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MG Midget and Sprite Technical - Bleeding Brakes Part 3

So, after using the Lazza method, I had a fair pedal - firm less than halfway down. But after 24 hours I had lost it again. The only explanation I can come up with is that air has re-entered the system - unless it was hiding somewhere immediately after Lazzage.

There are no leaks of fluid. Can air enter without fluid leak? And, where's likely?

Yesterday we clamped the rear hose and bled the fronts. The result was a lot of fizz - big stretches of little bubbles - and after the fluid ran clear and all was closed, we had a fair pedal. But taking off the rear clamp lost most of it again.

Where next?

(sorry to go on about this, but I drove up and down the drive this morning, and the lack of brakes was rather depressing)
Nick and Cherry Scoop

It sounds like clamping the rear hose isolated and reduced the volume of fluid to be moved alowing you to sucessfully bleed air out of the front brake hydraulic routes.
Unless there is a fault with the M/C those should now remain bubble free and now allow you to properly bleed the rear brakes. You could clamp the front hoses before doing this but it shouldn't be necessary.
GuyW

While doing Lazza, I had pressure on the pedal for 36 hours, and there was no noticeable movement towards the floor, so I have assumed that the MC is OK. Are there other things that can go wrong in the MC so that air is admitted? I used the best of the three I had, but it is fairly ancient, and I don't fully understand how it works.

In particular, what is the tiny hole for - upstream of the primary cup? I've not checked that it's open, though I assume it is.
Nick and Cherry Scoop

(that would be downstream)

After discussions with my Jaguar pal today, a partial dismantling of the m/c is called for. Perfect timing, as the bonnet has been on for 28 hours, and now it must come off again. Lucky I left my ropes and bungees in place (see below).


Nick and Cherry Scoop

Nick
I have not done this myself, and dont really understand the necessity, but since you seem to have tried everything, could bleeding the master cylinder be of benefit?
When I have changed a MC before, I have simply replaced it dry, and then bled through the brake and clutch slaves. But maybe I was just lucky?
Graham V

That's what my pal says, Graham. And there's no prospect of my doing that with the bonnet on. Grrr
Nick and Cherry Scoop

As a Frogeye owner I dont understand why you want to take the bonnet off just to work on the master cylinder.

3-4 years ago there were problems with new TRW brand dual msster cylinders. The complaints were mainly leaking or residual brake pressure. I did raise the issue with them at a trade Mechanex exhibition that they were exhibiting at in Sandown (Esher).

Alan Anstead

This TRW issue is bothering me. I bought a M/C from Moss when I was gradually buying parts for my Frog renovation, maybe 3 years ago, still in box. Will it not work properly? I doubt they'll take it back now.
Bill Bretherton

Bill, you may be lucky but the first one I had leaked straight out of the box and I had residual pressure issues with the replacement.

Trev
T Mason

Can't understand why you are blaming the mc
surely if you have a good pedal with the rears blocked off the front and the mc must be ok and the problem is aft
Are the rear shoes adjusted up and plumbed up correctly------
willy
William Revit

Look at mgaguru for info on brakes - the system is pretty much the same on both cars

The TRW MCs have always been hit and miss, the Caparo ones have a much better reputation
Dominic Clancy

Alan - if you like working on the master cylinder with the bonnet on, I salute you, and I envy you your spine.

Willy - I didn't say a good pedal: it was fair, by which I mean halfway down (compared to what I've had so far, which is nothing, this counts as fair). I will take a deep breath and start again - shoes, plumbing, reservoir full.

But the MC is the only thing I haven't tried over these months. Maybe if I got some fluid in ahead of the primary cup, it might help.
Nick and Cherry Scoop

If you have a bottle of soda water it only starts to fizz and the bubbles only start to appear and rise to the top when you unscrew the top and release the pressure.

So, (as Lawrence would refuse to say) if you wedge a stick on the pedal to hold the pressure overnight, you may get a firm feel to the pedal at some point in its travel, but any air in the system will remain there, unable to form into bubbles and rise up because of the held pressure, as in the soda bottle. It may seem to give a firm pedal but I think this will be a false impression as you haven't actively got rid of any of the air.

OTOH, if you can get at least a working though maybe still spongy brake, then driving for a few miles over typical bumpy roads whilst using the brakes will shake free the small bubbles clinging to unions and hiding in corners so that they form air bubbles large enough to bleed out at a second (or third) attempt.

Get the car going and drive up and down the lane a few times then re-adjust the rear brakes and bleed again.
GuyW

Nick
I have just finished installing a TRW master cylinder, and managed to bleed the clutch without too much problem (having said that, I hope I do t go out to the garage and find a soft pedal).
Initiall I bled it with, as advised in Mascot, the front right hand side jacked up, getting the help of "she who must be obeyed".

The pedal was fairly firm but the clutch bit very low to the floor, which clearly wasn't right.
I then found in my garage a "Vizibleed" tube that I had bought from Halfords many years ago but never used. It is for "one man bleeding", cost about £4 and is just a piece of plastic tube with rubber at one end to fit over the bleed nipple, and a one way valve at the other.
My first attempt was failure as it needs a lot of pressure to get through the one way valve so the rubber at the other end just came away with fluid going everywhere. So I took two very small cable ties and fasted the rubber piece both to the plastic tube and then to the nipple.
Then just about four or five presses on the clutch pedal and the job was done! I was very surprised that it was that easy so maybe it might work for you?
Looking at the Halfords website they now sell two versions, one has a small container, but I used the other cheaper one and made do with a jar!
If you try this, be careful to open the nipple just a tiny bit, as otherwise I found air escapes around the threads - but that might just be because of the set up on my remote bleeder.
Graham V

I've been lent a couple of visibleeds, Graham, but they don't really allow 'one-man'bleeding', I found. You're always having to get out and check what's happening at the nipple, and refill the reservoir, plus as you say, with the back pressure of the valve, fluid comes down the threads (and maybe air in).

