On 24/05/2022 at 18:36, KiNeL said:

For those who can't (or won't) get it, at 2 mins what the guy is effectively doing is pulling a stuck down pedal up from the floor when it snaps into the 'up' position - why, because it's being held in the locked down position by the helper spring being in an over centre attitude.

 

Clear now?

 

 

No its not clear because its not a salient moment at all but a red herring, no wonder both myself and Stubod could not see what it was, shame on you for not simply responding and making him watch it 3 times.

 

It is the control loading spring and in the absence of hydraulic return pressure from the clutch via the master cylinder to the pushrod will move the pedal to the upper stop or the floor dependant on which side of the centre dwell position it is, this is not a clutch fault but a manifestation/symptom of air in the system.

51 minutes ago, KiNeL said:

I bled the system and quickly got a good pedal but then noticed a weep from the pipe where it fits in the MC so removed it again, checked and refitted the rubber seal, after which is sealed correctly, as a check going forward I put a piece of black duct tape on the chassis member immediately below the connector which should immediately reveal any drips.

 

As stupidly expensive as they are I may invest in a new seal just in case.

 

What should have been a max 1.5 hour job turned into a half day marathon and being of 'an age' with all the contortions in the footwell I expect to be totally seized up on the morrow!

 

My first cylinder swap I also failed to seat the sealing washer properly, it had remained in the cylinder and I wrongly thought the pipe simply needed clipping back into place, I wasted a huge volume of fluid trying to bleed the system until I noticed the lake spreading out under the vehicle, the drips were falling hidden behind the sound insulation.

 

The seal has to be clipped onto the pipe first, not just pushed on but pushed on firmly until it clips.

 

I ended up doing the job so many times it became quite easy, removing and refitting the master cylinder I found relatively simple but being partially sighted I am very good at working by feel.  I found putting that clip in place quite difficult without stripping the pedal assembly as it had to be done with the pushrod ball already in place, I used a couple of screwdrivers, I presume thats what your special tool is for.

 

I had problems with the pushrods detaching from the piston on pattern part cylinders, one time I forgot that I had clamped the flexible hose, I had just fitted the master cylinder and then sheared the plastic pushrod trying to bleed it

8 hours ago, J.R. said:

My first cylinder swap I also failed to seat the sealing washer properly, it had remained in the cylinder and I wrongly thought the pipe simply needed clipping back into place, I wasted a huge volume of fluid trying to bleed the system until I noticed the lake spreading out under the vehicle, the drips were falling hidden behind the sound insulation.

 

The seal has to be clipped onto the pipe first, not just pushed on but pushed on firmly until it clips.

 

I hope never to be talking about an MC swap in the plural!

 

I knew about the seal from the video but it must have dislodged slightly when I fitted the pipe or perhaps the slight movement of putting it back into its support clip on the chassis rail disturbed it.

 

The fact that it bled and gave a working pedal is indicative of the extent of the leak though, i.e. dripping rather than gushing, start to finish I doubt I lost more than a couple of thimblefuls of fluid.

 

I don't know what sound insulation you're talking about as the connection is well away from the bulkhead so leaking fluid would drip directly down and pool on the naked chassis leg, hence my piece of black tape because being a white car a tiny drip would be difficult to see otherwise. Thankfully so far it's dry.

 

Being more familiar with hard brake pipes with flared ends secured nuts prima facia the push in design seemed unnecessarily minimalist but considering that it's widely employed not just by VAG group vehicles but also by other manufacturers that's obviously just me.

 

Curiosity of course demands that I disassemble the old cylinder to see exactly what has gone wrong inside it!

 

Edited 29 May, 20224 yr by KiNeL

Good luck with that!!!!

 

When you get fed up with struggling with the segmented collet clips let me know and I will give you the magic trick to getting it apart.

 

Mine was full of magnetised crud around the reed switch magnet (might be hall affect), if they are not leaking they cannot really fail, they are such a simple design, if the piston is pushed in then the fluid will be displaced, it contains no other valves or seals.

Having read the thread again then I would say you are correct, the master cylinder may have been sticking, if so then it will be the magnetised gunge that I had, I nevr could detect where it came from which is a little concerning for the future.

 

I was watching one of the UK TV road cop fly on wall episodes this week, the flic was chasing a speeder driving a vintage BMW 3 series, he was driving an Audi something, his clutch pedal went to the floor and didn't return!!!!

Autopsy done.

 

No problem getting in as I had no plans for keeping it so just hacksawed around the periphery.

 

Found loads of white crud inside but only a small proportion of magnetic debris.

 

Most of the crud in fact dissolved with water and the glass shows what I was left with which was crystalline and most of that had come from the segmented brown seal/bush

 

Seeing all that makes me think it might not be a bad idea to pull the slave and check that for crud although I suspect both the hydraulic pressure and push back from the clutch cover would overcome any sticking issues there.

 

I think if I were to encounter the problem in the future I might try an aggressive flushing first.

 

 

Nothing like what was in mine but it would definitely cause stiction.

Never seen anything like it in a car hydraulic system but I've been doing some research and come up with this, similar can be found in multiple places.

 

"If the brake fluid is not changed it will continue to absorb moisture, and eventually it will crystallize and form deposits inside the brake system that can cause the seals to fail and components to seize."

 

If that is the cause then the surprising thing is that it's happened so quickly (11 year old car which presumably had at least one or 2 changes during it's early life) when, like a great many I'm sure, I personally have never once deliberately replaced the fluid on any vehicle I've owned.

 

I suppose it's possible that typically higher background humidity in Spain could be an accelerating influence. 

 

That will change this week as I don't want to risk similar problems arising in the braking system where repairs could be a far more involved and expensive proposition. I'll temporarily evict the MGB from the garage so I can do the job in air conditioned comfort.

 

I already have 1lt of genuine VW fluid bought expressly for that purpose but being a lazy b****d..........!!!!

 

It will be very interesting to see what, if anything, gets flushed out.

Moisture crystallizing................................

 

An interesting concept which just goes to prove you can find anything you want on the internet.

 

In Alaska maybe, Spain? - I dont see it somehow.

 

None of which helps you identify what the gunge was nor what mine was, all I can say is they were completely different.

Those crystals are more than big enough to block the fluid return path through the clutch bleed block AKA peak torque limiter, on the downstroke there is no restriction but when you lift the pedal the fluid has only a tiny orifice to pass through, well less than 1mm diameter.

 

I would definitely remove the slave cylinder and bleed block, I think its one unit on your vehicle, strip and clean it as you have done with the old master cylinder, while its off purge the pipes before refitting.

 

You also need to empty and refill the brake master cylinder with new fluid , if you did not do this last time then the only way to be sure is to remove and strip the new master cylinder which you wont be looking forward to.

 

And of course as a matter of safety you should bleed the brakes and the ABS unit, the crystals whatever they are are equally likely to be present in the braking system and wont do parts with fine passages like the master cylinder and ABS block any favours.