Speed wobble at about 75

[timeconsuming]

Hey guys

Just picked up my first xs650 the other day (a 76 frame with a 79 engine) and everything runs great up until about 75 I get a bit of an intense wobble and was wondering if you had any tips for what to check and in what order.

My initial though was to make a fork brace (no fender), drain and refill fork oil, and check headset bearings. How would I go about checking tire alignment aside from the dropout notches?

Thanks and sorry if this is a repetitive topic! I'm new!

 

[peanut]

welcome to the forum
75mph eh ?! you're optimistic lol

have a look in the tech section under frame & suspension etc theres some really helpful stuff there.
http://www.xs650.com/tech.php

Do a search for 'Minton Mods ' also. Its an old article on improving handling etc but still very relevant today.
http://www.650central.com/tech/mintonmods.htm

Check your rear swing arms for movement .The oem bushes were plastic and notorious for wearing out

 

[jd750ace]

My initial though was to make a fork brace (no fender), drain and refill fork oil, and check headset bearings.

I'm surprised you are running that hard without a fork brace having not done the other two, however the fork oil won't necessarily save your bacon if the springs are total crap. It's a full package.
I also second what Peanut said on checking the swingarm bushings as well.
Loose steering head bearings, uneven fork oil height, or even an under-inflated tire could all cause head shake all on their own.
Don't "trust" ANY of it. Verify ALL of it is correct before you hang your butt out there. Only costs you a day or two in the garage. Way cheaper than even one evening in the ER from doing a Barry Sheene Daytona imitation down the highway.

 

[gggGary]

cupped tire tread will make it shake too.

What is the bike? stocker, hardtail, mono wheel pogo stick?

 

[peanut]

cupped tire tread will make it shake too.

What is the bike? stocker, hardtail, mono wheel pogo stick?

its a unibike
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[timeconsuming]

Here she is ^

I figure the fork springs may be old, but I have yet to drain and refill the oil, or fabricate a little fork brace for that matter, so I'm going to give that a go first and then if no luck I suppose I'll look into getting new springs.

Would the spring preload being stiffened help at all? I haven't checked that yet but I feel like the PO had it setup pretty springy and loose. I mean, the front end is generally very springy and not very stiff... so likely a case of old springs on their way out?

 

[jayel]

Align rear wheel by measuring swing arm shaft pivot to rear axle, center to center both sides equal then check this thread
http://www.xs650.com/forum/showthread.php?t=7025&highlight=string+method

 

[gggGary]

Looks like the front fender tabs are gone?
Would be nice to see a closer image of the fork.
Bike looks good by the way, not a unicycle but cool.

Don't forget to check those swingarm bushings.

I keep seeing an odd looking jog just above the rotor on the LH fork leg....
You might want to look under those gaiters too.

 

[5twins]

It looks like someone upgraded the front end to the newer 35mm forks, which is a good thing. Use 7 ounces of fork oil instead of the recommended just under 6, it will make a big difference. These forks really need something tieing them together even if it is just the fender. They flex terribly, especially under braking with that single disc. You might consider a Tkat fork brace. They clamp to the top of the lowers and don't need fender mounts for installation.

 

[timeconsuming]

Fender tabs are still there. Question is, would a fender be enough or should I consider getting an actual brace (either buying or making)?

 

[jd750ace]

It took me 3 times to figure out the disc lock!

A fender is better than nothing, but the braces offer better torsional rigidity, especially the TeeCat mentioned above. The one you have pictured would be a good step above the fender only setup.

Some here are experienced with several different types and combinations.

 

[timeconsuming]

Haha yeah that's my little theft preventative.

 

[5twins]

As mentioned, a fender will help but a brace is best. I've tried fork braces on practically every bike I ever owned. On some they helped, on others not so much. On my 650, the brace made a real difference, and I already had a fender.

 

[grizld1]

A speed wobble can be caused by a host of things--a wheel (front or rear) dinged or out of true, shot damping on one side (front or rear), clapped out swingarm bushings, clapped out wheel bearings, as well as the few things mentioned above. The tendency is to focus on the front end, but the problem originates just as often in the rear--the oscillation shows up in front because that's where the hinge is.

 

[jdizon]

Hugh makes this slick brace.

http://www.xs650.com/forum/showthread.php?t=28851

 

[650Skull]

+1 on grizld1.
Wheel Balanced?
Don't like the idea of no guard or brace

Gordon Scott makes one as good for less

Mikes looks ok when using a guard but i would go the Gordon Scott, (cheaper), or Hugh's without a guard.

 

[timeconsuming]

Guys.

So my bike has been non-op for a bit while I overhaul things and here's a few things I've discovered that probably attributed to the wobble:

-loose spokes! both wheels have a number of spokes i can wiggle freely with my fingers... wow.

-improperly installed headset! the race on the bottom wasn't fully pushed up so the headset was installed crookedly... nice.

-swingarm loose! bolt on the swingarm was incredibly loose... not necessarily finger-tight looseness but close.

Good stuff! Can't wait to get back on the road and feel the difference

 

[jd750ace]

Good deal. Told you not to "trust" that everything was OK. Those are some serious problems you have found. Check balance on those wheel and tire assemblies while they are off. those look like Dunlop 404s. Not a tire I will ever buy again personally. They have been little more than "rim protectors" in the past for me, albeit on heavier bikes.

 

[XSLeo]

I can't add much that hasn't been said yet, but on the tire balance Dyna Beads is the best thing since sliced bread.
On a tube tire it can be a bit of a PITA to install but well worth the effort. The bike is much smoother than any clip on or stick on weights will ever make a wheel/tire run.
www.innovativebalancing.com
Leo