1. 12" long 1/2"npt pipe
2. 3/4"npt TEE
3. 1/2 to 3/4 bushing
4. Hairpin Cotter Pin to match dog size (25 pound use a 3", and 40 pound use a 4")
5. Extension Spring 1" X 7" X.135"
6. 2 - Hose Clamps for approx. 2" pipe
7. Old inner tube to cut up
8. Leash - 3 foot length see step 8
9. Dog harness
Step 1: Cut the 3/4" npt pipe TEE in half
Step 2: Grind sharp edges off cut TEE
Step 3: Spring
When I bought this spring at the local hardware store, I walked to the plumbing section and sized up a 1/2 npt pipe to the spring and found that with a little force the spring would screw onto the pipe.
Step 4: Screw the spring on to the 1/2" shaft
I added gorilla tape to help protect the spring for the bit marks from the pliers, however the spring was still marred. You will need to add a lot of tape to protect the spring from marks from the pliers
Step 5: Assemble TEE and Pipe together
The great part about this is that when you don't need the "Dog Walker" you can unscrew the 12" pipe and bushing to remove it from your bike. The TEE stays on the seat post out of the way and is ready for when you need it again.
Step 6: Attach leash to break-away "Hairpin Cotter Pin"
To make the break-away feature work, all you need to do is put the leash in the large loop of the cotter pin and the spring in the small loop of the cotter pin. This configuration has worked well and is very easy to reset after it has been opened.
Step 7: Assemble Bike Dog Walker on the seat post
2 at 2-1/4"
1 at 3-1/2"
Insert the 3-1/2" inner tube on the seat post. Then insert the two shorter inner tube pieces and each end of the TEE. Clamp the whole assemble to the seat post with the two hose clamps.
Step 8: Taking it out for a test run
In these videos you can see that I was using a retractable dog leash, which I would not recommend. I really had to try hard to keep the leash out of the tire, unless you shorten the length.
Update: Aug 8th 2009, we went out for a ride with a yellow lab called "Bell", and a leash that was 3 feet long. That length of 3 feet worked the best for her. So I would like to change my original recommendation of a 6 foot leash, to a 3 foot leash.