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Poor front braking performance

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wornsprokets
the 900
the 900

Posts : 1154
Location : dublin

Re: Poor front braking performance

Post by wornsprokets on Tue 29 Mar 2016, 4:59 pm

@The_Wasp wrote:Right so fluid is flowing freely from the bleed nipple when using the brake lever and the pistons are stuck firm, I cannot push them back in by hand. I guess I didn't pay too much attention to their condition on the rebuild as they seem to have a multitude of pits on them.

I guess they're knackered and need replacing rather than the master cylinder?
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wornsprokets
the 900
the 900

Posts : 1154
Location : dublin

Re: Poor front braking performance

Post by wornsprokets on Tue 29 Mar 2016, 5:03 pm

Get old brake pad put them back in get two big screwdrivers to push  pistons back in and out (take off mastercylinder cover and put rag around it in case of spills) maybe pistons can be cleaned with a very light sand paper also
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Stooby2
Godzilla
Godzilla

Posts : 238
Location : Croydon, Sarf Laaandan

Re: Poor front braking performance

Post by Stooby2 on Tue 29 Mar 2016, 5:15 pm

I bet they didn't clean the seal grooves out before fitting new seals. Corrosion and other crap builds up behind the seal and pushes it out - a tiny amount, but when that happens all the way around, the seal grabs the piston hard.

If you can get pistons out, take out the seals and have a good look at the grooves they sit in.
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The_Wasp
Four's a...something...
Four's a...something...

Posts : 150
Location : Crewe, Cheshire

Re: Poor front braking performance

Post by The_Wasp on Tue 29 Mar 2016, 8:28 pm

Well it was me that did the rebuild so if the cleaning wasn't done properly it'd be my fault. I did go around the grooves with a small scraper to get as much dirt out as I could. I've got some new seals and pistons coming as I believe the pitting is too bad to repair and I'll give the grooves an ever deeper clean this time to get it right.
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liverpool_f_
the 900
the 900

Posts : 355

Re: Poor front braking performance

Post by liverpool_f_ on Wed 30 Mar 2016, 12:30 am

The pistons have a coating if it is a Brembo model. It starts to wear away after prolonged use. Your symptoms sound exactly like mine. Replacing the pistons with new coated ones cost me £20 per piston which isn't too bad. I don't know if you can replace them with the cheaper non-coated ones but probably not worth it for saving a few quid.
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Stooby2
Godzilla
Godzilla

Posts : 238
Location : Croydon, Sarf Laaandan

Re: Poor front braking performance

Post by Stooby2 on Wed 30 Mar 2016, 9:37 am

@The_Wasp wrote:Well it was me that did the rebuild so if the cleaning wasn't done properly it'd be my fault. I did go around the grooves with a small scraper to get as much dirt out as I could. I've got some new seals and pistons coming as I believe the pitting is too bad to repair and I'll give the grooves an ever deeper clean this time to get it right.

The last time I did mine it took about 15 minutes a groove to get them clean, using a small screwdriver and a Dremel with a round wire brush attachment.

If you have the red brake grease, give the seals a good coating before you put them back and smear the pistons lightly as well.
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The_Wasp
Four's a...something...
Four's a...something...

Posts : 150
Location : Crewe, Cheshire

Re: Poor front braking performance

Post by The_Wasp on Mon 04 Apr 2016, 5:50 pm

Well all is said and done, the pistons from M & P came the other day and I have fitted them to the bike. They were coated pistons so not bad at all.

The old dust seals were showing signs of shredding so that is likely the root cause of the sticky brakes. Any way I gave the grooves a good clean out with a a bent screwdriver and a rag, a toothbrush and plenty of brake cleaner to get any crap out of there. I popped the new seals in with some red rubber grease and then the pistons. One went in fine but the smaller on didn't want to go in no matter how much grease and pressure was applied. I think one of the fluid seals was badly made as I popped in one of the old ones (which was in perfect condition on inspection) and it just went straight in.

Anyway I filled the system from the bottom up and doubly checked there was no air in there. The wheel spins more freely than before and most importantly the braking is greatly improved. I can actually perform emergency stops again and I suppose this'll improve more once the pads bed in better, they were probably at an angle before so they've likely worn funny.
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davebike500
Silver Bullet
Silver Bullet

Posts : 103

Re: Poor front braking performance

Post by davebike500 on Thu 07 Apr 2016, 8:02 am

AS 1st post the leaver is firm then no amount of bleeding will make a difference
either:-

1 sticky piston
2 calliper not sliding properly (red or silicon grease)
3 pads new not matching worn disk
4 Pads not fitted properly or sticking anti rattle spring damaged  misplaced

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Re: Poor front braking performance

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