Just over a week ago, the Sirion’s brakes seized in a rather unpleasant manner. I pride myself on feeling a problem well before it becomes dangerous. With only 54bhp, the resistance caused by a binding brake was enough to arouse my suspicions. I shouldn’t have to accelerate downhill! Then I detected a wheel wobble. I was hurtling down a very steep hill at the time so I cautiously applied the brakes and pulled over. Sure enough, the nearside front wheel was hot to the touch. I’d only travelled about a mile from home! Ideally, I would have had something big and made of metal with which to wallop things – that can often force a sticky caliper to retract, or a stuck pad to free itself. I had no tools so just have the wheel a good kicking. This, amazingly, did free things up enough for me to drive another couple of miles to my destination.
I drove the car home the next day with no problems at all, but the very next journey revealed the same symptom. Life got hectic for a week and so the Sirion had to sit on the driveway and await some spare time.
That finally arrived today, so I began to strip down the caliper. It’s a floating caliper, so the first task was to remove the slider bolts. I’d replaced these not long ago and I could quickly eliminate them from my enquiries. With the caliper free, I could see if I could push back the piston. I could not. I opened the bleed nipple and tried again. Same story. This at least confirmed that the flexible brake hose wasn’t at fault – they can degrade internally and act as a one-way valve.
The only conclusion remaining was that the piston had seized into the caliper. I looked up the price of new calipers. Eek! At least £65. I looked up the price of a new piston and drew a blank. Not being particularly flush with cash at the moment, I decided to remove the piston and see how bad things were.
Removing the piston was quite easy. One option is to use compressed air. The other is to use the power of the braking system. I opted for this one. It involves pressing the brake pedal down until the piston comes out. Make sure there’s something beneath the caliper to catch all of the soon-to-be-free brake fluid! I did it gently, in stages. Press pedal, go and have a look, press pedal, go and have a look etc. Eventually, it popped gently out. Then I put a hose clamp on the brake pipe and undid the union on the caliper. The piston didn’t seem too bad really – a bit grotty in places perhaps. A good clean with a cloth improved things, and I used a very light emery paper to smooth things even more. Be very careful not to overly scratch the surface of the piston.
With the piston out, I could see that corrosion had built up on the bore, especially between the two rubber seals. I didn’t have a seal kit, so had to carefully clean the face of the bore – a screwdriver for the big chunks, then emery again. After that, I had to clean out the bore and seals very carefully. Any muck here is only going to give a problem later. With everything clean, I dug out the red caliper grease and applied that to the seals. I also smeared a little over the piston itself to aid its refitment. That worked a treat and it slipped home beautifully. I refitted the caliper and pads, bled the caliper (keeping a close eye on the level in the master cylinder – it needed a fair bit of topping up) and had a successful test drive.
The internet is full of people asking which grease they should use for calipers. I use red caliper grease for the piston, seals and sliders. Some claim it isn’t suitable but my experiences so far are that it is. Lithium-based greases can be bad news as they can destroy the seals and apparently don’t react well with DOT brake fluid. Certainly, you should NEVER use copper grease. This is not a suitable application. It’ll just turn into a sticky gunge and will definitely cause you problems!
It’s good to have the little Sirion back in use again. It makes me laugh with its daft looks and ridiculous exhaust bark. Six months this car has survived on the fleet. Will it make it past the tricky eight month stage?