Hm... wobble(in lack of better word)?

Posted: Mon Aug 11, 2008 3:57 am

I noticed something when I went to for a short ride today, it's subtle enough that could be in my head. I thought I noticed it a few days ago as well but could not be sure. Anyway, while riding on the street I notice sometime that the bike leans left then right in a very subtle, fluid motion. It probably cannot be seen, but I can feel it. I thought I noticed it while leaning into the corner, it feels like the bike is not settling into a solid lean. Please keep in mind that I'm newbie to riding and have spent only under 1000km on the F so far in the last month or so. I think I only noticed this recently. Today while coming to a stop at an amber light, I locked up the back wheel, the back slid to the left, I let go of the back brake while keeping slight pressure on the front and the bike straightened itself and stopped. I think I noticed the above mention motion for a few minutes after that, then it seemed to had gone away. After stopping for about 1/2 hour I did not notice it on the ride back, but last two block it seemed to happen again. It does not feel like the bike is trailing along the groves in the road, more like a very subtle lean bobbing from left to right.
Something to be concerned about?
Tire pressures are ok, I put the bike on the center stand to check for swing arm play and it does not seem to have any. In other news, seems like my battery is at its last legs, had to boost it today after the second stop and it seems like I, at 170lbs cannot put the F on the center stand by myself.

Thanks for any input! Smile

Posted: Mon Aug 11, 2008 8:26 am

Here are a few ideas:

Incorrect rear wheel alignment - check it and see.

Worn or old tyres? I run about 30 in the front and 32 in the rear on Metzelers...BT45s are nice tyres as well.

Steering stem bearings too tight or badly worn and 'notchy'...this can cause a weave if too bad...also 'self centreing' steering...

These bikes have a powerful rear brake and pretty average front brakes so be careful when applying too much rear...you need it but not too much...

Few things to go on with...

SR Wink

Posted: Mon Aug 11, 2008 5:06 pm

Sounds like steering head races are too tight to me. Put the bike on the center stand and have a buddy push the back down to lift the front wheel off the ground. Then gently turn the bars through their full travel back and forth. Should feel smooth and not at all notchy. If thats OK then grab the bottom of the forks and pull back and forth, should not feel any play.

On the rear brake locking thing, leave the clutch alone when you braking hard until your almost stopped. Surest way to lock the wheel is grabbing a handfull of clutch.

Posted: Mon Aug 11, 2008 6:41 pm

Thanks for the replies guys. I will look into the steering head issues. Tires are/should be alright, about 75%, Bridgestone Sptifire S11. I should also mention that I feel this when the bike is going straight.

What's the procedure for checking the rear wheel alignment?

Posted: Mon Aug 11, 2008 8:43 pm

Easy and best "redneck" way is to go to Odd Lotts or other and buy TWO of the cheap laser levels. These are the short 14" or so long usually yellow type made to shoot a line on a wall.

Lay the laser on the side with the "fit" side against the tire. By using two lasers one on each side,it will shoot a red line on the floor and you can see where it strikes at the front tire. The front tire is narrower so there will be a gap say 1" in the red line to the tire but EQUAL on both sides.

The cute little marks on the swing arm are a MILE off location on all bikes I have checked,not just these,new or old bike.

The rear tire is driving at an angle and the front steering stem is trying to straighten up the bike to repeat,this is your weave.

In old days or now you can sight over each side of the rear to see the front target or the old string or boards method. Regardless the rear is NEVER straight and makes all kind of funny feeling.

Those cheap laser levels are the cat's meow compared to the other methods I have used over the years. No problem with slack string or crooked boards,the line is always true.

You can use a couple of rubber bands to keep the lasers against the tire as it is adjusted,and maybe sitting on a brick to raise it up enough,but this method works good.

Posted: Mon Aug 11, 2008 10:15 pm

Aha, now that makes sense! When you put it that way, indeed recreates what I'm getting. Funny part is that I notice it only from time to time, not always. How precise/bang on does it need to be? As, if I check it with lasers(damn, I have one but not two!), how far off does it need to be to confirm that's the problem?

Posted: Tue Aug 12, 2008 1:38 am

Check it and find out. Usually there is no question since they are often a mile out. You can use one laser but if using two buy them from the same manufacturer,so the distance from gage point to the line is the same. I have seen differences in similar looking tools.

I have seen the red line actually "hit" the front tire and the other is then like 2" or more off. The wheel in this example would be at a large angle to the bike.

After you get close then use the "flats" on the nuts to move each side equal,or put some "windage" into one side or the other. Now you can see the effect of one turn,ie six flats,of adjustment. Usually it works better to have the chain side back a little from the brake side to allow for the chain tension under power making that side "shorter".

Since the distance to the front tire is a few feet this amount off is magnified compared to the actual amount the mark is off on the swing arm. The effect is pronounced when they are off as far as I have seen,sometimes one full mark on the swing arm. The handling will be markedly better and after you get close then can decide if further "tweaking" helps more.

