81' gs550L Front End on a an '83 gs650L?

[zach_denver]

Does any one know if this can be done w/o modification?

I believe the gs550L had progressive shocks and handled great. My 650 feels really loose, I had air put in the forks and that helped a little, but it's still pretty poor.

[aosmith]

I used an 81 GS550(?) front end on my 83 it fit like a glove

[Steve]

Have you tried changing the fork oil? Seems strange until you think it through all the way,
but the proper amount of the proper fluid will do wonders to improving the action of the forks.

I can't tell you how much fluid to put in there, but I would recommend either 10w or 15w fork oil.

If the springs sag more than an inch and a half or so by the time you get on the bike, you likely need new springs. You might get by with adding a spacer to increase the preload, but new springs will make it feel like a new bike. Treat yourself to new shocks, too. It will really feel like a new bike. \\/


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[zach_denver]

So I bought fork oil and was going to change it...

Then I looked at both bikes 81' gs550L -> '83 gs650L; 81' gs550L <- '83 gs650L -- hmmm. Got out my digital caliper, measured the fork size and everything seemed to be the same (except the 550 forks extend a little further below the eyehole)...

So, I decided to pull the progressive forks off the 550 and put them on the 650. Everything went fairly smoothly, the wheels both turned smoothly w/o the caliper installed. The problem started when I installed the brake-caliper (the brake-calipers appear to be the exact same (both bikes are single rotor) the rotor would press against the brake pads when I tightened the caliper-fork bolts (the 650 was rubbing a little before the fork swap too). I tried both brake-calipers. It was about 11:30 (once again, on the street) and had to finish up.

My questions are:

1. Does the brake line have to be connected to 'retract' the brake pistons (I hadn't connected it yet). If so, all I have to do is a bleed.
2. What would be advised if the brakes continue to rub the rotors (I previously tried putting washers between the fork and caliper to prevent rubbing (before the swap) -- it didn't seem to help
3. Could anything else be causing this

Thanks,

Zach

[Cathy344]

My understanding is there are piston springs to retract them away from the rotors in the absence of fluid pressure. It may be that your springs are bad? If it's the opposite pad that's rubbing, then maybe you just need more shims to mount your calipers to center the rotor between the pads.


My 81 GS550L only has the one brake rotor/caliper, and the forks don't have the mounting flange for the second caliper. I was thinking I could just get a pair of 650 forks to put on my 550 and get the second, matching caliper, and a new matching pair of rotors, and possibly a new master cylinder, and have dual front brakes.

Is this not the case? Do not all 650s have dual front brakes? Are the 550 forks preferable for ride and handling? How could I go about adding the second front brake to my 550 without sacrificing anything?

[SqDancerLynn1]

It's a vacuum action that retracts the pad slightly when not in use. Check that the disk is centered in the caliper opening

[zach_denver]

Got it. the speedo was pressing against the fork causing the pads to contact the rotor. (Also, the rotor's slightly warped) It's the kind of think you don't notice at 11:30 on a weeknight working in the street.

It handles great now! :-D The 550 shocks are slightly different, there's only a 1/4" of space between the tire and the rotor (the 550 ran on smaller wheels) and the speedo drive unit had to be angled down so it wouldn't contact the forks (per above)

Cathy, some 650's had dual rotors others had a single. My Clymer book shows that some of the 550's also came equipped w/dual rotors. I'm not sure if this applies to the 81's (Also, I believe the '83+ have a smaller wheel on the front).

I'd also verify (search, etc) that it is possible to add a second rotor to your wheel -- my 650 has threaded holes on the left side, but my 550 has a plastic cover (I don't know if the holes are beneath this...)

If you need me to check anything, let me know.

Z