FF: Forks M

[MarBl]

required positive counter steering input

I have that impression too. Since the modification it seems to need a bit more counter-"pressure". I perceive that as a slight disadvantage, but easy to adapt to and the massive improvement of the modified forks performance predominate that by a long shot.
When I finally sorted the modification out, I was really surprised by the excellent performance of the fork. I struggled with the setup for some time though. Being new to the Vincent world and with no experience with Girdraulics or Bramptons, I really underestimated, how the friction of all the pivot points (14) added up. I only noticed that, after assembling everything except the springs (but the boxes). After readjusting everything, the fork really surprised me by its performance, reminding me on typical 80s bikes. Nothing at all to complain about now and along with Vincents superb 7" TLS brakes a real joy to ride.
Many thanks to Norman, Greg and John Emmanuel for their enormous effort.

I watched the John Surtees video four times in slow motion and it appears to me, that the front wheel was already slightly bouncing off the ground, when the camera catches him. So it may be a problem of stiffening fork under breaking, then the wheel starting to bounce, making contact at a different angle, followed by a slapper. If that really is, what happened, I would say, the mod will prevent that.

 

[Bill Thomas]

The fact that you can ride for thousands of miles , Most of us have,
And not have one !, Has been the problem all along,
It takes a certain set of bumps etc ,
I used to do wheel balancing for cars , When I worked at a JAG' place,
And the wobble comes in at certain speeds !,
On the road it comes at 30 50 70 and I have heard of 100 !!,
Most strange !,
But for me an hydraulic Steering Damper is a MUST,
Like if you were riding The T.T. Races !!.

 

[Phil H]

In this case it is impossible to have a perfect design. The best thing is to find the best balance of factors (i.e. probably do nothing and leave it standard), and then use an hydraulic damper. Not fitting one is like throwing away your suspension dampers and then altering other factors in an effort to stop your Vincent from behaving like a pogo stick.

 

[Peter Holmes]

These type of accidents can occur in the blink of eye, thankfully I have never experienced a tank slapper, and I hope I never do, the nearest I have come to one was when my 1928 AJS K9 500cc, my Banbury bike, sadly no longer owned, developed a disconcerting weave, that turned out to be slightly loose headset bearings, once tightened the weave disappeared.

We have just recently returned from a very enjoyable holiday in the LLyn Peninsula, Wales and the North Yorkshire Moors, as an aside, if you are ever up that way, try the Rosedale Chimney Bank Hill, 1 in 3, very exciting going down it, all the time praying that my front brake cable nipple did not pull off!

But back to the point, we also took our electric bikes in an attempt to keep fit in our decrepitude, so here we are, going down a fairly steep hill (but not the Rosedale Chimney Bank) when my baseball cap flew off, I instinctively tried in vein to grab it with my right hand, lost complete control of the bike as I careered this way and that trying to regain control, really hurt something in my shoulder, so extreme were my efforts to regain control, I would describe it as a tank slapper, but there is no tank, so perhaps it was a battery slapper, pretty terrifying just the same, especially as I recently had bi-laterall knee replacement surgery, and really did not relish the thought landing on very hard tarmac at 30mph+, luckily I regained control, but my right shoulder is still giving me gyp.

 

[Chris Launders]

Forty years ago I had a Rapide that treated me to a tank slapper after hitting a bump. I blamed the fork geometry at full extension. I fitted Spax suspension dampers and a Kawasaki steering damper mounted on the left side by aluminium brackets. easy to fit. Handling at speed thereafter was impeccable. I have a clear memory of hitting a bump mid-corner at 80mph. When the Rapide landed it tracked true with no trace of a wobble or flex.
This might be your solution Bazlerker. From memory the back end of the steering damper was attached to a bit of aluminium angle which was secured by the left head bolts on the front cylinder, and the front end to a pear shaped aluminium plate that replaced the friction damper. The whole idea came from something that I read in M.P.H.
My experience with adjustable hydraulic steering dampers suggests that you start off at the minimum setting. I've tried starting at about the mid-way setting, and the results were memorable.

I have this style of steering damper fitting, I've kept it even after fitting the Modified stem etc. I'll go and take a picture when I've finished my cup of tea.

 

[bmetcalf]

See p.289 of 40 Years On.

 

[Chris Launders]

Ok so this is the one on mine, there is a general overview, the head mounting, the fork mounting and one awkwardly taken from the other side showing the single plate with piece welded on to support both sides of the damper end, the markings and cable end on the crash bar in the first photo is my rear damper travel indicator as I'm still sorting out my best preload/damping combination, and this allows me to see what's happening while I'm on the bike.

 

[Bill Thomas]

Bob, If you use a single side plate like me ,
It's best to fit a penny washer to the open end where the rubber bush is,
The rubber bush has been known to work it's way out !,
Sorry the rubber stays put , But the round metal ring can drop off !,
So the penny washer needs to be bigger than the end of the unit.

On the 3 rd photo I have used nuts as spacers to bring my plate down,
Away from the standard Friction damper plates,
I find it handy when working on the bike to nip up the standard damper ,
To stop the steering flopping about,
Just my thoughts, Bill.

 

[greg brillus]

Those kwaka H2 dampers are all i've ever used.......work well and dont look too bad.......the billet alloy ones look too modern for my liking........Only advice i can give is to make sure you use as much of the damper's stroke as possible from lock to lock.........The head shake issues are not just found on cornering and hitting ruts in the road surface, it happened to me on a straight high speed stretch of road........This was not long after I got my bike.......the 2 items that contributed to it were........probably didn't have the friction damper tight enough, and it was way over sprung in the front........that is, it still had the duel springs in either spring case.........It is worth remembering that many of these bikes once had sidecars attached where the owners might have installed stiff springs to suit........loads of bikes still have the duel springs up front and 0.320" wire size rear springs in the back end........no wonder the bikes are so ridgid on the road.

 

[Bill Thomas]

In practice laps at Mallory Park,
I had a Huge slapper that went on for SO long, Coming out the long bend,
Had a nervous laugh with one of the other racers,
Gave the standard damper a good old NIP UP,
Went out and she had me , A Big one, I am too big to fly,
With a load of riders behind me, Laying on the track was not a good idea,
Wound up like a small kid on hands and knees, Getting the hell out of there !,
What I am saying is , Doing up the standard damper tight , Does NOT work .