Stelvio mysterio .... Buffaloed by Brakes

[Lannis]

So I changed the front tire on the '09 Stelvio like I have 3 times - axle out, left caliper off, slide wheel out, change tire, slide wheel back in, fit disk in between right caliper pucks, slide left caliper pucks back over disk, bolt left caliper back on, axle back in, job's a good 'un.    Front brake lever pumps back up firm and normal in a stroke or two, ready to go.

Next day, lever still firm and hard, back the bike out of the shop, turn to go, front caliper has NOTHING, all the way back to the bar.

So back into the shop, lever pumps back up firm and hard in about 3 strokes.   Pop the top off front master cylinder, full of clean fluid, lever stays firm, put top back on master cylinder, lever still firm and hard.   Bleed each wheel cylinder, no air bubbles, lever firm and hard after each bleed.   Swing bars back and forth from stop to stop, lever stays hard.   Pump front end up and down while squeezing brake, lever stays hard.  

BUT ... rotate the wheel half a turn by hand and the front lever goes straight to the handlebar.   NO pressure.   Pumps back up in about three strokes and stays there, all day, over night, whatever .... but turn the front wheel about half a revolution and all the lever pressure disappears.   No fluid leaking anywhere, not a drop.

What could possibly cause this?  Wheels turns normally with a little puck drag as always, then all pressure disappears.   And then comes right back with a pump or two?   I can't even imagine the failure mechanism.

So time for me to learn something ....

Lannis

[twhitaker]

Wheels turns normally with a little puck drag as always, then all pressure disappears. 

Warped rotor?

Once you have eliminated everything it cannot be, that which remains must be the cause.

[Lannis]

Warped rotor?

Once you have eliminated everything it cannot be, that which remains must be the cause.

I'll go out and unbolt the calipers and check for a warped rotor - that's a variable that I MIGHT have introduced if I bent it while breaking the bead or something.

But why would a warped rotor make ALL the pressure in the system disappear?   Looks like the other side would still work, instead of everything going away?

Lannis

[twhitaker]

The master cylinder is displacing just a few cc's and it all goes to move the pre-moved pistons. Physics.  ;-T <shrug>

[Xlratr]

Hard to imagine that a warped disc would cause that. Any additional clearance on one side would be offset by less clearance on the other side wouldn't it? And surely it would be minimal anyway.

If it was my bike I'd think I'd messed up something with the abs, but the 09 doesn't have abs, right?

John


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[Lannis]

Well, I took the calipers off and set up a runout mike on the rotor and turned the wheel and it about knocked the mike off the stand.   Measured it with a ruler and the total runout on the left disk is about .200", really wobbly.

Either me or the shop during the tire change, most likely me not being careful while breaking the bead and putting the pressure on the disk.   Live and learn.

So I did a quick check and the Gixxer and CBR youngsters straighten out their warped rotors, but do we cautious and careful Guzzisti do those sorts of things, cheap though we may be?

I really want to have this thing on the road this weekend, lots of traveling to do ... but ....

Lannis

[Xlratr]

Measured it with a ruler and the total runout on the left disk is about .200",

Lannis

Wow! :-0


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[father guzzi obrian]

.200, I have never seen a disc so bent, that is bizarre, how could it be bent that much without you aware of it happening, that would take a hammer blow or something similar to it. I am surprised it did not fracture with that much distortion...  Good luck with it.

[Vagrant]

did you check the front wheel bearings? did it have a spacer in there?

[Wayne Orwig]

So I did a quick check and the Gixxer and CBR youngsters straighten out their warped rotors, but do we cautious and careful Guzzisti do those sorts of things, cheap though we may be?

I really want to have this thing on the road this weekend, lots of traveling to do ... but ....

Try to bend it back. You have nothing to lose.

[normzone]

Unless you think you did it, I'd at least have a word with the shop.

[Lannis]

Unless you think you did it, I'd at least have a word with the shop.

