Fluctuation of brake effort

[KTM28]

My front brake feels like it works very well and there is plenty of life left in the pads but when put on the roller brake test it indicated slight fluctuation of brake effort.

Passed the M.O.T but got an advisory notice.

Any ideas what would cause this fluctuation?

[MarkJ]

Discs starting to warp probably.

After a fairly sedate ride, are any of the discs really hot? One of my calipers has a siezed slider pin and has caused one of my discs to warp - the warped disc is really hot after my commute but the other is just luke warm.

Check you don't have a sticking brake piston or siezed sliding caliper.

[MarkJ]

Or, it could be crap that's got inbetween the disc and wheel, pushing a part of the disc outwards. You could take the discs off and make sure there's nothing behind there

[b-f-c]

[Walloper]

Disc/s warped.

I banjo-ed a Transit van a few years ago and the front brake was good-bad-pump-pump-good-bad-pump-pump-good......

I posted on here and it was suggested the disc was warped.
(Why didn't I think of that. )

New disc £120 and things were back to normal.

Motorbikes a stupid animals sometimes.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[KTM28]

Thanks for the answers.

I have never felt the discs after a ride but will do next time to see how hot they are.

When the bike is on the stand the front wheel rotates freely and does not bind at all but it wouldn't be a bdd idea to take the disc off and service the caliper.

A new disc is just under £50 including postage.

[stinkwheel]

[DrDonnyBrago]

I did this test a few weeks ago, after a "sedate" ride not a redlining down back roads type ride and one of my discs was quite a lot warmer than the other. I don't get pulsing or dodgy braking or anything but clearly one caliper is dragging more than the other.

What sort of things cause brakes to drag?? Dirty pistons, corroded pins/pads, dirty seals???

[Walloper]

[KTM28]

I wish I had read your post before I went out for a ride donny.
I felt the front disk when I got back and burnt the skin off my hand.











Not really, so thanks for the warning.

I cannot detect pulsing under braking and the brake is certainly effective (the tester said so too).
Thing is I am a bit annoyed at having an advisory on the M.O.T cert as I am planning on selling it.

[b-f-c]

[Robby]

Stripping and cleaning the caliper, using one of the howtos in this very forum, is a good start and doesn't cost anything. It is possible that the disc is warped and the caliper is full of crud and sticking. A good clean won't fix the warp (if there is one), but will let the caliper work more effectively and make the warp less obvious.

I don't think you said which bike, but if it's more than about 5 years old then there's a chance of a fair bit of corrosion built up behind the piston seal, which leaves brakes feeling wooden and prone to seizing. Easily fixed though.
Remove the piston(s) from the caliper. If you have multiple pistons, remember which ones go in which hole. Very carefully remove the rubber seal in the caliper (I use a very fine bladed screwdriver and good light). Expect to see white dusty crap behind where the seal was. Carefully scrape this out (I'm not that careful, I should be, I use a slim screwdriver) until no more crap is coming out, give the whole thing a good rinse down with brake cleaner, then refit the seal and piston. You should put a smear of red rubber grease around the piston as you slide it in so that you lubricate the seal but don't contaminate the brake fluid, I never bother because I don't have any red rubber grease.

If the seal looks knackered, replace it. If it won't go back in and seems to have either shrunk or grown whilst out of the caliper, this can be fixed. If it seems to have shrunk, letting it soak in some oil or ATF for an hour plumps it right up and makes it seem bigger. If can be shrunk by putting it in front of a fan heater for a few minutes. This is probably a bad idea, but my brakes still work.

[DrDonnyBrago]

https://cgi.ebay.co.uk/Castrol-Classic-Red-Rubber-Grease-500g-/280453507235?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item414c54e8a3


Red rubber grease is great, £10 for a tub so big it will be buried with me .

[Noxious89123]

I had new pads fitted incorrectly by a garage once. Made the brakes feel very sharp. When I got home I touched the discs to see if they were hot. One was mildly warm.

The other made my leather glove smoke when I touched it
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[KTM28]

[Robby]