Tips on brake bleeding please

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Offline antarmike

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Re: Tips on brake bleeding please
Reply #25 - Jan 10, 2022 - 11:28
Mike, you still get fluid flow with the vacuum approach, you could say that atmospheric pressure push it along. yep one end of the system is at ~14.5psi, the other depending how hard you pull on the syringe. yes pulling the syringe requires some force could easily be 7psi.
Agreed, you undeniably get a flow by vacuum bleeding, but flow rate will depend on the pressure difference.  Pressure bleeding in all cases can produce a significantly higher flow rate.

Offline Trakgrip

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Re: Tips on brake bleeding please
Reply #26 - Jan 10, 2022 - 15:04
... your statement "If the relative pressures differ by the same amount, there should be no theoretical difference" is incorrect. that is not the reality of pressure bleeding.
...

I disagree - my statement is 100% correct noting the qualifier with which the statement opens. I do accept that it is possible to create a much greater pressure difference if pressurising the reservoir than if using the vacuum method.

Be that as it may, I repeat that I have never had any problems (yet) bleeding a Series One, and although I didn't say so in my previous post I have never used a pressure bleeding device for the purpose, I have never found it necessary.

Offline antarmike

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Re: Tips on brake bleeding please
Reply #27 - Jan 10, 2022 - 15:11
I disagree - my statement is 100% correct noting the qualifier with which the statement opens. I do accept that it is possible to create a much greater pressure difference if pressurising the reservoir than if using the vacuum method.

Be that as it may, I repeat that I have never had any problems (yet) bleeding a Series One, and although I didn't say so in my previous post I have never used a pressure bleeding device for the purpose, I have never found it necessary.
Accepted, you do postulate an "if"  my point is easibleed recommend 20 psi and that is greater than any possible vacuum you could generate by any means....

I had intended to go back to my post to address the "if" you use, but I ran out of editing time, yet again and my post became locked for editing.

Offline Ivor M

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Re: Tips on brake bleeding please
Reply #28 - Jan 10, 2022 - 15:23
To add to that the greatest pressure differential is across the smallest aperture which restricts flow. Where are these small holes, they are  in the master cylinder. Only when the bleed screws are closed does the whole system see the applied pressure. Therefore  when using the vacuum method the pressure differential is greatest from the bleed screw to the master cylinder output and not the reservoir.

Offline fulltilt

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Re: Tips on brake bleeding please
Reply #29 - Jan 10, 2022 - 17:26
One thing to watch with pressure , actually with reverse pressure - if fitting new lined shoes and use a G clamp to wind in slave cylinder piston(s) , it is possible to flip a MC seal feather edge.  It is more a known problem using "wind-back" tools for disc calipers prior to fitting new pads.   If you can't get fluid pressure at the pedal - the last place you wish to look    :huh:

Offline nickuk

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Re: Tips on brake bleeding please
Reply #30 - Jan 10, 2022 - 17:59
As raised above I wonder if the "wetting out" of components during assembly is a significant issue - seems to be done less now than when brake fluid was cheap and repairs common?

Also subjectively I find bleeding with silicone fluid easier.  (And yes I do understand that using it is whole other debate but I prefer it on lightly used vehicles).

Nick. 
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Offline antarmike

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Re: Tips on brake bleeding please
Reply #31 - Jan 10, 2022 - 18:48
One thing to watch with pressure , actually with reverse pressure ........ it is possible to flip a MC seal feather edge.

Call me dense, but I am not following the logic.  If you apply reverse pressure to force fluid from the bleed nipples back to the reservoir, how do you flip the seal in the master cylinder?

If the M/c push rod is correctly set with free play, the port that allows fluid back into the reservoir when brakes are released will be open and this provides the route from bleed nipple to reservoir without having to go past the seals in the master cylinder to get there. 

Are you suggesting that the flow rate will be so large this open port cannot cope with the fluid going through it and into the reservoir, resulting in a  pressure build up at the lip seal to the point it is flipped backwards?   How likely is this? 

I am not a fan of reverse pressure bleeding but this is not a scenario I every envisaged would be possible.

Surely however you bleed*  (except the old fashioned foot down, foot up, foot down routine) will mean the return port will always be open and will be the route fluid takes, whichever way the fluid is travelling?   

* pressure bleeding, reverse pressure bleeding or Vacuum bleeding.

