Thursday, 15 February 2018

SQ4 Front Brake

As part of winter maintenance, I have my front wheel off for new bearings, a new tube and a look at the brake. It appears that I still haven't got it right.

Take a look at this, it is the leading end of the trailing shoe:


To me, this is indicating that I haven't got the adjuster tight enough - there is about 20-30% contact on both shoes, at the cam end - in both shoes, there is no contact at the adjuster end. Here is the leading shoe, trailing end:

In both cases you can see where the lining is worn by contact with the drum. The brake is nothing like as effective as the one on my W/NG, which is obviously a much lighter bike but the brake has much more feel. They are bedding in at the cam end (trailing end of the trailing shoe here):


I'm happy to see that the drum is nice and clean, with no trace of grease


Less happy to see the heat damage to the paint, but we will deal with that when the weather warms up.

Setting the drum up with emery tape and double-sided sticky tape in the traditional way results in much better contact. By the way, don't do this with one of the wheel bearings missing since the spindle, and the brake plate and shoes will not be concentric with the drum:

Set the brake plate up such that it is pulled down to the bearing and is held rigid (as far as possible with these pressed steel brake plates) - that way the shoes will be as cylindrical as possible. I've used a short tube spanner on the spindle to take the place of the fork leg, and I am holding the brake plate from turning with a tommy bar. I turn the wheel to sand the linings.

Start with adjuster backed off and gradually wind it in, turning the wheel a few times and then dismantle again for inspection. When your satisfied that the adjuster end of the shoes is ground down enough to fit the drum, put a bit of pressure on the brake cam lever and repeat. Stop when you have contact over most or all of the shoe.


Here's the leading end of trailing shoe:



Leading end of leading shoe

 Lots of dust after the process is complete:

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