david@st ives

hi all i am new to this group
i have been trying to bleed my brakes on my c4 90 i am using a pressure bleeder but i cannot get rid of the air out of the the system i have put about 5 ltres of fluid through the system and tiny air bubbles keep coming through is there any where an air pocket could be trapped has anyone had the sme problem
thanks
dave

garrett376

uh oh...
.... the C4's brake system is shared with the PDAS 4x4 system which can ONLY be bled out completely using a Bosch "Hammer" diagnostic tool. It sounds like you may have air in the PDAS system, which you won't be able to eliminate unless you take it in to someone with that tool.

Do a search on PDAS, bleeding, and C4.

Hope that helps.

Adrian

Dear Dave,
Which system are you trying to bleed?
Brakes front
Brakes rear
Hydraulic boost circuit
Clutch circuit
PDAS circuit
Which bleed port is the air coming out of?
Ciao,
Adrian
964C4

david@st ives

[QUOTE]Originally posted by garrett376
[B]uh oh...
.... the C4's brake system is shared with the PDAS 4x4 system which can ONLY be bled out completely using a Bosch "Hammer" diagnostic tool. It sounds like you may have air in the P

thanks for the reply

i have followed the proceedure as detailed in adrians book and i am merely asking about the difficulty of getting air out of the actual brake line
thanks
dave

david@st ives

[QUOTE]Originally posted by Adrian
[B]Dear Dave,
Which system are you trying to bleed?
Brakes front
Brakes rear
Hydraulic boost circuit
Clutch circuit
PDAS circuit
Which bleed port is the air coming out of?

dear adrian
thanks for reply
the air is coming out of rear calipers
i havve already bled boost circuit as described in your book

joey bagadonuts

David,

I think I know what's going on, here.

Make sure you have at least 35 psi in the bleeder system and that you are releasing the old fluid at a reasonable rate. If you slow down the flow to a "trickle" these bubbles will form--THEY ARE NOT COMING FROM THE CALIPER. These bubbles are coming from the exit airway.

You are probably fine.

dumluk

Welcome to the group, David. You will love the helpfulness here, as seen by above comments. I have read threads on quite a few different groups covering many topics, and the Rennlist 964 group is by far the most helpful and gentlemanly I've found.

david@st ives

joey
the exit airway is that the same as the open nipple

joey bagadonuts

You've got a tube connected to the nipple, right? Well, if you let the fluid exit slowly, bubbles will form as air displaces exiting fluid. The source of this air is the open end of the tube.

You should be giving the nipple valve a good quarter turn to get the flow going and then a quarter turn to shut it off.

david@st ives

dear joey
you have totally lost me now
i have the tube vertical into a collecting jar12 inches above the caliper i cant understand how the air can flow downhill
and i can only see air bubbles going one way and that is up even when the bleed tube is totally full of fluid and the air in the tube is pushed through totally into the collecting jar i still have a steady stream of very tiny bubbles flowing outwards from the caliper
thanks
dave

joey bagadonuts

Oh, sorry about that. I imagined the collection jar being on the ground.

This problem should not be hard to figure out, though. Are you creating bubbles or introducing air anywhere in the process? Think hard about this.

When I bleed my brakes, I add fluid to the reservoir, keep the pressure bleeder dry and simply add pressure. As I move from caliper to caliper, I add fluid and NEVER allow the reservoir to go empty. It's always near the max level.

The brake system holds a couple liters of fluid, correct? If you've added five liters properly, then all the air should have been eliminated.

So there really aren't many alternatives. Either the bubbles are not coming from the caliper or you are adding air along with fluid.

Final question: In what condition, David, were your brakes prior to this maintenance?

garrett376

A stream of tiny bubbles could come from air getting past the threads on the caliper bleeder screw itself. I've had that happen before where the system was free of air, but little bubbles kept appearing and I noticed it was because i had the caliper bleeder open too far.... just another idea...

mwildt

Hi,

And while we are bleeding the brakes use a flared wrench to open and close the brake bleeder screw. Much better than to get them rounded by a regular wrench.

Michael

chris walrod

Are you using a pressure bleeder, or a mity-vac suction type?