Progressive Suspension 420 Series
by Rick K. for webBikeWorld.com
Summary: Very nicely made shock absorber; looks like custom made.
Chromoly steel; rebuildable. Nitrogen gas charged. Comes with cool-looking progressive rate springs in black or red.
Internal bladder eliminates need for external reservoir. Five position damping adjustment.
Threaded collar adjusts preload but collar is a bit stiff and doesn't turn easily. Provides excellent ride characteristics and gives very smooth but controlled ride. Gives the bike's rear end a "silky buttery" feel without wallowing.
Our 1986 BMW R65 test mule came to us with a '70's style BMW suspension: soft and cushy. According to Roland Slabon's book "BMW Motorcycle Buyer's Guide" (review), only 364 of these rare monoshock BMW's were imported into the U.S.A. in 1986.
It was comfortable to ride in an old-fashioned sort of way, and it handled well enough for the vintage, so it didn't occur to anyone that the rear shock was knackered. Until the handling got very weird...
The bike felt like it was on ball bearings - as soon as the handlebars were moved in any direction, the rear end of the bike felt like it would swing out as if on a hinge. This was way more play than the "normal" BMW Airhead frame flex should allow, and it got too scary to ride.
At first, we thought something was wrong with the steering head bearing adjustment. Many attempts at changing this didn't do a thing for the handling problem though. A quick note to the BMW Airheads email list came back with recommendations to check the frame for cracking. But the bike only has about 25k miles on it, and the frame and engine mounting bolts seemed fine.
A visitor to the wBW garage, after hearing the story, walked up to the back of the bike and pushed up and down. The suspension had about as much stiffness as a wet noodle. It became immediately obvious that the monoshock, a Koni (probably a replacement for the OEM BMW part) was completely gone. The spring was the only thing holding up the rear.
Why hadn't we noticed this? Like old age, motorcycle suspension failure starts the day the bike is built and is a subtle but continuous process. You get used to the way the bike rides and subconsciously compensate for it, until one day there's a sudden realization that something is seriously wrong.
Well, Koni is long since out of the business of manufacturing shock absorbers for motorcycles. Apparently, they sold the tooling to a manufacturer who makes the shocks under the "Ikon" (Koni spelled backwards!) name. Hagon also makes a replacement monoshock, but many owners of BMWs and other brands of bikes recommended Progressive Suspension's products.
Their products are commonly available at many motorcycle dealers and online retailers, and one of the nice things about the Progressive 420 is that it's rebuildable, making it virtually a lifetime shock. The prices are reasonable also, relatively speaking, that is. Motorcycle shocks are not cheap, and high-end racing shocks can cost several thousand dollars.
We found this 420 with bright red springs on sale, and purchased both the shock and a set of Progressive Suspension fork springs for a grand total of $444.00, including shipping. We haven't been able to figure out how to disassemble the forks on the R65 just yet, so that story will have to wait.
Progressive 420 Monoshock
Only the 420 with red springs was available when this was purchased, but that was fine with me. The red complements the red pinstripe on the jet black R65's tank and battery covers, and gives the bike a custom look. There was a very small ding on the red finish on one of the windings of the spring, so we'll see how the finish holds up. It appears to be some type of plastic-like coating and not a paint or powder coat.
I wasn't sure how hard or easy it would be to install the shock on the R65. This bike has a set of BMW saddlebag mounts installed, and the frame rails for the mounts covered the existing shock. It's a pain to remove the mounts, but as it turned out, that wasn't necessary.
I found that it was only necessary to remove a single bolt (yellow arrow, photo left) from the lower saddlebag mounting rail, which provide enough play for the old shock to be removed and to install the new one.
The monoshock attaches to the bike with upper and lower mounting bolts. After removing the two nuts that held the old shock in place, it was possible to twist to top of the shock enough to slide it off the mount.
Sliding the shock off its lower mounting stud was slightly harder, but after some twisting and maneuvering, it came off without having to remove any other parts.
By the way, make sure the rear of the bike is propped up under the tire, because there's nothing holding up the rear of the bike once the monoshock is removed. As always, use caution.
This Progressive 420 came with 4 washers. One washer goes on each side of the upper and lower mounts, and they help to ensure that the mounts don't bind on the bike's frame as the suspension travels up and down.
Installing the Progressive 420
The damping was at the third setting from the factory, and that's where I left it. I toyed with the preload a little bit, but no particular setting seems to make much of a difference, probably because the bike's suspension is rather crude anyway and the small adjustments on the shock don't make it through all the rest of the chassis flex to make themselves noticed.
The shock comes with a preload adjustment wrench that works with a 3/8" drive ratchet. The spring has a lot of compression against the preload adjustment collar, making the collar difficult to turn. I'm also afraid that turning the ring will wear away the red coating on the spring's coils. I'm hoping that once the nice red coating starts coming off that it won't begin to peel away from all of the entire spring. Only time will tell...
But the bottom line is that the Progressive 420 is a revelation. The bike now handles better than it ever did, and it's a nice feeling to think that a nearly twenty year old bike handles better than some new ones I've ridden. It's hard to describe, but the shock really smoothes out all the bumps with a very silky feel.
There's no abruptness or harshness at all, and the best thing I can say about it is that I don't notice what's happening in the rear of the bike at all, other than it goes where I want it to with no fuss.
And the rear end doesn't wallow at all (like it did with the old shock), so it's a very controlled but smooth feeling, both on compression and rebound. If we would have known that this was possible, we would have replaced the shock a long time ago with a Progressive unit, even before the original unit was worn.
I also wanted to perk up the R65's front end; see the wBW article on installing a set of Progressive fork springs for more information.
Meantime, the 420 has made a huge difference in the way the R65 handles and feels, so I'm very pleased. Progressive makes an extensive line of shocks and springs for many different motorcycle brands and models, so chances are they'll have one for your bike.
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From "S.B." (09/10): "I recently read your article about installing a Progressive
Monoshock on your 1986 Airhead.
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