New master cylinder sticking

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jagnut66
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New master cylinder sticking

Postby jagnut66 » Sun Apr 02, 2017 10:35 pm

Hi,
Just wanted to pick peoples brains on this for any ideas.
I've bought a new Lockheed master cylinder, the old one was well overdue replacement, I even found rust in the bore.
However the new one keeps sticking on return, when under any sort of load. I have soaked the rubber parts in brake fluid for the afternoon, however although this has freed things up and the plunger mechanism returns fully nine times out of ten, just as you think it's okay to fit it will stick, just short of the retaining washer, which of course allows the fluid in the cylinder to seep out past it. Push it a couple of times and it will free up again, for a while............... :roll:
Any suggestions on how to stop it sticking will be gratefully received, as at present this is the only thing keeping her on axle stands and I'd really like to drive her again.
Many thanks in advance.
Best wishes,
Mike.
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beero
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Re: New master cylinder sticking

Postby beero » Sun Apr 02, 2017 11:23 pm

I have know rubber flexible brake hoses to perish inside and cause brakes to stick on. This could stop the fluid being pushed back to the master and could cause your problem. Do you know how old your flexies are? Older than 7 - 8 years I would change them anyway.
If flexies are all new then something I would try is backing off the adjusters by 1 or 2 clicks to give you more pedal travel. That extra bit of momentum when you come off the brakes might help.


kennatt
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Re: New master cylinder sticking

Postby kennatt » Mon Apr 03, 2017 8:43 am

I take it,by your comments that its not fitted to the car yet,but don't understand what you mean by saying it leaks because it isn't fully returning to the circlip. remember that the system is designed to hold slight positive pressure ,to hold the shoes close to the drums,so if on the bench may not return,because the positive pressure would assist the return spring.If fitted and still leaks,can't see how it can,unless its faulty, at any stage in the plungers position in the bore the washers should hold the fluid.

philthehill
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Re: New master cylinder sticking

Postby philthehill » Mon Apr 03, 2017 9:46 am

The line pressure (8lb sq in) is there not to hold the shoes close to the drum but to keep the cups of the brake cylinder seals expanded against the brake cylinder walls and eliminate the possibility of brake fluid escaping past the cup seals.
See Minor wksp man Section M, page M5 for full details.
The brake snail adjusters are used to keep the brake shoes close to the brake drum.

There should be no brake fluid leak past the seals whatever the position of the piston inside the cylinder.
I would suggest that the cylinder is stripped and examined to determine what is causing the piston to stick and not return and is allowing brake fluid to seep past the main and secondary seals.
I suspect that dirt has got into the cylinder bore and is causing the problem.


kennatt
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Re: New master cylinder sticking

Postby kennatt » Mon Apr 03, 2017 4:32 pm

yes I agree Phil,but must also assist the shoes since after a long stand of a couple of days,most need a couple of pumps to bring the pedal back up,perhaps a more exact wording would be it holds the pistons up against the shoes,yes maybe that's a better description.

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amgrave
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Re: New master cylinder sticking

Postby amgrave » Mon Apr 03, 2017 4:47 pm

Once fitted you will probably find the master to be OK. The shoe return springs acting on the slave cylinders will assist the master piston back to it's rest position.


jagnut66
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Re: New master cylinder sticking

Postby jagnut66 » Wed Apr 05, 2017 9:10 pm

Hi,
Thanks for your replies.
I have know rubber flexible brake hoses to perish inside
The front two I have replaced with new Goodrich items, there was one already fitted to the drivers side front, I removed this to fit a new one. (Why someone would fit one Goodrich style hose and not replace the other I don't know?? Anyway both the front are new now.....) The existing Goodrich style (don't know if it's genuine or not) hose appears to be in good condition and may not be that old, I can see light from one end to the other and no internal bulges, so I have used this to replace the original style rear hose.
All brake pipes up to the rear axle have been replaced with Cunifer pipe, the rear axle pipes will be changed when I sort out the axle.
The master was fitted to the car but then removed for a closer look.
I have now given the rubber parts another soak whilst I flushed out the bore to ensure no grit is present. All the parts were then refitted and Red grease applied. This seems to have freed it all up (touching wood -- as well as my head!! :P ).
However I still have a weep past the plunger as it returns to rest. At rest it doesn't appear to leak, nor during operation (this is on the bench, by the way). This may or may not be a problem?? Advice please, shall I try refitting / bleeding? Would it be wise to have another master cylinder on standby?
The seller has said he needs to consult his supplier and that they would then probably want it back to assess it, before commenting........................
Which, I presume, translated means: They will take it back and then blame me and say they are not responsible and I don't qualify for an exchange or my money back........
Best wishes,
Mike.
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kennatt
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Re: New master cylinder sticking

