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MG Midget and Sprite Technical - Frogeye master cylinder

Hi
I am about to change the clutch slave cylinder and while I'm about it, thought I would put in a new master cylinder.
Having a quick look, it seems as if the master cylinder will not come out unless I remove the pedal box first. The workshop manual doesn't mention that, so just wanted to check I hadn't missed a trick?

If I just decide to change the seals, I assume the same applies?

Thanks

Graham
Graham V

Yes it does need to come out. If you get a new one make sure its an AP Caparo one as the TRW ones sold by most are rubbish.

Trev
T Mason

Thanks for clarifying that Trev.

But first I am having a problem with the clutch slave cylinder. I haven't taken it out yet, but just taken a good look from under the car - it looks a nightmare.

Access to the bleed valve which is at the top of the slave looks almost impossible. I can barely see it, so cant see how I will be able to get a tube on it and open it to bleed it.

Any suggestions gratefully received!
Graham V

No, the seals can be done without removing the pedal box. The front bolt on the MC will come out OK, and then by slacking the rear one a little you can rock the MC up at the front a bit, which will both reduce the flow of remaining fluid and help you to get the forks over the pedal horns without losing your adjustment. I would put the front of the car up, too.

Good luck with those seals.
Nick and Cherry Scoop

Once you dive into the driver's side and pull the big grommet out, and get your head into the footwell, all will be clear. To get both hands into action down there, you may need to remove the steering wheel. And that bit of carpet out and a fat rag in, in case your fluid-catching mug tips over, or the tube hops out.
Nick and Cherry Scoop

I just did replaced the slave last week. Removing the old slave was a real pain. I slotted the top ear of the new one, putting the bolt partially in before replacing it. The important part was pulling the new slave down a bit and bleeding it before putting it in place. Another option is to put in place a remote bleed pipe up to the top of the gearbox. This has been discussed on here in the past. Of course it is easy to put the slave in place with the motor and gearbox out of the car.
J Bubela

Slotting the new one really helps. I used a rear brake flexi hose and three way connector with two calliper bleed nipples for the remote bleed - as per suggestions by others. Although not sure if the brake hose fits the earlier slave cylinder
S G Macfarlane

Thanks for all the really helpful comments. Eureka I have found the inspection window! Why on earth they didnt mention it in my workshop manual, I dont know.

Can you clarify, in terms an idiot like me will understand, what you mean by slotting the top ear. I am guessing you mean cutting a groove in the aperture that takes the bolt, so that the bolt can be fitted first, and then the slave slid sideways into the bolt?

In the meantime, I am now now having trouble as the clevis pin retaining the clutch fork to the slave wont come out. I obviously dont want to hit it with a hammer for fear of bending the clutch fork. It doesnt even have a split pin, just good old fashioned rust and corrosion holding it there. Any tricks to this part of the job please?
Thank you so much
Graham V

Yes, your understanding of slotting the top ear is correct.

For removing the clevis pin, you could try a bit of (localised) heat. You could also try a large pair of water pump pliers to press it out, fitting a small socket over the head of the clevis pin, so it has somewhere to go.
Dave O'Neill 2

If you really cant shift the clevis pin you could leave it attached and just remove the slave cylinder from the push rod if you don't want to risk the job escalating.... although I'm sure it will come free using Daves suggestion
S G Macfarlane

Why didn't I think of that? LOL
Dave O'Neill 2

Thanks for the posts. Some success, I got the clevis pin out using a G clamp with a large socket attached at one end. Wow it was very tight!!

Now I do need your help again please! What is the secret to removing the upper retaining bolt on the slave. I cant seem to get to it from below, nor from the "window" above. Which is the best way?

Thought this would be an easy job - no such luck :)

Graham
Graham V

To get difficult parts out cleaning arae and spraying and leaving to soak with PlusGas (not WD40) helps.

IIRC (but don't rely on me) slim spanner or altered sacrificial spanner(?).

