DIY Temp gauge repair - Solder issues

[Atrus]

Hey everyone.

I've read over numerous threads on the DIY temp gauge repair and decided to try it myself. I made a small brass adapter as the old tubing is a little larger than the new.

I have a 230 watt solder gun. I purchased some plumbing solder and flux, ~400 degree F melting point. I am definitely a novice at soldering - I understand the concept, but I don't have a lot of experience in applying it.

I cannot get the tube and adapter on the old gauge to heat up enough to solder the joint.

How did you all do it?

 

[Trevor Jessie]

How thick is that brass? I used copper tubing that was left over from an oil pressure gauge.

 

[JPSmit]

NOTE: I have never done this repair so take anything I say with a massive grain of salt!!!!

If I had the bulb in ice with all the inner liguid there, it might be easier to use a torch like you would use for plumbing repairs. A soldering gun is really more for electrical than for piping. essentially you are describing a plumbing repair.

make sure every surface is clean and dry. Put flux on everything to be soldered. - inside the tube and on the outside of the other - as long as it isn't stupid amounts, more flux is better. light the torch and heat from one side. As the flux melts, touch the solder to the joint on the opposite side of where you have the torch - the solder should be drawn in towards the heat, replacing the flux.

I'd suggest you do both sides at once as then you won't have problems with the solder building up a ridge inside.

 

[jvandyke]

I have used a propane torch for instant heat and plenty of it, not on this repair but for any solder job where I won't burn things down.

 

[Trevor Jessie]

NOOOO! No torches around the flammable liquids!

 

[dklawson]

True... the fluid is ether so an open flame is not advisable.

Start by getting the surfaces REALLY clean. This means things like sandpaper and strong caustic cleaners. Any residue on the old tube will prevent the solder from tinning the surface.

On repairs like this you may be OK with resin flux, but I prefer "No-Korode" or even acid flux. Regardless, apply the flux you choose liberally as it will help clean the surface and carry the heat into/onto the surface.

Pre-tin the area where you are going to cut both the OLD gauge's tube and the new/donor gauge's tube. After tinning both tubes, start by carefully cutting off the OLD gauge's tube in the area that you have tinned.

Once you've cut off the old tube in the tinned area, file the cut end of the tube and examine it to see that it's open. If not, use micro drill bits, a pin, a scribe... anything you've got to make sure the center of the tube is open.

Put your sleeve over the cut end of the old tube and apply flux sparingly this time to the end of the sleeve contacting the tube. (The tube should extend no more than 1/2 way down the sleeve). Heat the spot you applied the flux and then apply a small bit of solder to the joint. Do not keep feeding a lot of solder. You need just enough to see that it has gone "around" the gap between the tube and sleeve. Afterwards, use whatever you have to to look down the inside of the sleeve to make sure no solder has closed the center hole of the tube.

Now chill the expansion bulb of the donor gauge. When you're sure it's really cold, cut the tube and repeat the steps above to connect the other side of the sleeve to the donor gauge's tube.

Keep in mind that if you resort to acid flux to tin the tubes, clean them again thoroughly before applying the sleeve so you don't encourage corrosion. Lots of flux can be used for tinning, but go easy with the flux when making the joint to the sleeve and remember... not too much solder. You don't want it wicking down the sleeve and closing off the holes in the capillary tubing.

 

[Atrus]

No way will I use a torch around ether!

I don't have very precision calipers (accurate to .01"). I am measuring the old gauge tubing at .07" and the new at .05". The smallest tubing I could find is .09" I.D.


Do you think this .09" would work? My concern was that there'd be a decent sized air pocket in there, and I wanted to make sure there'd be enough ether to properly move the gauge.

The adapter I made is .5" long, .15" O.D. I drilled a 1/16" hole for the new (.05") tubing and a 5/64" hole for the old (.07")tubing.

I am just surprised that the 230 watt iron wasn't enough to heat up the brass.

 

[JPSmit]

OK I stand corrected - no fire near ether - good call thanks for catching it

 

[dklawson]

If the metal is clean and the flux does its job (both to further clean the surface AND to carry the heat into the joint) 230 Watts will be way more than enough. Out of curiosity... you don't have a Weller soldering gun do you? I have one and it's the worst gun I've ever owned. If yours is a Weller, consider removing the tip and cleaning its contact legs AND the holes they go in on the end of the gun, then clean the securing screws and collars before putting it all back together and attempting the repair. I have found this to be necessary almost every time I need my gun to develop real heat. I'm at the point of buying a good used gun from ANY other brand.

