I recently acquired my first bmx bike (used) and it has a detangler which is such a cool but new bike piece for me. I cannot get the rear brake to work. When I pull the brake lever arm to apply brake, the linear pull brake does move in towards tire rim however when I release the brake arm the cable just jumps out of the brake lever. Then it's unable to be pulled again. I've tried adjusting the 500 barrel adjusters but still it won't work. I did notice a little rust on the cable under the housing. Is it getting snagged and I should just replace all the cable and housing? Or am I not adjusting correct b.a.?
Detangler are tricky to get working even when new.
To work everything needs to be clean, cables/brake pivot points lubricated and adjusted correctly.
Pictured below is a Gyro diagram. There are many versions of the detangler. I used this picture to have a reference for part naming.
Remove the cables and lubricate them
Lubricating the "captured" cables can be hard (the cables that can't be completely removed). I like to use a silicone spray lubrication and shoot lube up into the housing as much as possible.
Check the detangler for correct installation
The upper and lower cable stops are aligned and the headset locknut holds the upper cable stop firmly.
All of the needed parts should be there. Some detanglers have adjusting barrels on the upper and lower cable stop. I like to start with them screwed half way in so that I can back them in or out of needed.
Clean and lubricate the brake and brake lever
Reassemble and adjust
checking that your cable routing allows the cables to move smoothly.
One trick to adjustment is to get the cable tension so that the "Gyro bearing unit" does not bottom out on the lower cable stop. You need all the cable movement you can get. The bearing unit needs to be adjusted so that with the brake lever released it's just a hair above the lower cable stop.
It will be a process of trying something, testing, learning, repeat.
I tried to source replacement cables for a detangler on a diamondback BMX, and they were either unavailable or silly price.
Short of soldering new ones, I resorted to an ultrasonic clean and a blow-dry, and then lubricate the cables inside the housing.
The back brake now works, but its not going to stop the bike very fast. If you can find the brake cables you need for a fair price, buy them. Good luck !