from an aluminum beer can and wrapping it around the stud to take up the slack but instead decided to hope that the now-bushingless urethane would relax a bit over time and swell to suit its environs. I often hope for mechanical things to fix themselves and frequently they do. The washers on either side of the stud sandwich the urethane a bit when the shock bolts are tightened so maybe they will smoosch the fit tighter.

After fitting the shocks I found the first spring preload position was too soft so I stuck a pin punch inside the nifty preload adjuster hole and cranked it up to the second position. That seemed about right. I wheeled the Yamaha out into the daylight and fired up the sweet-running two-stroke twin. It’s a sound that never gets old.

The first thing I noticed while riding was no squeaking, the eBay shocks were quiet. The roads around my place are sort of rough and there was a noticeable improvement in the bounciness department. It seemed like with the rear shocks working better the blown out front forks felt worse or maybe I just paid more attention. Corners were steadier and the rear tire rubbed the fender less than it did before. Still, it wasn’t the dramatic improvement I was shooting for. That might be down to the $47 price point.

Curious about the original shocks I compressed the spring with a long bar clamp and removed the spring collar along with the spring. Now I could test the shocks for damping action. Surprisingly both shocks still had oil in them and offered firm resistance to rebound. The compression action was much less as you would expect. It’s really hard to tell but I think the two Yamaha shocks offer slightly different hydraulic action. Certainly nothing I could feel on the road. I’ll go out on a limb here and say that there was probably nothing wrong with the original shocks. They work like they work I guess.

I’ll clean up the Yamaha shocks and pack them away to rot. In the meantime I’ll be running the eBay shocks to see if they hold up for 47 years like the originals. The new rear suspension has moved fixing the forks to the front burner. The RD350 handles well with clapped out suspension, I can’t wait to get both ends sorted and sample some of that legendary road-racer for the street performance RDs are known for.


More of the Gresh Resurrections!

Product Test: Progressive 412 Series Shock Absorbers

Most people I’ve spoken to are happy with their Progressive Suspension products. If you went by damping action alone I would be, too. The problem I had with the two sets of Progressive 412 shocks I’ve bought is that the damn things leak. When I say leak I mean like after a couple thousand miles of off road riding. Conversely, some of my riding buddies have the same exact shocks and report no leakage after several years.

Godzilla, my 1971 Yamaha RT-1B 360cc endure, has about 4 inches of rear wheel travel. When new, the Progressive shocks did a fantastic job damping that short distance. The bike would bottom out if you hit big ruts at speed but the rear end stayed in line and didn’t swap places with the front. It was a great boost to my confidence. I was able to gain some serious speed across open desert while the Progressives swallowed up big holes and bumps without spitting me off. I’m not saying it was a smooth ride, but it was controlled.

The shocks were great on hills. They helped the rear knobby tire follow the contours of the earth and allowed Godzilla to climb some really steep inclines. If I accidentally spun the wheel by feeding in too much power I could close the throttle and then bog the motor, taking advantage of the big two-stroke Yamaha’s grunt at low RPM without stalling the engine. It was a traction seeking beast, I tell you. I’ve replaced the 412’s with a cheap set of remote reservoir shocks and the difference in performance is huge.

The first set of Progressives lasted about 10,000 miles before one of them sprung a leak. I chalked it up to the rough trails Hunter leads me on. Since I liked the Progressive action so much I sucked it up and bought another set. The new set was just as good, except they started leaking after only 2,000 miles. The second set of Progressives failed dramatically: Both shocks went bad simultaneously and projectile vomited hydraulic oil all over the rear of the bike. I thought the engine crankcase had broken.

To give the shocks their due I was riding an extremely rough trail with lots of boulders and steep drop offs. The rear suspension was bottoming on the big stuff but I felt conditions were no worse than normal.

The leaking wouldn’t be a big deal if the shocks were rebuildable. Progressive 412 shocks are not. They roll the shock body over the upper shaft guide and seal. It’s a machine process that is difficult to replicate in the average home shop. Even if you did manage to un-roll the shock body, the seals are made by NOK and are proprietary to Progressive (and Progressive won’t sell the seal). The shocks are made in Mexico so I doubt they have any to sell. In my correspondence with Progressive the only solution offered was to buy yet another set of shocks.

At $250 a pair this was getting expensive, you know? Since I had so many leaking Progressive shocks I decided to cut one open to see if there was any way to modify the seal area to take a seal that is available. It looks doable. I will need to get my South Bend lathe up and running to spin out a new top bushing with an O-ring on the outer part to replace the crimped end. To keep the top bushing from popping out on full extension I’ll need a few screws around the circumference of the shock body. Any nitrogen charging will have to be replaced with air from a simple Schrader fitting.

I’ll do another blog on the seal/bushing refit but don’t hold your breath. None of this is going to happen in time for October’s Yamaha Enduro Fest held in Flagstaff this year. The remote reservoir shocks are so bad I’ve got a cheap set of Red Line shocks coming from Ebay to tide me over. For those of you keeping count, I’ve had the original shocks, two sets of Progressives, the remotes and now the Red Lines. Hopefully these last two won’t leak.


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