Offline msm80

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Re: Tips on brake bleeding please
Reply #32 - Jan 10, 2022 - 19:13
As raised above I wonder if the "wetting out" of components during assembly is a significant issue - seems to be done less now than when brake fluid was cheap and repairs common?

Also subjectively I find bleeding with silicone fluid easier.  (And yes I do understand that using it is whole other debate but I prefer it on lightly used vehicles).

Nick.

Thank you Nick. I do partially pre fill my slaves and master cylinders at least knowing these have large surface areas that are best wetted first. I seem to recall this was always recommended during assembly of overhauled units anyway.

Someone else did mention the production line approach as I’d inferred as during one of my JLR factory visits a colleague asked that very Q querying how and why it was do easily done. It is a form of back bleeding because the fluid is introduced at the slaves and not top down from the reservoir.

My whole point being it is particularly applicable to 80” brakes that use 1/4” dia pipes instead of the later 3/16” dia on later S1’s. To my mind the larger capacity of the 80” pipework should make bleeding easier but might instead appear to require more effort and of course more fluid which ever way one tries!
Again pumping fluid in and upward as per production line systems at each slave in turn works for me.

On the subject of Silicone I last used this over 35yrs ago and still have some left! Yes a subject for another thread as that will likely generate more controversy. In any event I hope Alun gets a good pedal!

Malcolm

Offline fulltilt

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Re: Tips on brake bleeding please
Reply #33 - Jan 10, 2022 - 21:44
Thank you Nick. I do partially pre fill my slaves and master cylinders at least knowing these have large surface areas that are best wetted first. I seem to recall this was always recommended during assembly of overhauled units anyway.

Someone else did mention the production line approach as I’d inferred as during one of my JLR factory visits a colleague asked that very Q querying how and why it was do easily done. It is a form of back bleeding because the fluid is introduced at the slaves and not top down from the reservoir.

My whole point being it is particularly applicable to 80” brakes that use 1/4” dia pipes instead of the later 3/16” dia on later S1’s. To my mind the larger capacity of the 80” pipework should make bleeding easier but might instead appear to require more effort and of course more fluid which ever way one tries!
Again pumping fluid in and upward as per production line systems at each slave in turn works for me.

On the subject of Silicone I last used this over 35yrs ago and still have some left! Yes a subject for another thread as that will likely generate more controversy. In any event I hope Alun gets a good pedal!

Malcolm
Call me dense, but I am not following the logic.  If you apply reverse pressure to force fluid from the bleed nipples back to the reservoir, how do you flip the seal in the master cylinder?

If the M/c push rod is correctly set with free play, the port that allows fluid back into the reservoir when brakes are released will be open and this provides the route from bleed nipple to reservoir without having to go past the seals in the master cylinder to get there. 

Are you suggesting that the flow rate will be so large this open port cannot cope with the fluid going through it and into the reservoir, resulting in a  pressure build up at the lip seal to the point it is flipped backwards?   How likely is this? 

I am not a fan of reverse pressure bleeding but this is not a scenario I every envisaged would be possible.

Surely however you bleed*  (except the old fashioned foot down, foot up, foot down routine) will mean the return port will always be open and will be the route fluid takes, whichever way the fluid is travelling?   

* pressure bleeding, reverse pressure bleeding or Vacuum bleeding.

Flipping of MC seal feather edge does happen -  Goooogle the subject.   The only way I know that it does is compressing the slave cylinder plungers.   Those who have experienced or are wised up - first clamp the hose , then crack the slave cylinder nipple to avoid back pressurizing the MC.

Offline antarmike

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Re: Tips on brake bleeding please
Reply #34 - Jan 10, 2022 - 22:03
Flipping of MC seal feather edge does happen -  Goooogle the subject.   The only way I know that it does is compressing the slave cylinder plungers.   Those who have experienced or are wised up - first clamp the hose , then crack the slave cylinder nipple to avoid back pressurizing the MC.

Sorry, but I still think this is an impossible situation in a series Land-Rover.

We need some explanation as to how can this happen if the return port on the master cylinder is open and the seal is sitting in a closely fitting bore?  The only way pressure can develop on the seal is if the push rod is too long, and the return port is closed. If the port is open there is free passage of fluid into the reservoir so there should be nothing but the smallest of pressure on the M/C seal

My problem is that when you apply the brakes gently the system is under a similar pressure acting in the same direction (but only if the return port was closed when it should be open) and yet there is no problem. The seal does not flip when you generate a similar pressure via the brake pedal does it?

