GS650 Rear End Instability - Where to start?

[yeaitsdave]

Hey guys, I'm clearly new. I recently picked up an '81 GS650 in immaculate shape with ~33k on it, for cheap.

My problem is with the back end, there's some definite lateral play while riding. On the center stand, I don't notice any major movement, just when loaded. I intend to update the suspension, but I'm trying to do this little by little (and the fork needs to be rebuilt, bad).

I'm curious what I should check first. I tried to search but didn't get a lot of response. What issues would be most common to cause the rear in not to track laterally consistently? Swing arm bearings? Wheel bearings? Shocks/bushing? I just don't want to start disassembling and fall down a rabbit hole of things that should be taken care of (read: I'm trying to spread the financial load out).

 

[Rijko]

welcome, you've come to the right place for help
Is that the chain version GS650E ?
Can you post pics ?

Checking for issues is the right way to start, sometimes issues can be solved easily/cheap.
Does the front fork need a rebuild ? Leaking ?
Tires may cause strange behaviour.

Sometimes the steering stem bearings have play, or are overtightened, which may feel like the back has issues.
Test on centerstand, (someone sitting on the seat ?) front wheel off the ground, squat in front of the bike, move front wheel left-right slowly and watch for grinding or other not smooth feeling.
Especially in the neutral straight position it may try to stick to center.
Next, grab the bottom of the front fork and pull it forward. If you feel play, that's not ok.

 

[yeaitsdave]

Oh right, forgot there's a chain driven version. No, it's a 650G.

Fork seals are definitely suspect, there's some oil traces. I ordered new seals, Progressive springs, and steering bearings; I know that needs to be done.

I'm new to motorcycles as a whole - will the slop in the front end cause the rear to have lateral play?

 

[Rijko]

Oh right, forgot there's a chain driven version. No, it's a 650G.

Fork seals are definitely suspect, there's some oil traces. I ordered new seals, Progressive springs, and steering bearings; I know that needs to be done.

I'm new to motorcycles as a whole - will the slop in the front end cause the rear to have lateral play?

Especially when you're relatively new to motorcycles, it may definitely feel that way.
If you can't find lateral play in the rear wheel (bearings) or swingarm, and the shocks are set to
the same dampening setting and not leaking, chances are the issue starts in the front.
Front fork is a usual suspect.

So start with the front fork rebuild and steering bearings, it may very well solve the problem.

 

[Rijko]

Have you found BikeCliff's site yet ?
Lots of nice info there.

GS650G Service manual

1981 GS650GX wiring diagram

Installing progressive springs

Fork Seal Replacement

btw, if the pump method does not work for you to get the oil seals out, a great way to avoid breaking a sweat and/or damage the lower fork legs using huge levers to pry them out is to disassemble the front fork and heat the rubber seals over a stove or using a torch shortly until they start to smoke.
Have a cloth ready incase the seal catches fire.
They should fall out with the slightest help of a small screwdriver.

 

[tom203]

It's possible that the bearings in swingarm pivot have loosened up or damaged somehow causing slop. Look at this link..
a threaded section fits into the large hex nut to locate and secure the bearing

http://www.partsoutlaw.com/oemparts/a/suz/50d3fd8ef8700230d8b4da60/rear-swinging-arm

 

[bonanzadave]

My problem is with the back end, there's some definite lateral play while riding.

Not sure where to tell you to start but my bike suffers from a high speed (80mph and up) weave that I have tried to adjust and have replaced everything that has been suggested to no avail.....

Do the easy (cheap) stuff first. Make sure the tires are fresh and properly inflated. Get the front end sorted and then start saving for some new rear shocks. Keep us updated....

 

[MechMessiah]

Sounds like you're talking about the shaft jacking that these bikes are well known to do. It's really noticeable when cornering. https://en.wikipedia.org/wiki/Shaft_effect here's a link about the concept.

 

[Charlie G]

Sounds like you're talking about the shaft jacking that these bikes are well known to do. It's really noticeable when cornering. https://en.wikipedia.org/wiki/Shaft_effect here's a link about the concept.

I thought Suzukis were noted for one of the smoothest shaft drives made?

 

[MechMessiah]

I thought Suzukis were noted for one of the smoothest shaft drives made?

I can't tell if that's sarcasm or not over the internet, but with my experience of owning two Suzuki 650 shafties I'd have to disagree with that statement.

 

[Guest]

I thought Suzukis were noted for one of the smoothest shaft drives made?

None of the shaft drive bikes with fixed rear housing are very smooth. Less power, stiff shock damping and longer swingarms reduce the problem but the only way to really solve it is to float the rear gear housing like some Moto Guzzi's and BMW's did.


Mark

 

[Gorminrider]

...when I did swing arm bearings it seemed very possible to get the swingarm too far to one side. The shop manual isn't great on this- just says something like "get it in the center when reinstalling" hmmm. how do the shocks line up...as in where do they "want" to be when bolted to swing arm...they should "want" the same washers in the same order at the frame posts that are shown in the manual? I wouldn't want to force them to where they don't want to be.... so, you could try, to set the shocks up B4 adjusting swing arm...and check out alignment to front. stuff like that. Obvious non-fits might be a clue.
I'm not sure if this could cause your problem but I am just saying start at the manual including inferences taken from their sometimes, somewhat, offhand instruction.

PS but your forks are first suspect...also, consider the tires...if you are keeping the bike stock, stay close to the originals...Bridgestones,avons Duros...