I was doing a routine brake fluid change on my daughters 1999 6N1 (no ABS) and ran into a strange circumstance that I think may have more behind it so thought I'd ask here.

I have a Halfrauds bleeding kit - little bottle and pipes that in theory should enable 1-man bleeding but in any event had her pumping and me at the bleed valve.

Back right - still very fine bubbles after maybe 300ml.

Back left - no bubbles

Front right - no bubbles

Front left - bubbles till I ran out of DOT 4.

First thought was leak in the bleeding kit but when 2 wheels went OK figure that is unlikely.

Then had a nasty thought that back right/front left are in some place a separate circuit so could be more than a coincidence hence this post - is there an obvious/known common place to look?

Really odd thing - no brake fluid leaks noticed anywhere in last 2 years and certainly no brake fluid top-ups needed, level has been constant.

Or should I just stop fretting and bleed another 500ml of DOT4?

Thanks for any insights

The brake circuits are crossed for safety, if they weren't in the event of a failure on one circuit you'd have brakes on only one side of the car and could cause the car to spin, So the front left is on the same circuit as the rear right, your problem could be the master cylinder

I'd try again with a new pot of brake fluid. Be sure the bleed nipples are open only just enough (so that the pedal has to be pushed fairly hard) and see if it is still bubbling.

Seems really unlikly but as Nige says - master cylinder seems the most likley place for air to be entering, if it was the balance valve then you'd only expect air in the rear.

Good luck and let us know how you get on.

K

Are the adjusters off?

Cheers for responses. First up I'll try 500ml of DOT4 through the back right as per kbs. Will try get done this weekend before she takes it to Le Mans.

Are the adjusters off?

Which adjusters? (The handbrake adjusters were fine when I replaced the rear wheel bearings a month ago and handbrake setting was fine this week. Also front left has same bubbles.)

Which class is she entering?

From (knackered) memory, if it's got drums on the back, it's a similar setup to the early cars, where there's a wedge between the wheel cylinder and the trailing shoe. This needs knocking upwards to make sure the cylinder is fully returning.

At risk of stating the obvious, make sure the lines and flexible aren't damaged.

A bit of a tip from days working on vans, if it has a load compensator on the rear axle, make sure this isn't leaking, and wedge it as if the car is fully loaded with a lump of wood or something so the rears get full pressure while you're bleeding it.

People will disagree, but I personally don't find the breeders that go on the header tank and a spare tyre work at all well. I prefer a vacuum bleeder or the old way with someone pressing the pedal.

The 'pressure bleeders' are great for getting fliud through new pipes and essential on some systems (if they are currently dry).

Not as quick as the truck rescue brigade who I've personally seen blowing fluid the wrong way through a system using a windscreen washer pump. Never do this, you will chase all kinds of muck from the bleed nipple, in to the master cylinder!! Might be tempted if I had a leaky clutch slave (on a seperate resevoir) that I couldn't bleed roadside though...

Once the fluid is moving, I prefer a one way valve on the bleed nipple - uses a lot less fluid.

As Yeti says for the rear brakes, make sure that the auto adjuster wedge is released before bleeding, or you may have a cylinder full of air that you are unable to get rid of.

It is quite possible that, when the pedal is returning, air is being drawn past the threads on the bleed nipple. To overcome this, close the nipple on the pedal return stroke and only open it on the pedal down stoke.

This obviously requires a fair bit of communicating between the 'bleeder' and the 'pumper'.

Regards

I'd try again with a new pot of brake fluid. Be sure the bleed nipples are open only just enough (so that the pedal has to be pushed fairly hard) and see if it is still bubbling.

Did this with caretakerplus tip to close nipple for the return stroke and pretty convinced the leak is on the bleed nipples threads. If it was very hard to push the pedal there were no bubbles, if I got the nipple just slightly more open there would be bubbles.

So job done for 2 years - thanks for the interest, tips etc.