Reverse bleeding is creating tens of psi, (but as said earlier only if the push rod is incorrectly set and the return port is closed,) hitting the brakes hard is putting typically 800 to 2,000 psi on the seal in exactly the same direction.

We need some explanation as to why the seal should flip or else you might  just repeating an apocryphal tale? What is the mechanism that would cause the flip? How can the M/C be pressurised by reverse bleeding if the return port is open? Even if thge M/C could be pressurised, why would this flip the seal when braking doesn't?  Sorry this still makes no sense to me.

My goooogle search brings up an awful lot of "is flipped seal a real phenomenon or is it just a myth?" links. An awful lot of posts say it is a myth.
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Offline Trakgrip

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Re: Tips on brake bleeding please
Reply #35 - Jan 11, 2022 - 18:38
Flipping of MC seal feather edge does happen -  Goooogle the subject. ...

Hmm, well I have Googled the subject and as Antarmike says can find no evidence whatsoever that it actually happens, and although there is ample evidence that there exist people who claim to "know" it happens, or who claim to know people to whom it has happened, there doesn't seem to be a single person who can actually explain how or why it happens. Furthermore I can think of no engineering nor scientific explanation of why it could happen, nor why pressurising the brake system by compressing a wheel cylinder could cause it to happen whilst pressurising the system (probably to a vastly higher pressure) from the brake pedal cannot cause it to happen. There is no evidence of it being "a thing" prior to the invention of the Internet, and I am fairly sure that it would have reared its head as a problem at some stage during the 50 or 60 years when hydraulic brakes were in widespread use prior to the introduction of the Internet, if it really was a problem. So my suspicion is that it is a falsehood given credibility through uncontrolled repetition online (like many other Internet legends).

If anyone can provide a credible explanation of this apparently improbable phenomenon then please do provide it, otherwise I'm afraid that this gets categorised in the nonsense category.
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Offline antarmike

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Re: Tips on brake bleeding please
Reply #36 - Jan 11, 2022 - 19:04
......If anyone can provide a credible explanation of this apparently improbable phenomenon then please do provide it, otherwise I'm afraid that this gets categorised in the nonsense category.

Thank you.  If putting pressure on the bleed scews caused a pressure build up on the M/C seal, then brakes could never release. Brakes release because unless the master cylinder piston has been advanced into the cylinder past the return port to the reservoir closing point, there is always a clear passage for fluid to return from the wheel cylinders to the Reservoir.  As a vehicle is driven and brakes get hot, Brake fluid expands.  Why does this not build up pressure and flip the seal? Because the return port to the reservoir is open?

If seal flipping does occur on some modern cars (as some claim it does) I can only assume it has something to do with ABS system that under some circumstances free flow from the brake calipers back to the reservoir is not possible. Does the ABS modulator not allow free passage of brake fluid from the disc brakes when the vehicle is stationary and the ignition is off?   Only some explanation like this would explain the alledged folding of the M/C seal when Brake pad retractors are used to push the pistons in. (an event normally claimed for modern disc braked vehicles which I presume run an ABS system?)

But in a series I there should never be a situation where back bleeding (reverse pressure bleeding) the brakes, or closing up the pistons in the slave cylinders by using a G Clamp over the brake shoes should cause the M/C seal to flip.

My experience of ABS is zero apart from driving such vehicles, I have never worked on an ABS system so I might be talking gobbledy gook.  But I do know Series Is reasonably well and I will stake my credibility on saying on a series I, where the master cylinder push rod is correctly adjusted with the right amount of free play, flipping the seals cannot happen in by reverse pressure bleeding, or clamping the brake shoes in together.

Offline antarmike

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Re: Tips on brake bleeding please
Reply #37 - Jan 11, 2022 - 19:21

If seal flipping does occur on some modern cars (as some claim it does) I can only assume it has something to do with ABS system that under some circumstances free flow from the brake calipers back to the reservoir is not possible. Does the ABS modulator not allow free passage of brake fluid from the disc brakes when the vehicle is stationary and the ignition is off?   Only some explanation like this would explain the alledged folding of the M/C seal when Brake pad retractors are used to push the pistons in. (an event normally claimed for modern disc braked vehicles which I presume run an ABS system?)



