Thin brake discs

[Steph]

If a disc is below thickness specs, anybody  ever heard of catastrophic failure on a Guzzi?

[Triple Jim]

How much below?  If it were something like ten thousandths under, I wouldn't give it another thought, but of course I'm not telling you what to do.

[Tom]

Put some new brake pads in till you get replacement discs.

[Arizona Wayne]

If you don't want your brake rotors getting thinner on you, stay  away from brake pads that have metal in them.  I have a Suzuki `91 VX800 with thinner brake rotors now because it came with pads w/metal in them that literally ate right thru the alloy rotors (front/rear).   So I switched to pads w/Kevlar in them instead and the rotor wear stopped or lessened.   Still have the original rotors on the bike @ 84,500 miles and they still work fine even tho they are definitely thinner now.  In fact 1 time I got the front rotor so hot it turned red but still didn't warp or anything.  That was years ago when I was really pushing it on twisty roads.  I didn't know it got like that until someone noticed and I looked at it.    The brake still felt OK.

[rodekyll]

It's not something I'd mess around with personally.  M/C rotors are very thin compared to anything automotive, and I've seen several automotive failures from worn out rotors.  Often it's not the average thickness, but the absolute thinness in a grooved area that will get you.  One test is to take them to a brake shop and see if they'll still turn them for you.

$0.02

[Steph]

If you don't want your brake rotors getting thinner on you, stay  away from brake pads that have metal in them.  I have a Suzuki `91 VX800 with thinner brake rotors now because it came with pads w/metal in them that literally ate right thru the alloy rotors (front/rear).   So I switched to pads w/Kevlar in them instead and the rotor wear stopped or lessened.   Still have the original rotors on the bike @ 84,500 miles and they still work fine even tho they are definitely thinner now.  In fact 1 time I got the front rotor so hot it turned red but still didn't warp or anything.  That was years ago when I was really pushing it on twisty roads.  I didn't know it got like that until someone noticed and I looked at it.    The brake still felt OK.

That's what I've been doing, 62k and they have a noticeable lip on the edge. Just wondering if anyone ever had one break because they were too thin
It's like the old limbo dance 'how low can you go'
It's a balance between being safe and frugal/lazy. Lol

[pete roper]

While there is obviously going to be an element of caution and conservatism in the minimum thickness it is there for a very good reason.

Since I am absurdly easy on brakes I've never had to change a rotor on any of my bikes but there is no way a customer gets a free pass if their rotors are below minimum thickness.

Pete

[Steph]

While there is obviously going to be an element of caution and conservatism in the minimum thickness it is there for a very good reason.

Since I am absurdly easy on brakes I've never had to change a rotor on any of my bikes but there is no way a customer gets a free pass if their rotors are below minimum thickness.

Pete

I'm getting a new disc, I'm assuming new bolts are also a must, no such thing as a free lunch eh

[Tom]

Impact wrench to break them loose and thread lock when installing.

[Steph]

Impact wrench to break them loose and thread lock when installing.

And a bit of heat if required too

[pete roper]

What bike Steph?

[Steph]

What bike Steph?

'02 Cali Stone. I upgraded with a second front disc (off a broken Ducati S4R & master cilinder).
The original thin left hand disc held up well but needs replacing

Edit: will go for a brembo serie Oro replacement

[Triple Jim]

And a bit of heat if required too

I'm pretty sure I would have broken the heads off the bolts that hold my Mille rotors on if I hadn't heated each one with a torch as I removed them.  Once they were pretty hot and the thread locker softened, they turned fairly easily.

[pete roper]

I'm pretty sure I would have broken the heads off the bolts that hold my Mille rotors on if I hadn't heated each one with a torch as I removed them.  Once they were pretty hot and the thread locker softened, they turned fairly easily.

This. Use a big torch and get a lot of heat in quick and they'll come out easily.

[SED]

Take your car to a shop for a brake job they will turn your drums or rotors as part of the job. After a few brake jobs your drums or rotors are shot even with soft brake linings.  Don't know bike shops turn rotors at every brake job but if they do it will shorten the life of your rotors.

