Front Brake Problem

[Motormike]

Looking for thoughts and ideas as I chase down a front brake problem on a 2004 Coppa Italia. The front disks pulse badly, becoming much more noticable as the bike slows to a stop. It's very much an on/off effect of "grab...release...grab...release" sensation, as if I were applying and releasing the brake lever. No pulsing or movement at the lever that I can detect. I just finished lifting the front wheel and putting a digital dial indicator on the disks. Almost no runout to speak of, maybe a couple thousands or so. So small it was hard to measure. So I think it must be something else than the usual "warped disk" blame. I've tried the easy stuff, like cleaning and spinning the carrier buttons. I'm thinking about buying a small brake hone and using it on the disks (tried scotch brite pads) plus some new brake pads. Is there any chance the master cylinder could be leaking? Like fluid by-passing the piston causing the grab..release sensation I'm getting? I'm getting stumped. The bike is all but unridable as it is now.

[Craig]

I had a similar issue on a K75 I used to own. The rotors ran true with plenty of thickness. I changed the pads to a very agressive compound and bedded them in and the problem went away. My hypothesis is that I inadvertantly heat treated and hardened a section of rotor which resulted in a different CF. This caused the pulsing. In any event, it went away with new pads, but only AFTER agressive bedding.

[Orson]

I had pulsing front brakes on my Tenni at about the 17,000 km mark.

 

I'm not sure if the rotors were warped, but new rotors cured the problem.

[grossohc]

Whatabout sticky pistons in the calipers. Like one piston is going out and staying there. clean and work the pistons a few times in and out, but not enought to pop the seals.

[pasotibbs]

Although the discs appear true(not warped) they may not be "floating" correctly, even though you've cleaned the bobbins the discs may be stuck slightly off centre in relation to the spindle so the pads are running on and off the normal swept area of the discs ?

I had the same issue and "cured" it by replacing the discs with some used Ducati ones,I was able to get the old discs cleaner off the bike but have never got around to testing them.

[docc]

All good thoughts here, but being a really *cheap* Guzzi owner (is that redundant?), I found freeing up all the pistons (+1 on grossohc) really made a difference. It's a fiddly operation, but cheaper than new discs.

 

Bedding fresh pads is also good medicine.

[68C]

I think I agree with Craig, I have heard that using loads of heavy braking and then parking up outside the pub can mean the section of the stationary disc under the pads will stay hot for a lot longer than the section exposed to the air and can affect its hardness. The thinking is you should move the bike a little a few minutes after parking under these circumstances to even the disc cooling.

 

Some aircraft turbine engines suffer a similar heat effect except in this case the heat in a recently stopped engine moves upwards so the upper section of the shaft is hotter than the lower half. The shaft then 'bows' often to the extent that attempting a start will damage the engine. If you know you will have to start the engine in the timescale that shaft bowing may occour you have to cool the engine immediately after shutdown by dry motoring it or with some engines winding the prop by hand.

 

Judging by his name HelicopterJim can probably explain this better than me.

 

Put simply, don't park and walk off if the discs are hot.

[Kiwi_Roy]

Helicopter Jim only flys little choppers

Duck waiting for the incomming.

[helicopterjim R.I.P.]

Helicopter Jim only flys little choppers

Duck waiting for the incomming.

 

You mean like this "little chopper"?

 

[Kiwi_Roy]

Helicopter Jim only flys little choppers

Duck waiting for the incomming.

 

You mean like this "little chopper"?

 

 

Jim,

Stop messing us around, I'm sure the members would be interested to see what you do for a crust

Roy

[abouc]

I had a similar problem with the stock Brembo rotors. Freeing the bobbins provided some temporary relief, but was not a complete solution. Switching to EBC rotors completely cured the problem. It was NOT cheap, but was well worth the investment.

[Chuck]

I had this very same problem with the Norge, after 2 days of running in the rain in Nova Scotia, and of course, very light braking.

Checked them with a dial indicator, and they were only running out .002"

Went out and did a couple of stoppies and all was well. It's just pad buildup.

On a related note, I put a second rotor on a Jackal back in the day. Bought a "warped" rotor from a Ducati hot shot that just had to have the latest thing. Bead blasted the crap out of it, put on new pads, bedded them in, and it worked perfectly. I've done the same thing to airplane brakes that are pulsing. Pretty darn rare to actually have a warped rotor..

[Motormike]

Finally decided to bite the bullet and installed a pair of new EBC rotors and pads. Must admit, looks great. Test ride soon as weather allows. Yeah!

[GuzziMoto]

Actual warped rotors is very rare. I am sure it can happen, I warped a rear rotor on a dyno by absent mindedly hitting the rear brake to slow the rear wheel down, way back it was not unusual to have a Dyno-Jet dyno with no brakes. But in normal use it is pretty hard to generate the kind of heat required to warp a floating rotor.

Stuck float buttons and/or pad build up is almost always the real story. And both can be resolved without new rotors using one or more of the methods discussed or others. But new rotors can be fun. Personally I prefer the cast iron rotors like most Brembos to the stainless steel like most EBC's and other aftermarket rotors. I do not mind the rust after they get wet and the high coefficient of friction is my friend. But that is just me, enjoy your rotors. New parts like that or tires always seem to feel so much better then what they replaced.

Follow the bed-in instructions as best you can.

[gstallons]

Finally decided to bite the bullet and installed a pair of new EBC rotors and pads. Must admit, looks great. Test ride soon as weather allows. Yeah!

 

 

Do you own a torque wrench ? You have to torque thes fasteners and do it in a criss-cross pattern or you will have more trouble.