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MG Midget and Sprite Technical - Replacing clutch fluid

It’s a long time since I did this but I need to replace my clutch fluid on my 1275 Midget. I remember how to do it and what a pain it can be but that’s not my question. What I want to know is how much fluid is contained in the system so I’ll have some idea as to when all the old fluid is out. For instance, if it were 100cc (say) then if I put 110cc in I must have completely changed the fluid. Of course the old fluid might be a different colour and that might help as well!
C Hasluck

I have a 1098cc car - so have the combined master cylinder, but as you have the separate ones I'd look into the master cylinder - my fluid was black !

Having just been messing with the clutch cylinder I'd get something like this fitted - https://www.petermayengineering.com/product/remote-clutch-bleed-kit/

I'm sure there are other ways

Malc
Malc Gilliver

I recently changed the clutch fluid on my MGB, which is a bit easier, as the slave cylinder is more accessible from underneath.

I bought a brake fluid tester, like this one

https://www.ebay.co.uk/itm/314806823681

Which I used to test the fluid beforehand.

I used gravity to drain the old fluid, topping up as it went down. I also tested samples of the fluid that were coming out, so I knew when to stop.

Dave O'Neill 2

It would be useful to know the full clutch system fluid capacity.

Same as the brakes.

So much easier when you could buy different colours.
anamnesis

Hi Dave
I have a brake fluid tester similar to that one. That’s how I know the clutch fluid needs changing urgently. Brake fluid tested okay but that was probably filled later. I think the Peter May extended line to a more convenient place is a great idea but I will try the normal method first even though I am getting a bit old for crawling around on the garage floor!
C Hasluck

Second thoughts - would gravity work on a Midget.
? It sounds a lot easier that way if it works.
C Hasluck

I think I read somewhere the capacity is 500ml.
Philip Sellen

Chris

There’s no reason why gravity won’t work on a Midget, as the system is basically the same.

Philip

Is that for the combined brake and clutch MC?
Dave O'Neill 2

Black fluid suggests degraded rubber seals. But clear fluid can also need changing if the water content is too high.

Anam, I didn't realise one could ever get coloured brake fluid? Other than slight variations in the yellowish colour from different brands. Some years ago I was suggesting on the BBS that it would be good if someone sold a colour additive one could add to the hydraulic fluid for just this reason
Idea sparked by some small bottles of food colouring dye in SWIMBO's cake ingredients cupboard!
GuyW

Dave,
As I recall the early dual cast iron cylinder, I can’t imagine it would be much different for the later set up.
Philip Sellen

On the later cars with separate cylinders, the clutch reservoir is quite a bit smaller than the brake.

Dave O'Neill 2

The clutch master cylinder on mine is definitely smaller than the brake MC. Clutch fluid is clear as a bell but my tester goes straight to red (not surprising as it hasn’t been changed for years).
C Hasluck

Guy, I remember red fluid, and pretty sure blue too. May be a false memory, but I think green was available too.

Here's the red stuff.

anamnesis

Here. But only 50ml. That's not a lot of use.

https://www.rapid-racing.co.uk/red-hydraulic-brake-fluid-50ml.html

anamnesis

https://www.compbrake.com/product/ate-racing-brake-fluid-1-litre/




anamnesis

Anam,

50ml, that size makes sense when you look at the size of the vehicles they sell.
David Billington

Lol. Toys. I didn't look at that. 😅
anamnesis

Ah.

"This Fluid supersedes the ATE Blue Racing Brake Fluid which has been discontinued by the manufacturer as blue fluid dye has been prohibited from being used in All Brake Fluids. This Brake Fluid Is exactly the same as the blue just without the dye."

Why?
anamnesis

A quick search on why blue brake fluid is banned got this among other similar postings https://www.hooniverse.com/braking-news-ate-super-blue-deemed-illegal-for-us-distribution/ ,

It isn't compliant with US DOT requirements that brake fluid is clear or amber in colour to stop possible confusion with other coloured fluids.
David Billington

<<requirements that brake fluid is clear or amber in colour to stop possible confusion with other coloured fluids.>>

A strange logic when there must be many, many more amber or clear fluids that it could be confused with than blue ones!
GuyW

Well Automec silicone fluid is a purple/blue colour in the bottle and is advertised ISTR as being used by the American military.

Must check mine as being silicone it doesn’t need replacing.
I know the old pros and cons but to date I’ve had no issues (famous last words !).
richard b

Well, I finally got around to the job of replacing the fluid (delayed by a relaxing holiday). Am I right that I must raise the car high enough to get fully underneath to get at the bleed nipple or am I missing something. I was sure there was a hole in the transmission tunnel but I must be mistaken. Lying on the floor with the car slightly raised I can barely get at the nipple let alone unscrew or fit a pipe.
C Hasluck

It's in the inner side panel of the driver's (RHD) footwell down by your left foot. It's fine if you're a contortionist IME.
David Billington

There should be a big rubber bung in the hole.
Dave O'Neill 2

Thanks David. I was sure a hole existed but was beginning to doubt myself.
C Hasluck

Chris,
Does hour car have a Heritage shell - ISTR it is missing as the tunnel is based on the 1500.

It’s a long time since I built mine but I think I may have added one !
richard b

Well, I found the required hole with its bung. It’s all coming back to me now! However, it is a bit of a squeeze to get to it. I wondered whether to remove the steering wheel (they usually don’t come off easily) or the seat to make more room. I’ll try in the morning when I’m thinner.
C Hasluck

As you've got to get at it with a spanner to bleed it, you may ad well convert to a remote bleed system. Completing the job, and any future clutch bleeding is then so much easier!
GuyW

Or was it the gearbox oil filler access hole that was missing?

Can’t remember- will have to have a look sometime.

It certainly is tight to get in there !
richard b

Guy's right. Get a brake hose, same as is used to connect rear brake line to rear brake pipes plus a female to female connector for same. Put clingfilm between master cylinder cap and filler. Screw connector to one end of hose then remove clutch slave bleed nipple. Screw new flexible pipe in its place. Screw bleed nipple to end of connector, which you have fed upwards adjacent to rear of engine so you can attach it with a bracket you make via an upper bell housing bolt. Bleed clutch from above. No more cursing, no awkward access.
Bill B

Richard, I have a Heritage shell and it’s true that some parts (e.g. boot floor) are based on the 1500 body shell but fortunately in my case both access holes are present. The best advantage of the Heritage shell is the hole in the floor that allows access to the prop shaft universal joint as it enters the gearbox!
C Hasluck

Well, clutch fluid replaced! Thanks to Dave O’Neil for mentioning gravity, it worked a treat. Just released the bleed valve and let the fluid dribble out. Kept the master cylinder topped up and put 500 ml through the system. It was a lot easier than I remember from years ago.
C Hasluck

This thread was discussed between 08/07/2025 and 20/08/2025

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