Sureal goings on at the rear!

[Darren69]

The problems made worse on the 916 style bikes because the master cylinder is bolted to the engine case. I've see a couple fail from the engine heat, the fluid expands and drags the brake pads. No such problem with the Monster but worth keeping an eye on, its easy to cook the rear caliper if its dragging.

[jerry]

i dont understand the floating caliper ??? none of my ducatis have floating calipers so am i missing something here ???

[Flip]

A floating rear brake assembly was an option available on many of the early bikes and came as standard I think on the 888 and then later (presumably to use up stock) when Ducati did the 'S' model Monsters.

This is from the accessory book that came with my 1997 900 when it was new:

[Mr Gazza]

Flip..Agreed that emzedder should put some pictures up...I've sent a request.

Jerry.. Flip is correct about the floater..It was also an option and kit for SS models, and standard on the SL (I think).

Nottsbiker, Darren..Yes so true, it's all too easy to ignore the rear brake and take it for granted..I've had my wake up call and I would urge all owners to just take the trouble to drop the calliper off every now and then give everything a really good clean and check over.
Dealers can be guilty of not paying enough attention to the rear brake too.
I lost a pad from my first Monster as a result of the pin not being passed through the hole... It had been dealer serviced by the PO prior to my buying it.

The rear brake has actually been the most troublesome thing on my Monster so far.
I had it lock up due to fluid expansion on my very first ride out on it..I had adjusted out too much free play at the lever...I run it with about 3mm free play now.
I later had to change the disc due it warping..and now this.!

[Dukedesmo]

Had a problem on the 916, dealer adjusted the brake pedal position at the first service and left too little play in the lever.

After 3-4 miles the bike started slowing and eventually the rear wheel just seized at a roundabout, when I looked around the pads were on fire and the paint on the rim of the disc had burnt off.

A couple of years later the caliper started leaking which, I assume was a hangover of the burning incident?

The mounting of the master cylinder to the engine cases causes the brake to go bad after time presumably due to the heat (needs bleeding despite there being no apparent leaks) and is very a poor design, but the fitting of the rear master cylinder support bolt to the same bracket that holds the exhaust to the engine is an absolute masterstroke in heat management!

The odd thing is that the 916 uses the same master cylinder and caliper setup as the Monster yet the rear brake is crap whilst that on my Monster is good and I don't think it's all down to the slightly smaller (10mm less) disc, rather just to poor setup.

I also have the floating caliper setup on the monster but, claims of transfering load to the engine under braking etc. apart, IMO the only real advantage is less drag...

[utopia]

Hmmm.
To be honest, my (non-floating) rear disc has been getting rather warmer than it should for quite a while now.
I regularly check that there is free play, even when "warm", and all seems fine there, but I'm starting to think that I should be more stringent and get to the bottom of it as a matter of urgency.
Nottsbiker's report of a seized caliper shearing the bolts and dumping the caliper into the wheel is making me rather nervous .. particularly now that said rear wheel is a £1k carbon jobbie.
All has been cleaned a couple of times and the pistons retract easily.
I'm thinking that increasing the free play is a next step, followed by new seals to ensure that they have enough elasticity to fully retract the pistons.
I will report back in due course.

I will investigate the backing plates further too.
They were fitted to the pads which came with my yr2000 750 which I bought at 2,000 miles old.
I'm pretty confident that the pads had not been changed from new.
I replaced them eventually at maybe 14,000 miles-ish.
They had worn to wafer thin but had not yet touched metal anywhere .. exactly the same both sides and even thickness (thinness) all over. (yes, I know !)
This kinda gave me confidence that the "lob-sided" backing plates were probably doing a decent job.
I hadn't seen them before, so I was curious.
Maybe an email to Brembo is in order.
I will also get a photo at some stage (I need to fit new seals anyway, so I'll be in there) and then maybe start a thread to see if other forum members know anything about them.

I'm never sure about copperslip, for the very reason you describe.
Last time I did use a tiny amount on the front pads .. but little more than a trace, and just dabbed it on the circular "witness marks" left by the pistons on the back of the used pads.
I'm still not sure about it though.

I'm a big fan of black, molybdenum disulphide grease (for the bush, and general stuff .. not pads obviously, dear other readers).