I ride old bikes and some of the brakes are unobtainium so I never have them turned. The only reason would be to remedy a warp or pulsation and so far I've only had to do it on one drum.

The drums on the bacon slicer seem very thin and I wonder what I can do to repair them - sleeve a drum?!

[Triple Jim]

Cars and brake jobs... one of the biggest money sinks there is.  When my father got old and slowed down on the car maintenance he use do to, he took his Taurus to a local shop for new brake pads/shoes.  He got a call to hear that he needed new wheel bearings.  Dad knew his wheel bearings were fine, so he declined the offer.  When the got the car back, he checked the work and found the crook had way overtightened the bearings that he had no business messing with in the first place.  I mean honking down on the nut with a breaker bar.  Obviously the clown had expected to ruin the bearings and have my elderly father have to come back for that work.  I hope I'm dead before I have to rely on others to do my vehicle maintenance.  No offense meant to the honest mechanics on the board.

[Tom H]

I ride old bikes and some of the brakes are unobtainium so I never have them turned. The only reason would be to remedy a warp or pulsation and so far I've only had to do it on one drum.

The drums on the bacon slicer seem very thin and I wonder what I can do to repair them - sleeve a drum?!

My Loops do have a "ummm sleeve", but, the sleeve seems to be not available from what I understand. If it can be found or made, my guess is that it would be a heated press fit.

Good luck,
Tom

[Arizona Wayne]

I've seen brake rotors with grooves or ruts in them that still worked fine.  In fact until you actually looked at the rotors you had no idea what their condition was like. The pads take the shape of the rotors.

[SED]

My Loops do have a "ummm sleeve", but, the sleeve seems to be not available from what I understand. If it can be found or made, my guess is that it would be a heated press fit.

Good luck,
Tom

Thanks Tom, something to look into.

[Arizona Wayne]

Cars and brake jobs... one of the biggest money sinks there is.  When my father got old and slowed down on the car maintenance he use do to, he took his Taurus to a local shop for new brake pads/shoes.  He got a call to hear that he needed new wheel bearings.  Dad knew his wheel bearings were fine, so he declined the offer.  When the got the car back, he checked the work and found the crook had way overtightened the bearings that he had no business messing with in the first place.  I mean honking down on the nut with a breaker bar.  Obviously the clown had expected to ruin the bearings and have my elderly father have to come back for that work.  I hope I'm dead before I have to rely on others to do my vehicle maintenance.  No offense meant to the honest mechanics on the board.

Then when your dad noticed his gas mileage was going down he would have had the same crook tune his car up unnecessarily, so the crook could screw your dad again. 

[Tom H]

Been thinking about the "sleeve" for the drum.

If I had a lathe, and a piece of proper steel tubing in a size close to the original, a sleeve of the correct size could be made. Maybe even a flat bar rolled and properly welded and turned to size?

Just a thought,
Tom

[Huzo]

The thickness of the sleeve would be in the vicinity of 50 thou' maximum wouldn't it?
Once you've warmed the drum and shrunk fit the liner, the new braking surface could be machined of course, but would the new liner stay solid in the drum, under the braking forces?
What would stop it "creeping" ? Wouldn't the pad to sleeve force, overcome the grip of the sleeve to drum surface?
As the drum heats in use, given the (much) greater mass compared to the sleeve, what stops the expansion of the drum loosening the sleeve?
Or am I totally underestimating how thick the sleeve would be? How much would you take off the old drum to accept the new sleeve?
I'd wonder if a decent chamfer on the sleeve and the drum would allow for a touch of bronze weld prior to machining the new braking surface, what's the drill here?

[mojoe]

I would have thought the new inner sleeve would heat up faster, as it is the friction surface, so would expect the initial temp increase to help lock in place, but 2-3 spot welds on the peripheral face would lock it?

Just on my for first cuppa of the day so brain is not fully engaged.

