Fixing Grace 707 Damping w/ Pics

[Johnny_Law]

When I bought my Luxman PD121, I quickly noticed that the tone arm lift handle's O-ring had broken. Chunks came out followed by dripping damping fluid. Quickly thereafter, the damping was gone.

Searching online, I couldn't find any guides other than a 2007 post on DIY Audio (here). But, that guide involves cutting out the Grace label, and the mechanism is a bit different from mine anyway. Most importantly, no o-ring! Here's what mine looks like (ignore the green reflection):



You do NOT need to cut out the Grace logo disc!



I tried a couple different sizes. In the end, I used a 5.5mm I.D. x 1mm wide o-ring (bought off ebay, $2 for 20). I had to trim it in order to get the pivoting shaft to slide in the hole - If anyone knows the correct size o-ring, please post! I imagine a ~0.75mm wide o-ring with a 5.5mm I.D. would be closer.



With the o-ring taken care of, I rebuilt the mechanism with fresh 300,000 cst damping fluid.







Back in and working great so far. Perhaps thicker fluid might be better - it comes down pretty quickly, but much better than a freefall.

 

[Old Guy8]

Thanks for documenting this with pics. I have a Linn Basik LVX that needs damping.

I have a Parker o'ring size catalog. But doesn't go that small. Your right, o'ring width needs to be narrower than groove. Giving it room to expand when compressed.

This chart of groove (gland) wides for o'rings only starts with 1/16" wide o'rings. But shows .093/.098" groove width for that size. For static application without backup rings. Approximately 50% wider groove.

If legible. Sorry poor copy. Came from a closed machine mfger standards.

 

[Johnny_Law]

Thanks- I had measured the diameter of the slot as well as the width but can't find the measurements now. Shoot.

By the way, I did find out in the meantime that the Kenwood KD550 uses the same tone arm lifter, and that Jelco sells something very similar (C$99 cost).

 

[Old Guy8]

BTW, I believe Jelco announced a while back, closing thier business down.

 

[doctor fuse]

Thanks for the amazing post! Viva G707 fans!

 

[gary7]

My 707 arm has a different cue. The outer cylinder housing is one piece. Unscrew and remove the top arm lift. Raise the arm and remove from the bottom. Has the black plug in the bottom. Remove the plug, unscrew and remove the lift lever. Carefully drop the piston from the bottom, care not to lose the spring. Add damping oil to the piston groove. reverse assemble.Test. I used 300K. had to do it about 3 times to get it right. Now drops near perfect.