Strugglin' to understand rear brakes - GT6 Mk3

[THe Maestro]

As my GT6 Mk3 failed on everything brake related in its MOT a couple of months ago I've set about overhauling them all.  Front brakes a doddle (so far), swapped the calipers and pads in no time, but then it came to the rears.  These are the late GT6 self adjust brakes, the same as in this other person's car:

http://www.teglerizer.com/triumphstuff/73gt6br_selfadjust.htm

I've dismantled the whole lot and cleaned everything out, replaced the brake cylinders and shoes and put everything bake together (see attached picture).  

Anyway I'm not sure how they are supposed to work - I can see how the top of one of the shoes will be pushed out by the wheel cylinder piston into the inside of the drum causing some braking, but it seems the bottom part of that shoe and the entire other shoe are not going to move at all.  So why have two shoes when only the top part of one of them does anything useful?

[willcolumbine]

Okay, so I'm not an expert on GT6 self adjusters but I the general idea is the same as the brakes on my 1500. Basically the wheel cylinder expanding pushes the one pad out but, because the wheel cylinder slides on the backplate, it also pushes the other shoe onto the drum as well. The peculiar adjuster at the bottom pushes out the bottom of the shoes to adjust for wear. That's pretty much it!  :)

[TimW]

willcolumbine wrote:

Okay, so I'm not an expert on GT6 self adjusters but I the general idea is the same as the brakes on my 1500. Basically the wheel cylinder expanding pushes the one pad out but, because the wheel cylinder slides on the backplate, it also pushes the other shoe onto the drum as well. The peculiar adjuster at the bottom pushes out the bottom of the shoes to adjust for wear. That's pretty much it!  :)

the adjuster isn't at the bottom of the brake shoe.  The adjuster is the ratchet on the wheel cylinder and pushes the tops of the shoes apart in order to adjust for wear. Otherwise your spot on.

[willcolumbine]

Ah right! So that'll be the 'self adjusting' part on the GT6 then! On the spit there's just a little adjuster with a 1/4 square drive on the back between the shoes at the bottom.

How does the self adjuster work? Does it just store a bit more fluid in the cylinder to push piston out to account for wear in the friction material?

[Richard B]

I think it's that ratchet operated by the hand brake lever.

Not quite sure how but a rotation must be applied somewhere and screw out the other part of the mechanism?


I know they were problematical in their time  :'(

[TimW]

willcolumbine wrote:

Ah right! So that'll be the 'self adjusting' part on the GT6 then! On the spit there's just a little adjuster with a 1/4 square drive on the back between the shoes at the bottom.

How does the self adjuster work? Does it just store a bit more fluid in the cylinder to push piston out to account for wear in the friction material?

Richard is correct.  The handbrake moves the lever against the ratchet wheel, this then turns the treaded bar out taking up any wear in the shoe. If there is no wear to be taken up then the lever doesn't move far enough to click onto the next tooth on the ratchet wheel.   Difficult to set up and very unreliable.

[THe Maestro]

willcolumbine wrote:

Ah right! So that'll be the 'self adjusting' part on the GT6 then! On the spit there's just a little adjuster with a 1/4 square drive on the back between the shoes at the bottom.

How does the self adjuster work? Does it just store a bit more fluid in the cylinder to push piston out to account for wear in the friction material?

The toothed ratchet type wheel on the self adjuster is turned by the lever above it when you use the brakes.  There's a threaded bit in the middle of the ratched wheel which one of the pads rests against.  This threaded bit progressively unscrews and gets longer if there is room for adjustment.

I don't think its very good though, it only takes one worn tooth and the whole thing will get stuck right there and stop self adjusting.  Sometimes it seems to get stuck when I've watched it and other times it will rotate 360 with no problem.  Mine was also seized up so useless.

Thanks for the explanation of the cyclinder sliding on the back plate willcolumbine, I didn't realise that.  I better make sure mine is sliding freely.  I still don't understand how the bottom pushes out though.

Dave

[Hugh]

If you look at the adjuster on the right you will see a ratchet/spigot type round part above that is a flat piece of spring steel when you press on the brake pedal the cylinder expands and pushes out the brake shoes. Each time there is some brake wear the cylinder has to push out a little more when this happens the spigot indents round one tooth of the ratchet and takes up any slack the wear in the brake shoes has. Anyway that’s how I understand the self adjusters to work :o

[THe Maestro]

By the way does anyone know the brake bleed wheel order for the car?  I'm guessing:

Left Rear
Right Rear
Left Front
Right Front

But I'm not actually sure if that's correct because I don't know how the pipes are routed.  

[willcolumbine]

That's quite neat! Or I guess it would be if it didn't have a reputation for seizing up. Seems a strange thing for Triumph to introduce though - it's not as though adjusting rear brakes is something you need to do often or is particulary arduous...

[TimW]

61 wrote:

The toothed ratchet type wheel on the self adjuster is turned by the lever above it when you use the brakes.  There's a threaded bit in the middle of the ratched wheel which one of the pads rests against.  This threaded bit progressively unscrews and gets longer if there is room for adjustment.

