Rear Springs

Bazlerker

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Non-VOC Member
About 25 years ago I fitted petteford springs, which I have cursed ever since. Every bump is transmitted to my posterior...I never carry a passenger, nor do I carry any luggage, my machine is unencumbered by a sidecar...So the question is..as I weigh 225-240lbs..what springs should I fit?
 

Albervin

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Bob, do you want to go to "fully sprung" as that will give a more comfortable ride. I have always found a standard Vincent rides better two up than solo on our Aussie roads. From memory I have a standard spring and a Comet spring on the rear of my Rapide but I only weigh 175 lbs.
 

Bazlerker

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Well, I certainly want more "give" in the rear suspension than I have now..Perhaps Ill try changing one spring at a time to a standard one..
 

davidd

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Bob,

I made rear springs for a while, but I did not like the way the spring boxes worked with them. I concluded that a coil-over was the only way for me to go and I built one for the racer. I think I used two 90 Lbs. springs with a smaller opposite wound spring that could fit inside the large spring to add to the spring rate. At that time I did not understand that both the front and rear springs had too much preload.

I don't know what you plan is, but I would consider switching to a coil-over. At a minimum, you might want to take a ride on someone's bike that has a coil-over. It has the advantage of adjustable preload as well as the choice of spring rate and adjustable damping rates. I know you may have other requirements but it has some compelling advantages.

The calculation for the spring rate would be roughly 320 Lbs. if it were a coil-over. This would be about what the spring should push back at one or so inches of compression. That would mean two 160 Lbs. springs if you use two spring boxes. This is the quick calculation in my head. I am happy to show my work, particularly if someone else has a better number.

David
 

Bazlerker

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Hi David..Many thanks for the information. I'll see if there is anyone at the North American rally in September who has fitted a coil-over, though I had hoped to have it sorted before then as I am retiring soon ( fixed income on the horizon..)
Alternatively, if there is anyone in North America who has a standard spring they would like to sell, or trade for a petteford...
 

timetraveller

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I think that there is something wrong here. The Petteford springs have a rate of 169 lbs/inch as compared to standard solo springs with 202 lbs/inch (both these figures obtained by me measuring used springs). They are also longer so should give a longer, softer ride. Fitting one standard spring on one side only will not improve things. If you fully spring the rear of the seat it should be more comfortable but generally the front of the seat is more comfortable than the rear so the question is what is wrong with your bike. Do you have a Koni damper which is set too stiff? Are the friction dampers slackened right off and if necessary the friction material in them lubricated? Are both top and bottom spindles to which the spring boxes mounted free to rotate in their housings? If you are sure that all those items are correct then the quickest and cheapest change is just to fully spring the rear of the seat with two struts which go from the rear, top holes in the pillion footrest plates (move the footrests one hole forwards) up to the rear of the seat. You will need to distance the bottom of these two struts outwards about half an inch to prevent them fouling the brackets which take the friction dampers. Almost any kind of a bodge up can be used to just try this out for one ride and then if it seems to have improved things a more serious modification can be made. I have never seen the taper roller bearings about which the rear frame triangle pivots lock up but if all the above do not improve things then have a look at those bearings.
 

Vincent Brake

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i have m all with works and coil over, only when fully sprung put on an other spring as i weigh 75kg.
perfect,

it took seconds of my lap time....

now who was sitting there...:p
 

Albervin

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VOC Member
I think that there is something wrong here. The Petteford springs have a rate of 169 lbs/inch as compared to standard solo springs with 202 lbs/inch (both these figures obtained by me measuring used springs). They are also longer so should give a longer, softer ride. Fitting one standard spring on one side only will not improve things. If you fully spring the rear of the seat it should be more comfortable but generally the front of the seat is more comfortable than the rear so the question is what is wrong with your bike. Do you have a Koni damper which is set too stiff? Are the friction dampers slackened right off and if necessary the friction material in them lubricated? Are both top and bottom spindles to which the spring boxes mounted free to rotate in their housings? If you are sure that all those items are correct then the quickest and cheapest change is just to fully spring the rear of the seat with two struts which go from the rear, top holes in the pillion footrest plates (move the footrests one hole forwards) up to the rear of the seat. You will need to distance the bottom of these two struts outwards about half an inch to prevent them fouling the brackets which take the friction dampers. Almost any kind of a bodge up can be used to just try this out for one ride and then if it seems to have improved things a more serious modification can be made. I have never seen the taper roller bearings about which the rear frame triangle pivots lock up but if all the above do not improve things then have a look at those bearings.
Agree. You cannot mix a Petteford and a standard spring. Always look at the basics first, friction damper and bearings. Are the springs and damper rotating freely? I have had a bike where the bolt?hex screw/bolt was bent. This caused a very rough rear end. This was caused by a bush that was not correct.
 

Bazlerker

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Non-VOC Member
Interesting reading...I have never lubricated the friction damper linings and the adjustment knobs are slightly snugged as I am afraid they will come loose - and be lost. What should I use to lubricate the friction linings with?

The rear damper is original, the grease fittings are given a shot once a year..
 

timetraveller

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To lubricate the friction damper linings one could use any 'grease'. One which is unlikely to leave stains is a PTFE based lubricant but really anything which will not oxidize and go solid or leak out and leave a mess. Once that is done I leave the knobs just tight enough not to vibrate loose and get lost. It is true that the original Vincent rear suspension is not the most comfortable, particularly for the pillion passenger, but on the front you should not be getting shocks up your spinal column and if it is as bad as that then something is wrong. I agree with those who say that the coil over dampers should cure the problem and the new AVO ones are turning out to be a good choice. A coil over and fully sprung seat rear is the way to go if you prefer comfort to an original appearance but remember not to put too much strain along the seat base frame by putting the bottom of the new seat stays too far forwards. See photograph posted on this forum recently.
 
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