MTB brakes

Lew · Post by **Lew** » Sun Jul 17, 2022 10:24 am

On the off chance that there are some bike enthusiasts reading the 'vehicle' maintenance section on here.

My son has got one of them junior MTB bikes. It has got a rear disc brake with a 140mm disc rotor. Braking on it is dreadful so I would like to replace it with a hydraulic one, you can get complete sets for like 25 quid. Problem is, they are all using 160mm or over rotors, meaning the calipers which are fixed to the frame don't fit. Apparently there are caliper adaptors to make this work, but no matter how hard I google - I can't find out exactly what I need.

Thx

mikew1972 · Post by **mikew1972** » Mon Jul 18, 2022 8:58 am

I'm no expert and not even a keen rider but I have a couple of bikes with cable operated disc brakes and find it hard to believe you can't get enough REAR, no less, braking on a kids bike from a 140mm disc brake and that you can get much more braking by switching to hydraulic. but you could get a whole lot more complicity and potential trouble from leaks, running out of fluid, pinched / damaged lines etc. Very keen amateurs / pros use hydraulic because they find it gives more precise braking and more feel rather than more braking power.
Sure switching to 160mm will give you some more braking but I'd fix what you've got as it should be more than up to the job if working correctly. Quality of parts also makes a big difference. My mountain bike has from Go Outdoors has adequate braking but my hybrid from Decathlon is far better quality and gives fantastically strong and precise braking. Both are cable operated disc, carefully adjusted by the same person (me) and cost the same to buy.
If nothing is obviously broken, seized or poorly adjusted my best guess would be oil contamination on the rotor and pads, probably from the chain. I'd fix this by cleaning the rotor with brake parts cleaner (or petrol or cellulose thinners etc. if you don't have any brake parts cleaner), fit new pads and make sure everything is correctly adjusted.

Lew · Post by **Lew** » Sun Jul 24, 2022 9:01 am

Thanks Mike,

I tried servicing the disc & pads but I find the braking performance really poor, certainly after a few weeks. My lad takes it to school down a fairly steep hill & rough track and it needs to stop better. The cable design on the bike is really poor (I think this is the same for a lot of these 'cheapo' kids MTB bikes), most of the brake cable to the back actually runs along the frame without an outer cable. It doesn't stop the ingress of dirt & water on the two remaining small bits of outer cable and especially the last bit of outer cable makes an almost 180 degree loop in a very confined space. I was just hoping a closed system like these hydraulic brakes would be much better.

mikew1972 · Post by **mikew1972** » Sun Jul 24, 2022 1:08 pm

No worries.
A few more thoughts for you. Hope something helps.

One thing you could maybe do is replace the cable with one that has an outer all the way along and zip tie it to the frame where required?
Fit a longer brake leaver, especially if the existing one is a 1 or a 2 finger type?
If you search ebay for "140mm to 160mm caliper adapter" most of the results look like they might be what you are looking for?
Think you would then have to measure the bolt spacings on the old and new caliper to pick which of the results is the right one for you? Some of the results have diagrams showing what you have to measure which you can then reference to the descriptions in other results.

Bob225 · Post by **Bob225** » Tue Jul 26, 2022 9:11 am

Don't buy cheap hydraulics they are not worth it, as above you can get adapters I had Shimano 160mm cable disc brakes front and rear, leavers are make a big difference to the braking

have a look on www.chainreactioncycles.com

ericmark · Post by **ericmark** » Mon Jan 02, 2023 5:36 pm

I took my bike down Symonds Yat Rock, on the road, and just a good job nothing coming up, I could slow down, but not stop, and what had happened was the cam had reached end of travel, so brakes seems good, until you tried to stop fast.

I realised there is a Allan key adjustment on the disc pads, this needs to be kept spot on, the new mountain bike also has mechanical disc brakes, and that is the same, keep them adjusted and they are really good, neglect routine servicing and you have a problem.

But hydraulic can also have problems, specially if bike not kept upright, my bike folds and goes in the back of the car, could not do that with hydraulic.

moderator2 · Post by **moderator2** » Mon Jan 02, 2023 6:31 pm

ericmark, Please stop digging up old posts.