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MG Midget and Sprite Technical - Brake & clutch fluid loss

Hmmm, this one has me baffled.

While tinkering around under the bonnet, I thought I should check the brake/clutch fluid. It's a frogeye so has a shared master cylinder.

The fluid level, was very low, down to the divider bar between the clutch & brake side. I immediately topped it up.

I have checked the slave cylinders on each wheel, all round the master cylinder, the stop light switch, driver's floor pan, etc. All looks fine. The clutch slave cylinder has a covering of oil, but no brake fluid from what I can tell.

Nothing I can see on the garage floor, and it should be pretty obvious as it's a lot of fluid that I am looking for.

I then got in the car and pumped the clutch pedal slowly a hundred times. Checked the master cylinder and no loss of fluid. I repeated for the brake pedal and again no loss of fluid. Both pedals feel firm.

I cant remember when I last checked the fluid, it definitely would have been last year some time. I have only had a few short test runs for 3 or 4 miles a time in the winter. Other than that I haven't used the car since probably September/October last year.

The only other thing I can recall is going out in the car last year and initially finding the brakes pulling badly, but then it was fine. I really cant remember if I checked things out after then, or not. I know of course I ought to have done so.

The fluid was relatively new as I bleeded the brake system in 2015 when I renewed a few slaves.

Any ideas?

Thanks, Graham

Graham V

Oh and I should also have added there is very little wear on the brake shoes - much too much fluid loss to be accounted for by a minimal wear on the linings
Graham V

Did you check the carpet under the pedals? If the masters are leaking around the pistons it might be dripping onto the floor by your feet.
Stan Kowznofski

mild rebuke.

The first thing you should think of before taking the car out after a lay up is brakes, and before every use really, certainly every time you lift the bonnet.

The engine is practically of no consequence compared to the brakes, they are always number one priority.

Brake and clutch fluid are often overlooked. For the brake side at least the fluid should be changed every 18-24 months even if you're not using the car.

The fluid level and colour in reservoir checked regularly.

If it's not under the carpet as Stan has already put have you also checked for evidence on the road wheels and all the pipes, unions and nipples for brakes and clutch.
Nigel Atkins

Also check the rubber brake lines. Are they soft or puffy.

As Nigel said, the engine is a minor detail. Only two things have to work on a car, the brakes and the steering. If they don't work, how well everything else works or looks is unimportant.

I disagree... yes brakes and steering are essential

But your losing focus stay on one system before moving on to the next

You have already started the engine... stay with it, once it's done THEN move on to brakes and clutch otherwise your looking at a mess.

Take good detailed notes and photos

1 Paper

I have found in the past the culprit is usually the slave on the clutch. Have you peeled back the boot to have a look for any evidence of fluid leak
Bob Beaumont

I have checked under the carpet, the entire brake and clutch lines, and all brake slaves & the clutch slaves.
As I said, I have pressed each pedal slowly over 100 times, and there has been no apparent drop in the fluid level in the MC and the pedals are firm.
Bob, you may have the answer, as there is some form of fluid on the outside of the dust boot of the clutch slave, but I'm pretty sure it's oil, not brake fluid. I've wiped it all off, but since there is no apparent loss at present, there will be nothing much to see!

I guess all I can do is keep a check on the master cylinder level every time I go near the car, and wait and see.
Graham V

Yeap strange, but now you have datum point, note the date and level of fluid then keep a note of what you do with the car.

If you've cleaned all areas then you should see any new fluid loss show up.
Nigel Atkins

Yes Nigel - I will do that.
Graham V

Hi Graham,

I had a very similar situation, albeit in a MKIII midget, so it was only affecting the clutch but there was no evidence of leakage apart from what appeared to be a little layer of dusty oil near the slave cylinder.
It hadn't been used very much due to house move and life! However, I topped it up and watched it carefully. The more I used the car the less the loss of fluid became. After about a month, 1000 miles, there was no loss so either there was an unexplained coincidence, or it was coming from the slave cylinder and was solved by use. This all happened last Summer but when I checked the car recently prior to the MOT there was a very, very minor drop in the level.
Ray Rowsell

Ray I wonder if yours might have been lack of use affecting the seals. With Graham's I wonder if the fluid has previously been lost to the road rather than garage as it's now possibly stopped. I was thinking if everything is clean and dry then using dust/talc/tissue might detect any further loss from the car being static.

BTW I'm trying an 88c stat again but getting twitchy with the gauge now the warmer weather is more frequent (well at the moment anyway).
Nigel Atkins

Thanks for your post. Interesting reading as I was beginning to think I must be going mad!
That would fit in with my use of the car, I didn't use it right through the winter.
If I do have a temporary phantom leak through lack of use, it would also more than likely be from the clutch slave, as inside all four brake drums, everything is as dry as can possibly be and there would certainly have been some tell-tell signs if there had been a leak at anytime. Especially with that volume of fluid loss.
The clutch slave however, is covered by a layer of oil as my 59 year old original engine leaks oil (or has an automated chassis rust prevention mechanism, as I call it). So there's no way of telling what has happened there.

I will put it down to that. But will keep a very regular check on the fluid level, and certainly check it every time I take the car out.

Graham V

The alternative is that you bled the system and just didn't top it up. Or one of the slaves was sticky with grit which breached the seal and was pushed out together with some fluid. If you pull the dust boot off the clutch slave brake fluid tastes quite different to oil. I assume you haven't got a servo. Put some cardboard under the car - it's wonderful stuff for pinpointing leaks.
f pollock

If your car is equipped with a brake vacuum servo, I would suspect the rear seal of the M/C has failed. The vacuum servo is sucking the fluid out of the M/C and into the intake manifold and the fluid is added to the fuel mixture. This is why you do not see any wetness.

Let us know what you find.


79 MGB
gary hansen

Hi Graham, just a way out punt.
Does your brake pipe to the rear go down the transmission tunnel? If it does is ther a leak in there?
Just a long shot thought.
Dave Squire

No servo, but good thinking.

It runs down the central chassis frame but no leak I could see

Although of course I can't be 100% certain, I am pretty sure I would not have forgotten to top up. But the grit theory is interesting as I did have an incident late last year when the brakes pulled to one side badly and then by shortly afterwards, righted themselves. But as I say, there is no tell-tell signs around the brake slaves of any leaks.

I will wait and see if the level goes down again.

Thanks to you all, Graham
Graham V

"Put some cardboard under the car - it's wonderful stuff for pinpointing leaks."

Second that. It's also good for noticing new leaks...
Jeremy MkIII

This thread was discussed between 14/02/2018 and 19/02/2018

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