FF: Forks Girdraulic Springs

druridge

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I removed the spring boxes on my Series C Rapide to a) get the spring case bottoms FF16AS rechromed; and b) work out what is going on with the springs.
Bike is a Touring Rapide, with 19" front and 18" rear wheels, its got a twin disc set-up on the front. I ride solo at a reasonable pace rather than insane, and am just under 12 stone before I put the bike kit on.
The bikes handles great, very precise and predictable etc, until I hit a bump in the road when I get a bad shock through the bars.
I presumed I had 'hard' springs.
Once apart I found the 2 outer FF13 springs to be slightly different lengths (15.25" & 15.5"). No inner springs at all, but the outer springs were packed out with a spacer of about 1.25" sat in the bottom of each spring box. the Girdraulics move freely with the springs off. No play detected. Grease in all the right places, I can feel and hear the oil within the damper moving. The damper appears 'standard' but seems to work. In the past, the bike had a sidecar fitted and rode distances over bad roads.
I now assume I have two 'tired' C springs. These appear to have been 'firmed up' with a couple of spacers, this having the effect of pre-loading the springs. Odd why there are no inner springs; or ( unlikely) have I got 2 very tired D springs?
Anyway; the Spares Co. stock inner & outer springs for small money, so one option is just to buy the 4 and fit.
My question would be if this is the best option? KTB mentions the option of discarding the inner springs; would fitting D springs be an improvement?
I've read a bit and there doesnt seem to be a concensus ?
Any thoughts?
Many thanks
 
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druridge

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timetraveller

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Oh Dear! you have opened a can of worms. A complete solution to your problem is to fit the John Emmanuel steering head, complete with my springs and an AVO damper. This is written about in great length in the thread 'Modified Steering head'. It is a long and convoluted read and if you are interested I can send a pdf to your email address which is a much shorter read and gives you the all the details and fitting instructions.

The mod you have found in your forks is typical of what people were doing several decades ago when it was realised that the longer, softer 'D' springs gave a better ride and people chose the cheap way of updating by taking out the inners and packing the outers. What it did not do was to remove an inherent design fault in the geometry of the girdraulics.

If you are interested you can either put your email address on here or send me a private message (PM) and I will communicate in private. The front end can be made much better than the one you have now.
 

davidd

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Druridge,

The stock spring is 15.5" long and produces 68 lbs/in. The stock inner spring produces another 9.5 lbs/in. This made the total stock twin spring rate 77.5 lbs/in, while the stock single rate was 68 lbs/in.

The Series D sported a 16" spring that produced 63 lbs/in. Hence it was the lowest rate of the stock springs.

Here is what I would propose for the consensus:

With a stock Girdraulic and brake it is best to run springs that are short enough to be adjusted so that you can make your lower link parallel to the pavement as you sit on the bike.

With a stock Girdraulic and an improved front brake a modified FF2 should be installed. Once done, almost any spring that is comfortable should be fine, including stock springs.


I think that the "Oh Dear!" part of the conversation is that it is difficult to have consensus on properly setting up a front end with a known defect that has not been minimized or remedied in some manner.

I am a little surprised that you have noticed the how strongly the chassis moves upward when your disc brakes are applied, but you may be accustomed to it.

David
 

macvette

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When I got my D about 15 yrs ago, I was new to Vincents. It ran but was in need of a lot of TLC. I rode it a few hundred miles to see what was needed and did a lot of reading. Very early in its life, it had a side car ( listed in the original log book). I found that it had C springs fitted i.e inners and outers. These were replaced with the series D single springs. They did improve the ride. I ride solo. There were many issues with the bike so I completely rebuilt it over a period of 3 or so years and used the D springs.
The bike was quite compliant for a bike of that era and I had no handling issues. I weigh about the same as you but have the standard drum brakes. I'm not a hooligan but ride quite vigourously.
Last year, I put the JE MOD on the bike with ball bearings in the lower link and fitted a hydraulic steering damper. The front end is more compliant but most noticebly, it now compresses when the front brakes are used, it didnt before.
I would put series D springs in as a first step and see how it reacts, read up on the JE mod, and do that if you feel its needed after you have tried the D springs.
 

timetraveller

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The inner springs were not fitted just for sidecar work but were fitted to all twins. It was rotating the clever eccentrics which altered/compressed the springs for increased weight resistance when a sidecar was fitted as well as altering the trail.
 

Bill Thomas

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I would first fit an Hydraulic Steering Damper, Then play with what ever you want, Different people want different things.
I would agree with David about, Lower Link Parallel to the pavement at rest, As we are seeing from
Older Photos, Don't know how they seem to have got longer Springs over the years !. But if they are standard forks, You don't want them to go too high or too low, Just my thoughts.
I am not a Hooligan but I like to push on sometimes !.
Cheers Bill.
 

macvette

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The inner springs were not fitted just for sidecar work but were fitted to all twins. It was rotating the clever eccentrics which altered/compressed the springs for increased weight resistance when a sidecar was fitted as well as altering the trail.
Hi Norman,
I was only trying to give my experience in comparing tired C springs with new series D springs and I understand the function of eccentics. In KTB, however, you will find a reccomendation to use inner springs to Ds when fitted with a sidecar.
 
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