Nigel Atkins

you can do it - from below with standard spanners, sockets etc - although I cant recall quite how - taking out the bottom bolt will allow you to swing the cylinder round to improve access once you have loosened the top bolt enough to get a little movement.
S G Macfarlane

Yes, you need to get under there from the offside, on your back, and feed your right hand in alongside the gearbox from the rear. A normal spanner will get it started - half a flat at a time probably, with your fingers getting more and more fatigued from flipping the spanner. If you're lucky it will be finger-turnable after a turn or two with the spanner.
Nick and Cherry Scoop

Once you have removed it, check the length of the bolts used. The standard ones are longer than needed which makes the job of loosening or tightening more tedious than it need be. So shorten the bolt, and if you have a grinding wheel shaping the end of the bolt into a cone will make it easier starting the thread when you refit.
GuyW

I always use a cranked ring spanner to reach the upper bolt. Seems to work without any drama.
Dave O'Neill 2

It sounds simple but its almost beaten me!
Spent best part of the day on it and have only managed to get the clevis pin off!
Just cant seem to get the spanner in position from under the car, probably because I cannot see or feel what i'm trying to do.
I did have a tiny amount of success from the aperture above, by bending a spanner to fit better, but once its turned half a flat, the aperture blocks it - tempted to cut the hole bigger.
I am thinking that maybe if I remove the pipe from master cylinder, and also remove the bottom bolt, I might be able to spin the slave round to give me access to the top bolt.
Off to swear at the dog!
Graham V

Success - have managed to undo it - well its almost off but I started to feel ill lying in the floor pan, so I am going to stop for the day
Its very hot in my garage, and combined with high blood pressure is not the best combination

Thanks for all your support
Graham V

Graham, do / undo the slave cyl bolts from under the car, lying on the floor. Fit a remote bleed while it's off and you'll never need to go back in that footwell again!
David Smith

As everyone describes - once you have the technique its not that difficult(I know - easy for us to say) - spend the time you would otherwise waste lying bent double in the footwell trying to bleed the clutch by fitting a remote bleed - note if you are going to do this connect the brake pipe to the slave before you fit it or you are back to square one!! See attached - there are more sophisticated solutions.......


S G Macfarlane

Graham,
Had similar problems a couple of weeks ago but with a midget.I had the loan of a pit and gave up on the foot well approach.You need a ring spanner of the correct size but the spanner should ideally be fairly short to gain access and good fit between the footwell side wall and your target.Unfortunately having a shorter spanner gives less leverage but it is possible with a bit of grunting and will make refitting easier.
Keep going,
John S
J Sloan

Dave / SGM /John
Maybe my hands are too big, but I just couldn't find the top bolt with a spanner from underneath. Or perhaps I just had the wrong orientation.
But at least I now have it loose from above. I'm planning to use the "ear slotting tip", so I hope replacing will be easier

Remote bleed sounds a good idea, (SGM, I assume you mean connect the pipe to slave before you "bleed" it).
But I also like the idea of just connecting a plastic pipe from the bleed valve to a brake bleed valve, opening them both up, and then pumping the brake pedal for as long as it takes to force fluid up through the clutch hydraulics until all air has gone. No need to even check master cylinder fluid levels with a dual cylinder.

Once again, thanks for all your very valuable help.
Graham V

Do you think this might work as a very simple remote bleeder? That is to say, do all these brake pipes use the same thread size. If so, I'm thinking male end into slave, and bleed valve into female end. Sounds too easy, so probably not!
http://www.minispares.com/product/Classic/Brakes/Hoses/HD26.aspx?0403&ReturnUrl=/search/classic/hd26.aspxBack%20to%20search
Graham V

probably not - but this will:
https://www.petermayengineering.com/product/remote-clutch-bleed-kit/
David Smith

Picture of remote bleed.


Alan Anstead

Picture of a slotted slave cylinder.


Alan Anstead

The cheapest remote set up comprises a rear brake flexi hose screwed into the slave cylinder (as above do this before you refit the unit), a three way connector and two calliper size bleed nipples - less than £15 - this works for later cars - not sure about the thread size on an early type slave cylinder
S G Macfarlane

You don't even need a 3 way connector. There is a double ended female connector that takes the hose at one side and a bleed nipple at the other.
GuyW

Even cheaper then, although the three way connector does have a handy hole in it to allow attachment to the footwell panel
S G Macfarlane

Yes, l made up a bracket. But for really tight fisted folk a zip tie would do it! ;-)
GuyW

With the remote bleeder, how do you depress the clutch pedal?
Strangely (I'm fourteen and a half stones) I don't have a problem with the footwell bleed - it's quite comfy in there - right hand for the spanner and left crossing over to push - though I have to enter in that configuration: if I go in with arms crossed the wrong way, I have to pull out and re-enter.

Guy - I will be very shocked if you give up the authentic sixties experience of grovelling in the footwell.
Nick and Cherry Scoop

with your foot......
S G Macfarlane

Nick, you use an eezibleed, or an Attractive Assistant. The latter would still retain the authentic '60s experience, at least in the memory!
GuyW

You must be very tall, SG, to reach over the windscreen and round the bonnet to open the nipple.

