brake bleeding from scratch

[mister bridger]

I've just read through the 4 page thread on brake bleeding and I'm none the wiser as to why I'm getting no "brake pedal". System has all new pipes, hoses and master and slave cylinder seals. I'm using the tyre pressure method of pushing fluid through and getting clear, bubble free fluid through every nipple. There was a comment regarding assembling the master cylinder "wet" to avoid air locks but not sure how you would go about this. Sorry if i'm opening an old can of worms!

[Richard Fridd]

I took 'wet' to mean filling the master cylinder with fluid 'on the bench' and making sure it works before reuniting it with the rest of the braking system components best regards richard

[andyc]

You could always try slackening the brake pipes(only by one or two flats) at the master cylinder and bleed there then try the same at any brake unions/connections working your way to the brake calipers.

[lancialulu]

Not wishing to upset but did you assemble the MC with seals correct way round?

I have never had to prime the MC on the bench but have often had no pedal.

Use gravity and wait. when fluid appears at the rear close the bleed nipples open the front. when fluid appears at the front close the bleed nipples. dont let the fluid go down too far in the MC. It takes time - go and put the kettle on! Do you have a pedal?? if so continue with gentle top pressure to the MC bleeding from the furthest back first etc.

Tim

[ColinMarr]

If you are getting fluid from the reservoir through to the bleed nipples on the cylinders, then the master cylinder must we ‘wet’ and should produce a pedal when the bleed nipples are closed. I suspect something is wrong with the master cylinder.

If you were bleeding in the more conventional way without a positive pressure on the reservoir, then you might suspect air being drawn back via the bleed nipples (as I have experienced!), but this seems not to be the case.

Good luck,

Colin

[Scott]

When I overhauled the brake system on my Fulvia I fortunately didn't have any problems like this (mine were more around seized bleed nipples!) and the Eezibleed system I opted for worked well.
From what you've said it certainly is sounding like a master cylinder issue. If you just do a search engine search for 'testing master cylinder' there are some good articles out there so you could at least start with some basic checks. You'll then know what to kick or swear at.

[mister bridger]

Spoken to Robert at Omicron who was very helpful. I've had the master cylinder apart about three times today to check everything is right and that the two parts of the front plunger are free (they weren't, but are now!) Everything is totally air free and, I believe, correctly assembled but there is still far too much movement on the pedal. One thing that seems wrong is that when pumping the pedal, fluid can be seen coming back up into the front part of the reservoir, suggesting that the front plunger is not moving forward as it should, but I can't for the life of me think why. Any helpful suggestions other than posting it off to Omicron for an expensive check over?

[lancialulu]

Sent you a PM

Tim

[mister bridger]

A friend came round this morning and we bled the brakes the old fashioned way - open nipple, push pedal, close, lift pedal, repeat ad infinitum - and got quite a bit more air out. The pedal feel is greatly improved but still not there, and there is still fluid pushing back up into reservoir at the front. Will try bleeding again in a few days perhaps when fluid has settled, but other than that totally run out of ideas!

[ColinMarr]

I don’t understand how fluid can come back up into the reservoir. The first millimetre of movement of the pistons in the master-cylinder should close off the hole that feeds fluid between the reservoir and the cylinder.

If your problem is just excessive pedal travel, one possibility might be that the push-rod between pedal and servo is too short. I had trouble with this and had to successively adjust it to increase the length of the rod. Beware, if you set it too long, the pistons in their relaxed position will cover the feed hole and as the brakes get warm they will seize on!

What fun!

Colin   

[Richard Fridd]

 I was told in the workshop last week :To detect which corner may be harbouring the suspected air some would iscolate each piston assembly by means of clamping the relavent hose and trying the pedal feel once again.I the feel is still not satisfactory with all hoses clamped the problem is upstream of the hoses.also if a bias valve is fitted this needs to be in a position to allow fluid to pass freely.if adjusting that pushrod which Colin mentions it is worth checking the are sufficient threads to secure the dome nut.best regards richard

[ColinMarr]

Just to clarify the point that Richard made about the domed nut. I never needed to adjust that nut on the rod between servo and master cylinder. I adjusted the other end where the push-rod to the servo fits over the ball on the side of the pedal. There's quite a lot of adjustment possible there and can be done standing on your head inside the car!

[mister bridger]

I don’t understand how fluid can come back up into the reservoir. The first millimetre of movement of the pistons in the master-cylinder should close off the hole that feeds fluid between the reservoir and the cylinder.

This is definitely still happening. I'm unable to do a road test as the car is not much more than a bare shell but I suspect the only braking effort must be coming from the rear plunger. Either the front one is not moving forward, or fluid is escaping past the front seal? Can someone confirm I have the front plunger assembled correctly? The order I have is plunger, cup washer, pierced alu disc, small spring, brass disc, circlip, main spring (shorter of the two).

[Davidb]

Just a thought: have you got the cup washer seal on the right way round? Wrong way could account for the bubbles and lack of pedal pessure.
The "open" side should face forward.

[Davidb]

To clarify having just read my own posting!: by "bubbles" I meant fluid coming back into the master cylinder.