The rear disc (brake) on my 1100 Sport injection seems to be running with a slight friction so that the disc heats up and eventually the fluid heats up enough to give brake fade. (Without even using the pedal.)
I have since cleaned the calipers and lubed the pistons
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Re: 1100 Sport i rear disc
Topped-up the fluid and put in new pads. The wheel spins OK when up on the stand and the brakes don't jam or even seem sticky when you try them with the back wheel off the ground —ie: calipers grip and open again as they should. But on the open road the pads still seem to rub just enough to generate a warm to hot disc. (And the pedal has the right amount of play before the brakes come on.) Since working over the caliper and re-bleeding the brakes etc it seems a bit better (no fading) but it still runs a little warm to hot.
I'm wondering about a complete service for the rear Brembo popping the pistons out and changing the seals etc but before I do (and I have to say it all looks absolutely fine as it is), is there anything else I should be looking at / thinking of? The disc seems true and unwarped.
I know there's some anxiety about getting the right type of Brembo pad for the rear brakes on these particular bikes. Some are too thick? The parts book says Frendo FD 72 GG 222, (Guzzi part no: 27 65 46 10) and the caliper itself is marked 204531.03 if that means anything. (Is this the P32 type?) The pads I have are supposed to be the proper Brembo ones with the code 98.5031.50. Is there something I don’t know about this? ,FWIW this was a problem with some Sportis when they were new, to the extent that I saw a couple with completely smoked rear brakes, overheated due to brake drag. Mine never did it, so I don't know the root cause. In at least one of the instances I saw, the dealer replaced the entire brake system under warranty.
There was a separate and likely unrelated issue with rear brake disks that were machined with a step in the middle of the pad's foorprint on one side. At the time, I heard people attributing the brake drag problem to the disk problem, but I can't see a correlation. ,,,
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The rotors are doing their job by getting hot
the purpose of the brakes is to change the kinetic energy of the spinning wheels to heat energy by the friction between the pads and the rotors (discs) This conversion of energy from kinetic to heat is what slows down the vehicle and stops it . The pads have no way of staying off the discs except by the air flow that is dragged under the pad by the friction with the disc So to sum up discs get hot by converting energy and the more energy you have the hotter they get
(watch high speed race cars at night and you will see the discs are white hot or bright red )
Back discs are slightly different as they don't come on as hard as the front discs and they also are affected by hand brakes out of adjustment
IF you feel that the discs are getting too hot for the distance covered there may be a problem in that the callipers are binding on the mounting bolts (pins) and are not centralizing and hence one pad will be in contact all the time This pad will show more wear then the other pad on the same disc.
I know a bit about cars but being English I don't understand about rear rotors. I am guessing it is what we call brake discs or disc brakes.
Unlikely I would have thought the actual rotors or discs would be worn to a thickness of 6mm (which would be bad news) and perhaps you are referring to the thickness of the friction material?
It is only a relatively small percentage of braking effort that is exerted by the rear brakes so the rate of wear is much lower than the front brakes so it isn't unusual to discover new friction material isn't much thicker than about 8mm, though many are thicker and some are as thick as those at the front.
It is a general rule that is adopted by most brake and car manufacturer that replacement of friction material or disc pads is not required until there is only 3mm left and I have seen manufacturer's recommendations saying 2mm.
With 6mm of friction material still remaining which is two or three times the recommended minimum there would be no grounds to refuse certification.
Take your car to the service shop and the guy in the greasy overalls will ask himself if 6mm will last you until your next visit and if he is honest he will replace only after asking you what sort of mileage you cover. If he is normal he will grab the extra profit with both hands...
Rusty disc rotors can sometimes cause this issue, dirt as well, but often times it can be caused by riding your brakes, the braking friction material becomes hard if heated enough, resulting in a high pitched squeek or squeal as you pull up, this doesn't effect the normal operation of the brakes, and in the cases of "high performance" brake replacements that use harsher friction materials, is part of normal operation.
Please get the disc brakes checked, it may be jammed causing friction on disc causing the heat. For a try, you can take car on empty road and do some short sudden acceleration and hard braking. This way jammed disc brake may free up and solve your problem.
Remove the copper washers and plug the brake hose.
CAUTION: Do not remove the guide pins or guide pin boots unless a problem is suspected. The guide pins are meant to be sealed for life and are not repairable. Use Silicone Brake Caliper Grease and Dielectric Compound D7AZ-19A331-A (Motorcraft WA-10) or an equivalent silicone compound meeting Ford specification ESE-M1C171-A for re-lubing the caliper slide pins. Other greases can swell the guide pin boots, resulting in contamination and accelerated corrosion or wear of the caliper slide pin mechanism. Remove the rear disc brake caliper (2552).
Remove the brake caliper bolts (2W303).
Lift the rear disc brake caliper off the rear disc brake caliper anchor plate (2C220).
Inspect the rear disc brake caliper for leaks.
If leaks are found, disassembly is required. Refer to Caliper in this section.
Removal and Installation
NOTE: When removing the rear brake disc (2C026) in this procedure it is not necessary to disconnect the hydraulic lines. Remove the rear disc brake caliper (2552). For additional information, refer to Caliper in this section.
NOTE: If the rear brake disc binds on the rear parking brake shoe and linings, remove the adjustment hole access plug and retract the parking brake shoe and lining. Remove the rear brake disc.
CAUTION: Use a hub-mount brake lathe if necessary to machine the rear brake disc. For additional information on machining brake discs, refer to Section 206-00 . Measure the rear brake disc, and resurface as necessary. Install a new rear brake disc if beyond specification.
CAUTION: To prevent interference with rear disc brake caliper operation, install only the correct caliper bolt. NOTE: Make sure the stainless steel shoe slippers are correctly positioned. Install new slippers if worn or damaged. NOTE: When installed, the locator notch on the brake pads will be located at the upper end of the rear disc brake caliper. Install the rear disc brake caliper.
Install the rear wheel brake hose.
Connect the brake hose and install the caliper flow bolt.
Use new copper washers.
Bleed the disc brake caliper. For additional information, refer to Section 206-00 .
Install the wheel and tire assembly. For additional information, refer to Section 204-04 .
Check your rear brakes. If the rears are not adjusted or functioning properly, they will put more strain on the front brakes, thus heating the rotors up too fast. Since the rotors in the front cannot dissipate the heat fast enough, they will most likely continue to warp until the problem with the rear brakes is fixed. Always remember: when installing brakes you need to lube all of the key points. On disc brakes, lube the area where the pads sit in the hangar, make sure the clips are free of dirt and rust. Lube the pad backing (not the part that contacts the rotor!) and be sure to remove and lube the sliding pins on the caliper well. I personally like using AGS's Sil Glyde or CeramLube. These withstand heat the best. On drums, lube the metal side of the shoe that contacts the backing plate, and be sure to lube your adjusters well. Also, very important: if you have rear drums, make sure they are adjusted the right way, you dont want them to drag, but you dont want to go thru another set of front rotors again! Good luck, 99% of the time, too much focus is put on the front brakes and not the rears. Focus on the rears!
sounds like you have a piston freezing up i n the caliper or maybe even a faulty hose that has collapsed --take the caliper off, open the bleeder screw and try to press the piston in slowly with very little force--if it will not move in with ease--u have a bad caliper that will need replaced. also check the caliper slides make sure they are free