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Discussion Starter #1
Hi guys

Just trying to get back into some work on my bike whilst it's still winter down here.

One of my front disks drags and throws dust everywhere and as I don't know whether and if so, then how extensively they were ever rebuilt in the past. I've decided to rebuild the lot. I've got kits for both cylinders and all calipers, plus new washers, bolts and bleed screws etc.

I've also been busy checking all available docs I could find for any pitfalls ort vital info.

I've come up with a few unanswered items:

Do I use the supplied grease or brake fluid on the pistons, seals and boots? I've seen people do it either way, but not both. It seems odd to smother the pistons in grease when they're going to spend the rest of their lives swimming in brake fluid. I'm leaning towards grease for the rubber parts only and fluid for the rest.

Torque for bolts - New caliper bolts are included in the rebuild kits, but what torque?

And Loctite on those same bolts - None... red... blue?

And regarding bleeding.. Falloon p241 bottom left says Brembo's don't bleed using only the lever. Says to use Mityvac. I'll be draining all fluid as everything is going to be rebuilt. IS he accurate with that statement or is there another way around this?

Thanks for any assistance with this!
Regards
ROB
 

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Hi Rob,

Good to hear from you. I don't know the answers, so all I can do is give my opinion: I have never Loctited the caliper bolts and they never come loose, but I guess Lock and Seal would be the obvious one, and I don't have a torque value, I've just used my inbuilt torque wrench and a normal allen key. I think that just gently lubing the moving parts with the supplied grease is the way to go, and will definitely ease assembly. I've never had any trouble bleeding the brakes from scratch, but there's always a first time!

Good luck,

Colin
 

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Hi Rob

1. Apply grease to the rubber seals, nothing much else required elsewhere. Apply the grease sparingly. The amount you get in an overhaul kit is very generous, enough to do 3-4 times over.

2. I have never seen a value quoted by Brembo (or anyone else, for that matter) for the bolts for the caliper halves. That's probably because there's no real need. They're not under stress, they are not stretch bolts. If you must use a torque wrench, use the same value as for the M10 caliper attachment screws: 37-40lb/ft. Otherwise, simple follow Colin's advice.

3. Do NOT use any thread lock. Not needed.

4. Brake bleeding is not difficult once you understand that the air wants to go UP!

People often make the mistake of thinking you can bleed the entire system using just the bleed nipples on the calipers, i.e. down at the bottom of the system. Not so. Those nipples are there to remove air that would otherwise be trapped within the calipers. Any air higher up in the system isn't going to magically defy the laws of gravity and move down the line to those bleed nipples ...

Now, if you have a Mityvac or similar, then you can use the nipples to suck fluid out, with the idea that it will take the air with it. But even that doesn't always work ...

So essentially, once you've bled the calipers (and if you push the pistons all the way back in before starting to fill, you can often avoid having to do that), you bleed the rest of system out at the high point, i.e. the master cylinder. This isn't perhaps the place to go into details, but if you have any concerns, by all means shout.

Ciao

Craig
 

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My Honda manual has a value of 16 Ft/Lbs for the Tokico caliper halves if that helps.

I would use brake fluid on the O rings and pistons and grease on the dust seals.

I would not use loctite.

If you have a Mityvac or similar it's good for filling the system with fluid quickly but you will usually need to finish the job by hand, start at the M/cyl, if there's no bleeder on it crack the banjo to expel air, then do the furthest point and revert back.
Often on the rear the bleed nipple faces down and even with a vacuum bleeder it's difficult to get a good pedal, unbolt the caliper, sit it on the rotor so the nipple faces up and bleed, then reinstall.

I would not try and force fluid from the bottom "back bleeding" it, it's messy and you can get a proper result being patient and bleeding from the top down.
 

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Discussion Starter #6
Thanks everyone and good to be back :)

I've got that PDF Ian, and also the one I've attached here. There's a couple of YouTube videos as well if one looks for old BMW, Laverda or Moto Guzzi brake rebuilds. Mostly pretty rough jobs though.

Based on the replies...

I'll torque the calliper bolts by feel, then check with a torque wrench to see what I did and even them up if necessary.

I'll not use any Loctite.

I'll 'wet' the rubber parts with the grease for assembly and I'll make a decision on any additional grease based on fit and feel. I'm thinking there might be a case to have some extra grease between the two, but leave the internals over to the fluid alone.

