Intermittent vibration

[gjm 3193]

I suspect this caliper (at least) has been apart before. Anyone who has worked on cars for any period of time will know what I mean - it feels like someone has been there in the past. It happens. What follows could be due to it not having been correctly reassembled, but could as easily be down to use. I'll give it the benefit of the doubt - it's worked fine for at least 12 months and many kms. Now isn't the time to suggest a problem is due to something someone else has done.

The piston was showing signs of corrosion. on the outside there is a land where the seal sits, and having removed the seal I could see orange in the land. There was also signs of corrosion on both sides of the land, but (fortunately) no similar signs in the caliper. However, the lips around where the seals go in the caliper are rough, but this doesn't appear to have affected the seals - there were no signs of brake fluid leaking, anywhere.

Removing the piston was interesting. Typically a couple of pumps on the pedal should see the piston pop out of the caliper, but this time it took 7 or 8 full depressions of the accelerator. The 3rd and 4th presses saw some significant stiffening of the pedal, too. I'll be checking the master cylinder once this is done. (Incidentally, it looks as though you should use a syringe or a funnel to get brake fluid into the reservoir - pouring straight from a bottle would require some luck given you can't get the neck of the bottle close to the mouth of the reservoir.)

Given the apparent unavailability of a piston in NZ - especially on a Saturday afternoon! - I've thoroughly cleaned everything, and will reassemble with my fingers crossed. If it works, then great. I'll source new pistons (one for the other side, too) and rebuild again anyway.

If it doesn't work... Looks like I may have a VOR until I can get parts.

[gjm 3193]

OK - this is frustrating. Learn from my mistakes, folks.

I bought seal kits for the two front calipers from BMW. These do not include a piston. They cost... A lot of money.

You can buy this - http://www.ebay.co.uk/itm/261453411443. Double the price for NZ$. Double again to cover both sides. Add $50 for shipping the two kits to NZ (this is a guesstimate) and it is not just cheaper than buying the BMW parts, but you also get the pistons, and the assembly greases required.

Alternatively, just buy a couple of these: http://www.ebay.co.uk/itm/231053828298. (Or similar.) NZ$120 (plus shipping) for a new caliper saves a huge amount of hassle.

I've not been in touch with Paul at Milland or anyone else to ask for prices. They may well be able to offer something similar.

I was in a hurry to try and get this sorted. Instead, it's taken a lot longer, cost more money, and will need doing again.

Grrr.

[yng_750 247]

Ive had many good cars take up to 15 pumps t remove the piston. The increase in pressure after the firstbtwo pumps could be the vac servo running out of pressure.

[gjm 3193]

Ive had many good cars take up to 15 pumps t remove the piston. The increase in pressure after the firstbtwo pumps could be the vac servo running out of pressure.

Possibly one thing less to worry about.

But where did I put the bleed nipple? Yup... I'd swear it was withe the wheel bolts and caliper bolts, brake pads and retainer. But, no. Nowhere to be seen.

<sigh>

I'll cannibalise one of the ATE calipers I have for the Merc.

[gjm 3193]

Never did find the bleedin' bleed nipple.

Right - it's all back together. Copious amounts of Mr Castrol's red rubber grease on seals and the slider pins, lots of molybdenum disulphide on the brake pad 'arms' and the caliper pad slides, sparing use of copper grease on any threads.

I will be doing it again, as I want to replace the piston. The thread Jooles linked to at the top of the page includes a pic of two pistons - this one came somewhere between the two in the picture. I thoroughly cleaned it (180 grit wet'n'dry was needed, then steel wool, then polish) but there is pitting above the seal land, and that's not good. Looks like the pistons aren't stainless, but more likely a hard-chromed steel.

Bleeding was easy. Some hunting in the garage for a piece of clear(ish) tube to use on the bleed nipple turned up the hose from a Camelbak. I've never had one, so thanks go to the previous occupants of the house. My daughter did the foot pedal honours.

Test drive built up to some aggressive, just off lock-up braking. No sign of any issue.

Fingers crossed. I'll be ordering a couple of full kits, including pistons, to do both sides. May even take a look at the rears - no point doing half a job.