[Huzo]

I would have thought the new inner sleeve would heat up faster, as it is the friction surface, so would expect the initial temp increase to help lock in place, but 2-3 spot welds on the peripheral face would lock it?

Just on my for first cuppa of the day so brain is not fully engaged.

No don't say that mate, mine's never fully engaged and as it happens I'm having my first one too in Epsom (Surrey).
But yes, as you say, it will heat up first but transfer that heat into the drum. The amount that things expand is a function of mass, all other things being equal, (which they're not), so to that end I do think empirically, that the drum will at least "try" to expand away from the liner, but who knows for sure? You will after this certainly.
I would think in principle, that yes, a few spots would lock it, but I reckon you'll have trouble with distortion of the liner due to it's (relative) thin girth. But if I were pursuing the idea, I'd for sure have a SMALL chamfer 1/16" on both parts and have a light run of bronze weld (brazing) around the perimeter.
Then once cooled it can be machined with (relative) impunity....
I think !!!?

[Tom H]

On my Loops, there is a sleeve inside the aluminum hub. How Guzzi secured it, I have no idea except that it may have had the hub heated and then installed. Maybe a locking liquid was used as well?????

I will have to look it up, I think there is a P/N for the sleeve. But N/A.

Tom

[Huzo]

On my Loops, there is a sleeve inside the aluminum hub. How Guzzi secured it, I have no idea except that it may have had the hub heated and then installed. Maybe a locking liquid was used as well?????

I will have to look it up, I think there is a P/N for the sleeve. But N/A.

Tom

Ok, so it's all do able. Just a matter of have a crack and see what happens I guess.
And buggerising around with drums on (relatively) low performance bikes probably won't result in a 200+ kph get off in the event of a failure, but a disintegrating disc would be catastrophic (of course)..

[rodekyll]

Ok -- I got the solution.  Hold my beer while I 'splain you it:

Get some friction material and bond it to the drum.  Use glue or rivets like a regular friction bonding.

Put a sole of metal (bronze, stainless or iron) on the shoe, also riveted, and arc it into the frictionized drum.

[Mike Tashjian]

 The stamped number on rotors and drums refers to the minimum you can safely turn them to when they re being serviced.  That is not the service spec which is not something everyone uses. Some manufacturers give you a spec to take the rotor or drum out of service if it falls below that spec.  That is a spec they feel the rotor or drum may not work well or be safe under.  Legally most people are OK running the parts to failure if they so desire, just don't expect any shop to give you the go ahead or do the work for that endeavor.  And as far as sleeving a drum, that was a very common way to make them.  They almost never fail and require no special assembly.  You simply freeze the sleeve and heat the hub.  Once they touch they stay mated until you mechanically remove the sleeve. Remember people, these are common knowledge parts and assembly techniques  for any brake shop in the early automotive days. Any machine shop can calculate the sleeve size from the bore size once you remove the old one.  Mike   

[Huzo]

The stamped number on rotors and drums refers to the minimum you can safely turn them to when they re being serviced.  That is not the service spec which is not something everyone uses. Some manufacturers give you a spec to take the rotor or drum out of service if it falls below that spec.  That is a spec they feel the rotor or drum may not work well or be safe under.  Legally most people are OK running the parts to failure if they so desire, just don't expect any shop to give you the go ahead or do the work for that endeavor.  And as far as sleeving a drum, that was a very common way to make them.  They almost never fail and require no special assembly.  You simply freeze the sleeve and heat the hub.  Once they touch they stay mated until you mechanically remove the sleeve. Remember people, these are common knowledge parts and assembly techniques  for any brake shop in the early automotive days. Any machine shop can calculate the sleeve size from the bore size once you remove the old one.  Mike

Now THAT sounds like common sense !

[Antietam Classic Cycle]

My Loops do have a "ummm sleeve", but, the sleeve seems to be not available from what I understand. If it can be found or made, my guess is that it would be a heated press fit.

Good luck,
Tom

As far as I know, the steel "brake drum" on Guzzi wheels has the alloy hub cast around it, so is not removable or replaceable.