The solder will easily fill the gaps you are talking about between your sleeve and the tubing. However, this is where you need to be careful. It will be very easy to put a lot of solder on the parts and have it wick down into the sleeve and close off the holes in the capillary tubes. Perhaps practice on some cut off bits from the old capillary tube and some extra sleeving. This will help you develop your technique before working on the real parts you want to join.

 

[bugimike]

Boy do I agree with Doug re: Weller!! I have one I got so frustrated with it has not moved from its spot in the back of a parts-bin drawer for years!! I opted for a $15 soldering iron from Home Depot, that has yet to give me a bad soldering joint!!!

 

[Atrus]

Thanks guys - I have an old Sears unit. Good point on cleaning it though, I'll make sure to do that as well.


So, Doug, you think the .09" ID tubing will work? If so, I'll definitely do some practice on old capillary tubing and the excess .09" tubing I'd have. I was afraid that the chamber I'd need to leave between the two capillary tubes would be too big in the .09" tubing and thus not have enough pressure to drive the gauge.

Ideally, I'd like to use the .150"x.5" adapter I made as I think it'd be a stronger and more precise joint. Hopefully cleaning the gun really well will allow for it to heat up enough.

Does it sound like the plumbing solder that I picked up is appropriate? I think it had a 436* melt point or something.

 

[dklawson]

Ideally you want a minimal gap between the tube and the ID of the sleeve. That's going to be hard to determine when you are limited to measurements close to 0.010" and not easily achieved if you're using a set of fractional drill bits. All I can suggest is to do the best you can to keep the clearances to a minimum. Watch for the solder to form a meniscus around the joint and stop applying solder as soon as it forms all the way around. When the solder is continuous it will fill the gap and prevent the ether from escaping. Just keep it to a minimum so you aren't allowing the solder to plug the hole in the capillary tubing.

The solder you bought will work. However, you may want to consider getting (if you can still find it) some 60/40 lead/tin solder for electronics. It will have a lower melting point and it will solidify without being quite so "crystalline" in appearance. I've always trusted it more for solid joints. Radio Shack's web site still shows they sell 1 lb spools of 60/40 resin core. (Their part number 64-009)

Mike, when I was a boy my dad bought me a Wen soldering gun. That served me well for decades in spite of broken cases (from being dropped). It finally gave up the ghost a few years ago so I bought the Weller. I thought the problem was just with my Weller gun, then we got one at work that has the exact same issue. It's useless. I'm eventually going to buy a used (something) off eBay rather than pretend I can keep using the Weller. It's just not practical.

 

[Atrus]

I'll check to see what I have - I do have a few spools of electrical solder - I wasn't sure if it was appropriate to use in this application so opted for the plumbing. Perhaps that'll melt a little better. I'll take a stab at it tonight.


Thanks for the help!

 

[Dadandson]

IMHO,the best way to get the heat to the joint is to use a piece of 1/4 steel rod, about 24" long. Using the propane or better yet, MAP torch, heat the tip of the steel rod until it glows cherry red or hotter. Then use the rod to heat the joint for solder. Using flame on electrical joints creates problems as the flame leaves residue so the solder will not bond. Water pipes are different as the torch should never come in contact with the joint, only the outside of the joint.

 

[dklawson]

That's an excellent alternative to a soldering gun or iron.

 

[Atrus]

Good idea, I could do that

 

[bthompson]

I was afraid that the chamber I'd need to leave between the two capillary tubes would be too big in the .09" tubing and thus not have enough pressure to drive the gauge.

I was wondering about that too. Would it be a good idea to solder up the capillary about an inch shorter, to account for the difference in sleeve diameter, and make up for any lost/evaporated ether? Would that drive the needle farther? (Dunno about yours, but my cap tube has several extra inches of slack to spare and still reach where it needs to go)

 

[dklawson]

I don't know how much effect there will be by minimizing the length of old capillary tube left behind. I think it would be a very small percentage of the total volume compared with what's in the donor gauge's expansion bulb AND the volume of the bourdon tube inside the old gauge.

 

[Atrus]

I agree - the ID of the capillary tube is SMALL.

 

[Hairyone]

I would have no hesitation using a torch, as long as it's away from petrol.
Sounds like you're not getting enough heat. Is the iron bit wide enough to make enough contact?
Can you take the whole thing out & put it on an electric stove on low as some background heat?

OR Is the capillary tube stainless steel? if so lead/tin solder won't stick to it. You'll nave to braze it.