Drove to work in my G27 (it was a nice day, still school holidays so less traffic), came to the first roundabout. Went to brake and not much happened!
stamped on the brakes and the rear brakes locked up and I came to a nice tail out sideways slew to a stop about 1' from a car on the
roundabout.
What did I learn:
- firstly the warning light for low brake fluid did not work ;-(
- I obviously made a mistake re-building the caliper ...!
The calipers are the princess 4 pot jobs with spacers for vented discs. I had a lot of trouble to get the pistons in to run smoothly and it too a
number of attempts.... thought it had sorted it and I saw no signs of leaking since I rebuilt them around 2 months ago.... I have re-built calipers
before with no probs before but these seem "hard work" to get the pistons running smoothly
What could have I done wrong... the pistons were a bit corroded so was planning to get some st.stainless replacements even though they did not leak
before the re-build. I guess I should use new seals for the second attempt at the rebuild (I am a bit more nervous doing this now!).
Any recommendations on how I should re-build them?
I used plenty of the proper grease
Also plan to replace the pads whilst I am at it... was planning to get some mintex pads - which pads should I get and which type (was thinking of
1144)
[Edited on 2/9/16 by AlexXtreme]
Was the pedal hard or go down to the floor?
Unusual for both front ones not too work, sounds like the brake cylinder???
Pedal did not go to the floor but was considerable softer than normal
Could it be air getting in from a faulty seal?
dont think so... not stripped it down yet and there was a small patch of fluid on garage floor when I looked
Just order new pistons just in case this is the issue... anyone know which pads go with the std princess calipers so I can get the job done in one go?
quote:
Originally posted by AlexXtreme
dont think so... not stripped it down yet and there was a small patch of fluid on garage floor when I looked
Just the one ... the one I serviced :-(
You need to go back to square one to diagnose this properly, for the pedal to go onto the 2nd part of the dual system & give rear brakes only
there has to be a substantial loss of fluid, if this was from just one caliper, then you would expect significant pulling to one side from the front
b4 you lost sufficient fluid to cause only the rears to work.
If you've stripped the calipers down, presumably you've had the hoses off? Are you sure you don't simply have a leak from a hose or
pipe?
I would be topping up with fluid, bleeding brakes & then checking under pressure to look for the problem b4 jumping in & assuming it's a
caliper, it's actually pretty rare for a caliper to leak significantly
Hi Russbost.. thanks and good advice. I will have a look this weekend and report back.. yes I have had the hoses off.
Thinking about it I did notice a slight pull to one side however this only occurred once or twice... feel bad about ignoring this now as it could have
ended up a lot worse than it did!
Brakes stripped down - it is a mess with brake fluid sprayed around the arch and soaking the inside of the wheel. One of the pads is soaked with fluid
and the disc was coated... One of the pistons had leaked.... !
Have ordered new st steel pistons and already have a set of seals. I read somewhere it is easy to pinch the seals when installing them which can cause
leaks. If this was the issue how do I avoid this? Is it best to use the red grease that is supplied with the kit (which feels quite thick) us use
brake fluid... I do soak the seals in fluid before installation
I would guess that almost certainly that piston has been leaking ever since re-assembly, whenever doing brake work involving hydraulics you should
always do a pressure check after bleeding & cleaning up. Put your foot on the pedal & stand on the brakes as tho' doing an emergency
stop, hold the pressure for around 30 seconds, if the pedal gradually sinks then either you have a leak or a knackered master cylinder. Get someone
else to check each corner hoses/calipers etc (or to stand on pedal while you check) whilst the brakes are under full pressure.
Always worth checking fluid level after the first few miles as an additional check, can save moments such as the one you describe
Re fitting the seals, there is no easy way, no need to "soak" the seals as such, just a wipe with fluid or the red brake grease should
suffice, you need to gradually tease the caliper piston in, if you are having to apply massive amounts of force then something is wrong, seal pinched
or similar, remove piston, check for damage to the seal & gently try again
thanks for the advice... I did check the fluid for the first few weeks and did not notice any change however should have done the test as you mention below.
Found the source of the problem... the leaking piston almost fell out and I found the seal that I fitted had gone very hard .... it seamed that I must have picked up a rubber seal of almost the same size compared to the correct seals from the work surface and fitted it to the calipers :-(. I am sure I would have noticed it being so rigid I am guessing that in the brake fluid the rubber hardened then after a while stopped becoming an effective seal. The evidence was pretty obvious in that I had a 5 seals left for the other caliper - ... never done anything like this before and am blaming old age! Now do all similar work on a separate clear area of the work surface