Rear Brake Arm Position

DWS · Post by **DWS** » Sat Jun 18, 2011 3:00 pm

Just setting up my rear brake assembly and having doubts as to whether it's correct?

Picture 1 shows the Brake Arm in the upright position and, as you can see, most of the adjustment is taken up?

Picture 2 shows the Brake Arm moved back one flat on the spindle, adjustment now looks OK but the arm seems to be laying back too far?

In both cases the Brake Pedal is in the correctly adjusted position. Brake Shoes have very little wear and there are no thrust pin adjustment washers fitted. In some diagrams I've seen in the manuals, the correct position for the Arm seems to be somewhere between these two positions, but the positions are limited by the flats on the spindle? Any thoughts and comments please?

Edited by - DWS on 18 Jun 2011 3:17:09 PM

Rob Harknett · Post by **Rob Harknett** » Sat Jun 18, 2011 3:12 pm

simple, fit thin washes. if you have no thin washes. Put a wooden block in the vice hammer pins all round the washer, punch heads down so they just hold and then file the washer thiner. Just a couple of thin washers, one under each mushroom will give you more adjustment

DWS · Post by **DWS** » Sat Jun 18, 2011 3:46 pm

Hi Rob, Not sure what you mean, I have tried putting the correct washers under the thrust pins but it made very little difference. With the arm in the vertical position (photo 1) any pressure on the brake pedal moves it past the 90 deg. point, reducing brake pressure.

zwarts · Post by **zwarts** » Sat Jun 18, 2011 5:09 pm

If you fit the correct thickness of thrust washer under the pins (trial and error) you should be able to achieve a situation where the shoes just clear the drum and the angle between the rod and arm is 90 deg. or slightly less when the brake is fully applied. Your first photo shows the brake arm in its correct position.
Bob.

Don Madden · Post by **Don Madden** » Sat Jun 18, 2011 5:51 pm

New AMC brake linings are much thicker than most others, worn ones will look like new to those not familiar with them. Fit the washers as recommended. Cheers, Don.

DWS · Post by **DWS** » Sat Jun 18, 2011 5:56 pm

I'll fit some washers under the thrust pins and report back...

Lance · Post by **Lance** » Sat Jun 18, 2011 6:35 pm

Check the rod length. Don't know if yours is a new one or was replaced at somepoint in its previous restorations but the new one I got had to be shortened by 2 inches to match my original one. I'm thinking they are made for swingarm or later models perhaps. I just cut mine at the brake pedal side and recut new threads in the end and all was perfect.

Steve Surbey can confirm those details as he knew of them being too long as well.

Your first picture is closer the right angle, though, so if the rod was shortened, you'd have plenty to adjust with. The second picture seems way off.

Additionally, I have seen brake levers with flats in two different locations. Again, I had a discussion with Steve Surbey (AMC Classic Spares) that confirmed two variations of brake arms with the flats not in the same spot. I had a few in my box of bits that were different. Sorry, I can't remember the reasoning or uses for which went to which use, etc.

Regards,
LanceEdited by - Lance on 18 Jun 2011 5:40:56 PM

RayRST · Post by **RayRST** » Sat Jun 18, 2011 6:50 pm

On my 16M the brake arm is set as per your top photo. I suggest that Lance is correct and the rod is too long. Mine measures 14" from the centre of the brake pedal pin to the washer at the end of the spring and 18" from the brake pedal pin to the pin on the brake arm clevis. Does that help?

Rob Harknett · Post by **Rob Harknett** » Sat Jun 18, 2011 7:02 pm

Surely the the rod what ever the length would make no difference at all, take the rod off, the lthe rear arm would still go to the same possition before it starts to bite.
A couple of washers of correct thickness will do ther trick very simply. I've being doing for the last 54 years, and that was from when the bikes were not many years old and all correct..

Lance · Post by **Lance** » Sat Jun 18, 2011 7:49 pm

Rob,

The length does matter. If Dave has run out of threads to adjust when the arm is in its proper position, then shortening the rod to its proper length, that is if it is wrong to begin with, will effectivly move the rear threads forward by the same amount that was cut from the front.

Ray's first measurement is exactly the same as my original one is and what I had to cut my repro one down to to make it fit exactly as it should (on my '48 rigid). The second measurement is more subjective depending on brake lining size, etc. Total length of a rigid arm from center point of brake pedal clevis to end is about 19 3/4 inches whereas the early swingarm is showing 20 1/2 inches.

That 3/4 inch would make a big difference in Dave being able to adjust without having to add washers every time there was wear.

Dave - do you have any measurements of what you've got?

Regards,
Lance