I'll have a fiddle with the bleeding. I only have my hands to do it. I think the rear should be ok as the hose remains horizontal between the calliper and the cylinder. For the front pair, I'll take my time and see what happens. I take the point about needing to get any air out the top end.

I do have one of those brake hose clamps for retaining fluid in the hoses, but I'm reluctant to use it because the (original style) hoses look like they might have some sort of internal structure.. like a metallic weave or spiral, and I don't want to risk busting that.

I'll post some pics!
Rob
 

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robax: a couple of things:
  • I used compressed air to remove the pistons. I split the halves first then placed a tiny disc of plastic in between the halves to seal the interconnecting port and lightly rebolted the two halves together. Then I placed a rag in the middle, put on my safety glasses and applied a short burst of air down the bleed nipple hole and the piston on that side popped out easily. I think I had to undo halves to remove the piston completely. Repeat for the other side. I've got Goldline calipers with a feed on one side and a bleed on the other.
  • Bleeding was easy but only if done correctly; squeeze the lever, hold it in, open the bleed then close the bleed and release the lever then repeat. I've read on other forums people just squeezing and squeezing with the bleed open and wondering why the bubbles keep on coming. Do one caliper then the other. Really important: Cover your gas tank and front fender with rags. Sometimes when squeezing the lever, there will be a little burp of air that results in a small spurt of fluid that can escape the open master pot.
Good luck, post pics!
 

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Discussion Starter #8
I'm planning on doing what the guy shows in the third image in the PDF linked in my last post. He leaves the pads in after removing the calliper (but with hose still attached) and then applies the brake to squeeze the pistons onto the pads without the disc in-between. I'll confirm back here if that works nicely.

And yes, good point on closing the screw each time! I remember doing that way back but it wasn't in my mind until you mentioned it. I was actually standing in a shop looking at a vacuum kit and then decided to check here for more replies before I bought it.. I decided not to buy it and will just do it manually.

Wife is away until next week so I'll be onto this shortly.. and will definitely be careful with the fluid. I've already removed all the bodywork. I like to be super-clean.
Rob
 

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Rob, If you do spill any brake fluid, don't simply wipe it off. That won't work. WASH it off using loads of water.

I always give everything a good wash off anyways, once the job's finished. Better safe than sorry.
 

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Discussion Starter #10
Will do I'll be very careful!

After all the questions it turns out there's a huge instruction sheet in every packet of rebuild parts... Open the box!

It says exactly what matters.. you can use either the grease or brake fluid. If you use the grease, use it only to 'wet' the internal ring and the outer edge of the piston, nothing else (well the tiny o-ring as well, but the instructions don't go into splitting the calliper). I went with the grease method just to keep the process a little cleaner.

It also gives a torque value of 50nm for the bolts to the fork, but nothing for the calliper bolts. My Ducati user manual says under half that for general m10's, which agrees with loonie's Honda manual further up. I'll see how 20nm feels and go up from there if necessary.

I did the rear calliper this evening. I cracked the big bolts first. I suggest also cracking the banjo and the bleed screw while it's still attached to the plate. I didn't but I will on the front ones. Then I took the calliper off the bracket and operated the brake to check that both pistons were moving. I moved the hose out of that clip/bracket thing that keeps it away from the tyre and then took the banjo and switch off with the hose held higher than the other end. I put towels on everything to catch any drips. In the end, nothing came out and so I wrapped the banjo up and zip tied it to the top of the brake plate, roughly in line with the other end at the master cylinder.

Then I just pulled it apart in my oil tray. The fluid didn't really want to drip out but pushing the pistons in with my thumb sorted that. I didn't know if these brakes had ever been rebuilt, but chances were they had been done by the previous owner, probably about 15 years ago. This one had the new Teflon pistons and it was all in pretty good order. It'll be interesting to see why the front right one drags if it also has the same bits.

I scrubbed the callipers with degreaser and gave it a final clean with brake cleaner, I have lots of bushes for cleaning little details and got it it all real clean.

It's all back together now. I gave the pads a rub on some 240 emery and cleaned the anti-squeal stuff of the backs.

I used a tiny amount of copper anti-seize on the two bolts as that's what I found the previous person had done. It certainly helped me this time. I haven't torqued them up. Will do that when it's back on the bike.

I note that the bleed screw very nearly touches the body at the point where it seals (see image below). The old screw is exactly the same. It does seal fine but I'd have thought it would have a couple of mm clear. Is the same for others?