In retrospect, I'm sure I did it.   I used (for the last time, I can assure you) my HF bead breaker on the bottom of the HF tire changer that I've had for years to break the bead on the tire.

I have a wooden block that I put under the rim to support it.   But as I was putting pressure on the top bead, the block slipped out and I'm sure that the pressure (me leaning on a 3' pipe) all went right onto the rotor.   I guess I was hoping it hadn't, but I'm betting it did.    All the shop did was use their Cheetah bead-seater to reseat the bead when done, no reason to bend a rotor there.

At any rate, I just got back from taking the wheel and rotor to the shop (they're an old-fashioned place that's been there since I were a lad) and they're going to try to true the rotor back up.   At the price of new ones from Italy, it's certainly worth a try!!

At least I've seen this symptom and will be The Wise Man when it happens to someone else.   Another "wrinkle in my arse" even though I have to pay for it.

Anyway, it's not enough to "know" what good shop practice is; you have to actually DO it for it to work for you   :-[   :-[ 

Lannis

[malik]

Bad luck, old mate.

I had the same symptoms recently on the V7C after changing the front tyre. After two days working on the problem without success, I surmised (another duh moment) that the reason the rotor wasn't sitting in the centre of the calipers was that I'd reversed the spacers on the wheel on reassembly. The drawings in the parts manual are not helpful.

Is it the rotor bent, or the rotors' mounting hardware?

Mal

[Lannis]

Bad luck, old mate.

I had the same symptoms recently on the V7C after changing the front tyre. After two days working on the problem without success, I surmised (another duh moment) that the reason the rotor wasn't sitting in the centre of the calipers was that I'd reversed the spacers on the wheel on reassembly. The drawings in the parts manual are not helpful.

Is it the rotor bent, or the rotors' mounting hardware?

Mal

Not sure where the actual distortion is.   The rotor is solid-mounted to the wheel with 6 allen cap screws, but it's "two-piece" and I don't know which piece (or both) is bent.    The guys in the shop are pretty careful - if they feel that anything has gone past its "elastic limit" and isn't repairable, they can sell me a new one and no harm done except to my wallet.

Lannis

[Lannis]

Well, a nice shout-out is due to our local Honda-Suzuki-Aprilia shop.

They took my wheel with the bent rotor, which was out about .200", and trued the rotor up to .002".    They said that because of the way it was bent (not overheated or road impact) that there's little or no fatigue danger, and should be fine.

They were almost apologetic in charging me $16.50 for doing the repair.   Compared to $408 for a new Guzzi item from Italy, or $250 for an EBC aftermarket one (in stunning blue), I'd say I got off easy.

No more ham-handed treatment of these things while breaking tire beads!!!

Lannis

[twhitaker]

That's about as good of a deal as one could hope to get. The lesson was worth a whole lot more than 16 bux.  ;-T

I'm surprised the rotor passed through the caliper without a couple screeches per rev.

[LowRyter]

wow  good new Landis!   ;D

 :D

[twhitaker]

wow  good new Landis!

I've worked on numerous Landis grinders.  ;D

[LowRyter]

I've worked on numerous Landis grinders.  ;D

[Chuck in Indiana]

That's about as good of a deal as one could hope to get. The lesson was worth a whole lot more than 16 bux.  ;-T

I'm surprised the rotor passed through the caliper without a couple screeches per rev.

Absolutely. Education is normally *expensive*..  ;D
Experience is a tough teacher. It gives you the test first..then the lesson.

[Lannis]

That's about as good of a deal as one could hope to get. The lesson was worth a whole lot more than 16 bux.  ;-T

I'm surprised the rotor passed through the caliper without a couple screeches per rev.

I know, I already had my "pay to play" money out.

Funny thing is that the wheel turned just fine - when I reinstalled it after changing the tire, I turned it by hand to make sure that the bearings weren't binding and that it turned freely, and it did.

A bit too freely, actually.   But the runout was enough to push the pads back into the cylinders, but not enough to actually contact anything hard, or bind up.

As mentioned, cheap lesson!!

Lannis