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Variable Pressure Clutch Kit Question

Variable Pressure Clutch Kit Question

(OP)
Does anyone have any info on these devices? Their claim states... It will reduce up to 50% of the clutch lever pull. Being that the VPC operates on centrifugal force pressurizing the clutch plates. What good would this device be when the engine is at idle or low rpm? I can understand how it would help to engage the clutch plates as rpm increases. But I do not understand how it would assist in lowering the actual clutch lever pull pressure. At low engine rpm the actual work performed in the clutch basket relies on the clutch diaphram spring pressure and the pull of the hand lever completely excluding the centrifugal force of the variable pressure clutch plate????

RE: Variable Pressure Clutch Kit Question

I think I have detected two different tricks:
- shim the anchor point for the spring(s) away from the clutch plates so there's less preload applied to the clutch pack as you tighten up the retaining bolts.
- interpose something so that the diaphragm spring, where one is used, is anchored at a different radius from stock.

Both result in less total force applied to the clutch pack at idle, making it easier to pull the lever to disengage the clutch.
Both result in it being necessary to use an adjustment procedure different from that for the stock hardware, so don't lose the instructions.

Both result in it being more likely for the fully engaged clutch to slip at low rpm with a lot of throttle. That's exactly what dragster 'slipper clutches' do.

The other side of that coin is that it's less likely for the fully engaged clutch to slip at high rpm than it otherwise would be, thanks to the extra force exerted by the centrifugal weights.

The sharp edge of the coin is that the centrifugal weights that apply extra force at high rpm also make it harder to disengage the clutch at high rpm. If adjustment is provided, e.g. variable number of weights, you might not want to overdo it, unless you've modified the engine for extra power.

I'm assuming you can manage a quick hard pull on the clutch for a gearchange, or maybe just use the kill switch, but are having a hard time slipping the clutch in traffic. The VPC should help with that.



I could not find any sort of power booster to be inserted in the cable itself. It's probably more of a packaging problem than an engineering problem. ... and the market is small, unless you can make it universal enough to fit newer bikes as well as yours.


Mike Halloran
Pembroke Pines, FL, USA

RE: Variable Pressure Clutch Kit Question

(OP)
Again Mr. Halloran I would like to thank you and appreciate you taking the time to help me with my problem.
You mentioned shimming the anchor point for the diaphram spring away from the clutch plates. There is a 3 position adjustment directly above the clutch diaphram spring (the 4 bolts that hold the clutch basket in place ) that allows this spring to exert firm, medium or soft pressure. depending on which diaphram spring is being used. I will upload 2 scanned pages of the factory H-D manual relating to my wet clutch and send it with this post. These pages refer to the spring preload. And adjustment. When I first opened up the derby cover . The adjustment was on the greatest compression setting. Of course, I switched it to the least setting . I am somewhat confused. The factory manual is not very descriptive and somewhat vague. By what I understand this adjustment is not for the pull pressure on the hand lever but for the engagement pressure on the plates. With the harley recommended 40% reduction kit I cannot feel much difference in the lever pull pressure. In regards to your comment Mr. Halloran, yes I can manage a quick hard pull for a gearchange. The problem is not the pull. It is how hard I must pull it that has injured my wrist. The only noticable difference has been the replacement of the cable and is not very much.Please let me know if both photos uploaded.

RE: Variable Pressure Clutch Kit Question

I got img005.jpg of page 6-15.
This site accepts only one file at a time.

Mike Halloran
Pembroke Pines, FL, USA

RE: Variable Pressure Clutch Kit Question

(OP)
Oh and the engine has not been modified it is all stock 1400 cc (1398cc)

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