Play in SF1 brake linkages

C

chrissoz

Senior member
Location
Sydney, Australia
Pulled my front wheel off to figure out why my speedo was not working (totally mashed worm drive - anybody go a spare one?). Had a look at the brakes while it was on the bench - one shoe had good wear pattern but the other looked like it wasn't doing much - see pic.
Looking at the linkages there seems to be excessive slop in the second link (see red arrow in pic) - the whole arm moves about 3mm before it starts actuating. This corresponded to the shoe which does not look like it is doing much.
Is this expected? Can just tighten up the rod so they both shoes start moving at the same time? Is there a good setup guide for these brakes anywhere?

Thanks

Chris
 

Attachments

  • 20141205_054333.jpg
    20141205_054333.jpg
    83.6 KB · Views: 24
  • linkage.jpg
    linkage.jpg
    52.2 KB · Views: 40
Chris,

Eliminating all the slop in all the linkages is the secret to getting the bugger working!  Not only do the internal link plates/pins and rod ends develop play, usually the actuating shafts and their bushes are just as knackered.

Rectifying is not easy.  The axles can usually do with a light grind, thus requiring new bushes in the brake plate to suit.  Rod clevis are easily reamed out and new pins made to suit, things are a bit more difficult on the inside.  The small link plates are hardened, as are the corresponding pins.  I sacrificed a reamer to get the plate holes equal and machined pins from mild steel, these will hopefully wear without ruining the link plate holes any further, making a future reburbishment somewhat easier.  The bushes in the brake shoes are also hardened and quite difficult to machine.

Once the slop is eliminated, the shoes can be re-lined with thicker friction material.  Turning the assembly to size finishes the job, making the setting up and adjustment a doddle, resulting in a brake that actually slows you down instead of just heating the drum slightly. :D

You can of course keep it as it is, adjust as much play out of it as possible, find out the lever geometry is completely wrong which sacrifices a great deal of lever advantage, and keep on cursing about what a shit design the whole brake is. :D

piet
 
Chris my rear brake is the same,less important at the back.It still works ok but you can see at least one of the rod connectors doesn't move till well after the first one.After Piets description its not going to be easy to find someone with the gear and interest to sort this.I will ask around,maybe a retired Toolmaker I know  might be interested.
 
Having looked at all the linkages there is some play in most of them but the one at the end of the rod is much worse. Will see if I can get a mate with a lathe to turn me up an oversized pin and see how I go from there.

Thanks

Chris
 
I managed to get one of my drums working really well by having the wheel out and horizontal then actuating the lever on the brake then adjusting the equalizing rod so the second shoe was making contact with the drum the same time as the primary shoe was contacting, the drum. Locks up real easy now...
 
I have to do the same on my SF1 - these should be a good front brake if properly adjusted.  At present my one hardly heats up at all, thankfully rear brake is a good one.
 
First undoe the 6mm locknut on the connecting rod, then undo the 8mm bolt on the second linkage and you will be able to turn that without removing the pin, Its abit hard to describe but with the small linkage free you will be able to turn it flat while you turn the 6mm thread in or out.
easy peasy.
M.
 
Pulled the pin out of the linkage and the holes are about 6,5mm (and round so I don't thing they have worn bigger) - the ping is just over 5mm - which is correct the pin or has someone drilled the holes out?

Thanks

Chris
 
Tippie said:
And remember the rule for drum brakes. Hold the brake on firmly to centralise everything when you tighten the axle.
Click to expand...
Too true, Leeton. Makes a huge diff. Explanation: the shoes shift the backing plate assembly (depending on the amount of lateral play b/w axle and the backing plate). If the linkages aren't too bad it will allow both shoes to contact the drum while the axle is tightened.
Oh how glad I am that I no longer have to live in fear of mediocre drum braking!  :o  I did love my Yamaha TZ 4LS setups but sadly they were too fragile. Also wish I hadn't virtually given them away - one sold a few weeks ago for AUD$1950!!! A fool and his money are soon parted, say I.
qf
 
You must log in or register to reply here.
Back
Top