Sunday, March 30, 2008

Home Wrenching: Variable Pressure Clutch Upgrade

Back about a month ago, I installed a rider back rest and did a clutch upgrade on the bike. I also replaced my bumper cover on the cage. Not a bad weekends work.

The clutch modification/upgrade was to install a Variable pressure clutch kit to give me almost a lockout clutch at high RPMs but allow an easy pull for stop and go situations. It was a fairly simple mod. Start to finish it took me about an hour including changing out my primary chain case fluid.

The VPC works because it has these weights that add increased pressure to the pressure plate to supplement the spring pressure by centrifugal force. The higher the RPMs, the higher the centrifugal force, thus higher pressure added to the pressure plate. I though it would be a worthwhile modification to supplement my heavy duty clutch friction plates and SE heavy duty clutch spring. I ask a lot of my clutch with all the Sherpa duties that I need to do. Not to mention I like to explode out of tolls at WOT. Gail got me addicted to this. If I’m going to pay, I might as well get some enjoyment out of it.

The parts in the kit
VPC, base plate and cap screws with washers

I started by draining the primary chain case fluid. Nothing in the directions said to do this but it was due so I decided to get it done while I was there.

After fluid is drained center bike upright on bike lift

Remove passenger foot rest.

I had to put all the slack in the clutch cable at the adjuster.

Then remove the derby cover.

Next the Clutch spring retainer came off

I had to loosen the primary cover screws because the clutch spring pinned against the cover when I took the retainer off. This is where changing the fluid came in handy. I don’t know how you could do it with the cover bolted down. I didn’t need to remove it, I just backed them out about 3/8”.

Bend the base plate (from the kit) tabs slightly to match the contour of the clutch pressure plate.

You don’t have to remove the spring just pull it up a bit and slide the base plate through the center of the spring and place against pressure plate.

Put spring back in place.

Install VPC where old Spring retainer was using the new allen cap screws provided. Don’t forget your blue Loc-tite. This is a Harley after all and loc-tite is an HD’s best friend.

I then adjusted my clutch as per HD’s instructions.

Cut out the derby cover gasket like below. I used the old one as it seemed in great shape. I don’t have any leaks so it went ok. The gasket is pretty tough. I used an awl to start a hole in the center than sheet metal sheers to cut out the center. Piece of cake.

Refill Primary Chain case with fluid

Reinstall Derby cover and Passenger foot rest.

Check for leaks

Then the fun part… Test Ride!

The VPC worked as advertised. The clutch pull at idle and low RPMs was reduced. Neutral was easier to find with less clunking through the gears. At higher RPMs the clutch pull was elevated a bit but still not bad at all and the clutch locked in with no slippage. I tested it with hole shots, burnouts and a little wheelie off the line. Still no slippage. IMO this is a worthwhile upgrade.

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