It all started after I met an amazing couple who were the second owners of a beautiful 1932 home in the Austin Texas area. They just needed some work on one little dormer window, and everything looked straightforward and easy. Everything was going smoothly on extraction when all of the sudden one of the tapes broke! It sounded like everything went horribly wrong as the spring snapped back at full force. I let the client know and she was more than happy to have the window not operate when I let her know how difficult these were to source. But driving back to the shop I figured they really couldn’t be too hard to fix so I would take on the task on my own time since I hate leaving something technically unfinished.
After searching all over google and any random forum that I could find related to windows I could not for the life of me find anyone talking about how to rebuild and rewind some Caldwell Sash Tape Balances. They aren’t the most common type of balance system out there but I know that there were tons of them made. So I turned to a Facebook group just for wood windows restoration professionals, and from what I understand there really isn’t any information about rebuilding them out there. Turns out no one has been able to get any info from Caldwell (L&L Concepts), but others have spoken with Pullman (the other tape balance company) and they stated that each company had specialized machinery that was needed to do any work on the balances. But after taking the broken balance apart it really didn’t look all that difficult. Now I will say that these clock springs are made out of thin metal and wound pretty tight so I do see where things could go wrong, so if you attempt this repair take all necessary steps needed to stay safe.
Spoiler alert! I was able to get everything rebuilt and rewound back in great working condition. I wanted to do a breakdown of how I was able to do it and all of the things that I learned along the way.
The first thing I needed to do was to measure how much pulling force and returning force these tape balances generated. I pulled out my handy dandy luggage scale and got to work.
Here is my super high-tech setup!
Pulling back on the tape balance while the luggage scale was secured in the vice showed me that I was looking at 10 lbs of pressure on sash pull down.
And the return pressure looked to be around 5 lbs. These would be the numbers that I needed to replicate when I rewound the broken clock spring. Now the big question was, how many times do I need to wind the clock spring.
Let’s start with a fully disassembled tape balance. Here I have fully disassembled and cleaned all of the components. I went ahead and add a thin layer of high-performance grease, that I use in my trailer axles, on all of the moving parts.
Here we can see the components stacked back up in the order that they were removed. The brass tape on the right is what went wrong with the balance I am working on. After many times of going up and down the metal became fatigued and broke right where it attached to the clock spring cartridge. So I cut away the bad material and bent it with some needle-nose pliers just how they had originally done at the factory. Thankfully I had the tiny bit leftover on the clock spring drum so I knew how it was attached and what the dimensions were. But it meant that I had shortened the tape so I would have to change the mounting point on the sash. Wouldn’t be a big deal since I only lost about 2” total and had the room to move it up on the sash stile. All I had to do was use a chisel to widen the area the rope normally sits in for the end of the tape to fit in.
Get the 2 screws holding the body together inserted and turned a few times into the square retaining nuts as pictured since you’ll be wishing you had three hands by the end of this.
Here you can see how the clock spring drum fits onto the faceplate, once tightened the 2 square retaining nuts will hold it all together.
This next part gets a little tricky, but to help keep in mind that all of the pictures are oriented so that the top of the picture is the top of the balance and how it will fit into the jamb. I did however find myself having to go back to make sure that everything was oriented correctly since it will look backward and upside down at times. But if you take your time and stay organized it shouldn’t be too difficult.
Here you can notice that the top is more narrow and the bottom is flared out. If the details are overlooked there will be binding of the tape upon operation.
I also made sure to note how the tape was orientated when all wound up in one of the other functioning balances.
Another reference picture of how the clock spring sits inside of the cartridge.
The way I had everything laid out I would need to turn the clock spring cartridge clockwise to start giving it tension. The hardest part here was remembering how to attach the tape since it will be backward and upside down sitting flat like this.
After a few dry runs, I decided to keep my phone open to this picture since I would be attaching the tape to the clock spring cartridge while it was under a lot of pressure.
Another reference picture of how things will ultimately go back together. Also, note the zip tie I added to the end of the tape which made it much easier to pull through the body while under pressure.
I started with a base amount of 5 turns to the clock spring since that was how many rotations it took for the tape to become fully unwound on the still-functioning balances. I now knew that I would have to wind it at least 6 revolutions if I wanted there to be any significant lift to the balance. I didn’t have to redo my experiment many times because the magic number turned out to be 8 full revolutions. With 8 revolutions to the clock spring, I got my magic 10 lbs and 5 lbs numbers my luggage scale gave me earlier.
I added a ½” lip to my workbench to brace the clock spring cartridge against and started turning. I made sure to keep my thumb on top of the clock spring while winding it clockwise. This made sure to keep everything seated in the cartridge, and also reduced how hard the assembly was trying to rewind and undo my work.
After getting my 8 revolutions I went ahead and attached the tape with one hand while keeping everything all together with the other.
I then left the clock spring wind up onto the cassette except about 3”-6” of the tape and was left looking like this. Whatever you do, don’t let go yet, everything will still be wanting to come apart.
While still holding everything tight I pulled the zip tie through the body opening and then flipped the clock spring cassette upside down to attach it to the body. Utilizing the square nuts I preinstalled to lock the clock spring cassette to the body of the balance. When tightening the screws on the front I found that I needed to tighten them all the way down to make sure everything was aligned, but I then needed to back off the pressure to keep a smooth movement. It seemed that with them fully tightened the whole mechanism would bind up and not operate correctly.
On installation day I was honestly a little worried to see if all of my work would be in vain. To my surprise, everything went back together smoothly and the only thing I needed to do on-site was a little wood removal on the sash stile to make room for a higher mounting point. To figure out exactly where I needed it I placed the lower sash into the jamb and then pulled down the balance to see where it naturally want to be attached to the sash stile. I think this type of fix is possible for anyone out there and with a little patience, it can save you a ton of money and time waiting on replacements.
Removing some wood on the stile to make room for the new mounting point
INSTALLATION PROCESS FOR TAP BALANCES