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MG Midget and Sprite Technical - Brake failure

It happened today,found an excuse to take the midget out and half way into a 30 mile trip the brakes gave up.
First symptoms were having to pump the pedal to get any braking effort and it got progressively worse to the point where I was having to apply the handbrake to bring the car to a halt. I managed to get to my destination (my daughters house)where I have left it and got a lift home.
On closer inspection there doesn't appear to be any obvious leak of fluid and the reservoir is at the normal level. When the pedal is pressed it goes gently right down to the floor. When it is pressed and released, the fluid level fluctuates up and down in the reservoir, which I suppose it should do.
My first thoughts are that the fluid is getting past the internal seal in the master cylinder without doing it's job. Any ideas?
Dave
Penwithian

typical of worn seals in the master cylinder Dave

if the cylinders on the wheels were worn the fluid would be on the floor after blazing a trail down the inside of a wheel

I dont know how hard it is to replace the master seals though, but somehow I have a "yukk" moment when I give the job a thought

Seem to have read something about it!
Bill

Bill.
I don't much fancy replacing the master cylinder seals either, having not done it before, but the cost of a repair kit at £16.65 as opposed to a new master cylinder at £125 does tend to concentrate the mind somewhat.
Dave
Penwithian

oops

not half

many have done it in here though

sit back and wait for advice
Bill

I did a 1500 Midget brake master rebuild while a college student, it worked. Did my current one, on '63 Midget, 1098. It worked although occasionally I'll get the same symptom which means I need to do it better. I did not hone the cylinder last time, just rubbed it down with some sand paper, not good enough I guess. Here we go again!. BTW you can probably get just the cup seals, (need to know what bore your MC is) for a few cents a piece that's what's failing though many will recommend replacement of the whole MC over rebuild as it is one of the most important parts on the car!
They really are very simple (some harder than others, I think you may have a troublesome nylon washer to melt out in a 1500?) to do and if you pay attention to how it came apart (take pictures) and put it back the same way you really can't loose.
Here's what mine looked like when I got it all apart.
http://gallery.me.com/jvandyke/100153
J Van Dyke

The dual masters are newly manufactured since last year. Mine was rebuild by myself but that one lasted 10K km, and I did hone the bores:-(. Last winter I fitted one of the new ones. New units are cheaper then the 2 later seperate units.

But thats not interesting for Bill.

Bas
Bas Timmermans

If it's the dual circuit MC, there are a few tricky bits, but it's not really that difficult.

The Haynes manual is useful here, but not quite accurate, I seem to recall.

You need to somehow remove the nylon spacer in order to get to one of the circlips. I ended up drilling several holes around its periphery and removing it in pieces.

I also had to gring a pair of long-nosed pliers to produce some circlip pliers long enough to reach the deepest circlip.
Dave O'Neill 2

As Dave O said, you need to get or make some long circlip pliers, but otherwise it's worth a shot at rebuilding the MC. I did mine and it's still working, but if your MC has ANY pitting inside the bore, you should replace it.
Lee
L Fox

Save yourself the hellish nightmare...and send it off to be re-bored and sleeved and rebuilt...its a mess

one note...thats not in the hayne manually....

there is a washer called a spiral washer....you have to get a flat jewellers screwdriver find the lip and spiral it out...I cant remember how to install it...but it was bad...and haynes says (remove the sprial washer....to install the spiral washer is the reverse of removal)...good luck.


Im glad I not in your shoes...if you have a 3 year old child with expendable fingers that will work vary well.

Also get a kit that is made for petrolium based rubber...not natrual rubber....The only one I know of is ray beastous...if you get a kit for natral rubber and use todays dot 3-4, you will have to rebuild it in 6 months....caause your seals will turn to bubble gum and you will get lots of black slimy junk in the bottom of your master cly reseivoir


prop
Prop

Thanks lads,
Truth is - I've ordered a new master cylinder and damn the expense.
The thought of drilling out nylon spacers and undoing inaccessible circlips and finding that the cylinder bore was badly scored didn't really turn me on. With my mechanical aptitude it would have taken ages, and I desperately want to drive the car.
I have since read that when bleeding the system there is a little item called the PDWA valve to consider. I didn't know my car had one! Should be interesting.
Car is a late 1500 with dual circuit braking by the way.
Dave
Penwithian

Or is the PDWA valve only on USA spec cars?
Dave
Penwithian

No, it's on UK cars too.

It turns on the warning light when one circuit fails.

Dave O'Neill 2

The saga continues,
Received my shiny new dual line master cylinder the following day - just plain sailing from now on.
Was it really - first problem was getting the old unit off. The mounting bolts are so close to the m/c casting that you cant get a socket on them and there's not enough room to wield an open ended spanner due to the edges of the pedal box. By removing the clutch master cylinder as well to provide a bit of room I managed in the end with a metric spanner which was a bit slimmer.Fitted the new unit, Had enough and went home.
Returned today armed with eezibleed, it's going to be a breeze, just the bleeding of the system to do, lets start with the n/s rear wheel.
Oh yeah? How the hell do you loosen those miniscule bleed nipples on the rear wheel. to get a tiny ring spanner or socket over them, it seems that the head of the nipple is larger than the hexagon which is so small (7/32 or even a BA) that you can't get a decent purchase on it with an open end spanner.
Forget that for now, lets try a front wheel. Well the fronts have a sensible sized bleed nipple, so the fronts have been bled and I now have brakes of sorts, probably just the front circuit. anyway it was sufficient to enable me to nurse the car home. at least it's back on the premises.
Any advice out there regarding these rear wheel bleed nipples and their removal? Lets not talk about the PDWA valve, as the facia which carries the cigar lighter and brake warning light has been removed by the P.O. in order to fit a radio.
Dave
Penwithian

Dave,

A six-point socket should work well on the small bleed nipples. You can loosen them with the socket so that they will be easy to turn with an open end or box wrench. I will suggest that you not break the nipple off while trying to loosen it.

