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MG Midget and Sprite Technical - Bleeding clutch ... again

Slowly driving me potty, this clutch.
The master cylinder was leaking so have replaced the seals (this is the second 'reconditioning' but it's NOS and has done less than 20k miles).
Now there is zero pressure in the system.

The set up is a la Lawrence/Guy with a remote bleeder at the same height as the master cylinder but despite using a vacuum tool to pull the fluid through and having the very glamorous assistant spend half an hour pumping the clutch pedal, there is still no resistance and no pressure.

Can I have installed the seals in the cylinder back to front and if so would that make any difference?
Is the cylinder shot and if so does anyone have a recommendation for a replacement - Paul Hunt?

I did get a tiny bit of resistance twice but on the next press of the pedal it disappeared - might that be a sign of something amiss?

Many thanks!
Jeremy MkIII

Jeremy, does the fluid level go down in the m/c when you press the pedal?
And, when you press the pedal is there any movement at all underneath of the clutch arm or pushrod?
GuyW

Thanks Guy,

no, the fluid level remains the same when the pedal is pressed. It has dropped when I've applied the vacuum and fluid has been transferred to the container.

Haven't checked if the pushrod moves, will need to ask the very glam assistant for her help again.
Jeremy MkIII

I did mean to watch the fluid level as the pedal is pressed down. You will need long legs, long flexible neck or an assistant. The level should drop a little. If, as you say isn't dropping at all, then to me that would suggest a fault with the m/c.

If there is movement down below (as sarah milligan would say) then it suggest there is still air in the system. Try pushing the slave piston back up the bore and wedging or clamping it there whist you then bleed the system.
GuyW

Just checked. No movement at either end ie the reservoir level remains unmoved as does the slave cylinder piston.

So it seems it maybe the m/c.
Anyone any experience of this
https://tinyurl.com/y5sddsls
(Image 1)

or these people
http://www.speqtox.com/index.php?main_page=product_info&products_id=227377
(Image 2)

I'd prefer the latter but am a bit reluctant to order from an unknown European (other continents also included) website.





Jeremy MkIII

Mike will probably be along to discuss the second item.

The first seems very low priced, I've no idea it might be better quality and/or longevity than others, or the same or worse.

The generic plastic ones I've got from MGOC haven't leaked and bleed very easily.

I worried about the piss-poor rubber of the repair kits also being in the new m/cs but not so far.
Nigel Atkins

you may be better to call a recommended and reputable specialist supplier such as Powertrack
https://www.powertrackbrakes.co.uk/wcylinder.html#cylinder
David Smith

Buying new, from a reputable supplier, may be the solution. But if you have replaced the innards, perhaps you assembled the valve disc and/or the piston seal wrongly. Maybe worth a check first?
GuyW

Nigel,

thanks for the MGOC pointer.

David,
thanks for the Powertrack suggestion but I think that is Paul HUnt?

Guy,
yes I wondered if that might make a difference (see opening post) so will do it first - noting to lose but a bit of time:)
Jeremy MkIII

Jeremy,
do remember my luck with parts, mine's now probably leaking as I type, and I looked it up and it was 5 years ago it was bought and fitted so the good stock might have been all sold by now(?), but no worry as I'm one of the few to get the faulty parts! :)

By Paul Hunt I thought you meant mgb-stuff Paul Hunt.
Nigel Atkins

Yes there are two Paul Hunts (a lot more obviously but for MG related stuff)
The one mentioned is the PowerTrack chap and a very nice chap he is too.
Jeremy MkIII

Jeremy - no idea if PowerTrack = Paul Hunt, but a pal of mine who runs a historic racecar preparation business has used them for decades and says their knowledge is encyclopaedic and he won't use anyone else unless he absolutely has to,
David Smith

Thanks David, that's a great endorsement so will give them a shout if it turns out the m/c is shot.
Jeremy MkIII

Jeremy
I feel your pain - I've been there and its so frustrating.
Hopefully further inspection of the M/c will reveal the answer.
Last time I had that problem I went out and bought an eezibleed and it sorted it for me.
The other thing I have done that helped on my MGA (which has a shared m/c with the brakes) is to connect a plastic pipe from a brake slave cylinder, direct to the clutch slave, and pump the foot brake. As that pumps the fluid in the opposite way to traditional bleeding, it can force locked air up and out of the m/c, the way air likes to travel, rather than in the opposite direction.
Not sure if it could work for you, as you would be more challenged not to (a) let the brake m/c drop too low, and (b) spill fluid out of the clutch m/c. But I mention it in case you fancy a try.
Graham V

Something I do when first filling a system, clutch or brakes, and it occurs that with all the discussions I have never seen this mentioned. I crack open one bleed nipple - rear left wheel or clutch, before starting to put any fluid in the m/c. It helps to control spillage to put a length of tubing on the nipple. Then I start to slowly add fluid to the m/c, checking for when it appears at the bleed point. Once there is a reasonably consistent flow there I close the nipple and complete filling at the top end.

Only when this is done do I then bleed in the normal way, although I usually use an easybleed as I work alone and it makes things quicker. I was shown this pre-bleeding routine for filling an empty system nearly 60 years ago and assumed that is how everyone does it. But if one were to fill with all the outlets closed it seems obvious that it will result on odd pockets of air getting trapped. I believe this filling routine helps to purge air out and I can honestly say that I have never had the difficulties so often reported.

