|The Trials and Tribulations of riding a
CJ750 in China Part 1 by Dave Vella
Fixing the Brakes inside an M5 wheel hub.
One of the advertised upgrades touted by the shop I bought my bike from was a set of fancy new aluminum wheel hubs. This had little to do with the reason for my decision to purchase the bike from this particular shop; I did not make a study of the different braking systems available; I knew the bike came stock with drum brakes, I have drum brakes on my old Triumph and they work just fine. I dont mind having drum brakes on my new sidecar; end of story.
When the bike arrived I noticed what I considered a significant lack of braking power. I had read where Changs had a little difficulty in the stopping arena, so I just chalked it up to having a big heavy sidecar bike with drum brakes. I would just have to compensate and adjust my driving habits to accommodate oozing to a stop. I live out in the countryside so I dont have to deal with as many panic stops as my city friends do, and if a rabbit runs out in front of me; well; hes just gonna be toast.
It wasnt long after that I had my first flat tire. I wasnt out on the road; I discovered it one Sunday morning when I uncovered the bike to go for a ride. When I removed the rear wheel I was quite surprised at the condition in which I found the braking assembly.
The actuator cam was missing parts, the camshaft hole in the gear housing was worn out, the brake block set shaft was a mangled mess, and the brake shoes werent even running on the hubs steel insert. To give the guys credit, there were some cut up pieces of an aluminum beer can wrapped around the set shaft and brake cam to soften things up, but Holy Cow!! No Wonder I Had Trouble Stopping!!
I immediately complained by e-mail to the guys at the shop; I have to do this of course because they are in Beijing and I live a four hour train ride south of Shanghai, there is one English Speaking guy there and even though Im taking lessons, my Mandarin is still No Good!!
I did receive a prompt reply with all the appropriate apologies; I was promised these new shoes, this, that, and other things, but after several sets of correspondence with no results, I got fed up and decided to fix it myself.
The main problem would be to get the brake shoes spaced out far enough from the gear case to actually run completely on the steel liner cast into the hub. On a trip to Shanghai I ran into a couple of guys with these same hubs on their bikes. I found out that the way they moved the shoes out was to use the spacers normally found between the engine and frame.
I bought a set of spacers from one of the shops in Shanghai, as well as replacements for the other broken parts I found, but when I put it all together, I still wasnt happy with the results. I knew there had to be a better way and it shouldnt be that hard to figure out. Im an Engineer and a Good Mechanic, one of the other Engineers in my office was a Master Machinist in a past life and now has a little hobby machine shop set up in his apartment. This is a simple project, we have the technology, so lets get going!!
First we had to fix the damaged gear case. This entailed going through it piece by piece to look for other problems (and yes we did find some), making the Camshaft Hole round again and removing the mangled Brake Block Set Shaft. We were careful not to remove too much aluminum from the housing around the camshaft hole; just enough to make it round again. We were going to machine a new cam anyway so we could make the shaft whatever diameter we wanted. The set shaft was drilled out and the hole was tapped to fit a 16mm bolt as this proved to be a perfect fit for the stationary end of the shoes.
We carefully measured the height of the aluminum hub and its relation to the gear case; as it was important to get the shoes to run on as much of the steel liner as possible without jamming the cam and the set shaft into the back of the hub.
Once we had the dimensions the brake assembly had to fit in, it wasnt hard to draw up the new parts necessary to make things work.
In total we had to fabricate six parts.
The brake block set shaft was made from a long 16mm bolt. The head was cut off and the shaft trimmed to length, then a groove was cut in the top to hold a c-clip retaining ring.
A 10mm fender washer was modified to make the keeper for the stationary end of the brake shoes. We wanted the keeper to fit snugly around the set shaft, and since it proved impossible in our little town to find a washer with an exact 16mm hole in it, we just made one.
The spacer to go between the gear case and the stationary end of the brake shoes was machined from a piece of aluminum round stock. Due to the design of the brake shoes, this spacer had to be a little taller than the one on the cam end.
A 28mm bolt was used as the base material for the cam. Rather than try to put a washer on top of the cam to make a retainer, as in the stock originals, we decided to machine our cam as one unit. A 1/16 retaining piece was left on the top, the groove for the brake shoe was milled 1/16 taller than the height of the brake shoe to give the shoes a little breathing room. The base was cut ¼ short of the required dimension in order to put an aluminum spacer/softener in between the aluminum gear case and the steel cam. The cam shaft was cut long enough to extend all the way through the actuator arm to the opposite side of the gear case. This way if the retaining screw ever comes loose the actuator arm cannot fall off. Additionally, if the retaining screw does disappear, the lobe configuration will still operate the brakes.
The ¼ thick spacer/softener under the cam was cut from the same piece of aluminum round stock as the stationary end spacer.
The actuator arm was machined from a piece of steel bar stock. The configuration follows the basic dimensions of the original arm that came with the bike, except that the originals have splines and ours has a big lobe. It took a little old school file work to get an exact fit between the cam lobe and the arm, but the end result is snug tight with no wobbles.
The end result of all this is a remarkable improvement in stopping power, which is not surprising since now there is double the surface area of the brake shoe running on the steel hub liner. Instead of having a sensation that the only thing slowing me down is I that am running through a thick pile of sludge, I can actually feel the brakes grab, and if I push too hard I can accidentally lock up the rear end.
If you run into a similar situation I hope this article will help you out. I have intentionally left out some critical dimensions because you will need to take your own measurements. One thing I have learned living in China is no two things are exactly the same. Another is Buyer Beware!
Take Care, Ride Safe, and Have a Great Day!!