Hopefully, you've cured the root cause of the problem, BUT its not a certainty.
I'd recommend that you inspect it frequently in the future .. but I'd be wasting my breath because I'm certain that you're already well primed there.

What's the bush made of ?

Cool about the seat.

I now use a fine touch of high temp ceramic grease (http://www.dirtbikebitz.com/putoline...ce=GoogleBase1 ) rather than coppaslip on the pad rears.
It seems to hold up better.

[Mr Gazza]

Glad I'm not the only one with rear brake problems. Also glad that this thread is being sensibly picked up and hope that folk will be inspired to give thier rear brakes a little service.
It wouldn't be too much of an exaggeration to say it might even save a life.

Utopia, I wonder if the heat conductive properties of Carbon Fibre has anything to do with your disc warming up...It's normally bolted to a large three spoke alloy heat sink....No idea if your wheel has a metal hub or insert of some kind?

Very interested to see what you can find out about the backing plates..As mentioned, Luke found them absent on his parts list for the 2000 M900Sie, but that doesn't mean to say that Brembo didn't supply pads with backing plates at the time.
I think they were fitted to cars to prevent squeal?

I am also starting to have grave doubts about Coppaslip after a lifetime of useing it...Talking to my Dad about it, he said it was probably better to leave everything dry to let the dust fall off. I might just wash it all off when the Graphite grease arrives for the bush.

I plumped for Graphite grease for the bush in the end, but the choice is quite bewildering. It is blended with Lithium, Molybdenum Disulphide, Copper and even Calcium!! Not knowing which would have any particular advantage in my application I went for a basic Graphite grease. I think frequent grease changes are going to be the key anyway.

I am thinking in terms of about a 2000mile service interval, given that the previous bush only lasted 6000miles I am sure non-floaters would go longer and overhead mounted callipers, longer still.

The fixed, inner, "Top hat" parts of the bush are steel. The bush pressed into the bracket is a split steel tube with a coating of a brassey/bronze type material on the last new bush (now the old bush!) the newest bush has a dark charcoal or Graphite coloured coating...I wondered if it might be Teflon?

Thanks for your comment on the seat...It gave me a very warm feeling to see it used again.

[utopia]

The carbon wheel has an alloy hub.
Not that I would expect it to make much difference.
The contact area between disc and hub is very small and I can't see it providing a significant heat path.
And the problem was there with the old wheels anyway.

[rbt1548]

I am afraid I am going to have to revive this thread.

On a particularly wet and dirty few hours on the bike, 2000 M900Sie, I thought I could hear a slight noise from the front brakes taking off from a standstill so I decided to give the brakes, F&R, a thorough clean, usual, off with callipers, pads out and into them with a toothbrush and brake cleaner, refitted and bled fronts no problem, discs ok too.
When I moved onto the rear, the wheel was very reluctant to turn backwards like Mr Gazza's. The calliper seems to be the floating type with the torque arm like the one in Flip's post , No.18 in this thread.

I removed the calliper to give it a clean and noticed the front and rear edges just before the pads on the outside half of the calliper, (the side furthest from the wheel), look as though they have been scored, see pic, possibly touching the disc, the disc looks fine and is 4.1 mm thick, so plenty meat on it.

I did notice, however, that the calliper mounting bracket could be moved on the spindle a bit, so I took it off and held it in a vice and with the bushes in I could get a .5mm feeler gauge between the top hat bush and the bracket when moving the bracket.
I take it that there should be NO movement between the bushes and bracket and they should be a snug fit?, if this is the case I would imagine it is possible that this movement caused the scoring on the calliper and I need to get a new set of bushes?

The parts book for a 2000 M900Sie lists another rear brake set up, but '98 900SS F.E. looks the same, can anyone tell me if I'm on the right track and enlighten me on the parts I may need?

Cheers

[Nickj]

The metal bits are anti rattle shims, you usually find them where you will have some lateral float in caliper or rotor. If you look at these they usually cover the piston area and they are often slightly offset and need to be positioned relative to the rotors rotation.
You want the trailing edge of the pads to hit the disc first or you get a brake that feels really on/off. It will be just a few thou rather than a few mm
Floating caliper or floating disc ... in either case the pads will float over the rotor and maintain clearance
UNLESS the pads or a pad don't float back properly then as soon as one edge touches the disk rotor when the float in the rotor/caliper allows a pad surface to work like an auto hill start device. typically just one pad (If it's both then something is actually broken). Rotate the correct way and it clears itself. If there is some rotation in the caliper mount then it is easier for this to occur
Often there's some friction in the system that isn't helping, often just a layer of scrubbed off pad material stopping the rear face clearing properly (symptom is wedge shaped pads). The old pad material will build up and be quite hard as it gets bloody hot.

