Help with brakes please

[nimbus145]

Hi

i have just replaced my rear brake shoes. Once bled and back together when I press the brake pedal it goes almost to the floor a second press of the pedal and it applies the brakes immediately just as it should and feels good and firm. Any further pedal push and it remains firm but if left for any length of time again on the first push pedal goes almost to the floor and firms up again on second push.

i thought I hadn’t readjusted the rear brakes correctly as it felt like the first push was taking up ‘slack’ and then on the second push the shoe was in the right place so worked ok. I used the adjuster until the brakes just bit and backed off a bit. This has made no difference.

i am not losing any brake fluid.

Does anybody have any ideas?

many thanks

Nimbus145

[glang]

Try the brakes with the handbrake well on to discount the possibility that theres still 'play' in the shoes. If you leave the handbrake on once the pedal has gone solid it should stay good no matter how long you leave it. However if it still goes soft it looks very much like youve still got air in the system and you need to repeat bleeding starting with the closest front calliper and finishing on the furthest drum....

[Clive]

Did the brakes do this before changing the rear shoes? And did you do anything else to the brakes?

When adjusting the shoes, it is best to disconnect the handbrake cable, adjust the shoes, he adjust/reattach the cable. Also did you check the wheel cylinder moves OK on the backplate?

However, I wonder if the seals in your master cylinder are beyond their best from the sinking pedal bit. It may be worth getting a new seal kit and fitting that.

 

[glang]

ooops looks like I got the bleeding order wrong! First most distant then last the closest, although the end result is the same....

Clive if it was seals surely you wouldnt be able to pump it up and hold pressure would you?

[nimbus145]

Hi all,

Thanks for the ideas, I thought the same about the seals.

Hopefully I’ll get some time at it today and will work methodically through again.

Thanks

Adam

[drofgum]

Quoted from glang-

ooops looks like I got the bleeding order wrong! First most distant then last the closest, although the end result is the same....

Clive if it was seals surely you wouldnt be able to pump it up and hold pressure would you?

Gentle pressure on the pedal will often show worn seals before they fail so badly that a hard push won't apply the brakes. The symptom is a sinking pedal when the pedal is held gently. Extra pressure will force the lips of the seals out against the cylinder walls for an effective seal.

Regards,

Paul

[glang]

makes you wonder though why the seals would start doing it after just changing the shoes? Think its more likely to be air although now Im not sure why it needed bleeding in the first place if just putting in new shoes.....

[Clive]

It can happen if the seals are pushed into an area of the bore that has not been used much, and may be rough/corroded slightly etc. Typically when bleeding brakes on old systems, or possibly centering shoes/pads after a change? Or even a bit of dirt stopping the little end seal doing its job.

[glang]

well theres two easy checks for the seals:

Look in the reservoir when pressing the pedal for the first time. If the fluid level goes up as the pedal goes to the floor its a problem with the end seal.

And if theres oil from the end of the mc under the rubber covers its the main seal leaking....

[nimbus145]

Obviously ran out of time so it’s now become a job for next weekend.

Good question on why I bled the brakes, I forgot to include in the first message that I had spare new rear wheel cylinders and as the old ones looked pretty ropey I thought I just as well swap them over. These seem to be functioning as advertised so were discounted from the problem. 

Many thanks for all the other useful info.

[Nick Jones]

I think you may still have some air in the system.  It doesn't take much to produce the effect you describe

[Bitumen Boy]

Another problem with the M/C is that the various small parts that work in conjunction with the small valve seal on the end can wear, although this is more a problem I'd expect to see in a clutch M/C that had done a lot of miles. Residual air in the system is a definite possibility, certainly worth bleeding the system again.