Something else of interest were the spacer washers between the calliper and the brake plate. They had obviously been selected to align the brake. I checked the parts manual and there are 4 different ones form 0.2 to 0.8mm in there for this purpose. The ones on this bike don't match any of those. I'll check the alignment closely when it goes back together.

The other thing I did was attempt to replace that large grommet that feeds the hose and switch lead through in the rear fender. I've had a selection of them here for years waiting for this moment, but none of the fit right so I used the original again. Not an easy item to find in the right size and shape!

I'll have ago at the rear master tomorrow. That one has tiny bubbles when operated so I'm planning to make sure that is resolved.


IMG_20200723_001109.jpg
 

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Discussion Starter #11
Oh and lastly..

Although the pistons weren't stuck or seized in any way, they just would not come out, partly because one can't really get hold of them unless one is prepared to damage them. The air method worked easily and instantly with a tiny squirt.
 

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Coupla comments:

1. Dragging piston: Normally caused by a thin crust of old brake fluid on the outside of the bore, towards the front. Especially common if the fluid hasn’t been changed for 15 years (Gulp! Should be every 2), and the seal has been leaking a little. Be very fussy. This crust of old brake fluid is transparent, thin and can be surprisingly difficult to see. Feel for it with a finger. If you don't remove it, you risk a leaky seal.

2. Bleed screws: These come in different lengths, some having more exposed thread than others. As long as it’s sealing on its taper - measure it and its hole with some calipers if you're not sure - don’t worry about it. P.s Do NOT overtighten. That serves no purpose, and they can snap.

3. Alignment washers: Their purpose is to centre the caliper over the middle of the disc. Again, don’t worry too much if yours don’t match what’s in the book. However, if you’re having to install particularly thick washers, it means something is out of alignment, wheel- to-swing arm. Calls for further investigation.
 

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Same comment for the front end re. spacing. Following my rebuild and during the check-out of my front wheel components, I noticed that the ally speedo drive washer was dished and squished. it's important that the speedo drive+washer is the same thickness as the spacer on the other side, assuming that the wheel bearings are pressed perfectly on both sides. After some Internet reading, I found that this is a common issue which is why stainless steel replacements can be bought. With my new washer in place, the caliper splits were exactly centered over each disc.

robax: Did you clean the speedo drive? Mine was very dirty after 23k kms of riding and 38 years of life.
 

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Rob,

you probably already know this, but just in case - the four jaws that clamp the rear wheel to the swinging arm are not all the same thickness, the one that goes next to the brake caliper plate is thinner.
 

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Discussion Starter #15
Thanks for the comments again!

Yes, I figured that issue with the swing arm clamps back when I first got the bike and gave it a going over. Definitely one to catch people out!

In this instance I'm not removing the rear wheel, but I will be taking the front off, so I'll check that speedo drive. It looked good when I checked it last time I had it off. The bike had been sitting for many years but that was after being 'restored' and so it was in very clean condition. It is obvious to me now that the guy just left it sitting after doing all the work and then finding that he couldn't get it to run properly. I've done a ton of work on it and the brakes are the next part for me to deal with.

That bleed screw works when I suck or blow through the nipple. It stops the flow just at the point in my photo. It seems ok.

So last night I did the rear master cylinder. My finding there is that the instruction guide in the packet is completely wrong for this version, so throw that away.

Everything came apart fine. I had a drift that happens to fit just right. I aimed for the rim of the piston to avoid the drift getting stuck in the hole in the end. It all popped out with just a tap.

This is the cylinder that always produced very fine bubbles in the cup. A loupe showed me that there was some fine unevenness on the rear of the two ring seals and it matched some scruffiness on the last part of the piston. However, the bore is nice and smooth so I don't see how or how the piston got like that.

I cleaned everything out and put the new bits in with the grease. That metal washer that holds the whole lot in clicked in easily but couldn't quite hold everything in against the spring, which was quite strong. I resorted to tapping it further in with the piece of pipe I have for the purpose and that held fine. I realised then that the piston is in fact pushed and held in by the lever that one attaches afterwards. This stops it pushing that washer and rear seal out. So really, that washer doesn't have to be tapped in too tight. That's something to note for next time.

I'll bleed this out today and see how that goes. I'll be happy if the bubbles no longer show up, as I expect they won't.

One thing I'm looking for is a replacement for that wonky bar that goes from the foot lever to the cylinder. Mine has the rear fork completely seized inside it. I've tried everything to get it out, heat etc. I'm likely to break the fork off if I go any harder. I won't risk breaking it without a replacement on-hand. It looks to me as if the previous owner had the entire bar with the fork and locknut replated as a single item, suggesting he also never had it apart. Adjustment is only available ion the banjo piece at the lever end.

