Odd rear instability

Been fixing up my old girl bit by bit , not only making her a more comfortable ,safer machine, but building my skills and confidence as well, with side road excursions during my daily commute.
This has led to the discovery of many issues and subsequent repairs.

The most recent problem to turn up has me stumped.
Coming down a freeway split doing maybe 85mph at first everything was smooth as glass then as I tightened up a bit ,with just enough gas to maintain speed or at least about 80mph, the rear starts to wallow around it didn't feel like the tire was slipping as much as loading and unloading giving a constant back and forth wobble in the rear going back and forth maybe 5 or 10 times a second. It continued on through the curve until I decreased lean angle a bit.

Tire pressure is good at about 34-35 cold in the rear 32-33 front.
Swingarm has no side to side play, although when I checked it felt like it might have had a tiny bit of give in a twisting motion (bottom of tire to right when top is pushed to the left, can't be sure as I couldn't feel any play with the rear off the ground, felt like maybe a bit when pushing and pulling on the passenger bar with the bike on the kickstand( could have been slack in the kickstand)

Tire does have a bit of a flat strip around the middle due to the daily commute being mostly highway.
I don't have any instability when hitting dips or bumps in curves at moderate speeds.

I don't think it is necessarily dangerous on the daily ride, but it certainly doesn't help my confidence, and could definitely make a difference during spirited riding. I would hate to think what the result might be if I were moving on and had her layed way over in a curve w/ tires near their limit and it started wallowing in the rear. Sounds to me like a recipe for a low side or worse if I held her until the rear hooked back up.

Is this something that just happens with a tire that is a bit squared off.

 

Maybe your seat is loose.

 

It will whallow thru corners like a pig when the tire is like that.

 

There's definitely a few screws in my head that's loose and rattling around. My seat however is tight, and has a crack in it. Lol none of the above explain where that wallowy feeling is coming from.


Except for the explanation about the tire

 

So is this just an unsettling feeling, a small reduction of traction due to less rubber on the road, or is it going to start sliding out in the rear / completely let loose

 

Bet it the squared off tire--- time fer new shoes Herman


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Tyre pressures. Also maybe check your rear suspension may be a bit on the soft side.

 

The seat with the crack is anatomical and would require surgery to effect major change. There are recorded instances of loose stool and as well, no stool in some corners. These would be physiological, the former being the more damaging to attire.

 

is your brake rotor warped? could be applying rear brake once every turn of the wheel,overloading then unloading the tire.

 

Check your front tire too. If it has a flat spot, it can cause that also. I had this problem on my older bikes.

 

If bearings in your rear hub and swing arm are good, than only 2 things can do what you describe.
Rear shock is worn/not enough rebound.
Excessive scalloping/squared off rear tyre, which also points to worn rear shock.
And a possible third on my list of two, lose steering head bearings.

Just realised it's a VF700, most probably an old worn bike (mainly rear shock).

 

First thing I would check is the wheel alignment.

 

One of my bikes is a Kawasaki EX250, which is a cheap bike and is considered by many to be a "learner bike" and therefore a use-and-discard, disposable commodity. The result is that lots of EX250s never, ever receive any continuing maintenance. They just get older and more decrepit as the years go by.

The odd handling feel you described sounds very similar to one of the common (poorly maintained) EX250 complaints and it comes from the rear shock linkage and/or swingarm bearing being dry which results in a lot of static friction.

On the EX250 servicing the shock linkage and swingarm bearings brings back the positive, connected road-feel (even in spite of the bike's crap OEM rear shock).

 

Edit: as usual I ended up writing a book the short version is I now believe it to be a combination of rear tire pressure (30 psi) at the time, rear tire squareness, and rebound left on low when air was added to rear shock.
All but the square tire have been dealt with.
Plan to service steering head bearings and rear shock/pivot points very soon.
Thanks guys





Got alot of things to check , so far it only happened this one time.
I definitely need to service the linkage and swinger bushings even if this wasn't the cause. The PO of 12 years wasn't a mechanic and really didn't have the means to keep her properly serviced especially since he barely rode it enough to keep it alive.
After the wallowing experience I added a couple pounds of air to the rear tire to get it back up to pressure since it was down to around 30℉ and 70-95℉ when I last checked/set the pressure. Now it's 40-75℉.