Maybe it's too obvious and everyone does this anyway?
GuyW

Thanks Graham, not heard about your idea of connecting brake and clutch circuits so that's another solution to bank!

Guy, will your method work with a slave cylinder extension which has the bleed nipple at (or about) the same level as the m/c such as yours and Lawrence's (and which I've copied)? My logic says it should but does it?!

Took the m/c out again this afternoon, a job done now with eyes closed so will strip it down tomorrow and see if the seals have been correctly (or not) assembled.
Jeremy MkIII

Yes Jeremy, it does. As the fluid goes down into the slave cylinder it then rises up until it spills out at the bleed nipple which, although raised near to the top of the bellhousing, it is still below the m/c level.


I am only really suggesting this for when filling an empty or drained system for the first time. I believe that the flow of fluid drives the air bubbles out before it and gets rid of at least most of the air before bleeding properly.

Incidentally. my 1275 car uses a concentric slave cylinder for the clutch, with a bleed nipple extension up beside the clutch housing. That one actually self bleeds. All that it requires is to open the bleed nipple and count a few seconds and then close it again. One doesn't have to press the clutch or use any sort of assistance, it bleeds any air out unaided.
GuyW

Well I followed the advice in this link - worked first time.

No I didn't need to remove wheel or seat but I'm on the smaller size to start with ! or get and assistant to do the pedal.

http://www.spriteparts.com.au/tech/bleeding.html
richard b

Jeremy
One other simple thing just in case.........

Slave cylinders are often sold with the bleed valve in the wrong aperture. That is to say, at the end, rather on top. Why? - so it fits in the box.

If your bleed valve is at the end rather than the top, there will always be a small reservoir of air that can’t escape.
I don’t think this is your problem, as I believe you are not getting any fluid through yet. But just in case.

Graham
Graham V

Guy, oh I wish mine did the same!

Richard, thanks for the link and good to know it has worked for you. Not sure I'm supple enough to perform the task!

Graham, think the nipple was in the right place but it's been replaced with an extension pipe which brings it up level with the m/c, so it should bleed easily and tbf it has in the past so my thoughts are faulty m/c.

Jeremy MkIII

Jeremy, Alan Anstead did a further article in Mascot (MASC mag) about drilling out the original bleed hole when the extension pipe is fitted that then removes the potential air bubble resting place in the cyclinder.
It only involves drilling out the original nipple seating andd oes not damage the threaded portion of the hole or the area swept by the cylinder if I remember correctly.

I'm not good at filing such good ideas away - maybe Alan will see this and post it.

R.

Oh if you want to use the method I linked to, just get an assistant to pump and do the blled bit from below.
richard b

I followed that advice of Alan's for my Frogeye clutch. It of course ONLY applies if you are using an extension hose of the sort used for the rear brake lines. Not if you were fabricating a hard pipe extension ;-(

The other thing that largely gets rid of the same problem is to push the slave cylinder piston right back up inside the bore, and clamp it there whilst then pumping and bleeding the clutch. This also takes the clutch spring compression/ movement out of the equation, so giving greater control over the bleeding process.
GuyW

It is good to know that someone reads what I submit to MASCOT Magazine.
As Guy quite rightly points out it can only be done if using a flexible hose to the remote bleed nipple as drilling the cylinder port removes the seating required for a 'hard' line.
Alan
Alan Anstead

Richard, I read Alan's article in MASCOT too but had forgotten it applied only to flexible extensions. As mine is made from metal brake pipe it still has the need for the 'seating'.

I tend to read the technical stuff first in MASCOT so that usually means something in Alan's reports or articles and then move onto the social gatherings stuff.

Guy, I opened the bleed nipple as you suggested, topped up the m/c and lo and behold fluid flowed out of the nipple. However the pedal pressure was non existent.

Just had a thought whilst writing this, did I close the bleed nipple before pumping the pedal?

To the garage!

Yes bleed nipple was closed but a quick application of the vacuum pump has produced a rock solid pedal. I have a clutch again :)
Who'd have thought just one seal the wrong way round could have made such a difference?
Jeremy MkIII

Jeremy
Good news that you have solved the problem.

A little project if you have to do it again, make a little converter - steel pipe nipple to flange sealing and you can enjoy the AA mod !
richard b

Jeremy
Pleased you have it sorted. That feeling of finally getting a hard pedal is fantastic isn’t it (and no it’s not a double entendres !)

Graham V

Thanks Richard and Graham, yes it's a good feeling; nothing like a bit of problem solving especially when there are so many people more than willing to chip in with advice and encouragement.

BTW Richard I do have a set up similar to the one described by Alan in MASCOT but with a 'hard' line rather than a hose. Guy and/or Lawrence Slater I think it was who came up with the idea. Red arrow shows top of pipe in the attached image.

I too can now recommend the vacuum pump method for bleeding the clutch. I overdid it the first time and had to refill the m/c. It took less than 5 minutes to get from no pressure to hard pedal. That was £10 well spent.

Thanks for all the help!




Jeremy MkIII

I certainly wouldn't claim that idea as mine! Alan probably pre dates me with it but I think it has been knocking around for many years, it just resurfaces from time to time.
GuyW

This thread was discussed between 21/10/2020 and 26/10/2020

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