Forget that bit about ABS Modulator, I was not thinking.  Modulator is between Calipers and master cylinder so whatever it was doing, passing or not passing fluid through it, it would not cause a pressure build up in the M/C.

Offline fulltilt

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Re: Tips on brake bleeding please
Reply #38 - Jan 11, 2022 - 20:01
People often change slave cylinder / seals and disregard the MC , consider it serviceable bleed using pressure on master cylinder seals that are worn / showing tears but have remained serviceable until that point in time. Fully foot stroke the cylinder so the seals are out of normal operating position into a part of the bore that is not too clever - result no foot pressure available to bleed.  That is MC seal failure , it is not 'flipping a seal' , yes a term used - but is it possible ?  , I take it that a seal has been dislocated or displaced - winding back slave cylinders getting the blame.
                 If you take such as a CB type or any standard design single-line master cylinder the piston should fit like a spool in the bore - a very neat fit.  Normally the gland.pressure, recuperating seal are so well restrained (in grooves)  and piston such a good fit in the bore - it should be impossible for the seals to be able to turn, I suppose some recuperating seals by valve design could.

If we look at Dual System MC - these tend to follow a standard design with a inner & outer piston , some of these tandem MC - the pistons can be as close fitting as a spool in a oil control valve (think Vickers/Sperry Rand) - so as above applies, some are not quite as close fitting by design , again to flip a seal would be difficult.      However there are almost identical tandem MC - where the piston fit to the bore - is not a fit, the design is such that the clearance is too great.  These pistons are not a spool as such - they never contact the bore , the seals are much heavier , at the time of a MC failure (internal bypass) the feather edge of the seals are worn off and the piston should still not contact the bore - it should be riding on the well worn seal.    If seals do - flip , then this is the type I would expect it (because there is sufficient clearance to reverse a seal feather edge).  The best way is to check and re-seal at same time as attention given to slaves calipers.   I fully replaced calipers recently on a Mondeo with 100K +  didn't take the MC off to check (for reason stated , lots of work , poor access etc.)
                 Today I was working on a Peugeot 207 with 106K miles up,  front calipers to live longer (wound back slowly) , discs, pads renewed,  handbrake cables replaced PITA   ,  tomorrow fit new rear slaves, new shoes, new springs,new auto. slack adjusters.   Again - not going near the MC , so - it may be liable to flip a seal.    btw -  apparently the Mondeo has a bit of a reputation as a flipper  MYTH or REALITY  - I don't know , not had the problem & didn't go looking for it   :huh:
There's more to life than Land Rovers , or as one garage owner said to me last week - they are a life sentence not motoring or a hobby   ;D

Offline antarmike

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Re: Tips on brake bleeding please
Reply #39 - Jan 11, 2022 - 20:48
The Master cylinder seal is slightly conical on its outside form.  The seal is actually a frustrum, but wahtever. At rest the very tip, largest diameter of the seal, is against the cylinder wall. Almost line contact.

The side walls of the seal are straight and since they form a conical shape, there is an increasing distance between the side of the seal and the cylinder wall as you move along its length, front to back.

At the back of the seal, smallest diameter of the frustrum is held more or less at the same diameter in all situations since ot attaches to the back of the seal.

As the seal is pushed forwards and presure develops, the sides of the seal bulge outwards under the presure.  As the pressure builds slowly more and more of the tapering sides bulges out to contact the wall of the cylinder and the seal becomes cylindrical rather than conical.

As the pressure increases almost all of the frustrum / cone has distorted outwards until it touches the walls of the cylinder being forced outwards by the increasing pressure.

Are we expected to believe that somehow the lip of the seal then folds back on itself and tucks itself between the cylinder wall and the sides of this cup shaped seal?, even though hydraulic pressure is forcing the side walls of the seal tight against the walls of the cylinder?

I think not.

But where does the pressure come from?  The port to the reservoir is open when reverse bleeding?