Charley
C R Huff

Charley is spot on, that's how I do it, crack 'em with a socket - usually my 1/4" stuff suffices - and then use an open-ended during the bleeding process. If I remember in time I remove them completely, clean up on the wire wheel and add a smear of copaslip to the threads before refitting.
David Smith

Charley/David
Thanks for your comments, do you know what the A/F size of the nipple hexagon is?
I tried several small sockets but either they wouldn't pass over the head of the nipple or weren't deep enough to reach the hexagonal bit.
Dave.
Penwithian

Sorry Dave meant to answer this question last night but for some reason it did not happen

For some reason that I must admit I do not understand why, there are 2 sizes of rear brake cylinder nipples on a mini/spridget. Whilst the thread size is the same the 2 sizes of hexagon heads are 7mm and 8mm.

If these will not budge with a ring spanner then I will try a six sided socket, if that fails I simply buy a new wheel cylinder for a few quid.
Bob (robert) Midget Turbo

I came down that problem too. Took an old metric spanner and grinded into the correct shape.

Bas
Bas Timmermans

7mm does the job for me, 9/32" is a tad loose and might round off if they are stubborn.
David Smith

All ofthe modern replacement wheel cyliners I have used were 7mm. Possibly due to being made in Italy.
Dave O'Neill 2

Dave,

Sorry, I don't remember the size. But, use a six-point socket, and if it won't reach, you need a deep well socket.

Charley
C R Huff

And the old trick of bouncing a hammer head off the damn things a few times (with pressure on a flare wrench) can persuade them to loosen without breaking. Making do, I've had to bleed using the brake line fitting. Flare wrench (six sided box end with a slot for the brake tube) is worth the cost.
Tom

New bleed nipples arrived today, a six point 1/4" socket fits the new ones fine.
Still can't remove the old one though, as it's completely rounded off. I've taken Bobs advice and ordered two new wheel cylinders. The next hurdle is the fact that the pipe union nut to the back of the wheel cylinder is also rounded to some extent and won't budge. I've given it a good dose of plus-gas, so hope to make some more progress when the wheel cylinders arrive.
It always amazes me that when you fix one problem, it usually throws up another one elsewhere. Hey Ho!

Dave
Penwithian

Dave,
Brake systems often get "done" and then forgotten. Yours sounds much like mine did. Poorly done, then totally neglected cause the car stopped about as well as it ran.
I did everything to my system exept front calipers and the hard line to the back union. Im sure they'll get done eventually.
Being as this is the singlemost important system in your car, take the time and spend the money to do it right. Stainless brakelines, pads, springs, rotors, shoes. Replace them all as you can.
IMHO
Phil
Phil

Dave,

Do you have a proper line wrench to use on the back of the old cylinder? If not it might be an excuse to buy some. It may just be time to replace the lines, but that will likely also require line wrenches so that you don't start spoiling your new ones.

Charley
C R Huff

Charly refers to a line wrench.
Is this a special type of spanner that will fit over the brake line to undo the union fitting?
If so, any idea where they can be obtained in the UK, and what size would I need for the union nut?
Dave
Penwithian

Yes I assume Charley means a brake pipe spanner also. These are readily available at all motorists discount centres or anywhere that you can buy car parts from.
You could even make one yourself simply buy a spanner 7/16th AF isn't it? and with a cutting disc in the grinder cut a small slot into the end of the ring. Even better is you go and buy a 6 sided ring and make a slot into that, so you get a better grip.
Bob (robert) Midget Turbo

Called flare nut wrenches over here and made to avoid exactly what you have; rounded corners on the nut. A vise grips clamped down hard may do it.
J Van Dyke

I had to buy an 11mm spanner from Halfrauds last week, due to the SO's darned Citroen Saxo needing brake attention.

I mainly have imperial tools and the 7/16" brake pipe spanner didn't fit!
Dave O'Neill 2

Dave,

Sorry I don't know what they are called over there. I think it is what Bob and J are talking about.

Essentially it is a box end wrench (if you know what that is) but it is split so that you can pass it over the line. One of the most important parts is that it is a six-point rather than a 12-point. So, if you decide to make your own, make sure to start with a six-point box end wrench.

Charley
C R Huff

Most box ends don't have nearly as much beef as a flare wrench, good luck with cutting a slot in one. Buy the real thing.

Getting the rounded off bleeder may still be an option with vice grips and a hammer and penetrating oil. Patience, tapping the wrench and the end of the bleeder with a hammer (both ways). Wiggling, tapping cussing, breaking the damn thing off. Good that you ordered new cylinders.

Those spring loaded ball bleeders sound cool, never used 'em yet. EZBleed. Never have to recruit the missus to help (up up? up! ...down down? down! ...not too far, you'll make me have to rebuild the master..etc.)
Tom

Some heat from a propane torch on the pipe nut usually helps.

But if the nut is that rounded you may end up needing to replace that length of brake line anyway.

Guy
Guy Weller

This thread was discussed between 03/08/2008 and 14/08/2008

MG Midget and Sprite Technical index

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