Brake rotors and front tire check out good.

Steering head bearings aren't really loose (no play), but the front wheel moves back and forth with almost no resistance when on center stand, it needs serviced.

Also, cranked the rear shock (works OK but definitely needs a fluid Change) up to #3 of 4 (from 1) should have done this when I added air pressure (it actually holds pressure) to reduce sag and help with a definite undersprung feeling.
Alignment had been previously set to get rid of a similar feeling but more an instability in the lean at a certain angle in one direction only at all speeds almost like the rear was balanced on the corner of something it was real difficult to hold that certain angle. Setting alignment fixed this sometime ago.

Hasn't happened again so far but I feel it definitely feel it could have been the shock ,especially since I upped the air pressure a good bit without adding and rebound damping only a couple days earlier. It is the only thing that was unique to that one ride (to and from work) all the other things had been like that for a while. Except for maybe Tire pressure had only been below 32 for a day or two, I put it up to 35 psi after the incident at the same time I upped the rear rebound.

Appreciate the info guys as I wasn't sure what could or could not cause my problem, got alot of work to do this weekend if now that I know a bit more.
If I am gonna keep the ancient old' girl running smooth hard and safe.

I got 1 more Napa gold oil filter before I go to the mini filters, and install my oil cooler adapter along with carefully selected oil lines , Of course I will want to take care of the steering head, and rear pivot points ASAP.

 

How many miles on that bike ??

Stock OEM shocks are usually getting weak by 35-40,000 miles, and i think that's your main problem.

 

Bike had almost 24K when I got it and now has almost 27K.
The rear shock works predictably and responds to air pressure (which it holds) and rebound adjustments (as long as the knob is set in the center of the detent for whichever (1-4) you choose) The rear shock feels alot like the front forks did before I flushed the nasty black sludgy stuff out of them and put in fresh 10wt. hydraulic fluid.
That said I believe the rear shock to be in fair shape and plan to get a seal and service it with the rest of the rear: linkage, swinger bushings etc.
I really want to get a good JDR resivoir shock for the rear, not only for the improved dampening but peace of mind as well.
Also on the want list is the gold emulators, programmable cdi box set ($180), and stage 2 cams with adjustable gears when mine eventually go. I may get fork springs as well but when I calculate for my weight the stock spring rate (which as most of us know as soft for the average rider) is what it comes up with.

I plan on getting a more modern fuel injected probably pre v-tec vfr (which would be a different thread) so that I can park the old vf long enough to do some of the heavier work.

I think the biggest problem with the shock on that day was user error or my ignorance playing with the settings I had the pressure was cranked up to near max. and the rebound set to lowest, that with at least 13 year old tired old fluid certainly didn't help matters. With the condition of the rest of the bike I really expected the rear shock to be bad , but the seal isn't leaking and fortunately the previous previous owner and possibly original owner -'02 obviously took gold care of her. It has the most recent design cams in it , the newest version of the banjo bolt coming out of the case, a star stamped on the VIN which should indicate completion of a major recall, as well as other things which show that it was healthy 13 years and 4K miles ago (3K I put on it).

Gonna try to do the steering head next weekend and service the rear one weekend when it's too cold to ride. I already got some lube with high Moly content for the swingarm pivots, and plenty of 10w hydraulic fluid ,gonna get the rear shock seal, and maybe some bushings before then. What I find when I do the rear will determine how soon I look to get the new rear shock, once suspension is done , then I will look to doing the engine, ideally.
I will get a vf750 engine that needs rebuilt and have any upgrades done to it then drop it in.