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BLACKBOX
06-17-2015, 12:57 PM
Today my Gaffrig II speedometer malfunctioned. It will only register up to 30 mph. Any ideas?

Just Say N20
06-17-2015, 01:37 PM
More throttle. :)


GPS or pitot tube?

BLACKBOX
06-17-2015, 09:07 PM
Non GPS -- I've been told to disconnect the tube from the speedo & force air through it - but the last time I tried doing this (not on a boat), the PSI was too high and caused more damage - so, what is recommended?

Ghost
06-17-2015, 09:53 PM
Where is the pitot pickup? If it is on the drive, sometimes a small drill will break up debris right at the intake.

If worried about damage, you can disconnect the tube at the speedometer end as well.

Conquistador_del_mar
06-18-2015, 02:27 PM
My experience is that when pressure type speedometers read too low there is a leak in the tubing leading up to the speedometer.

mc donzi
06-19-2015, 12:17 PM
I have a 22C with a 454/385HP with the Volvo DPX drive. My boat came with the Gaffrig II gauge cluster with the 80 mph speedo. My boat ran 75 mph on the speedo but 71.6 on GPS.

In the spring of 2013 when I launched the boat the speedo was "pinned" at 80 mph and thats where it stayed for the season. I tried all that has been suggested in the previous posts to no avail.

I removed the speedo and took it to Florida for the winter and checked every marine supplier and salvage yard between Ft. Myers and Sarasota trying to locate a replacement speedo.( the Gaffrig II series had been discontinued and replaced by Livorsi branded gauges). Couldn't find one anywhere. The speedo is a sealed unit but does have a small hole on the back of the gauge.

As it wasn't working anyway, I thought that if I screwed it up completely it was no big loss. So I inserted a small screwdriver into the hole and kind of worked it back and forth until the speedo rested at "0". The speedo now reads a little slow... 65 mph. at WOT instead of 75 and returns to "0". It's worth a try.

Pat McPherson
06-19-2015, 01:36 PM
Found I was getting water in my bilge too. Unhooked the speedo tube at the drive. No more water in the bilge so I'm 99% sure the speedo tube has a crack...

BLACKBOX
06-19-2015, 03:38 PM
Thanks all - I will try looking for clogs, if that doesn't work, I'll just leave it be till my next annual service and have it checked then.

BLACKBOX
06-23-2015, 12:30 PM
It's working again - used the 1/8" drill bit method & the compressed air method - don't know which one did the trick, but it's all good...

gcarter
06-23-2015, 01:18 PM
I have a 22C with a 454/385HP with the Volvo DPX drive. My boat came with the Gaffrig II gauge cluster with the 80 mph speedo. My boat ran 75 mph on the speedo but 71.6 on GPS.

In the spring of 2013 when I launched the boat the speedo was "pinned" at 80 mph and thats where it stayed for the season. I tried all that has been suggested in the previous posts to no avail.

I removed the speedo and took it to Florida for the winter and checked every marine supplier and salvage yard between Ft. Myers and Sarasota trying to locate a replacement speedo.( the Gaffrig II series had been discontinued and replaced by Livorsi branded gauges). Couldn't find one anywhere. The speedo is a sealed unit but does have a small hole on the back of the gauge.

As it wasn't working anyway, I thought that if I screwed it up completely it was no big loss. So I inserted a small screwdriver into the hole and kind of worked it back and forth until the speedo rested at "0". The speedo now reads a little slow... 65 mph. at WOT instead of 75 and returns to "0". It's worth a try.

These are all Bourdon Tube gauges. If you Google "Bourdon Tube gauges, you'll find they have a rather delicate linkage arrangement at the end of the tube and a tiny gear train.
Ideally, they should have a range of 20% higher than your planned maximum speed so the linkage never binds.
IMHO, 100 MPH speedos should be the minimum used in our boats.