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Triumph TR6 - Rear brakes

Just replaced the rear brakes shoes and even with the adjustment all the way down, can not put the drum back in. Do I have to sand the shoes down to fit?
Angel TR6 1971
Angel L. Traverso

Make sure that the parking brake is not set and the adjustment is backed out for the parking brake (this is different than the adjusters). The adjustment is achieved by taking out the clevis pin at the lever at the back of the drum, loosen the lock nut right at the fork end (shackle), and lengthen by unscrewing the fork end to the proper length. This should be the fix.

DO NOT SAND THE SHOES, eventhough asbestos is not in them there are other hazardous organics that comprise the friction material.
Steven

Another thought is make sure the shoes are seated in the notches for the cylinder and the adjuster. It is very easy to have one of them out in the back and a visual will not confirm this. Also make sure that the springs are correct and not binding. And finally you have to play with the shoes moving them around to make a nice circle so that the drum fits. There is lots of lateral play and one of the shoes could be offset slightly, also make sure the locating pins are in the right holes.
Steven

While you are freeing off the parking brake make sure the cylinder slides easily a few millimtres along the back plate. Its retained by a flat spring but gets clogged with dirt, and can prevent the new shoes from centreing. I use a liberal coating of waxoyl and moly grease to keep it freed.
Peter
P H Cobbold

Be sure and take a heafty C clamp or something of the sort and push the slave cylinder ends back in - they migrate out as the shoes wear down.
Brent B

- Too bad I can't edit the last post -

If you haven't pushed the slave cylinder ends in, make sure you use a method that applies the pressure to both sides, otherwise when you push one side in, the other will probably pop out. That would be a pain...
Brent B

Wow! Love this forum...5 responses to my problem...thanks everyone...found the problem...the adjustment was not all the way out. But have another question. When the parking brake is applied, the front shoe is the only that moves, same when pedal brake is applied. The rear shoe does not move at all. When examining the piston cylinder, noticed that the rear end was punched out, therefore the notch does not come out.
Angel L. Traverso

Angel, A simplefied explaination of how it works:

The cylinder is a single piston design and without something to push against only the leading shoe will move. With the drum attatched and if the brakes are applied (including parking brake), the front shoe first makes contact and then with continued pressure it moves the cylinder back to engage the rear shoe.

If you take the cylinder off you will notice that the slot cutout for it is longer. It held in with plates to allow it to slide. In reference to one of Newtons Laws..."for every action is a reaction". Think of it as you sit in your office chair, extend your arm (piston) to press your hand (leading shoe) against the table where your computer is, by pushing hard your chair (trailing shoes) will slide backwards on the wheels. Now think there is a wall behind your chair (drum) the harder you push there will be almost equal pressure on the desk as the wall.

As a sidebar: this in essence the same way most calipers work (single piston design) as the caliper 'floats' slides on pins. Other designs are double or four piston design but they are fixed and the equal 'pushing' is done by the opposing pistons. Our TR's are a double piston caliper design.

The most important thing to remember is to service the brake sliding mechanisms for single piston designs. If the plate clips are rusted together or the pins are dirty or not lubricated then the brake will not function properly loosing a significant amount of braking power. I use anti sieze on the backing of the wheel cylinders, around the cutout and the plate clips so that it slides easily, unbinded. Make sure that it is high temperature rated and never use grease or oil.
Steven

One other point.
NEVER APPLY THE BRAKES WHEN THEY ARE DISASEMBLED. (You can check /test though the parking mechanism)

With nothing to push against, the hydraulic pressure force the pistons out and then you will have to rebuild the parts and re-bleed the system. The only time that you would do this if you have a sieze piston and can not get it out. I had both inner pistons of my front calipers seized and could not get them out by hand. what I did was un-bolt the calipers and hang them (supported) in a large pail and apply C-clamps on the outers holding the piston in. By applying pressure it finaly forced the inners out along with a burst of brake fluid (reason for the pail and have it covered. With the seized pistons forced out, now it was time to rebuild it with new seals and pistons all around.
Steven

Steven- Thanks for the clinic. I have always thought i understood how the mech. works and now that it was spelled out it makes sense.
Don K.
DON KELLY

Oops - forgot about the single piston wheel cylinder. I guess that shows how little trouble I've had with the rear brakes in that past 12 years. It should still be pushed back in - just no worries about using equal pressure to "both pistons".
Brent B

Steven, have you all figure out...you must be an school teacher...your simple but somewhat vivid explanation of how the brake system works on a TR6 is by far the best explanation that I have read in many years.I nominate you for "TR Garage of the Year" award...!!!Thanks again.
Angel L. Traverso

Angel thanks for the compliment on my simplified analogies in the way things work.

Sorry to ruin the myth, but I am not a school teacher but rather an account manager in the advertising business. I do though happen to be a certified ski instructor and have been teaching the sport regularly for the past 22 years so I do have some teaching abilities

Unfortunately I missed my calling as I am very mechanically knowledgeable and understand how things work and where the problem is. I should have gone in to engineering from the get-go. My weakness though is electrical that is why we have others well versed in the subject such as Rick C, Bill B, and Peter C.
Steven

This thread was discussed between 20/02/2003 and 24/02/2003

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