Probably a good idea to clean the caplier(s) when using soft pads on a more frequent every so often basis and ensure that any dust is shifted and any heavier 'baked' on stuff is too. The pins need to be round and smooth with no rough corrosion or wear steps, surface damage will stop the pads moving properly and if the pad is left with a little clearance with the piston it can start to rotate as the brakes applied and start to wedge.

I've found disc systems much easier to sort out than stuff like fontana 4LS drums... another story there are you can get a bit of auto servo effect enhancement when there's wear which is fun

[Nickj]

Rbt ..
A very little lateral movement relative to the rotor is going to be OK, Rotational movement isn't. Ideally you'd have none of either unless you have a floating caliper where you should only have lateral.
Lateral movement makes allowance for tolerances in build, if it wasn't there you'd be having to shim the caliper/rotor.
The caliper can also take out a little lateral offset but you want this to be as small as poss.

[rbt1548]

Hi Nickj,

Thanks for that info, but I don't have any rattle shims at all on either the front or rear pads, the bits that are scored are actually parts of the calliper casting.
The pads are worn even, I bought a new pair just in case but when put side by side there is very little wear on the ones that were on.

I will check on the rotational movement and if there is any maybe need to adjust the rose joints a tad. They seem also to be in decent nick and well greased.
Thanks

[Mr Gazza]

Robert, I'm going to have a go at answering your query, but first let me bring the thread up to date.
The MOT that followed the last one mentioned here, showed up that the rear brake problem had not completely gone away. The rolling road brake meter showed that the rear brake was hanging on a little after release. Instead of the needle dropping when the brake was released, it just slowly fell with a damped sort of action. The tester commented on this.
So. I changed the master cylinder for a new one and did a fluid change. The new master has transformed the rear brake. I should have done it in the first place when I originally ordered a new master and ended up sending it back...Mistake!!
Do not dismiss a draggy master. All appears to be working well but the slow return of the master causes a lot of problems.

So to answer your post Robert.
The ratchet like effect of not being able to turn the wheel backwards may be caused by wedge shaped pads, which in turn is caused, I believe, by a draggy master, or in your case it could be caused by foreign matter everywhere just making a nuisance of itself.

Check the pads for even front to back wear.

The calliper bracket is supposed to move in and out on the bushes about half a mm or so, ( a little more should not be a problem) that is the way in which it floats, as well as moving radially on the bushes when the suspension moves.. adjusting the torque rod ends will achieve nothing.
What you don't want is any twist in the bracket, which will allow one edge or other of the pads to lead. So get hold of the calliper and try to wring it on it's bushes, there should be no play in this sense.

The damage to your calliper does not appear to have been done by contact with the disc, if it was it would be even, flat and probably shiny. It would also match marks on your disc. The calliper body should clear the disc by about 2mm either side (float not withstanding).
I would suggest that the calliper damage has been caused by very hamfisted maintenance by a previous owner.. Maybe that half of the body has been gripped in a vice, or hammered when split? I think it's unlikely that the damage would have been caused by stones or whatever on both forward and rear edges of the calliper... The leading edge only, maybe, and then it would be matched by deep scores in the disc.

Can you check the calliper to disc clearance? Even with the natural float pushed towards the disc.

If the calliper is contacting the disc then there needs to be a serious investigation as to why, as something is badly out of order. A mis-placed spacer or bent bracket perhaps?

At the end of the day the noise and "hill start" effect could just be caused by dirt... At this time of year it comes with salt too, so is extra evil.
Have you tried rotating backwards after cleaning it all down?

Hope you get to the bottom of this sooner than I did.

[slob]

It’s normal to have more wear at the leading edge of a pad. The friction of the disc causes a turning force on the pads, drawing the front in with more force. Thats why on multi piston calipers you often have different sized pistons, front to rear, evening out the wear.