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Full Version: Gummy wheel repair , Need O=-ring size
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In the repairs section there are two excelet articles on repairing the gummy wheel problem of card readers. Both articles mention using o-rings for the repair but they don't give a size for the o-rings needed.


I've tried to measure the ones I've been using successfully. Be mindful that these are made of rubber hence, are a bit difficult to measure.

The ID is from 0.1181" (3mm) to 0.125" (1/8"). I suspect a tight fit would be correct to hold snugly on a 1/8" shaft.

The OD is ~0.250" or 1/4".

Sorry I don't have a gear out right now that I could directly measure for you.

Hope this helps,


PS If you have any problems finding the ones you need, drop me an email.

The ones I used recently are 1/8 inch inside diameter and 1/4 inch outside diameter. In British Standards this O-ring is designated as BS006 (see here).

Brian Gladman

I've found that '1 size smaller' -- the shop I get them from calls
them 005 (so presumably that is BS005) is a better fit. Something like 7/64" ID.

Size 006 is ideal for the rubber O-rings in a 9100 keyboad BTW.

There is two guys on ebay who sell the rings, one in the US, the other in Italy. In the US, they are USD 5 for 10 pairs of rings, I think. Try http://cgi.ebay.com/HP-Calculator-HP67-HP97-Gummy-Wheel-Repair_W0QQitemZ5823642197QQcategoryZ11713QQrdZ1QQcmdZViewItem
as an example.

If you are interested in pictures to repair HP41 card reader, I could also offer my guide:
HP 41 Card Reader Repair http://www.pmgeiser.ch/calc/index.php?id=HP82104A

Best of luck

In the UK I got mine from here, where I got 30 for their minimum order of £5. I bought BS006 O'rings but I am pretty sure they will have the BS005 ones as well.

Brian Gladman

I am now getting the "Malfunction" error message intermittently after a "gummy wheel repair" of two years ago. The cause feels like a misadjustment of the little gold contact switches. Does your guide explain how to make the adjustments for these switches?

Jim Chumbley