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Smiths Dual Guage Repair


Jedi Knight
I thought that I would share my success with everyone because it saved me about $120.

As you know the most common failure on the Smiths Dual gauge is the Temp side. This is usually due to a broken capillary tube. When this tube is kinked or broken the Ether in the tube either escapes or can no longer apply pressure to the Bourdon tube inside of the gauge head. If your gauge looks good cosmetically and the Bourdon tube mechanism is undamaged the cost for repair from Hollywood Speedometer is about $120 plus shipping. You can test your head unit with simple air pressure applied to the sensor tube(s); if the needles move then your head unit should be ok. With these instructions you can repair it yourself with the bulb and tube from a $16.99 generic temp guage from your local auto parts store and about an hour of your time.

Tools Required:
1. Wire cutters
2. Soldering Iron
3. Solder
4. Small length of brass tube, roughly 1/16-3/32 ID
5. Bowl filled with crushed ice
6. Metal tin full of boiling water
7. New generic Temp gauge. Approx $16.99 from local auto parts store.

1. Cut the existing capillary tube approx 12 inches from the rear of the gauge. Remove about 2 inches of the protective spring material, this will give you room to work.
2. Test Bourdon tube mechanism with a small amount of air pressure to make sure that the needle does move.
3. Immerse the new temp gauge bulb in bowl of ice while we perform the rest of the steps to get the Ether as inert as possible.
4. After successfully testing the old gauge clean any old grease and grime off of the old capillary tube and prepare it for soldering. Make sure that the hole in the tube is open by using a small sharp object such as a sturdy straight pin.
5. Slide the short piece of brass tube over the capillary tube. Insert the capillary tube a little less than half way.
6. Solder the tubes together but be careful not to let to much solder get into the tube as it could clog the capillary.

- These next few steps must be performed pretty fast so that the Ether doesn’t have time to escape from the new gauge.

7. New Gauge- Cut the protective spring in two places approx 2 inches apart.
8. Cut through the capillary tube at the cut int he spring closest to the gauge and immediately place your finger over the end of the tube. You should smell a small amount of Ether in the air as it will begin to evaporate.
9. Using the small sharp object quickly inspect the end of the tube to make sure that its open.
10. Prepare the end for soldering by scuffing with a piece of scotch brite pad.
11. Quickly insert the new capillary tube into the small brass patch tube and immediately solder.
12. Inspect solder joints for a complete seal.

-Time to test and calibrate
13. Place the new bulb into the bowl of hot or boiling water. The needle on the gauge should begin to move immediately.
14. If the water is boiling wait for the needle to stop rising and reposition at approx 212deg.

A few words about safety!
Ether is HIGHLY flammable so make sure that no open flames are present during this repair. DO NOT use a torch for the soldering! Ether fumes are also very toxic. Avoid breathing in the fumes and work in a well ventilated area.


Staff member
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I need to read this about 4 times to make sense of what you actually did but CONGRATULATIONS. I'm always so thrilled to hear of an LBC repair that costs less than anticipated never mind the satisfaction of doing it yourself.



Thanks for providing the instructions. Takes some time to digest what you actually did.
I did this same repair back in July.It worked well. Be sure that you use a salt ice water bath to keep things as cold as possible. Someone here gave me a link to a website with pictures.


My Bourdon tube was beyond repair, new gauge was easier...Yes, more expensive, but with that tube kaput. It was Dead, my thanks to Doug Lawson for checking it out.


Baz's old gauge was going to be another step in my learning and practice curve on repairing dual gauges. Sadly, the PO of his car must have really abused the gauge because it was beyond repair. So far I've only done the dual gauge repair and recalibration once... so it does work using the instructions above (and at the link) but the salt/ice bath is about 30-40 degrees colder so use it in preference to just ice water. If you have the mechanical skill and the desire, the repair might save you about $100. You only have the donor gauge cost as a sacrifice if it doesn't work.


You made me go look at what's left of Baz's old gauge. His measures 78" from the tip of the expansion bulb to the back of the gauge.


Hold on Fred!!!
I did cut that tube in two places, either side of the firewall as it was stuck in the grommet. Add about 1/4 to 1/3 of an inch for that chunk!!! /ubbthreads/images/graemlins/hammer.gif


Jedi Knight
sounds good .. i keep a little black book for information like that. it really helps so i don't have to track down this thread later on ..
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