New rotors or not

kalex

Retro Guru
I've got shimano xt brake set and didn't realize how bad the brakes had gone as not ridden for a while. The rear I can pull fully on and it eventually slows me. The front is better but not brilliant. I think I've just got use to them and was shocked when I used my son's stumpy and I nearly went over the bars.

I've fully flushed them with new fluid and they're still rubbish ( no bubbles coming through in to the reservoir thingy). I've ordered new pads but I'm hoping to keep the rotors (shimano rt76).

I've removed the rotors and run some wet and dry over and gave them both a good clean and rub with brake cleaner.

I've also measured thickness with vernier calipers and still loads of use in them

Do you think what I've done with the rotors will be ok or would you replace before I put these new pads in.
 

mattr

Old School Grand Master
Just be aware that some brake cleaners contain a light oil, ok on cars, terrible for bikes

Check there are no leaks on the piston seals, some models/batches of shimano calipers had some leakage issues (loss of power and contamination of the pads/rotors. You'll have to google for which ones!
 

kalex

Retro Guru
Thanks for the tips as it was holts car brake cleaner I used. I may take them back off and clean with petrol then.

All calipers and joints are dry with no oil even before I did some maintenance on them, so hopefully there ok.

The feel from the brake levers are good, it's just that when the levers are pulled as firm as I can I still only come to a gradual stop. I can't even get it to lock up when riding on grass with my weight over the bars
 

ishaw

Gold Trader
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I have had this issue with 2 sets of brakes. Shimano deore had what I've seen referred to as a micro leak. Levers always felt fine, but the rear brake was awful until I replaced the calliper and pads and cleaned the rotor with bike specific disc brake cleaner. Fine after that, the micro leak just dropped enough fluid to maintain a level of pad contamination. It was only really noticeable if the bike wasn't ridden for a period of time.

The other set are maguras. No leaks as far as I can tell but it always took an age for them to actually work when riding. Ive changed pads, bled and rebled them countless times, cleaned the rotors and no change. I think the rotors need changing as they are the only part I haven't, but despite them being barely used, I think its the only option.
 

MartinYorkshire

Retro Guru
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Thanks for the tips as it was holts car brake cleaner I used. I may take them back off and clean with petrol then.

All calipers and joints are dry with no oil even before I did some maintenance on them, so hopefully there ok.

The feel from the brake levers are good, it's just that when the levers are pulled as firm as I can I still only come to a gradual stop. I can't even get it to lock up when riding on grass with my weight over the bars

As far as I'm aware, it's not possible, under normal circumstances, to contaminate rotors to such an extent that they cannot be cleaned. I would recommend isopropyl alcohol, as strong as you can find. I get mine on Amazon and it lasts ages. Whilst not pleasant to use, its far less obnoxious and safer than petrol. Nitrile gloves are also helpful to prevent oil from your fingers contaminating the rotors.

What type of pads are installed, organic or sintered? Glazed perhaps? In any case, it wont hurt to give them a light sanding over some emery paper. I use 200 grit for this and it takes a few just a few strokes on a flat surface (outside, toxic dust). Personally I leave the dust on them when I reinstall as it helps them bed back in.

Is the surface of the disc showing that the pads are centered correctly on the rotor?

Lastly, are you breaking the pads in enough? I know a lot of people say it's not necessary and its true it comes down to riding style, but in my view theres no reason not to do it and in my experience it definitely does work. Around 20 strong braking applications per wheel from around 15mph to zero to get the discs heated and the pads acting correctly over the braking surface.

I'm sure you've thought of the above, so please treat this as a reminder or for the benefit of others if so.
 

kalex

Retro Guru
No offence taken on all the above at all.

All pads were positioned as good as it gets on the rotors.

I didn't mention ( as these are being replaced ) that I'd taken the old pads out and done the sand paper trick as this has worked before and I fully presumed it would have done the trick this time. I was that confident of this working I didn't even try them before I went on a longish ride ( that's where I found out how crap they still were ).

I'd only cleaned the rotors with meths after the sand paper on pads at that moment. As like you the rotors are hard to contaminate as any oil residue will just sit on the surface, that's why I just used meths.

As they braking was still rubbish I took the rotors off to use brake cleaner as I wanted to be fully sure they were clean and oil free before replacing and using new pads.

The old original pads are shimano g04s sintered so that's what I've purchased again.
 

kalex

Retro Guru
I've got nail polish remover handy but Google says that may not be as good as pure acetone.

I've cleaned them again with petrol this morning. I'll wait till these pads come and see what result I get.
 

MartinYorkshire

Retro Guru
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No offence taken on all the above at all.

All pads were positioned as good as it gets on the rotors.

I didn't mention ( as these are being replaced ) that I'd taken the old pads out and done the sand paper trick as this has worked before and I fully presumed it would have done the trick this time. I was that confident of this working I didn't even try them before I went on a longish ride ( that's where I found out how crap they still were ).

I'd only cleaned the rotors with meths after the sand paper on pads at that moment. As like you the rotors are hard to contaminate as any oil residue will just sit on the surface, that's why I just used meths.

As they braking was still rubbish I took the rotors off to use brake cleaner as I wanted to be fully sure they were clean and oil free before replacing and using new pads.

The old original pads are shimano g04s sintered so that's what I've purchased again.

Sounds like it has to be pad contamination, so hopefully the new ones sort it out for you.
 
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