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Front end damping

Mickthevin

Well Known and Active Website User
Non-VOC Member
Just returned from the big red fellas first foray into europe. The bike ran really well and kept up with modern bikes even though we were fully loaded (thanks to the rack donor who shall remain nameless) and two up. The one major problem we had was every time we went over a pothole or speed bump the front end bottomed out with a horrible bang. Is this the front damper or something worse? I will be taking the front damper off later this week and checking it out but am asking just in case somebody may instantly recognise the problem. There wasnt anything on the front end that should not have been there
thanks for any input

mick
 

BlackLightning998

Well Known and Active Website User
VOC Member
Hi Mick

Mick,

Assuming the forks are set (eccentircs) for solo use (I'll check your photos) then I would look at the damper first of all. It may well have failed and lost all it's oil - perhaps swap it with one of your others and see if that sorts it?

There are two different eyebolt lengths from memory too, I'm assuming that it has the right ones in place.

If it didn't do this when you were running it in the UK then I guess a failed damper has to be first suspicion.

Either that or too many pies!!!!!!!!

Cheers

Stuart

Just returned from the big red fellas first foray into europe. The bike ran really well and kept up with modern bikes even though we were fully loaded (thanks to the rack donor who shall remain nameless) and two up. The one major problem we had was every time we went over a pothole or speed bump the front end bottomed out with a horrible bang. Is this the front damper or something worse? I will be taking the front damper off later this week and checking it out but am asking just in case somebody may instantly recognise the problem. There wasnt anything on the front end that should not have been there
thanks for any input

mick
 

peterg

Well Known and Active Website User
Non-VOC Member
Howdy Mick,

Are your sure the shock was indeed bottoming as opposed to just going almost rigid and the shock bushings pounding the top or bottom securing bolts or the eye bolts slackened off on their perches? I just returned from several hundred miles on the Shadow, two up at 390lbs, on expansionstripped and (excitingly on occassion) potholed roads up North and the only sensation oft repeated at the front on abrupt bumps was reluctant fork travel compliance before seemingly going rigid and then the hop....


You have several scenarios for making a very firm unyielding ride at the front: 3.00x21 tire has little sidewall depth to yield as a springing medium, there's an awfull lot of unsprung mass to accelerate quickly on a girdraulic machine with cast iron shadow drums, and a rather unyielding vintage designed shock. You may have noticed when you stroke a stock unit - especially the front - that there is a dead space of compliance before (overly) firm dampening commences (if you've observed this bled into a clear graduated cylinder, a stroke accompanied by an incedible amount of frothing - don't expect the same results twice).

Know Thy Beast (I think) provides a section of aiding fluid distribution in both jounce and rebound to mitigate this characteristic which it does to a degree. I mod'd accordingly and then started at 20wt and worked down to 5wt oil on the Red Rap to at least have a transition. The outcome is a nice floaty feel with entertaining rise and fall of yokes under acceleration/decel with some semblance of dampening no doubt aided by running my front 3.50x19 at only 26psi. Semi suitable for a dignified fat tired touring rap spec machine, but not at all in keeping with the Shadow's MO.

I have not dissembled and performed same mods with the later VOCS stock units fitted to that machine but will drain off and fit first, ATF and then Penske 0 Weight shock oil No great expectations, unlike the true road warriors here abouts, I'm just looking to preserve the true vintage Vin riding experience...but with some degree of safety and without concern of squirting my spindle bushings out each side when pounding an unavoidable crevice in the road.
 

Mickthevin

Well Known and Active Website User
Non-VOC Member
Front end

Either that or too many pies!!!!!!!!

You arent the first person to say that Stuart and I will ignore that with what I like to think is lofty disdain. A couple of PMs sent me in the right direction. After removing the spring boxes and checking the length of the springs I found that the outer springs were nearly 1.5" shorter than new ones. Also I didnt have any inner springs. Russ supplied me with a new pair of each and I hope to get them in tonight/tomorrow. Tony also noticed that one of the sleeves had a small dent in which was restricting the spring from moving. This has been rectified now and hopefully will return the front end to normal.
Will report

Mick
 

peterg

Well Known and Active Website User
Non-VOC Member
Howdy Mick,

Mercy! Knowing the level of game face required to ride on B, C type roads over there coupled with the speed a Vin encourages, can't imagine the sensation at the helm when truly bottoming a girdraulic front end and having the suspension go immediately rigid...probably along the lines of tank slapper, me thinks.
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Front springs

