Brake 'Fade' ?

James_Russell

I had a lovely ride last night, I went from my home (epsom downs) through headley, box hill, dorking, ranmore common, wotton, westcott etc and ended up doing 40 miles (which is a lot considering the severity of the hills. It was my first challenging ride in a month or two. heres a pic from the summit of box hill (I know I'd get a better one in dawn light)


..Thats a good pay off for climbing box hill!
later on in the ride, I was descending a terrifying road in ranmore which is an 18% downhill gradient with a hairpin at the bottom. I left it a bit late to brake, and found myself heading straight for the steel barrier- I applied the brakes very hard, I squeezed until the levers touched the bars, but the brakes just howled and I hardly got the speed down enough to turn into the corner. It really was scarey, I've never had the levers touch the handlebars before and I have a habit of braking late and hard. They both did it simultaneously at this crucial moment.
The brakes are schimano M525 hydraulic brakes from 2005 with 160mm rotors. I'm using Aztec pads ( sold to me by my LBS for £17 a pair, with the schimano ones I usually use being £8 ) The brakes have felt slightly spongy ever since, but this improved when I stopped and pumped the levers a few times. I don't know whether to blame air in the system, the new pads or some dodgy seals or anything, I don't want to have this happen again!
Please Help!
-James

supersonic

Sound like they need bleeding. Also check the pads are not contaminated.

James_Russell

the mineral oil is two years and a half (5200 miles) old, should I use new?
Is there a chance air was drawn into the system at that moment for some reason, as I've never depressed the levers by more than half way to the bars before. I was hoping I could blame the pads as they are the most expencive I've ever used and don't seem to work as well as the cheap ones. the cheap ones were always silent too, never got any squeal.
I bleed by putting a clear tube on the bleed nipple, slacking the nut off and pumping fluid through until there are no bubbles right? and I top up at the resevoir as I go?
just checking, i've never done this before.
-James

supersonic

If the brake starts to overheat when there is air in the system, as it can do on long descents, the lever can go spongey as the the air expands rapidly. The Shimanos are pretty easy to do - full instructions available on their site and I do believe there is a guide here too. Always use fresh oil.

James_Russell

Okay thanks very much

James_Russell

yeah according to my dad I was boiling the fluid. I think this effect was exaggerated by the fact the brakes needed bleeding anyway, although I can't get the levers as responsive as they were before. must still be some air in there, pads aren't contaminated.
-James

dave_hill

When you've finished bleeding the brakes, pump them right up then strap the levers back to the bars (you can use cable ties or some velcro straps) and leave them overnight.

This will allow any micro-bubbles left in the system to rise up to the reservoir and should help eliminate any sponginess - you can assist their movement by lightly tapping the hoses with a small spanner or somesuch, starting at the caliper and moving up towards the reservoir.

I've used this trick many times over the years on both MTBs and motorbikes and it really does make a difference!

dave_hill

When you've finished bleeding the brakes, pump them right up then strap the levers back to the bars (you can use cable ties or some velcro straps) and leave them overnight.

This will allow any micro-bubbles left in the system to rise up to the reservoir and should help eliminate any sponginess - you can assist their movement by lightly tapping the hoses with a small spanner or somesuch, starting at the caliper and moving up towards the reservoir.

I've used this trick many times over the years on both MTBs and motorbikes and it really does make a difference!

dave_hill

When you've finished bleeding the brakes, pump them right up then strap the levers back to the bars (you can use cable ties or some velcro straps) and leave them overnight.

This will allow any micro-bubbles left in the system to rise up to the reservoir and should help eliminate any sponginess - you can assist their movement by lightly tapping the hoses with a small spanner or somesuch, starting at the caliper and moving up towards the reservoir.

I've used this trick many times over the years on both MTBs and motorbikes and it really does make a difference!

dave_hill

Apologies for the multiple posts, my server threw a wobbly at the crucial moment... :oops:

James_Russell

thanks for that tip, I spent two hours this morning trying to get the levers to feel right and it just isn't happening- I will try this! I'm using halfords mineral oil £5.49 for a liter, seems better value than all the others considering my mates are probably going to need their brakes doing too! and because I'm an amateur I've already used enough fluid to fill the brake system three times over so I'm glad I got the halfords stuff.
-James

dave_hill

Another good dodge is to use the "bottom up" brake bleeding method.

You need to get hold of a large plastic syringe (vets can usually supply them) and a short length of rubber or pvc tube which fits over the syringe nozzle at one end and the bleed nipple of the caliper at the other.

Fill the syringe with brake fluid, then attach it to the bleed nipple. Remove the reservoir cap and have plenty of rags handy to mop up any spills. Now open the bleed nipple and gently pump fluid into the system from the caliper end.

When the system is full, close the bleed nipple and replace the reservoir cap. Job done. Provided that you made sure there was no air in the syringe to start with the system should have fresh fluid in it with no air.

NikB

I can send out a syringe if needed!

RIKO

Dave, thought i'd try that trick of strapping the levers down and leaving overnight my brakes were well bled and rebuilt recently so they were pretty good anyway BUT you're not wrong it certainly does make a difference great tip!

pyro_maniac

does the bottom up method work better then normal bleeding?
i am a newbie to hydraulic discs too so am looking at any possible tips and hints

nicklouse

pyro_maniac wrote:

does the bottom up method work better then normal bleeding?
i am a newbie to hydraulic discs too so am looking at any possible tips and hints

yes, no, maybe.

what brakes.

read the manual.

pyro_maniac

ok, i have shimano brm-485 brakes, the manual ays to bleed in the normal way
just didnt know if the bottom up method was an easier/better way to do it

James_Russell

to be honest I'd never heard of it before, but I suppose (logically) it should work and makes better sense that the traditional method- If you keep the syringe 'needle' end down for a few minutes beforehand all the air should rise to the piston end, so provided the syringe volume is enough to fill the whole system it should work. I'll try it on the rear brakes and get back to you (provided I can find the syringe) I may try the science dept. at my college, failing that I'll see If I can get one off NIKB or my vet.
By the way, DAVE_HILL's hint worked for me- I used a slice of inner tube to hold the levers to the bars overnight and it worked a treat!
thanks guys,
-James