Guy, I'm going to pretend this is my first attempt, and go through the whole process, but I might just do a little with the mc first, in case the fluid in there is flowing along the walls, around a long bubble. Is that tiny hole downstream of the cup supposed to let air out? I must check that it's open.
Nick and Cherry Scoop

Nick
The way the piping is attached to the front brakes, getting air out is a problem
Air can be removed from one wheel cylinder via the bleeder but the other cylinder is an air trap and the best way is to bleed at the bleeder first then get someone to hold the pressure on the pedal and bleed it by loosening the flexi hose at the wheel cylinder enough to let the air out then tighten up
Don't pump the pedal fast as it will froth the fluid if there is air in there, and, once you let a bleeder loose and tighten it again only release the pedal back slowly to allow time for fluid to get back in the mc instead of sucking air in past the cups
By the way, that's what that tiny hole in the mc is there for ,to feed fluid into the mc cylinder--If you're getting fluid at the wheels and you can pump the pedal up then that hole is clear
Slow and steady wins the race--------

Usually if I'm having bother I use the stamp method-messy but works
2 people needed-open a bleeder and put your receiver hose on it and hold it on the bleeder so it can't get blown off-one person absolutely smashes the pedal to the floor and holds it firmly down-person 2 nips the bleeder up immediately , then slowly release the pedal and slowly pump the pedal up again and then repeat and then move on to the next victim

willy
William Revit

Willy, My dad (who ran a small garage business) used that method. I was given the job as a young teenager to stamp on the pedal. Great fun trying to get fluid all over dad who was at the business end!!
Bob Beaumont

Thanks, Willy. A couple of different methods to those I've used already gives hope. Tomorrow I will entice the AA out there with coffee and bonbons, give her a print of your latest post, and see whether she can spatter me with Dot 4.
Nick and Cherry Scoop

That's quite a picture you're painting Nick! I can't help wondering what Prop would have made of the whole scenario......
Bill Bretherton

Nick
I am really feeling your pain.

If you aren't losing fluid, I would have thought its unlikely more air is getting in the system.

Have you tried using an Eezibleed kit? I know many people swear by them as the continuous pressure doesn't give expelled air a chance to sneak back in as can happen in the traditional two person method.

A friend of mine once mentioned he used a suction method, with a suction pump, a bit like a sophisticated turkey baster, to suck the fluid and air out at each nipple.

Or if you have tried everything else, maybe you could try reverse bleeding with the idea to force the fluid together with air back up through the system so the air releases through the master cylinder. I guess that would need to come from the clutch bleed nipple connected to each brake nipple in turn, but you may be running the risk of fouling up the clutch hydraulics, which would move you from bad to worse! I remember reading a long time ago about a system of connecting a reserve of fluid, sited at a higher level than the MC to facilitate reverse bleeding.

Good luck
Graham V

Blimey, Bill - I hadn't seen it like that. It still sounds good to me on Sunday morning, though.

Thanks, Graham. Glad you didn't say your heart bleeds for me. I've tried everything except reverse bleeding, which doesn't appeal much - though I have gone so far as to connect a tube to my oil can in readiness. We'll have a go at Willy's ideas today.

The clutch bled perfectly, first time, but then, it's such a short run, with no sticky connectors on the way. My clutch hydraulic problems in the past have been more about the rubbery bits.
Nick and Cherry Scoop

I may have lost understanding of the sequence, but:
I thought that overnight sustained Lazza pressure was followed by an ability to bleed quite a lot of fine air bubbles out of the front. That is why I went on about the fizzy water bottle analogy. Maybe pressurising for 36 hours, then sudden release of pressure encouraged the gas bubbles to be released from the fluid enabling you to bleed them out of the front brakes.

I would then have immediately clamped off the front hoses close to the fixed pipework and bled the rear brakes, whilst this post Lazza effect was still active. If the Lazza treatment followed by release of pressure was like the bubbles in fizzy water then you should then have got any remaining air out of the rest of the pipework.

GuyW

Braided hoses on the front, Guy.
I wasn't allowed an assistant today, so I did some other things, including an all-round check on shoes and plumbing.
By the way - you know what we said about clutch slave travel? Well, 3/8" is too tight, and I'm going to give it a bit more, maybe 1/2". The three pivots ahead of the slave rod are obviously losing me a bit.
Nick and Cherry Scoop

Even without clamping off the front, if you had just bled them then I would have immediately bled the rears whilst the fronts were known to be good.
GuyW

yeah -closest wheel first and work your way out
William Revit

Nick
Dont know if you have sorted it yet or not. But if not, do you have drums or discs on the front?
Its just a long shot but the reason I ask is I just saw a youtube video, where someone couldnt bleed their brakes fully, and the reason was that they had fitted the two front callipers the wrong way round, with the result that the bleed nipple was at the bottom of the assemblies, rather than the top.
As I say its a long shot.
Graham V

No - it's drums on the front, Graham.
I still haven't managed to book a slot with the AA.
Nick and Cherry Scoop

Is it permissible to depress the brake pedal while Eezibleeding?
Nick and Cherry Scoop

This thread was discussed between 23/07/2018 and 07/08/2018

MG Midget and Sprite Technical index

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