Offline fulltilt

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Re: Tips on brake bleeding please
Reply #40 - Jan 11, 2022 - 21:10
https://www.youtube.com/watch?v=w80LkZrlp34

Follow the commentary - regarding the clearance between the piston(s) and where pistons are well clear of the bore by design ,  this is where the possibility of a seal feather edge being reversed (most reversals being done when the MC has a age in years and seals are part worn).  It's all very well talking normal max. design operating pressure of the fluid being greater than any wind back pressure  ?  However when winding back you are applying pressure to the piston(s) where positioned foot off the brake pedal, pressure being applied at a abnormal position.

Offline fulltilt

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Re: Tips on brake bleeding please
Reply #41 - Jan 12, 2022 - 22:44
btw  -   some people have problems with soft pedal / air present with S1 - obviously ,  others have same problem with LR  11"  TLS  ,  well - I have had my moments , but never have I removed hubs to remove back-plate horizontal to shift air from one cylinder to another & then purge (and this is even using a Ezi-bleed).
                       I work on a few makes of cars , even though I am a highly qualified engineer working through EITB , C&G Craft / Technician to T5 , extra evenings for ONC / HNC - I am not so stupid not to buy a Haynes manual prior , I take notice of 'dire-warnings' often slightly different if ABS & other systems fitted.  Haynes do quite a good tech. job - I find it is such as the instructions of removing plastic trim etc. to get to where you need to be like fascia & trans. tunnel stuff.  If Haynes say there is just one Chinese finger securing a centre console - you can guarantee there are several & screws too.

So I just looked at a Mondeo Haynes No. 4619  - Braking System  9.7  15

Caution : Pushing back the piston (post 2004)  causes a reverse flow of brake fluid,which has been known to 'FLIP' the master cylinder rubber seals, resulting in total loss of braking.  KISS  -  new vehicle to me , if assistant available - I always try foot pumping brake pedal , no joy so soon went to pressure bleeding , tried the normal corner route , fluid flow at front but nothing to rear , BIG syringe used for vacuum as well as pressure , Son 1 complaining of how difficult it was to hold syringe plunder out (1" dia.) while I was spannering the nipple , no joy  , pumped the barrow tyre up to 30 psi+  & joy - I had a gusher at rear port & starboard   ;D
--------------
I did have bleeding problems that were overcome , I had left the battery connected so the vehicle could be central locked - warned son 1   don't switch the ignition on ,  did I that afternoon hear the car radio   :undecided:    Did I have air in the ABS module   :undecided:      (trailer job to main dealer to sort)  ,  two paracetamol & coffee break , returned to fray & found the barrow tyre flat that was to pressurize the Esi-bleed    ;D

Offline msm80

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Re: Tips on brake bleeding please
Reply #42 - Jan 13, 2022 - 09:36
 :we_need_pics:

For the sake of clarity on this flippin subject!
The recuperative seal in the master cylinder does both a pressure seal on depression and reverse seal as it is withdrawn backward, hence ‘recuperative’ seal. I fail to see how any flipping of this seal can occur given backward applied bleeding if the slot clearly visible in it is forced against the main bore of the cylinder. Same applies to the other seal that is totally enclosed within the bore and annular groove of the piston. What is key are the small ports in the recuperative seal seat cast into the main body. Akin to a steam chest in a steam locomotive or even a two stroke ICE movement of the piston dictates the fluid flow or closure depending on its relative position at the time. Crucial in all this is the length of the connecting pushrod which due to the multiplicity of variants out there for sale folks often find despite adjustment they cannot set it all up in the first place to either bleed or even operate the brakes in the first place. This is one time when a proper manual is essential to my mind.
Malcolm
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Offline lurch032003

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Re: Tips on brake bleeding please
Reply #43 - Jan 13, 2022 - 12:54
Hi okay everyone is going in about pressures and bled kits etc and checking wheels correctly adjusted up first but the master cylinder needs to be adjusted up right fir pedal height and checking it’s set right can make all the difference before bleeding and after bleeding as the book gives measurements to how to set up but you have to take in wear and tear of the vehicle can offset measurements, I found after days of using different  t types of bleeders that I tightened up the clutch pedal to take up slack and kept adjusting it up till I got a firm pedal and that was all it took ! Each wheel stopped perfectly , stopped in straight line and emergency all lock up then adjusted handbrake so everything despite bleeding about a gallon through was all down to master cylinder and pedal adjustment.
Well that’s what worked for me and may be worth a try and I do hope u find a way that gets yours all set up nicely , remember after a couple hundred miles or less go around and readjust wheels for bedding in .
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Offline Ivor M

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Re: Tips on brake bleeding please
Reply #44 - Jan 13, 2022 - 13:05
clutch pedal?