Posted: Tue Aug 12, 2008 3:40 am

Thanks Bill....that was useful, now maybe I can get mine to stop.

Posted: Tue Aug 12, 2008 4:23 am

I was looking at those in the Harbor Freight store originally,and I thought there must be a way I can use these to line up a rear wheel.

We used to it by the sight over the tire method,did this for years when we were a dealer. Those marks are always off.

Same type of thing on the drag bike,since these did not have "marks" on an extended arm.

So after I did this on various bikes the handling is just so much better.

Now you can improve this method by going past the tire to strike on the rim,but basically any version is a lot closer than the marks.

After you get straight,then just always move the adjusters the same amount of flats to maintain it. I always snug up the axel first then put some tension onto the adjusters to drag out the play,THEN tighten the axel fully.

You will just be amazed at how far out the marks are,assuming the marks were even used to start with. The wheel crooked will make the bike turn different right to left,like "stagger" or "wedge" on a dirt track or Nascar type car.

Stopping wise,I prefer the SBS type pads that are some version of metallic. Those babies really grip,so watch it,does not take much squeesing.

Posted: Tue Aug 12, 2008 5:11 pm

Don't forget to check your swingarm bearings. The 79 CB750F actually has a plastic bushing that wears in about 500 miles. There is a kit out there to convert these to roller bearings.

Posted: Tue Aug 12, 2008 6:24 pm

stoutblock wrote:

Don't forget to check your swingarm bearings. The 79 CB750F actually has a plastic bushing that wears in about 500 miles. There is a kit out there to convert these to roller bearings.

Mine is an '82, does that make a difference? I already checked for play in the swingarm and it does not seem to be any. Confused

Posted: Tue Aug 12, 2008 6:50 pm

The later bikes were all alike in using needle rollers in the swingarm. It was only the earliest 750 that had the plastic bushings and the pivot bolt diameter was smaller as well.

Posted: Tue Aug 12, 2008 10:46 pm

sonicrete wrote:

The later bikes were all alike in using needle rollers in the swingarm. It was only the earliest 750 that had the plastic bushings and the pivot bolt diameter was smaller as well.

Good to hear.

On the battery side, I need to get the famous Big Crank. For now, I bought a cheap regular battery as I want to go on a small trip within 2-3 days. And I mean, real cheap, I found it for CDN$33 taxes in, at Edmonds Battery. Once I get the BC, this one can be the backup.

Posted: Wed Aug 13, 2008 7:46 am

I have driven many a mile with the rear end out of line and never had a low speed wobble from it, many times i have had the axle loosen enough that when hitting the back brake it would move far enough to turn me.. Smile

My point is if its close, you should not still see any low speed wobble from it.I never have anyway. Check it out tho, its free! Same with the steering head bolt, mind you when its loose you will get the shimmy all the time at certain speeds.

Hope you get it sorted out..sounds minor either way, As for a battery, whats the problem with the reg one? If your starter and wiring and tuneup are good, thats all you will ever need. I have never had a battery problem in 27 years with my f's using the cheapo's. just be aware they only last a few seasons.
Ever read the technical articles regarding 2 wheelers?, they all say bikes oscillate from side to side all the time,(or something like that) just the way it works..maybe you are just sharp enough to feel it! Smile

These are old bikes,they do have lots of little quirks. Some are normal, some arnt, all are worth checking out, but some are never going to go away.. Smile

yours doesnt sound too bad! good luck.

Posted: Tue Aug 19, 2008 5:41 am

Nitro wrote:

I have driven many a mile with the rear end out of line and never had a low speed wobble from it, many times i have had the axle loosen enough that when hitting the back brake it would move far enough to turn me.. Smile

My point is if its close, you should not still see any low speed wobble from it.I never have anyway. Check it out tho, its free! Same with the steering head bolt, mind you when its loose you will get the shimmy all the time at certain speeds.

Hope you get it sorted out..sounds minor either way, As for a battery, whats the problem with the reg one? If your starter and wiring and tuneup are good, thats all you will ever need. I have never had a battery problem in 27 years with my f's using the cheapo's. just be aware they only last a few seasons.
Ever read the technical articles regarding 2 wheelers?, they all say bikes oscillate from side to side all the time,(or something like that) just the way it works..maybe you are just sharp enough to feel it! Smile

These are old bikes,they do have lots of little quirks. Some are normal, some arnt, all are worth checking out, but some are never going to go away.. Smile

yours doesnt sound too bad! good luck.

Thanks for the optimistic reply! Very Happy

As I said it's very subtle so it might be normal.

Posted: Wed Aug 20, 2008 11:32 pm

And you could be a very observant person. Motorcycles actually do progress in a series of very shallow ellipses.