The silver coating known as Dacromet is meant to come off instantly on the swept surface. A sticky nearside front brake on an A4 suggest corrosion inside the servo, have you had the passengers side foot spa option?
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The silver coating known as Dacromet is meant to come off instantly on the swept surface. A sticky nearside front brake on an A4 suggest corrosion inside the servo, have you had the passengers side foot spa option?
Yeah in the process now of taking the caliper off as we speak, will see if I can clean the piston and put it back.together cheersQuote:
Originally Posted by jonathanfenton
As in the battery compartment flooding and getting the footwell wet? Yes the winter just gone but I sorted it out.Quote:
Originally Posted by Crasher
Wouldn't a servo issue affect all the brakes?Quote:
Originally Posted by Crasher
I posted on this situation last year, post no. 6 in this thread. Rear Brakes ... getting 'hot'
Since then I removed both my front calipers and cleaned them out. To do this I seal the top of the reservoir to slow down the flow of fluid, disconnect one hose at the top and seal off the fixed pipe with a blank plug. This enables me to remove the caliper, take out the piston and examine/clean the piston and cylinder. I found blank plugs on Ebay.
I found a substantial amount of solidified crud in the lower inner part of both cylinders, which had built up far enough to reach the bases of the pistons, and had left a dirty mark on them. Fortunately this cleaned off easily with a stiff cloth, but I had to dig out the crud with a thin piece of hard wood and careful use of a small, blunt screwdriver. The nearside caliper, which often runs in puddles and gutters, is usually worse than the offside one.
I don't recommend using sand paper on any of the surfaces, rubbing with a hard cloth should remove any deposits. If the surfaces are bad the parts should be replaced. Very fine abrasive crocus cloth is the roughest material I use, but only on the pistons, which are hard chrome plated. If the aluminium inner surfaces of the cylinders are corroded to the point where the groove for the seal is damaged or evn suspect, the caliper should be replaced.
I replaced all the seals and covers, and also the hoses on this occasion, as I didn't know their age, and they are relatively cheap.
I remove only one hose and finish one brake caliper, replace everything and bleed that line before doing the others. I complete the front brakes, which are more important, before doing the rears.
I change the fluid every 2 years, using the procedure in the Bentley manual. I never push back brake pistons when renewing pads, as it is much easier to dismantle and check inside the cylinders than to find brakes seized on when miles from home.
EDIT: Before disconnecting the hydraulic hose, I take the top bolt out of the caliper housing, swing it down, remove the pads, put a suitable piece of wood between the piston and the other side and operate the brake pedal to push the piston partly out of the cylinder, enough to be able to get hold of the end to pull it out the rest of the way. If I forget to do this, again putting a piece of wood under the piston, I use a tyre foot pump to gently pressurise the cylinder via the hose connection.
Due to the way the system is designed this fault hits the near side front first and then the offside rear, after this it does not go much further... Diagonal plumbing.Quote:
Originally Posted by MrPresident
This piston is long gone in my opinion, the seals weren't great either. I think maybe after pushing the piston back to fit the new disc and pads kicked up a dormant issue as it didn't stick before. I've rebuilt calipers myself before however I just bought a refurbed OEM caliper and traded in my old one for a discount at a local motor factors. Was £62 from "Brake Engineering".Quote:
Originally Posted by jonathanfenton
Seems to have sorted the issue, after pumping the pedal it moves freely. I bled afterwards but braking isn't the best. i'll see if it needs rebedding a little or perhaps a bleed all around? as i did degrease the disc and pads. I think the the master cyllinder might have run dry when i took the piston off as I clamped the hose but it was dripping wthiout me realising and pushing the piston out lost some fluid as well.
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Aye the little bit of corrosion is enough to make it stick. I’ve found best way to bleed up new calliper is to put a gclamp on it to keep piston fully in and that seems to yield best results. If your let it run dry then you’ll need to bleed all 4. I had a nightmare with my A3 ended up using VCDS to bleed the abs pump. Hopefully you’ll just need to go round all 4 wheels a few times with a pressure bleeder. I tend to go for about 20PSi and then let about 1/4-1/3 litre run though each corner staring with furthest plumbed away calliper when I have a stuck air. Like as I said I found when I had a mare with mine I had to use a
G clamp on the piston to gently hold the piston all the way in and it suddenly came back solid again. Especially with new callipers.
Cheers I'll try bleeding all corners. Didn't know you could do abs with VCDS! I have it, but not used much. I've only got the £5 one man bleed kits basically the tube with a valve that goes into a bottle. What pressure bleeder do you use? Worth the extra £££?Quote:
Originally Posted by jonathanfenton
I used Gunson easy bleeds for years then upgraded to a sealey pressure bleeder. So much quicker and easier
Sealey VS820 Brake & Clutch Bleeding System Sealey VS820 Brake & Clutch Bleeding System: Amazon.co.uk: Car & Motorbike
Highly recommended. (Probs cheaper elsewhere but link so you know the one I have and recommend).