Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Brake problem MK 4 Sprite

6 months ago I changed the brake master cyl due to a leak, I have added no fluid from then but the master cly now overflows when the brakes are applied and ive had to remove some of the fluid with a syringe. Any help with this would be appreciated. Trevor

Have you put new brake pads in since? Pushing the pistons back into the calipers to put the thicker pads in forces the fluid back up into the master cylinder so if it was at the correct level before it will become over full.
Greg H

No Greg havent put new pads in but thanks anyway. Trevor

If the fluid level is OK but spits out of the top of the reservoir when depressing the pedal, it sounds like you have a faulty master cylinder.
Dave O'Neill2

It is certainly an odd thing to happen!
It implies that either the volume of the fluid has increased, or the available volume in the system has reduced! Fluid does absorb water but I would doubt that would be in sufficient quantity to make any measurable difference.

Alternatively the available volume within the hydraulic system has reduced in some way. If not new pads perhaps the front pads may have been nudged away from the disk if the wheel bearings are bad. Problem is, application of the brakes would at least temporarily correct this.

Another possibility is that the rear brake pistons are not extended out as far as before. This could happen if a brake lining has detached from the shoe and moved around the drum such that it is now doubling up the thickness and forcing the piston back. But with properly adjusted brakes I think it would just jam the drum. Worth removing the rear drums to check though?

As Guy states this is very perculiar.

OK firstly if you suggest the master cylinder overflows when you press the brake pedal then it must be somehow producing fluid?? Or has it overflowed just once? You would think that if it overflowed once then any excess fluid would have been ejected wouldn't it?

When you press the brake pedal the action causes the piston to move in the master cylinder. This will force fluid up into the reservoir until the piston passes the vent hole in the cylinder that is connected to the reservoir. So initially the action of pressing the pedal will pump a small amount of fluid into the reservoir, the amount of which will be dependant upon the ajustment of the actuating rod. Normally we do not see this as when the fluid is at the correct level there is plenty of margin for this small amount of fluid.

So the question is of course now that you have reduced the amount of fluid in the reservoir is everything normal and the fluid is NOT rising?

If this is the case then no worries except how did you manage to get excess fluid in to begin with?
First of all when you installed the new cylinder perhaps you slightly overfilled it and perhaps now if you have had a build up of corrosion on your disks then perhaps that will force the pads back and increase the level. Pure speculation on my part.
Bob Turbo Midget England

Thanks Bob and Guy I will give your suggestions a go.

This thread was discussed on 14/02/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.