I've seen some remanufactured ones around, but they are either zinced or aluminium. I'd like to find a perfect or re-finish-able (new word there) original part for this if anyone has seen one. This is the one with more bends in it than the earlier versions.

The image has everything back on the bike, but no fluid yet.

989968
 

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An important note for anyone else doing this for the first time is to make sure that the outer metal ring on the new piston seal is pointing in the right direction with the tiny taper on the inside, pointing towards the cylinder to help it fit. As robax notes the little rear caliper lever does hold the piston in place once it's on but it is critical that the seal is pushed in hard enough that it doesn't come loose. I also have a small steel tube, hand filed to fit the seal ring to enable the piston seal to be pushed into place.
 

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It is funny Rob, but when I bought my 900 new the rear brake was useless (still is, but hey) bleeding it showed air bubbles coming out, but no matter how much I bled it, they still came out. Later I changed the seals in the rear cylinder and cured it, but it was weird.

BTW, I believe that Brembo brakes always drag a little; maybe the seals do not allow for much movement in the calipers. The Lockheeds fitted to my 750 never dragged.
 

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Re the wonky bar with the frozen fork, most likely you're not using enough heat. A propane torch has its limits so next up is Mr. Acetylene. You have to be careful not to over heat it so that the metal - assuming steel here - does not get soft. And, using this, you will probably frag the chrome. The other thing to try while still using propane is to place the rod in alum soft jaws with a rag on a vice and then whack the fork at its deepest point near the threads with a hammer and a piece of maple after it's hot. This will shock the threads. Note also that if the jam nut is truly snugged up, most likely virtually no amount of reasonable force is going to get the fork to unscrew. The jam nut has to be loosened first.

I believe that the rod is actually a tube so, from the other end, remove the opposite fork and spray in some penetrating schmutz and let it soak.
 

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My old Brembos only drag for a split second when the discs are rusty! Otherwise, the pads back off front and back when the levers are released. I did wonder about the rear brake line hoop as it goes from left side up, across and back down again to the rear caliper, maybe 3cm or 4cm vertical rise at the most. This is the high spot in the system and a possible air bubble location. It doesn't seem to be an issue for me; my rear brake works fine.
 

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Discussion Starter #20
Back again!

The bleeding turned into a drama. Took forever and another disassembly to get anything to pump through at all. I finally got it going by filling up the calliper and the cylinder through the hose connections. I tried a manual vacuum pump, but that refused to suck anything through even though it was able to build up 25psi quite easily. All it does is suck air down the bleed screw threads.

The fluid was still coming through quite cloudy and grey. With the calliper and cylinder completely spotless it had to be coming from the hose. All I could do was keep flushing, and also sucking the cloudy fluid out of the reservoir as it would gather at both ends. Eventually it all cleared up.

One thing that seems dumb is how the bleeder is perfectly located to dribble fluid all over the pads. I kept bits of paper towel stuffed in everywhere but it was hard to keep it all clean.

I also decided to replace calliper washers, split washers and spacers with stainless steel items I found locally. Kept the original bolts though.

I've got a video, but will wait until I've done the front as well and then post the most useful one.

So I've moved onto the front now. I decided to take the callipers, splitter and lever off all in one piece, with hoses attached. That worked fine... just be sure to crack all the bolts including the banjos whilst still attached. All those bits are in pieces and cleaned ready to rebuild. I'm installing an emulator kit in the fork at the same time.

All of the pistons were in good condition. Nothing was stuck and nothing corroded.. perhaps one was just a little stiffer than the others to get out. So it's not clear why I get the excess brake dust and the sandy/dragging sound. I'm wondering if it's the pads. I'll put them back in for now, but I'd like to get some fresh ones anyway.

I think the number on them is 07418320, which seems to bring up two types of current Brembo pads as in the screencap here:


990417



It's not clear in what way these two differ.. though one says compound and the other Carbon Ceramic.

I can see one of them listed on Ducati Paddy's site where he says "CC The carbon-ceramic compound has evolved from the previous organic compound, thanks to its higher carbon content. This type of material features good durability, good performance hot and cold, wet and dry. It is has a slightly more progressive initial bite and is slightly less aggressive than the sintered pad and is compatible with both steel and cast iron discs. "

What do you guys reckon... anyone using these?
Regards
ROb

Here's also a pic of the pads in the bike

990418
 
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