Club 80-90 Forums

if you bleed them nice and slowly even if it does go onto the dirty section the seals will not flip its when people wang the pedal up and down to fast, sure any manual will tell you to push the pedal slowly!

This phenomonon has been around for years, I even teach my motor vehicle students about it during chassis tech lessons (IMI L2) this is nothing new and not unique to VW's.
I think it was the slightly exagerated and sensational way this was put across that ruffled feathers but it has been obvious by the replies that not all owners are aware of this and the cautionary note when bleeding brakes that we have been made aware of by the original post was in some way helpful.
From my understanding this particular phenomonon can occur after 'old fashioned' manual bleeding as the piston and it's seals move across the worn ridge in the cylinder bore (where the seals have previously worked up to)
I pressure bleed mine, 3 times in the last 4 years, usually after carrying out work (last time was after changing the flexi's for steel overbraided type) but I accept most owners don't have access to such equipment so will not have the option...slow pedal movement with I suggest limited travel or take it to a garage as bleeding brakes should be on the set pricing menue (about half an hour labour plus fluid)
It is rare....very very rare, I've personally never seen it but I'm sure it does happen.
As for alerting owners to the dangers, where would we we stop; Fuel lines leaking, corroded metal brake pipes, corroded and leaking petrol tanks/filler necks and expansion tank pipes, under rated wheels and tyres collapsing and bursting, wheels falling off using adapters, rubber steering couplings perrishing, electrical fires from bad unfused wiring, power steering pipes bursting etc etc but we are aware of all these things aren't we...lol

The reality is, we own old vehicles that need good maintenance and regular safety inspections by knowlegable specialists but for a lot of owners (not all), the anual MOT is the only time the van is looked at properly from a safety perspective, perhaps there is the cautionary foot note accepting that some owners are very knowledgable but not all.

Martin

why do some people have to be so bloody arrogant.............

bruce wrote:why do some people have to be so bloody arrogant.............

care to say who is??????

OK so I didn't know that there was a potential issue, I will add a note to the wiki warning of excessive pedal travel during bleeding to prevent master cylinder damage.

Note: Excessive pressure on the brake pedal during bleeding could in rare cases lead to master cylinder damage.

if anyone wants to add to that then feel free to post it up for addition to the wiki. heres what we have currently.

https://club8090.co.uk/wiki/Te ... s/clutches" onclick="window.open(this.href);return false;

It might be worthwhile putting effort into improving the procedure for other folks with all these combined decades of experience.

My 2p.
I sufferred sudden and total brake failure on the autobahn.

The cause was a critical failure of the master cylinder seals.
This type of failure will become more likely the more a vehicle is used, the likelyhood of the failure ocurring is still minimal.

To all those getting worried I should point out that most vehicles adopted the split braking system by the early 80's, where the master cylinder has a pair of seals and two outlets, each supplying two brakes, either front to rear or diagnally split. This was a safety feature in case one of the two seals failed and if it did two of the four brakes would continue to function albeit in a precarious manner.
Therefore it would be even a rarer occurance for both seals to fail at the same time.

Martin

...Big Deep Breath...

I wanted to mention split brake circuits beceause they will provide that safety net. Though for that split second when there are no brakes is probably one of lifes more horrible moments (yes something similar happened to me). Are the earlier and later models different?

Mal.

Then of course there is brake fade...when the friction between brake pads and discs greatly reduces with very high temperature.
And
Vapour lock....complete loss of the brake pedal due to the brake fluid boiling (The gas bubbles in the boiling fluid compress under pressure where as non boiling fluid does not)
Brake fluid is Hygroscopic (attracts and absorbs water from the atmosphere) just 3% of water contamination in the brake fluid leads to a 100C drop in the boiling point of the brake fluid.
This is why regular 2 yearly brake fluid changes are so important.

Martin