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Author Topic: Swingarm replacement tips  (Read 1094 times)

AgentX

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Swingarm replacement tips
« on: September 20, 2012, 02:39:13 PM »
Hi all-

My 1977's swingarm is slightly-but-visibly tweaked, and the bike pulls pretty hard to the left when you let go of the bars.  The rear fork-ends also seem to be ground out a little.  So, thankfully, a new swingarm is about $25 equivalent...just took a little waiting to get one, with new bushes already pressed in.  It's been repainted to match and is ready for install.

Anyone have any tips, tricks, or advice before I try to mount it?

Thanks-

ace.cafe

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Re: Swingarm replacement tips
« Reply #1 on: September 20, 2012, 05:04:25 PM »
When you tighten up the swingarm pivot, it should be at a certain height, so that the bushings don't get over-stressed in one direction during use.
There is a factory tool for this, but I think you can just measure the distance from the shock mount bolt on the frame.
I don't remember the exact distance, but somebody around there in India must have the tool, or know the distance.
Or maybe somebody here does.
I have the info somewhere, but I don't remember where. It might be in my old computer that crashed and died.
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ERC

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Re: Swingarm replacement tips
« Reply #2 on: September 20, 2012, 09:54:00 PM »
The distance between the bolt holes on the tool is exactly 10".   ERC
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AgentX

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Re: Swingarm replacement tips
« Reply #3 on: September 21, 2012, 01:04:02 AM »
Thanks--that is essential info.

So I just ensure the top and bottom shock eyelets are 10" apart when I tighten down?

AgentX

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Re: Swingarm replacement tips
« Reply #4 on: September 21, 2012, 04:20:20 PM »
Wow.  38mm socket.  That is...big.  Luckily someone found me one and a 3/4 to 1/2 drive adapter in a local industrial market.  Had no idea my adjustable wrench wouldn't open wide enough to turn the swingarm's axle nuts!

Anyhow, swap completed.  Had to find a newer-style chain guard, too.

Unfortunately, the rear wheel still seems misaligned.  Frame itself doesn't appear misaligned and the problem really seems to be local to the rear wheel axle.

Seems like the only possible culprit is the QD drive unit...maybe I can just shim it  or something so the wheel axle sits straight.  I'll find a few thin washers that will fit around the stub axle between the outer brake plate and the swingarm and see if they can straighten it out.

 

ace.cafe

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Re: Swingarm replacement tips
« Reply #5 on: September 21, 2012, 04:46:25 PM »
Thanks--that is essential info.

So I just ensure the top and bottom shock eyelets are 10" apart when I tighten down?
Yes.
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ERC

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Re: Swingarm replacement tips
« Reply #6 on: September 21, 2012, 06:40:55 PM »
It could be your rear wheel is out of alignment with the axle.  ERC
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AgentX

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Re: Swingarm replacement tips
« Reply #7 on: September 24, 2012, 09:45:47 AM »
Looking at it without the wheel on, I think there's definitely a cant to the axle as it sits in the drive-side QD unit and the right-side fork end.  That is, the center of the axle is further forward on the drive side than the non-drive side.  It's slight, and hard to measure with any true objective precision at first blush.

Pushing the right side of the axle forward in the fork end squares it up but you can see the QD drive begin to flex the flat of the swingarm on the drive side.

I think this would account for the behavior of the bike...it dives left when you take your hands off the bars.  If the rear wheel is off-line pointing right, it would tend to rotate the front to the left as you move forward.

Question now is, how to get an objective measurement of this and how to fix it.  Guess measuring from the swingarm pivot to the axle center on both sides would be a good way.

Fixing it, however...can I just shim the qd drive unit?  If I left the forward fixing point for the backplate alone but added a slim spacer between the swingarm's fork end and the QD drive (adding to the thickness of the existing large chrome washer in the same space) that might help this align.  Or should I seek a new brake backplate or sprocket?  I guess a new backplate would be cheap enough here and available new.

This isn't a huge deal--don't notice it when riding, even with one hand lightly on the bars--but it does bug me, especially when putting the wheel back in.  You have to force it into better alignment and tighten it down while holding it there.

So I really don't think it's the wheel.

barenekd

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Re: Swingarm replacement tips
« Reply #8 on: September 24, 2012, 09:08:50 PM »
The swing arm slots are what align the axle. If it's just forward on one side, then the chain/axle is just not adjusted right.  With the wheel installed loosen all the bolts on the brake back plate (3 including the axle), and shift the wheel/tire assy until it is square. Measuring between the axle and swing arm pivot is a good way to to do it although most of us use a long straight edge from the back tire to the front tire so if any thing is out of square the wheels won't be.  You are probably setting the chain adjusting snails where they are in the same "Slot". That is not correct, those snails differ from one side to the other so you cannot adjust both the same and have correct wheel alignment. When you're done aligning the wheel and have the chain adjusted, about 1-1/2" slack sitting on the center stand, and the snail in the proper spot, crank the brake adjuster nut down until the rear wheel is locked up. Tighten the inside nut, the big one, that holds the brake backing plate, then the axle nut, then the brake shoe pivot nut, the little one. You can loosen the brake adjuster now and that should get you all lined and and the brake properly set up.
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AgentX

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Re: Swingarm replacement tips
« Reply #9 on: September 25, 2012, 05:19:53 AM »
The swing arm slots are what align the axle. If it's just forward on one side, then the chain/axle is just not adjusted right.  With the wheel installed loosen all the bolts on the brake back plate (3 including the axle), and shift the wheel/tire assy until it is square. Measuring between the axle and swing arm pivot is a good way to to do it although most of us use a long straight edge from the back tire to the front tire so if any thing is out of square the wheels won't be.  You are probably setting the chain adjusting snails where they are in the same "Slot". That is not correct, those snails differ from one side to the other so you cannot adjust both the same and have correct wheel alignment. When you're done aligning the wheel and have the chain adjusted, about 1-1/2" slack sitting on the center stand, and the snail in the proper spot, crank the brake adjuster nut down until the rear wheel is locked up. Tighten the inside nut, the big one, that holds the brake backing plate, then the axle nut, then the brake shoe pivot nut, the little one. You can loosen the brake adjuster now and that should get you all lined and and the brake properly set up.
Bare

Thanks, Bare...I was tightening down the QD unit as a whole to set the chain slack properly, then installing the wheel.  Snails were different on both sides but still had to wrench the wheel into alignment.  Will try aligning the wheel with the whole thing loosened, then tighten it down.

juliia.zoee

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Re: Swingarm replacement tips
« Reply #10 on: October 31, 2012, 06:45:22 AM »
Thanks for the prolific info... was wandering for it....

ERC

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Re: Swingarm replacement tips
« Reply #11 on: October 31, 2012, 07:43:49 PM »
Huh?  ERC
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