Binding Brakes

pos · Mar 22, 2010

Hello,

It turns out that my front brakes are binding quite badly - which is no doubt the cause of my power loss (as well as gear box oil), particularly on hills. The level in the brake fluid reservoir is fine and it doesn't bubble when the brake pedal is pressed. I am assuming that at least one piston on both callipers (over rated 110 callipers on my 90) has stuck which is making my wheels bind. If I whip the calliper off and then stamp on the brake pedal until the pistons pop out of the calliper (or even if I have to pull them out), should a good clean of the housing and each piston with a wire brush have them back in order? Also, what should I lubricate them with when I refit them? I'm thinking copper grease but I'm not too sure.

Thanks in advance!
-Pos

G-man · Mar 22, 2010

are you sure its the callipers?

[JP] · Mar 22, 2010

when rifiting the pistons, just lubricate with the old brake fluid

G-man · Mar 22, 2010

[JP];1037149 said:
when rifiting the pistons, just lubricate with the old brake fluid

surely you mean new clean brake fluid!

to be honest if you don't know exactly what you are doing don't go taking the callipers apart!

pos · Mar 22, 2010

I'm not sure it's the callipers no, but considering that the brakes are binding that'd be my first port of call. I'll whip them off tomorrow, pop the pistons out and re-assemble them cleaned up and lubed. What else can cause binding brakes besides stuck pistons?

-Pos

G-man · Mar 22, 2010

i have seen brake hoses, brake pipes, servo and mastercylinders all cause sticky brakes

Sean · Mar 22, 2010

treat yerself to some new pistons and seals, only use a wire brush on the casing to get it clean - it'll wreck the pistons

pos · Mar 22, 2010

G-man said:
i have seen brake hoses, brake pipes, servo and mastercylinders all cause sticky brakes

So the best thing to do then would be to uncouple the callipers from the hoses and pump fluid through the system to check that they run through properly? The back brakes don't bind at all. How would I diagnose a faulty servo?

-Pos

pos · Mar 22, 2010

Sean said:
treat yerself to some new pistons and seals, only use a wire brush on the casing to get it clean - it'll wreck the pistons

I believe I may have to do that. I was thinking about wire brushing the pistons on the leccy grinder, is that not a good idea then?

G-man · Mar 22, 2010

its not the fluid getting through that would be the problem its would be getting back away from the calliper, i doubt it would be serco in your case (it would cause the problem on all 4 wheels)

the most likely thing is rusty pistons on your callipers. to eliminate the hydraulic side crack the bleed nipples off to release any possible pressure then try to spin the wheels, if they still bind its yer callipers

Sean · Mar 22, 2010

pos said:
I believe I may have to do that. I was thinking about wire brushing the pistons on the leccy grinder, is that not a good idea then?

are they that corroded or dirty looking ?

Shifty1962 · Mar 22, 2010

Never use a wire brush, wire wool. scotch brite, or brillo pad on the pistons or the bores. They are easily scratched and will always leak if you do scratch them. Use some fine wet/dry paper (almost like flour paper)and plenty of brake fluid to polish the pistons and bores. Only use your fingers and dont wrap the paper round any kind of former. If there is serious evidence of corrosion, pitting, or deep scratches that wont easily finger polish out, then its time for a new calliper. Once finished thoroughly clean the callipers with clean brake fluid and blow through with compressed air to get any residue out. Then flush again with more clean brake fluid.
If you're going to the trouble of popping the pistons I'd fit new seals while they are out.
Only use clean brake fluid when reassembling. Cooper grease is a big no-no as it is abrasive and lithium based grease will attack the seals.

pos · Mar 22, 2010

G-man said:
its not the fluid getting through that would be the problem its would be getting back away from the calliper, i doubt it would be serco in your case (it would cause the problem on all 4 wheels)

the most likely thing is rusty pistons on your callipers. to eliminate the hydraulic side crack the bleed nipples off to release any possible pressure then try to spin the wheels, if they still bind its yer callipers

Cheers for the tip, I'll do that tomorrow

-Pos

pos · Mar 22, 2010

Sean said:
are they that corroded or dirty looking ?

I don't know, I havent whipped the callipers off yet!

pos · Mar 22, 2010

Shifty1962 said:
Never use a wire brush, wire wool. scotch brite, or brillo pad on the pistons or the bores. They are easily scratched and will always leak if you do scratch them. Use some fine wet/dry paper (almost like flour paper)and plenty of brake fluid to polish the pistons and bores. Only use your fingers and dont wrap the paper round any kind of former. If there is serious evidence of corrosion, pitting, or deep scratches that wont easily finger polish out, then its time for a new calliper. Once finished thoroughly clean the callipers with clean brake fluid and blow through with compressed air to get any residue out. Then flush again with more clean brake fluid.
If you're going to the trouble of popping the pistons I'd fit new seals while they are out.
Only use clean brake fluid when reassembling. Cooper grease is a big no-no as it is abrasive and lithium based grease will attack the seals.

Cheers Shifty. I'll get on with them tomorrow and I've taken your advice on board. I'll get some fine paper to clean them up.

-Pos

Binding Brakes

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