Rear shocks later 60's models

Classic short-frame models

Rear shocks later 60's models

Postby ThumpStreet » Fri Feb 03, 2017 9:40 am

Good Morning to all,hope a good day is on the way.My focus has turned to the rear shocks on the 69 CH.The beauties that came with the as purchased unit were as follows: R/H side damper rod bent seized solid.L/H side zero damping.At my stage of life with the discs in my lower back being virtually extinct,the rigid ride is not perferred.I purchased another set of period correct shocks from a guy on Fleece Bay that were marketed as nice only to find that one pumped oil at the rod seal like a Texas pump jack.The other had some damping qualities but the bottoming bumper was slaughtered.What the heck,they're about 50 years old.So, I started spending some time looking through Munroe and Gabriel dimension charts wondering if I could spy damper bodies that could be modified to replace the original units.Looks to me that you could cut the weld off the spring cam adjuster platfom/lower washer.Similar thinking goes for the upper spring collar retainer. So, my question to everyone is has any one all ready traveled this path and located a suitable set of dampers to keep the shocks as original as possible?I have seen offerings ocassionally of NOS dampers for the 67-69 era for high prices(200.00) each.My concern is they're approaching 40-50 years old and if they've been laying dormant on a dusty shelf for that long would rubber seals hold up.Final question,what do you experienced guys do to get the rear suspension in top shape?Peter
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Re: Rear shocks later 60's models

Postby EKHKHK56 » Fri Feb 03, 2017 10:09 am

Hi Peter. The Progressive Spring & Shock company sells #412 available new in 14.25" or 13.5" length. 14.25" is what your bike takes stock. Available with full covers like original style. Twin body construction gas charged with 5 way preload adjustability. I think Ohlins builds some but haven't looked for vintage Sportster. I built up some FoxAirshox for mine that are very smooth. But far from stock. :) Fournales is building fine covered style shocks also for about twice the cost of Progressive.
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Re: Rear shocks later 60's models

Postby sportsterpaul » Fri Feb 03, 2017 10:43 am

Can't help on the shocks, but I can relate the racer Vance Breese's comments about the swingarm pivot bolt. When I complained about the absurd procedure in the service manual-- using a Chatillion scale to get 6 pounds of drag, Vance said the proper procedure was to find the longest cheater bar in the garage and tighten the big nut as tight as you possibly can. When I said "But that will brinell the outer races!" Vance looked at me and said "And your point is?"

So OK, he was being a wise guy. But his attitude was to keep the swingarm really tight and just slap new bearings in periodically. I like it a little looser, I gave up on the Chatillion scale method and just move the swingarm with one hand while I tighten with the other. I use the shortest socket driver in the toolbox and choke up on it to boot. You get a sense of what is "too tight" after a while.

Vance also explained why some guys never get off the throttle in curves. It keeps the swingarm in compression, with the chain pulling on the right side, so when you do let off the brake and hit the throttle, the swingarm does not flex as it goes from resting tension to acceleration compression. Point is, that having that whole rear end snug makes for a better handing bike. Its an analog world, how snug is up to you.

While we are back there, I note that I had a chain adjuster break under acceleration, and that let the axle pull forward and that put so much slop in the chain it broke, taking a chunk of the case and the sprocket cover with it. Now I tend to really snug up the rear axle, although I wonder if it would have helped.
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Re: Rear shocks later 60's models

Postby EKHKHK56 » Fri Feb 03, 2017 11:05 am

Standard preload on most Timken bearings is 1 foot pound. I don't know why any more would be desired.
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Re: Rear shocks later 60's models

Postby ThumpStreet » Fri Feb 03, 2017 11:52 am

Great input from both replies.I've been eyeballing the Progressive 412's.Progressive does make a nice cost effective shock in my past experience with them.Is it possible to use the stock cam adjuster cover and top spring cover to make the Progressives to look that much more original?On the note of swing arm tapered bearing preload setting, I agree 100%.I have several brands of motorcycles in the stable that utilize tapered bearing swing arm set ups and I'm quite familiar with setting them up.I also have had the education of a incorrectly set up swing arm on a brand new in 1984 BMW R100 CS.At 80 mph it would enter into a near death speed wobble that upon inspection was found the factory did not set the preload on the swing arm bearings.So much for some dealerships pre delivery check lists.Any way I'll be looking even more closely at the Progressive shocks and doing a full rebuild on the swing arm pivot point.Thanks for your views.Peter
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Re: Rear shocks later 60's models

Postby sportsterpaul » Fri Feb 03, 2017 7:46 pm

Standard preload on most Timken bearings is 1 foot pound. I don't know why any more would be desired.

Agreed, but the swingarm bearing has different duty than a front wheel bearing that is rotating at a higher rpm. Roller bearing life is the pressure times the velocity, PV. So you can load the back of your mini-truck with wet cardboard, as long as you drive really really slow, it is not too hard on the axle bearings. There is very little velocity on the swingarm bearing so it can take more pressure, even if that is pre-load pressure. Vance's point was that reefing down on the bearing would make the stiffness of the swingarm greater, and yeah, that is at the expense of making the rollers into little eggs.

But he was racing Iron Sportsters, and was fine with inspecting the bearings every race and slapping in a new set once the dents showed up in the outer races. I suspect that a pound-foot of preload would not get us the 6 pounds of drag the manual specifies. What puts that drag in there is the tiny egging of the rollers, its just that Vance wanted way more deformation of the rollers.

Like I said, I tighten the nut until I feel drag, not enough to hold the swingarm up unsupported, but enough so I can feel. What would be nice is to have the bike on its side so it was easier to separate the pre-load drag from gravity.
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