C5 Mk1 2001 2.2Hdi - Advice On Brake Bleeding

[aspire_helen]

Hi, iam replacing my rear calipers/discs/pads and front pads (at 13years, 150000miles). I intend to bleed each rear caliper after fitting, and then fully bleed/replace the brake fluid when all 4 wheels are complete. I intend to use the 2man brake pedal up/down/up/down method as detailed by Haynes. However, i have read elsewhere that the c5 with abs needs special bleeding to avoid problems such as: getting air into the abs system, pushing dirt back into the master cylinder, inverting the master cylinder seals due to excessive foot pressure on the pedal etc.

Has anyone got any advice on the definitive diy method?

 

I have also read (not Haynes) that when winding back the front pistons, the bleed nipple should be opened. In this way, any dirt in the caliper fluid channels is pushed out via the nipple and not back into the master cylinder or abs system. Any thoughts?

[paul.h]

There are pinned posts in the Problems and Fixes section on doing the front and rear brakes that are worth reading.

 

New brake pads take maybe about 100 miles to bed in before the brakes are back to normal so care needs to be taken for the first few days of use. It is probably best not to replace the front and rear pads at the same time so at least one end of the car will have good brakes.

 

Before you replace the pads check that the discs are not worn to their minimum thickness. For the 2.2 hdi -  front new 28 mm, min 26 mm and rear new 14 mm, min 12 mm.

 

When pushing/turning the front or rear brake pistons in, I now usually open the bleed screws to let out the fluid. The bleed screw is kept at a high point so air will not get back in, then opened slightly when starting to push the piston back in by turning if needed or just using a clamp, and then at the last push the screw is tightened so air does not get in. I use a bleed hose on the screw in to a container to catch the fluid and you can see any air/dirt that comes out. Before doing this it is best to clean up the pistons/rubber seal/caliper.

 

I have given up with the 2 person bleeding method, causes too many arguments and there is also a risk of the master cylinder seals being reversed on any wear ridge - a common problem when we had an Astra. I have also used the Easybleed pressure bleeding system but that is too much bother and now use a Mityvac hand pump that sucks the fluid out of the bleed screws. This can pull air around the bleed screw threads so is not ideal but is the easiest one person method. The standard Mityvac container is a bit small at about 100 ml and needs frequent emptying so I made a larger one from a 300 ml plastic container with a screw top that could hold vacuum and fastened a couple of bleed screws to the lid for clear bleed hoses - 1 to the pump and 1 to the caliper, fastened with small fuel hose clips. I marked it at 50 ml levels on the outside. The vacuum test for the container was to screw the top on and put it in the freezer - if it holds vacuum it will squeeze in a bit as the air cools and contracts, which it did.

 

When replacing the rear calipers, try not to get any air in to the pipework. I have read that pushing the brake pedal down and clamping it there will stop fluid running out of the open end and should stop air getting in (until the pedal is released) but I have not tried this and you may just be best to hold the pipe end up, connect to the new caliper and then let fluid run in to it with the bleed screw at a high point and open so fluid runs in and pushes out any air by gravity. Fit the caliper and bleed it before doing the other side. This way there should be no need to use diagnostic equipment to bleed air out of the abs system. I had to remove one rear caliper to drill out a bolt and vaguely remember plugging the end of the pipe and putting it in a plastic bag with a tie wrap to seal it so air did not get in - and once refitted used the Mityvac and that was enough to remove the air.

[paul.h]

Some things I forgot when replacing the brake fluid.

 

It helps to extract the old brake fluid from the master cylinder reservoir as much as possible and then top up with new fluid. This limits how much has to be bled out of a brake to remove all the old fluid. A syringe or Mityvac can be used to do this.

 

At least 1 litre of new fluid will be needed. Do not let the reservoir fluid level go down too low once starting to bleed. This will avoid the risk of air entering the master cylinder and then possibly the need to use diagnostic equipment to bleed the abs. The fluid take off for the clutch is usually at a higher level than for the brakes.

 

If there is no air to remove, then it really does not matter in which order the brakes are bled. I prefer to start with the front one nearest the master cylinder and use this to pull all the old fluid out of the reservoir until it changes colour to the fresh fluid. Then the next front one and then the back. If doing it on the floor and with the suspension on max height, to do the front ones it helps access to point the relevant wheel out. If you have alloys, it is possible to do the back ones through the wheel spokes but put a rag/tissue around the bleed screw so fluid does not run down and on to the wheel.

 

The clutch also needs to be bled and I have found the easiest way is using the Mityvac to suck the fluid through since pedal pushing is not that effective but it may also be possible to use a syringe or possibly just by gravity. There are various bleed screw designs used on the slave cylinder - some need it to be opened several turns for the fluid to flow, some are quarter turn ones that can be done by hand and on our latest C3 it is a stupid system that involves pulling out a clip so the slave cylinder supply pipe is pulled slightly out and then fluid pours out, but possibly not flushing through the cylinder.

[madmadmax]

the abs is full flow so as you pump the brake pedel it will go throught the abs pump and to the calliper

[aspire_helen]

Paul, thanks for that - i will digest all you say.

Ref blanking the brake pipes- i used a female-female coupler (size M10x1.0) from ebay, £1.89 for two delivered. The brake pipe screws into one end, and i used a bleed screw from the new caliper to seal off the other.

Helen

[aspire_helen]

Brakes bled without problem using 2man process, thanks.