hydraulic brake problem after pad change

fatbob109

Hi - I took my bike to the local mechanic who diagnosed that I needed new pads for my Shimano Deore LX Hyd brakes.

A few weeks later I noticed that the front brake was spongy and had almost no stopping power so I took it back and they claimed they bled the brake. Got it back earlier this week and the problem persists, but also has a new problem in that the disk now squeals after I start riding it. I dab the brake lever, the squeal goes away momentarily then it returns. The mechanic reckons that a seal has gone and I will need to replace the whole brake system.

Any ideas?

thanks.

cooldad

Find a new mechanic.

But you don't need a mechanic to tell you you need new pads - just look at them and if they are very worn change them. That would have nothing to do with spongy brakes though.

The Rookie

If it's leaking it would explain why it needed bleeding, in my experience Shimano NEVER need bleeding unless yo open the system or have a leak.

Pushing the pistons back (to fit new pads) on old callipers can damage the seal, either due to corroded Pistons or crud not being cleaned off before pushing them back.

fatbob109

Thanks for the answers. for clarity, the pads were changed by the mechanic and then the problems started. I can't see any leaks.

swod1

or when the bike shop fitted new pads you've ridden the bike and something like dirt etc has got on to the pads to make the squeal noise.

Did you bed the pads in when you got the bike back from the shop?

fatbob109

Yes I did bedd the pads in.

Took it to another bike shop today for a second opinion. They couldn't see any leaks and thought that there was nothing wrong with the brake. Then they decided to remove the cover of the reservoir. The screws were stiff with corrosion and when they finally managed to get the cover off there was no oil in the reservoir! and the squeal was coming from the front wheel not being seated into the forks properly.So a bit of crappy service from the original guys and a very friendly and attentive service from the new guys. Hmm, wonder who I'm going to use in the future...

Thanks for all your time and interest.

cooldad

Yep.

cooldad wrote:

Find a new mechanic.

But you don't need a mechanic to tell you you need new pads - just look at them and if they are very worn change them. That would have nothing to do with spongy brakes though.

Rightarmbad

The Rookie wrote:

If it's leaking it would explain why it needed bleeding, in my experience Shimano NEVER need bleeding unless yo open the system or have a leak.

Pushing the pistons back (to fit new pads) on old callipers can damage the seal, either due to corroded Pistons or crud not being cleaned off before pushing them back.

Shimano do need flushing after a 2-3 years.
What you will notice is a small increase in lever free movement and less snappiness of the lever return.
Depending on how hard you push them you may also note a little bit of pumping up after hard use.

The treatment is to take pads out and pop in a bleed block, put cup in lever and open bleed valave and let out any accumulated water in the caliper, it pools there as it is generally the lowest spot.
You will easily see the water and a bit of dark contamination come out and when it comes clean close it up and then fit a syringe and pump in some new fluid from the bottom until what comes out the top looks nice and clean.
You may need to empty the cup once and the fluid will generally look dark with a bluey tinge. keep feeding new fluid from the bottom until it looks nice shimano red, close off the bottom bleed valve, pump the lever until no more bubbles come out and remove cup and close the system.
You will feel immediately a much snappier lever movement and slightly less dead zone than before.
Go ride for another 3 years and repeat.

Shimano use ceramic pistons so don't corrode, but they do get blackened crud accumulating around them.
As always clean this before pushing back pistons.

kinioo

fatbob109 wrote:

Hi - I took my bike to the local mechanic who diagnosed that I needed new pads

thanks.

I would call him a doctor - what a genius !!

kinioo

fatbob109 wrote:

. Hmm, wonder who I'm going to use in the future...

Thanks for all your time and interest.

I would use your hands and a bit of DIY next time, its nothing too complicated.

An you can always ask here before you do anything. There is a bunch of guys here with massive knowledge (Rookie or CD etc.) who should be able to help (I guess )

C.

poah

brakes can squeal after new pads if they are a different compound. easy to sort though just sand the discs to remove the old pad residue.

swod1

POAH wrote:

brakes can squeal after new pads if they are a different compound. easy to sort though just sand the discs to remove the old pad residue.

