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MG MGF Technical - Brake Fluid

I'm due to replace the brake fluid on the car tomorrow.

Are there any rules when it comes to mixing and matching grades of fluid.

basically I cant remember if I put 5.1 or 5.0 in the last time and the manual says Dot 4. Is it just a case of the higher the better?
Bob Millar

Yep, 5.1 is fully miscable with 4 (and 3) yeilding the lower value.

5 is not - it is a diffrent type of fluid and requires a full flush (and sometimes replacement of all rubber parts!)
Will Munns

5 is silicone based - 5.1 is what you need Bob :o)
Rob Bell

Cheers guys.

The memory's getting worse and I cant remember what I bought two years ago but I'm pretty sure it was 5.1 as i remember silicon being mentioned
Bob Millar

To make your life A LOT easier get yourself a brake bleeding kit (if you haven't already got one!). This will save a HUGE amount of time.


Yeh I've got an eazy-bleed kit. Piece of piss with that
Bob Millar

If you drained the system fully last time then you _might_ have put 5 in (not if you asked here though!) Otherwise it will have been 5.1.

If it was 5 then you won't need to change it.
Will Munns

Not sure if this applies to the MGF system, but silicon-based 5.0 usually doesn't contain the lubricants that some ABS systems require. I opted for 5.1 to be safe.
Mike Hankin

After the 5 year cam belt change I vowed to do my own servicing. Oil and filter I can do with my eyes closed, coolant change was messy but easy. How easy is a brake fluid change, and is it really necessary?

Hi all,

when you have the brake fluid can handy, do change the clutch fluid as well. At a sportscar gathering here in Sweden 2 years ago we were given "free" check of the boiling point of the brake fluid. A good thing as all of us was to do extensive laps on the circuit later that day.
My brake fluid was OK, over 200 degC. BUT the clutch fluid was a low 130 degC. This means that the fluid is full of absorbed humidity (water). Probably due to the fact that the system "breaths" heavily every time the clutch is being used.
It is a bit messy to reach the bleedpoint at the clutch side and attach a bleed hoose ,but the rest is simple.I just let a fair amount of new fluid thru the system to get it renewed.
I think the whole clutch main and slave cylinder system will last much longer if the fluid is renewed at the same time as the brakesystem is attended.
BR, Carl.

Did the brakes today. Found the remains of the brake fluid from two years ago in my folks garage. Castrol Dot 4.

Nightmare with a seized piston on front nearside brake. Had to pump the pedal to get the piston right out the caliper then remove the caliper and take everything into the garage to clean it all up and re-insert the piston. I got so much air in the brake system. I easily pumped the brake pedal over 100 times to get all the air out.

And in the pouring rain as well!

Bob Millar

But good clean fluid in the system now!

Basicly Standard fluid absorbs moisture, this moisture attacks all the steel surfaces, like the inside of the brake pistons and the inside of the master cylinder. Every two years you are ment to change the fluid to minimize the amount of water and as such the damage caused.

If this hasn't convinced you - the water also lowers the boiling point of the fluid, in a normal system the fluid is incompressable, (try to compress a bottle _full_ of water) under heavy or sustained braking (such as an emergency stop from 90) the fluid gets hot - if it boils then the some of the brake system becomes gas (try again with 1/2 air). This gas compresses easily and so you cannot compress the brake fluid and hence the brake pads - which means NO BRAKES.

Of course, you can reguarlly buy new brake calipers and live with the fact that you cannot brake from high speed, or repeatidy. but calipers are
Will Munns

>It is a bit messy to reach the bleedpoint at the clutch side and attach a bleed hoose ,

Carl, this is nothing against the Thermostat screws availability ;)

Sourced a simple bleeding kit at Ebay (Non return valve with piece of hose)
Works can be made alone then without the usual shouts with the _better half_ while bleeding.
Notice the bleed sequence and take care with utmost urgency that no air gets into the system through the expansion tank if ABS is installed.

And while you are on the clutch. Put some white grease spray to the clutch lever to prevent it from rust and getting stuck.
See the second image here:
(Bleed screw also shown with yellow arrow)



No, hit enter to quick.

It's of course there.

See the second image:
(Bleed screw also shown with yellow arrow)

This thread was discussed between 27/05/2005 and 29/05/2005

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