Good one, Guy. I never get enough of my attractive assistant's time, and I expect that was the case in the sixties too.
Nick and Cherry Scoop

Nick - I use an easi bleed so no need to reach the pedal.
I assumed the alternative was a pipe off the nipple submerged in a jar of fluid while you pump the pedal- If you need to reach the pedal AND the nipple then i assume you just have an open ended bit of tube expelling into fresh air - not the way i'd do it
S G Macfarlane

Has anyone tried connecting a plastic bleed pipe straight from a wheel valve to the clutch bleed valve? The theory is to crack open the valves at both ends and then just pump the brake pedal for a while whilst drinking tea.
It sounds a clever idea. No need to check the master cylinder fluid level (with a dual master cylinder) and the clutch is bled backwards, which apparently expels the air more easily.

Incidentally thanks for the comments, I have bought the bits and hope to have time Friday to finish the job
Graham V

Just for info, Graham, I did the MC seals change this morning, on the car and with everything in place around it. One hour only, and I'm quite deliberate.

Plus I wanted to say that if you do the tilting of the MC by removing the front bolt, keep an eye on the two pipes coming off the back end. The curves on mine are fairly generous and flowing, but some people have them very tight, and you don't want to stress them.
Nick and Cherry Scoop

Thanks Nick. I have decided to replace the master cylinder rather than just change the seals. But cant release the pipe work from the rear so think I will need to replace the runs from M/C to four way brake terminal, and to the clutch.
Graham V

Graham

If you are replacing the master cylinder I'd suggest using a genuine one (AP Caparo) from Powertrack Brakes Ltd. The TRW made ones have been reported sometime lacking.

Cheers
Mike
M Wood

Hi Mike
Thanks for the advice. Trev Mason also made the same point. But funnily enough, I was indeed thinking of fitting the TRW as I have it on the shelf, and think I know the problems, but very happy to be corrected.

I had originally bought the TRW unit to fit on my MGA. I was then given similar advice to yours and spoke to the supplier (MGB Hive) who said they had sold very many and never had any problems reported.
I fitted it, but found that after pressing and releasing the brake pedal, the front disc brakes, did not release. The rear drums released as normal. I read up about them, (in particular on the MGA Guru site which is a very useful resource) and apparently it can be fixed with a very small hole drilled in the brake release valve to allow fluid to return more quickly. I wasn't prepared to mess about with it so bought the Caparo one you suggested and it worked perfectly.
As I understand it, the reason it was ok with the drums was because the springs pull the shoes back after the pedal is released, but obviously there is no springs on the discs.
So I already have the spare TRW on the shelf, and as I am drums all round, thought it should be OK to fit. But as I say, i am happy to be corrected if I have misunderstood as would prefer to avoid even more problems.
The existing MC is probably the original fitted in 1959, and so it is probably sensible to replace it completely.
Graham V

Graham, that is exactly the problem so you should be ok. I also had to adnust the pushrod a bit as well.

Trev
T Mason

Graham

Is your car on front disc brakes or drums?

In the standard set up for late MkII Sprites and MkIII Sprites that use the dual master cylinder and front disc brakes, there is a different valve inside as well as different standard master cylinder bore compared to drum braked MkI and MkII Sprites (3/4" compared to 7/8" for the drum brakes version of the dual master cylinder). Also different pushrod lengths.

See:

http://www.gerardsgarage.com/Garage/Tech/DbrakeUg.htm

&

http://www.gerardsgarage.com/Garage/Tech/DBrake/TandemMC_Part1e.htm



If you are using the 3/4" master cylinder on a former front drum braked car, the easy way to get matching year brake wheel cylinders is to fit Morris Minor 1098cc rear wheel cylinders (3/4" bore, replacing the 7/8" originals) sliding type that fit into the existing backplates, instead of needing to change to later Midget backplates that suit the later style 3/4" wheel cylinder. Alan Anstead gets my thanks for this great tip!

Cheers
Mike
M Wood

Mike
Interesting articles thank you, but mine is drums all round. So I don't think it applies.
Graham
Graham V

The job is now complete and the car is back on the road. I just wanted to thank everyone for their tips and encouragement. Couldn't have done it otherwise, that's for sure.
Slotting the slave cylinder was a great help, as was fitting a remote bleed point.
For the benefit of anyone accessing the archives, bleeding was finally achieved using a very cheap Vizibleed kit, but with both ends secured with cable ties.

Thanks, couldn't have done it without this great community.
Graham V

Graham, I am very pleased.
Nick and Cherry Scoop

This thread was discussed between 02/07/2018 and 28/07/2018

MG Midget and Sprite Technical index

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