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MG Midget and Sprite Technical - Brake fluid full change

I intend doing a full change of the brake fluid. But I'm not exactly sure how best to do this.

Should I
a) open all of the bleed valves and pump the brakes / allow all fluid to drain out. Leave it to drain and then flush through with clean fluid. Then refill as if it were a dry system.

b) bleed brakes as normal (easibleed assisted) and just keep topping up the master cyl. until fresh fluid appears to come through at each corner.

I suspect b) is less likely to give problems with potential air bubbles

If b), then which order is best to get an effective clear out of the old fluid from the system, rears first or fronts first? It a simple single circuit system with no compensator valves.


Personally I would use option b and start at the front with the shortest run, finishing with the longest run.

T Mason

Have plenty of water to hand in case of splashes on paintwork
Nigel At

I use synthetic.

Guy, do you mean silicone?

Synthetic is still the paint eating kind.
Norm Kerr

amazing I was going to put I don't know why more don't use silicone

especially on rebuilt cars

EAT: and now Norm show up my assumption :)
Nigel At

Quite right Norman, I did mean to say silicone. It does last a lot longer than normal stuff but this has now been in there for over 10 years so it is definitely time for a change! Although the brakes are still good and hard.

Guy. I think option B would be the best because if you go the pumping pedal route it could cause problems with leaks afterwards. ie. The pedal when pressed with the system in full working order, only goes a little way down the cylinder bore, but when you are pumping to remove the fluid it's going all the way down into the area that's not normally swept and can over time become slightly corroded from the water that brake fluid attracts and will rip the seals as they go up and down on the rough bits of the cylinder. then you can get leaks and have to clean the master cyl out and fit a seal kit.
The same procedure is advisable when renewing pads. Having pushed the caliper pistons back to fit new pads only pump the pedal in short strokes to keep the seals out of that area at the bottom of the stroke when pumping the pistons back up.

b higginson

Sorry. People must have been posting at the same time as me, didn't see that you are using silicone, which doesn't attract water, but the short stroke thing is still a good method.

b higginson

All done.
Interestingly, the fluid that came out of the front was just a nice golden honey colour. The stuff from the rear was a murky grey. I suspect the rear cylinder seals are of poorer quality since those cylinders are so cheap (about 6 each IIRC) Anyway its all done. The only alarm was that the steering felt odd when I went for a test drive, although that is now sorted too! Anyone like to guess why that was?

Bernie, thanks for those tips about the short stroking method. Useful to remember that one, as you say for pad changes too.

front suspension settling back down

silicone on tyres

silicone on hands/steering wheel

loose wheel nuts

bleed pipe left on
Nigel At

None of those Nigel. You've had all of the clues though!

Left the jack under the car?
Left Hazel under the car?

could it be problems with your rear end sir
Nigel At

The clue is in my very first post.
Incidentally I also bled and refilled the clutch at the same time. An hour and a quarter start to finish, both systems and including a test drive. Not bad?

But don't take that as another clue.

open valve
Nigel At

OK, you've given it a try.

I said I used an easibleed. Pressure is supplied from front tyre. I had just forgotten to re-inflate it.

I should have followed the bleeding pipe

I wouldn't have got it, I've only ever been on two-man jobs, I can't be trusted by myself
Nigel At

This thread was discussed on 23/08/2011

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