Postby kennatt » Thu Apr 06, 2017 7:14 pm

under the sale of goods act the seller is responsible for repair replacement or refund ,his supplier doesn't enter the equation, try fitting it and see if it still weaps.

DAVIDMCCULLOUGH
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Re: New master cylinder sticking

Postby DAVIDMCCULLOUGH » Thu Apr 06, 2017 9:09 pm

I fitted a new cylinder a few years back and the seals went after about 1 1/2 years and probably around 8000miles. I sourced a set of genuine Lockheed seals and its been in place now with no issues for several years. If you are having doubts change them now whilst its out on the bench, rather than going through the whole process again!


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Nickol
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Re: New master cylinder sticking

Postby Nickol » Fri Apr 07, 2017 7:42 am

According to the manual there should be a dished (copper?) washer with holes fitted into the MC. Mine did not have one when I then fitted new cups and None of the normal suppliers can provide one. The MC seems to work without it........

Could however, this be the cause of the return problem?
Gott schütze mich vorm Sturm und Wind und Autos, die aus England sind.
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jagnut66
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Re: New master cylinder sticking

Postby jagnut66 » Fri Apr 07, 2017 9:20 pm

Hi,
I have now purchased another from one of our main suppliers, via eBay, for a considerable saving, not one I could ignore anyway. Hopefully this will prove to be okay and will get me back on the road.
Thanks for pointing that out Nickol, I am also in discussion with my original supplier, so that is ongoing at present.
I also note David's suggestion about getting some Lockheed seals and replacing my existing ones, so I will start looking for some straight away. Once sourced I will store them for future use. The securing bolts for the master are round the right way for sensible removal and will be well greased (good old copper grease), so this should make for (relatively :wink: ) painless removal next time.
I shall pick up the replacement master from the Post Office in the morning, so keep your fingers crossed and hopefully Olwyn will be back on the road by Monday.
Watch this space..............................
Best wishes,
Mike.

PS: By 'dished copper washer' you are not referring to the one at the back (inside the cylinder bore), just ahead of where the rear pipe connects are you?
This has holes in and is the one they tell you to remove the rubber seal from when fitting front discs, see below:
Attachments
Morris Minor brake master cylinder adaption diagram.jpg
Morris Minor brake master cylinder adaption diagram.jpg (30.95 KiB) Viewed 1049 times
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Nickol
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Re: New master cylinder sticking

Postby Nickol » Sun Apr 09, 2017 9:53 am

Morris%20Minor%20brake%20master%20cylinder%20adaption%20diagram.jpg
Morris%20Minor%20brake%20master%20cylinder%20adaption%20diagram.jpg (39.77 KiB) Viewed 1031 times
this is the culprit.

I have not seen this modification for the seal removal bevor but mine does not have disc Brakes anyway, which is probably why..
Gott schütze mich vorm Sturm und Wind und Autos, die aus England sind.
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jagnut66
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Re: New master cylinder sticking

Postby jagnut66 » Tue Apr 11, 2017 11:38 pm

That washer is in both of my new Master Cylinders Nickol, just a plain one though, no holes in it?
Best wishes,
Mike.
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jagnut66
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Re: New master cylinder sticking

Postby jagnut66 » Wed Apr 19, 2017 11:33 pm

Well a thorough clean and flush through seems to have done the trick, I now have working brakes and a road friendly car again.
Well I would do if the engine hadn't decided to play up.................... :roll:
So the fun continues....................
Best wishes,
Mike.
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