Offline lurch032003

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Re: Tips on brake bleeding please
Reply #45 - Jan 13, 2022 - 15:22
clutch pedal?
Meant brake my apologies

Offline fulltilt

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Re: Tips on brake bleeding please
Reply #46 - Jan 13, 2022 - 22:27
I have had a search through a few Haynes manuals - can't find it but one has a warning about tearing the seals -  I think it must have been a Fiat book.

Peugeot 2006 to 2009  (4787)   and  Focus  2001 to 2005  (4167)   -  both have the 'wind-back- warning  -  "as well as preventing any chance to master cylinder seals".

I was very wary of overhauling / bleeding on a system with ABS first was a  Xsara Picasso - I had no problems at all.   Other ABS cars I have had general bleeding problems - overcome with a Ezi-bleed , by myself - I also use a Europat Visibleed  (the one with the plastic bottle with valve inside) - no fuss no mess with plastic pipes in jam-jars , abt.  £4 from Halfords,  like the Ezi-bleed I can't praise it enough.

All I can suggest is LR - don't believe all you read (I don't about the LR 11" TLS that have a terrible reputation - I think people who do and haven't changed their flex. hoses should.

Don't fear  ABS  systems ,  follow Haynes to the letter , you will learn more that you can put to use with primitive systems.     Talking primitive but  'vorsprung durch technik'   ATE  manuf. systems  ,   in 1975 I renewed slave cylinder seals on 1  1968  VW  1300cc  Beetle,  brakes had been good , but I could not bleed at all, much head scratching - must be the MC  ,  I looked at it - just a rusty lump , so I chopped it out . Paid top £ at a franchise VW dealer  (IIRC  £40)  for a VW boxed ATE  master , re-piped all with IMI  Kunifer - bled perfectly no problems.  So - that was a MC that failed when foot pumping  !

btw  -   I understand car manufacturers have no grief or mess on the floor at the end of the line & they use vacuum bleeders , they may be just a Sealey  ?

Offline Trakgrip

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Re: Tips on brake bleeding please
Reply #47 - Jan 13, 2022 - 23:06
I'm sorry to have to say that I haven't seen a Haynes manual I consider to be worth the (revolting recycled) paper it is printed on since about 1979. They seem progressively to be becoming dumbed down to the point where even simple tasks are considered too complex for an owner to undertake.

For example, in the TD5 Disco manual even a straightforward diff overhaul is considered too difficult, whereas the first Haynes manual I bought (BLMC 1100 & 1300 series, circa 1972) covered a full strip and overhaul of the gearbox.

I suppose it probably reflects the dwindling practical skill of today's average Joe Public, but I simply wouldn't bother buying one now, it's manufacturer's service manual or nothing for me now.

Offline antarmike

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Re: Tips on brake bleeding please
Reply #48 - Jan 13, 2022 - 23:23
Have we concluded that flipping back the master cylinder seal cannot and does not happen in a humble series I?

Is that all we need to say?

Whether or not it happens in some more modern vehicles (with or without ABS) is surely taking this conversation too far and into a realm completely out of scope for the LRSOC forum.

Can we conclude that if we feel it useful to push the cylinders in with a G Clamp over the shoes, the seal will not flip?

Can we conclude that if anyone wants to try back pressure bleeding feeding fluid into the bleed nipple, the master Cylinder seal will not flip?

Has anyone ever personally flipped the seal on the M/C of a series I

Only if someone can say, yes, I myself did it because I did this or because I did that, does the possibility of series I seal flipping move from being an Apocryphal tale to become a real happening. 

If there is someone who has done this maybe they should now explain exactly what they were doing on their series I for this to happen.

Can anyone say that have done this themselves or actually seen it happen to someone else on their series I?

(Not heard about it happening , not read about it happening, not read in a Haynes manual that it can happen, but actually done it or been there when it happened.)

Is it time to leave the seal flipping debate behind us?
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Offline Trakgrip

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Re: Tips on brake bleeding please
Reply #49 - Jan 13, 2022 - 23:30
I think the answer is "yes" to all the above (except the last three or so where the answer inconveniently is "no") and it is time to leave the flipping flipping debate behind.

It can't happen on a Series 1.
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