So following on from the earlier thread about the master cylinder we now will deal with the front caliper`s which are by far the most troublesome part of the brake system.

 

Lost count of the front caliper`s I dealt with in my time that were either seized partially or fully !! of the four pistons in each caliper it is very common for just one or two to be stuck fast and this is why the brakes seem to work but just not great, and given that many owners have already been told the brakes are rubbish on zeds it gets accepted.

 

So the biggest problem with stuck pistons is getting them out especially in DIY situation, however there is a way you can do it, slowly but it works, but first off buy a new seal kit from the big red brake company ( ebay) they have them all in stock usually and cost around £30 for 8 new seals, 6 new dust covers and 6 new snap rings, they even add in two new bleed nipple covers.

 

So take a look at the pictures what you will need to do is set your self up with a couple of G clamps, a bleed tube and a hose lock off clamp, also a big tray.

 

The method is simple enough, to use the brake system power to force them little buggers out of the caliper, now this can be done on your own but its much better to have two as you will see in a moment when dealing with particular stubborn one`s.

 

 

1) Ok fast forward to jacked up wheel off caliper off and disc off, now bolt the disc back onto the hub to hold it, lock off three pistons.

 

2) Unclip the outer dust seal snap rings, most likely these will be ripped and part of the problem, spray the inner seal face and piston edges with WD40 or similar.

 

3) So pressing the brake pedal is designed to push out the now single free piston, if it is seized it will require a lot of pushing, sometimes you will need to start the engine to help. Take it in several stages and it will come slowly and if not, do not worry, open the bleed nipple and put the pipe on into the tray, lock off the brake pipe clamp, this is important so no pressure goes back up to the master cylinder because it can flip the seals on it. With the nipple open and the hose locked off now use a pry bar against the piston to push it back into the caliper a bit, close the nipple and release the lock off and get the assistant to press again, a combination of pushing and pressing each time locking off the hose and opening the nipple will eventually release even the hardest piston.

 

4) So when it pops out and it will a fair bit of fluid will come out so hence the tray, put the hose clamp on to stop this.

You can now deal with the piston, it will look corroded and dirty but all it needs is cleaning off, that little bit of rust film is enough to make it stick in the seals.

 

5) Cleaning the piston is quite easy, get a damp cloth and wipe over, then with some T cut, its very slightly abrasive of course and will work magic on them, after they are cleaned up wipe it clean and put aside.

 

6) So now the harder bit, looking inside of the caliper there is seal that needs flipping out, use a small screwdriver VERY carefully no scratching the cylinder bore, stay within the seal recess. Once removed clean out with a clean cloth and almost certainly the leading edge will need rust cleaning off, this I normally do with some wet and dry paper, say 800 grit, this is a bit boring and makes your fingers ache but hey ho all in a good cause when all is clean and included in that is the recess that the dust cover snap rings fit in it time to rebuild.

 

7) So the seal needs dipping in some fresh brake fluid and dropped into place, this is quite easy and whilst your in there give the cylinder walls a bit of fresh fluid too. The piston needs some fresh fluid on too and away you go, pushing it into place can be a bit tricky as it needs to be well positioned to slot in, opening the fluid nipple with the clamp on will allow the air to escape as you push it back, do not push it fully back as you need to get the dust seal on and it is a pain if the piston is in too far. The snap rings can be troublesome but I acquired a knack eventually and really its a case of just doing it, it will try to ping off but once in place push the piston back and move the G clamp to that position, lock off the nipple and start the process all over again.

 

8) Whilst you doing the work keep an eye on the master cyliner as you don`t want that to drop too low, when one complete caliper is ready, bleed that one fully before moving on to the next one.

 

So there you have it, what you will find is brakes that now feel like they are connected to the car and work as they should, of course you can get rebuilt calipers off e-bay for around £150 but what`s the fun in that eh??

 

Happy bleeding.........

 

Jeff

 

 

 

 

 

Edited October 15, 201510 yr by JeffTT

Very good write up Jeff.

I did my front calipers 4 years ago with a seal kit from Bigg Red. I recently inspected them when I was changing the pads and the dust seals had perished! I made sure no oil or anything harmful to rubber came into contact with them. I can only out it down to a poor quality kit.