I took one of my front inner springs out, to soften the front and stop the wheel skipping over bumps when cranked over. (Like the rear, they are Petteford springs, lighter apparently than standard, but to what extent I don't know.) I can do this with next to zero risk of steering malfunction for two reasons. The first is that I have Thornton dampers, much, much superior to anything else commonly available, and as good as the best modern shocks. This combination gives a very comfortable ride, and because the damping really DOES work, the fork neither bottoms nor tops. Or at least if it can, it hasn't yet.
Nor does a bump mid-corner mean an involuntary lane change to the outside of the bend.
Taking the spring out was a Sid Biberman suggestion. It also follows the precepts of Ron Williams (Maxton) that for good roadholding you need not a superstiff frame (the Featherbed Norton isn't particularly stiff, but has very good geometry, which doesn't alter much with suspension movement.) but soft springs and stiff damping. If you have stiff springs and soft damping, the case with virtually every British bike from 1945 onwards, then the wheels bounce off bumps, allowing the bike to crab sideways.
Why are they like that? Well, damping was in its (relative) infancy, and springs had to cope with loads from 8 stone to 20 stone. 8 stone springs would break under 20 stone loads, so they fitted 20 stone ones. Handling might have suffered, but warranty claims were minimised.
The other reason is an hydraulic steering damper. There's never been even a hint that a feared "Vincent tank-slapper" was beginning, not that there's always any warning. However having survived three of them (all on bikes of "legendary handling" and none of them Vincents) I have absolutely NO inclination to risk a fourth. The third one narrowly missed breaking my neck.
There might actually be a third reason. I weigh 12 stone soaking wet, and rarely carry a passenger, so I've set the bike up accordingly. This means I have to take it easy when I do have a passenger (Oh look, daddy! A blue moon!) and I doubt that "fully laden" with camping gear (and tools...) I'm carrying more than 50 lb.
Has anyone tried the latest Thornton "coil-over" shock yet? I know that John Crispin made a coil-over front shock for Bramptons, which he said worked very well.

Tom
 

johncrispin

Well Known and Active Website User
VOC Member
coil over damper shock

Tom,
Nice to be mentioned in your column Tom!
twas not me that made a coil over damper spring for bramptons, but I have got one made by Hagons for my Rudge Ulster. Not quite the authentic look, but I have now only a use for the old friction dampers on either side of the links (in my view the best girders of the thirties despite the weight) to keep the whole assembly working in a straight line. I oil them infact. A pal down here in the west has fitted skinny roller bearings inplace of his, OTT perhaps, but works well also.
It was kicked off by your countryman in Rudge club called John Shaw. Hagons made a batch and as far as I know would make more given a minimum order ( initially 10, they made 20 ) last I heard they had a few left. It completely stops the fiddlers elbow antics of the whole lot with the o.e.
A similar thing could work well for Bramptons but the bottom fitting would have to be bespoke and it is far from a straightforward peg like the Rudge. It is this simplicity which made it a fairly straightforward, task to cut of the eye s of a conventional unit and replace with welded 10mm threaded studs a la Rudge. (10mm rather than 7/16" because it has to allow the s shaped movement of the girders at either end of the rigid damper, the original spring being flexi, ..... 12 stone eh you lucky !!!
 

Tom Gaynor

Well Known and Active Website User
VOC Member
On Bramptons, and the even better Rudge forks, copied by PEI for Girdraulics....

Now is that a provocative heading, or is it not? But it is true, PEI copied the Rudge one-piece links for Girdraulics, and said so.
Thanks for the implied compliment.
My point is that DAMPING is the key, and the ideal is to have soft springs, and stiff damping. This is the very opposite of 1) what most bikes had and 2) popular opinion (including, at the time, mine), was. I can remember cranking up the preload, racer style, on Girlings, to the point that the springs wouldn't give except under the most severe provocation (underpants packed with depleted uranium), which meant the bicycle skipped lightly outwards (grossly understeered) unless the road was like a billiard table. Generally, and still, it wasn't/isn't.
Don't know John Shaw.
Regardless, if this correspondence shifts the emphasis from springs to dampers, good.
And, nice to hear from you.

Tom

.
Tom,
Nice to be mentioned in your column Tom!
twas not me that made a coil over damper spring for bramptons, but I have got one made by Hagons for my Rudge Ulster. Not quite the authentic look, but I have now only a use for the old friction dampers on either side of the links (in my view the best girders of the thirties despite the weight) to keep the whole assembly working in a straight line. I oil them infact. A pal down here in the west has fitted skinny roller bearings inplace of his, OTT perhaps, but works well also.
It was kicked off by your countryman in Rudge club called John Shaw. Hagons made a batch and as far as I know would make more given a minimum order ( initially 10, they made 20 ) last I heard they had a few left. It completely stops the fiddlers elbow antics of the whole lot with the o.e.
A similar thing could work well for Bramptons but the bottom fitting would have to be bespoke and it is far from a straightforward peg like the Rudge. It is this simplicity which made it a fairly straightforward, task to cut of the eye s of a conventional unit and replace with welded 10mm threaded studs a la Rudge. (10mm rather than 7/16" because it has to allow the s shaped movement of the girders at either end of the rigid damper, the original spring being flexi, ..... 12 stone eh you lucky !!!
 

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