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Rear Shock

PostAuthor: Biggs » Tue Mar 10, 2020 4:36 pm

I don't know if anyone is still reading these, the bikes are rather old after all. But I still love mine so here goes.
I can't believe no one else has had a problem with the shock, but I couldn't find any.
My bike's rear shock isn't holding air any more. The stock spring is too soft initially without air.
The Progressive Suspension spring is no longer available. Has anyone found a replacement spring?
I'd like to keep the stock shock but if anyone has replaced it please let me know how that worked out.
Thanks
Last edited by Jake on Tue Mar 17, 2020 12:28 pm, edited 1 time in total.
Reason: Moved from Tech Articles to Tech

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Re: Rear Shock

PostAuthor: Flyingdog » Wed Mar 11, 2020 12:56 am

Biggs wrote:My bike's rear shock isn't holding air any more.


What happens when you try putting air to the shock? Is there a noticeable/audible air leak? Try taking the air valve body apart and check the 0-rings in the adjustable valve body (appears these have nothing to do with air), and/or the 0-rings in air line that run from the chuck to the shock body. Never tore one open, myself, but have noticed screws/nuts/coupling with threads, holding it together. So, I would think it possibly comes apart. Noticed there's even 0-rings in the damping cable lines.
https://www.yamahapartshouse.com/oempar ... ear-shocks
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Re: Rear Shock

PostAuthor: chrismalm » Fri Mar 13, 2020 12:39 pm

:yup: , or the valve stem.
Take the thing off, put it in a tub of water, give it some air and see where it leaks. That should tell you if it's fixable. If it's a dead doggy, there are replacements on EBay.
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Re: Rear Shock

PostAuthor: Biggs » Tue Mar 17, 2020 10:55 am

Thanks for the replies.
False alarm gladly, the bladder is still good. I don’t have a convenient work area so I couldn’t get back to this right away. I made a modification to the air hose and it slipped off the fitting when I reinstalled the shock after I advanced the rebound adjusters. The spring is too soft without air but adding enough air pressure makes the rear too stiff, but it handles much better with the back end up. I’m not that heavy, so... I reasoned that was because the small air volume in the shock causes the pressure to increase too rapidly when compressed. Adding volume should allow more static pressure to have a lower spike. To that end I fashioned an air chamber out of PVC tubing, re-routed the fill hose to the chamber, and ran a new hose from the chamber to the shock. That last part wasn’t easy because I could not find a hose barb with the machine threads of the shock body. It took several attempts, and drill bits, to drill a hole through the center of a bolt of the correct thread, and to get the hose clamped on. I’m sure it doesn’t work as well as a larger volume at the shock would, but it does allow me to run twice the pressure as I used before, with a better ride. A definite improvement. The hose isn’t easy to get installed securely so it came off. I would still like to get a better spring but have not been able to find one for the stock shock.

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Re: Rear Shock

PostAuthor: Flyingdog » Wed Mar 18, 2020 2:47 am

Biggs wrote: The spring is too soft without air but adding enough air pressure makes the rear too stiff

:huh?: What's "enough"? Couldn't get something in-b-tween (0-enough)? I could see if using a compressor to air the shocks, could be pump'n too much, too fast. Been awhile since I've look, but pretty sure minimum pressure is 7#..and..Yamaha recommends "always" run 'atleast' minimum air pressure (if riding stock bike). That is... for damping to work correctly. Was quite surprised at around 10#, the 750 was very adequate for either wife or I.

Biggs wrote: Adding volume should allow more static pressure to have a lower spike.

:huh?: What's a spike? Approaching stiffness?

Biggs wrote: I would still like to get a better spring but have not been able to find one for the stock shock.

I would imagine any aftermarket spring is going to be stiffer. Maybe more controllable, but would probly end up in the same boat when adjusting pressures. Maybe...maybe not. You running air in the front? That will change how the rear acts. This isn't a bike made for the track. Unless one, radically, changes the overall design, by way of cafe and/or bobb'n the thing. Admittingly, though, I've only ridden "one" 920 thru our canyon roads..and it "WAS" something else. What with those different kind of handle bars and a drive shaft, instead of chain drive...just couldn't tame the whallow'n. Yes...I had a bicycle air pump in my back pocket for adjusting. :bg: Glad I wasn't asked to fix that part. Was just check'n some tires I just mounted. Thank gawd, it didn't have a fairing to deal with. :bg: Whelp..good luck how ever you approach this.
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Re: Rear Shock

PostAuthor: Biggs » Wed Mar 18, 2020 9:54 am

A spike is a rapid increase in pressure due to a small volume being compressed. A larger volume will increase more slowly.

The Progressive Suspension spring available back in the day, would allow running with no air pressure. I asked them and they said it's no longer available and did not offer an alternative.

If set up properly these things handle incredibly well. Not track sport bike well, but street well.
I drilled new holes to allow the handlebars to be rotated further forward into a standard position. I raised the fork tubes a little more than an inch, as much as possible before they hit the handlebars.
I don't run air pressure. I should have gotten new springs but just added shims to get some ride height back. Without air and no shim there is only about two inches of travel left. I also changed to 20w fork oil.
I run a MT90B tire instead of a 130/90 because it's a little taller. With 30 psi in the rear, and the volume I added, the back end is up where it should be and the ride is good, and it handles great.
I just needed to advance the rebound cables to get a little more rebound for that pressure. That's when I screwed up the air line on reassembly. I'm trying to find a hose barb again so it won't slip off.
If you're not leaning back and there is more weight on the front wheel, it's a whole other bike. Stock it's vague and imprecise but ok if you are not interested in grinding pegs.

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Re: Rear Shock

PostAuthor: Flyingdog » Fri Mar 20, 2020 1:57 am

OK, whatever works for ya. Sounds like you gotta plan. Dunlap? Personally, wouldn't put a 402 on a tricycle. :bg: But like many things..people like em. That Alpha Code tire (MT90) is actually "shorter" (.1") than the (OEM) metric size. Least on my (oldish) charts.

FYI: I assume you're talk'n about that purple "touring(?)" bike. Since this is older, you may wanna check the oil filter that's nestled neatly behind the footpeg mount. It's just a little black bulb connected between that tube hang'n down next to the kick stand and air filter box. #30--> https://www.yamahapartshouse.com/oempar ... 75c9/frame It's for blow-by vapors and with the age of yer bike..probly full if ya got lotta miles. Could eventually start pee'n oil. (Well, mostly drips, but still annoying.) Tons of various filters available. Inline, open-ended, closed end. Cheap-to-pricy/fancy.

One of the more fancier ones:
https://www.revzilla.com/motorcycle/gol ... -collector
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