I had squeal on a back brake one time due to a bent disc which then glazed a new set of pads as you couldn't centre the caliper didn't notice at the time wanted to ride so put in new pads, I take more care now.

The Rookie

Rightarmbad wrote:

The Rookie wrote:

If it's leaking it would explain why it needed bleeding, in my experience Shimano NEVER need bleeding unless yo open the system or have a leak.

Pushing the pistons back (to fit new pads) on old callipers can damage the seal, either due to corroded Pistons or crud not being cleaned off before pushing them back.

Shimano do need flushing after a 2-3 years.
What you will notice is a small increase in lever free movement and less snappiness of the lever return.
Depending on how hard you push them you may also note a little bit of pumping up after hard use.

The treatment is to take pads out and pop in a bleed block, put cup in lever and open bleed valave and let out any accumulated water in the caliper, it pools there as it is generally the lowest spot.
You will easily see the water and a bit of dark contamination come out and when it comes clean close it up and then fit a syringe and pump in some new fluid from the bottom until what comes out the top looks nice and clean.
You may need to empty the cup once and the fluid will generally look dark with a bluey tinge. keep feeding new fluid from the bottom until it looks nice shimano red, close off the bottom bleed valve, pump the lever until no more bubbles come out and remove cup and close the system.
You will feel immediately a much snappier lever movement and slightly less dead zone than before.
Go ride for another 3 years and repeat.

Shimano use ceramic pistons so don't corrode, but they do get blackened crud accumulating around them.
As always clean this before pushing back pistons.

Nope, all completely wrong for my M765, no need to bleed, they stayed exactly the same as logic would suggest, alloy Pistons and no cups, good effort though!

Rightarmbad

The Rookie wrote:

Rightarmbad wrote:

The Rookie wrote:

If it's leaking it would explain why it needed bleeding, in my experience Shimano NEVER need bleeding unless yo open the system or have a leak.

Pushing the pistons back (to fit new pads) on old callipers can damage the seal, either due to corroded Pistons or crud not being cleaned off before pushing them back.

Shimano do need flushing after a 2-3 years.
What you will notice is a small increase in lever free movement and less snappiness of the lever return.
Depending on how hard you push them you may also note a little bit of pumping up after hard use.

The treatment is to take pads out and pop in a bleed block, put cup in lever and open bleed valave and let out any accumulated water in the caliper, it pools there as it is generally the lowest spot.
You will easily see the water and a bit of dark contamination come out and when it comes clean close it up and then fit a syringe and pump in some new fluid from the bottom until what comes out the top looks nice and clean.
You may need to empty the cup once and the fluid will generally look dark with a bluey tinge. keep feeding new fluid from the bottom until it looks nice shimano red, close off the bottom bleed valve, pump the lever until no more bubbles come out and remove cup and close the system.
You will feel immediately a much snappier lever movement and slightly less dead zone than before.
Go ride for another 3 years and repeat.

Shimano use ceramic pistons so don't corrode, but they do get blackened crud accumulating around them.
As always clean this before pushing back pistons.

Nope, all completely wrong for my M765, no need to bleed, they stayed exactly the same as logic would suggest, alloy Pistons and no cups, good effort though!

Your are on a couple of generations old technology there. Newer models have a completely different topology around the caliper, ceramiv pistons and also carry much less total fluid volume to save weight.
This places somewhat more stress on the fluid, just ask any xtr race owners how they deteriorate after a heavy season.
Next time i open one up and change fluid, if I remember I will take a photo of the fluid for you to see.
As for water contamination, maybe you never ride in the wet?

As you have never had to flush yours, you probably have adjusted to the changing feel of the brake, so don't realise the need for service.

The Rookie

Indeed I am and look at the model the OP is using, same gen as mine, which is why my observations are relevant and yours not.