Topic: Head shake

[invisiblecouch]

Any suggestions to cure the headshake problem with my 78 CB750, mosly on decel. It seems to be sprung too stiff for my 155lb weight. Its a nice bike, I know bikes well and do all the work myself. Has new 5wt for oil.

[GammaFlat]

How are your steering head bearings?  One of the "tells" of bad ones is a feeling there is a notch in the straight ahead position.  This is an indication the bearing races are dented in that spot.  If they're bad, go tapered (All Ballz is good). 

Also, there has been much talk of the front wheel being offset slightly (by the factory).  Align the front wheel with the rear. 

Another possibility I've heard here on the forum is a problem with the swing arm bushings. 

I had a little bit of head shake on my K6 - deceleration down hill got it going.  I changed the head bearings, fork seals/correct fluid level and new tires all at once it seemed to go away.  Too many changes at once to draw any good conclusions....

[invisiblecouch]

Has new tires, bearings are all good. Swing arm and neck. It got much better with new tires.

[j squared]

How are your steering head bearings?  One of the "tells" of bad ones is a feeling there is a notch in the straight ahead position.  This is an indication the bearing races are dented in that spot. 

Interesting, did not know that.  My 550 has that feeling (where it seems like there is a notch at dead center) and I thought it was by design.

Guess its time for new bearings, thanks man

[scunny]

check out the thoughts of hondaman in the faq's, I think he addresses this issue there.

[Duke McDukiedook]

Ribbed tires help.

[the technological J]

it could be any of the forementioned issues.. but it could also be your tires are improperly inflated.... i thought i needed new wheel bearings and(you might)it ended up my rear wheel needed air....... how ever on my 550 i did need new wheel bearings if i let up any tension on the handle bars it would shake like crazy to the point of almost losing it... start with the easy stuff and work your way up

[BobbyR]

it could be any of the forementioned issues.. but it could also be your tires are improperly inflated.... i thought i needed new wheel bearings and(you might)it ended up my rear wheel needed air....... how ever on my 550 i did need new wheel bearings if i let up any tension on the handle bars it would shake like crazy to the point of almost losing it... start with the easy stuff and work your way up

+1

I found that the modern tires need to be inflated higher than recommended in the 1970's. When I switched to BT45s I had to go up several lbs from the sticker and the decell headshake went away. Having said that, it could be any of the problems listed above, pumping and extra few lbs in the tires is the easiest thing to do as a start.

[KingCustomCycles.com]

If you have new tires, check the bead line around the rim is even all the way around.  I have had this problem with many tires I have had done by shops in a hurry that aren't careful. The bead is not seated evenly leading to all sorts of decel shakes and rythmic vibes while riding. Balance could also be an issue.

[steam-powered man]

musings from an old fart:

head bearings can be replaced, but not adjusted properly.  gotta remember to loosen some triple bolts, but not all, adjust bearing preload, then re-tighten.

a slight bit of wear at the swingarm can mean more than expected (by some) side-to-side movement at the wheel.  did you take off the wheel, shocks, everything, when checking the swingarm sideplay?

were your tires mounted properly, then spin balanced?  some folks save a few bucks by mounting their own tires, but end up marring their rims, having beads not centered, have tire balance issues, etc.  i spend the $30 for mount/high speed balance and the ride smoooth.  phooey on ribbed tires 

has anyone attempted to speed up turn-in by raising the forks in your triples?  in my experience, more than 15mm on a 750 and the bike will get squirrely.

when set up correctly, you will not have headshake on a cb750.  have had 3, with 2 more in the "shop" right now and a 550 w/no probs.  am 155 wet.             

[Spanner 1]

I'm + 1 on the tire bead not even, causing a weave....

[GammaFlat]

If you have new tires, check the bead line around the rim is even all the way around.  I have had this problem with many tires I have had done by shops in a hurry that aren't careful. The bead is not seated evenly leading to all sorts of decel shakes and rythmic vibes while riding. Balance could also be an issue.

I had a tough time getting my tires straight.  Someone here on the forum told me to watch out for that alignment "bead line" and sure enough my tire passed the "eyeball test" but the little line wasn't the same distance to the rim edge all the way around.  I think I wound up deflating some and persuading the tire gently with a rubber mallet. 

Frankly, I don't know what I'd do without this forum.  So many little things come up like this from our more experienced and knowledgeable members. 

[seaweb11]

How are your steering head bearings?  One of the "tells" of bad ones is a feeling there is a notch in the straight ahead position.  This is an indication the bearing races are dented in that spot. 

Interesting, did not know that.  My 550 has that feeling (where it seems like there is a notch at dead center) and I thought it was by design.

Guess its time for new bearings, thanks man

You made me laugh out loud. But not in a bad way
It reminds me of many of my own lightbulb moments here over the years.

[invisiblecouch]

Tires are mounted correctly, I did it myself. Worked at a tire store for years. But I did not balance them. I drove home from work yesterday, hit 90-100 mph several times. (Yeh I know I broke the law) No tire vibes. It seems the more aggressive I ride it, the better the suspension reacts. I think its just a little too stiff. Seems the fork doesn't absorb small road irregularities. Kinda packs up and doesn't move at slower speeds. Get her moving and she runs, real nice.

[invisiblecouch]

I think I may try a little more air pressure in the front as suggested.

[the technological J]

I think I may try a little more air pressure in the front as suggested.

do the front and back its amazing what an under inflated back tire will make u think

[nancy]

Are your tyres standard size? If so - try 32psi front 34psi rear, instead of 27/29 or thereabouts that was suitable in 1978

[Steve F]

has anyone attempted to speed up turn-in by raising the forks in your triples?  in my experience, more than 15mm on a 750 and the bike will get squirrely.

when set up correctly, you will not have headshake on a cb750.  have had 3, with 2 more in the "shop" right now and a 550 w/no probs.  am 155 wet.             

I raised the forks in the triple about 1-1/4" about 31m, and I can ride hands free and be totally stable. 
My thought on the head shake could also be the front-to-rear wheel alignment is not right.  The bike's rear wheel wanting to go straight, but if it's not parallel with the frame, the frame is going down the road at an angle, aka "dogtracking".  This could tend to make a bike unstable.
Steve F