I don't think its very good though, it only takes one worn tooth and the whole thing will get stuck right there and stop self adjusting.  Sometimes it seems to get stuck when I've watched it and other times it will rotate 360 with no problem.  Mine was also seized up so useless.

Thanks for the explanation of the cyclinder sliding on the back plate willcolumbine, I didn't realise that.  I better make sure mine is sliding freely.  I still don't understand how the bottom pushes out though.

Dave

Dave
the bottom of the shoe doesn't push out.  When your shoes are worn enough to replace them you will see that it has very little wear at the bottom of the shoe but the top can be down to the rivets!

[TimW]

908 wrote:

If you look at the adjuster on the right you will see a ratchet/spigot type round part above that is a flat piece of spring steel when you press on the brake pedal the cylinder expands and pushes out the brake shoes. Each time there is some brake wear the cylinder has to push out a little more when this happens the spigot indents round one tooth of the ratchet and takes up any slack the wear in the brake shoes has. Anyway that’s how I understand the self adjusters to work :o

are you sure it's not the handbrake that operates the adjuster?

[THe Maestro]

339 wrote:

Dave
the bottom of the shoe doesn't push out.  When your shoes are worn enough to replace them you will see that it has very little wear at the bottom of the shoe but the top can be down to the rivets!

Thanks, that's what it looked like to me too but couldn't believe that such a wasteful design was used.  Disc brakes seem so much simpler and better.

[THe Maestro]

339 wrote:

are you sure it's not the handbrake that operates the adjuster?

It looked to me like either will do it when I was examining mine.  The cable operated handbrake bit and the hydraulic wheel cylinder look like they will push on the same thing and both move the level which turns the ratchet.  Not 100% sure though, the handbrake definately turns it.

[Paudman]

339 wrote:

are you sure it's not the handbrake that operates the adjuster?

Yes it is, the action of the handbrake ratchets the adjuster. It moves out only the threaded side but with the cylinder sliding in the backplate both shoes adjust evenly.
My setup was so poor on my last late model Mk3 that it actually loosened the brakes rather than tightening them, so I found it no bonus at all.

[willcolumbine]

61 wrote:

By the way does anyone know the brake bleed wheel order for the car?  I'm guessing:

Left Rear
Right Rear
Left Front
Right Front

But I'm not actually sure if that's correct because I don't know how the pipes are routed.  

Its drivers side rear, passenger side rear, passenger side front, drivers side front - well at least it is on a RHD car!  :)

[Hugh]

willcolumbine wrote:

That's quite neat! Or I guess it would be if it didn't have a reputation for seizing up. Seems a strange thing for Triumph to introduce though - it's not as though adjusting rear brakes is something you need to do often or is particulary arduous...

It may have been fitted on other Triumph models so to cut cost they fitted them to other models plus I guess you delete the manuel adjusters the piston cylinders and replace them with one single item hey presto one cost saving plus you reduce risk by always having the correct adjustment on the rear brakes thus avoiding any lawsuits in the good old USA.

[TimW]

61 wrote:

Thanks, that's what it looked like to me too but couldn't believe that such a wasteful design was used.  Disc brakes seem so much simpler and better.

I have converted my self adjusting drums to disc on my late MK3.  I used mgf disc and calipers. unfortunatly i now need a brake balancer because the disc/caliper set up is too strong!  says my MOT tester!!

[Hugh]

490 wrote:

Yes it is, the action of the handbrake ratchets the adjuster. It moves out only the threaded side but with the cylinder sliding in the backplate both shoes adjust evenly.
My setup was so poor on my last late model Mk3 that it actually loosened the brakes rather than tightening them, so I found it no bonus at all.

You could well be right about the hand brake adjusting the spigot Tim

[Nick Jones]

Looks like the system used on Dolomites.  It's crap on those too.  There are self adjusting systems on drum brakes that work well (Audi 80/90 is system is very cunning) - but this is not one of them  :(.  You can do no more than make sure than everything is clean and free moving.  You also need to make sure that the handbrake cable is not too tight (otherwise you won't get enough travel for anything to self adjust).  If that fails, converting back to the manual adjusting system is probably the only way way to preserve sanity.....

Best of British  :P

NIck

[THe Maestro]

Thanks everyone, that's reassured me that I've not put them back together wrong.  Now just got to fill em up with fluid - any tips?

[TimW]

61 wrote:

Thanks everyone, that's reassured me that I've not put them back together wrong.  Now just got to fill em up with fluid - any tips?

don't spill it!!! ;D ;)

[THe Maestro]

willcolumbine wrote:

Its drivers side rear, passenger side rear, passenger side front, drivers side front - well at least it is on a RHD car!  :)

Yes its RHD - I thought you started off with the one furthest away from the master cylinder?

[willcolumbine]

You do - the piping runs down the passenger side therefore the drivers side rear IS the furthest from the master cylinder.  :)

[Llessur]

61 wrote:

By the way does anyone know the brake bleed wheel order for the car?  I'm guessing:

Left Rear
Right Rear
Left Front
Right Front

But I'm not actually sure if that's correct because I don't know how the pipes are routed.  

That's the order I went for when I did mine. Just presumed the old rule of furthest away from the master cylinder first...