Brake random soft pedal

[JeremyC]

I had my concerns that the brakes were too hard when I first bought the car https://www.mgfregister.org/forum/viewt ... 70#p202970 however they improved with use (previous owner had done 700 miles in 6 years) and I've been very happy with both their efficiency and feel.

However at the weekend I went out for a 30 minutes drive (with some time parked outside Screwfix!) and in the last mile the pedal went soft though a second push returned the feel. I've done hundreds of miles over the last few months and have not experienced this before. Today I went out for about ten minutes and the pedal was absolutely fine.

Some facts:

• Pads are about half worn
  Discs OK but I suspect they are the originals
  Fluid level OK but the fluid is quite dark
  When I got home today I felt the wheels and the OSF was noticeable warmer than the rest.

My best two theories are a) a piston stuck out temporarily b) the OSF is binding slightly and got warm and boiled the fluid (or the water in it as it is of suspiction provenance). a could of course be the cause of b.

My plan of action is to do a fluid change at the weekend and just check over the OSF calliper. Longer term I think pads and disc would be a good investment.

Any alternative theories or thoughts or experience would be hugely appreciated.

Thanks.

[Notanumber]

A temporarily stuck piston would give the effect of a normal/ hard pedal but with noticeably uneven braking, the pedal would then go soft mid travel and could need to be released and pushed down again to brake. Is this what you experienced ?

[JeremyC]

No, my recollection is that it was like air in the system, soft/long (though not to the floor) with some breaking effort on first push and then firming up to normal on the second push.

[JeremyC]

Another pertinent fact is I'm not a heavy breaker under normal circumstances. I prefer anticipation and balance. Whilst the old/wet fluid is a seductive theory I'd be surpised if the brakes were that hot, though I was coming down a hill when it started.

[RobboMC]

When I put my car back on the road after a number of years in the garage I of course changed the fluid,
but also removed each of the 4 calipers and made sure the slides were greased and working.

Start with that, you might find something that needs fixing.

After 20 plus years it's possible the front discs have been changed, they tend to wear faster.
Modern discs are a wear item on most cars, check thickness and replace when needed.
You can usually see the step or lip on a badly worn disc without the need for calipers.

Make sure you re-tighten the caliper bolts to the correct torque.

[Kasper]

Another pertinent fact is I'm not a heavy breaker under normal circumstances. I prefer anticipation and balance. Whilst the old/wet fluid is a seductive theory I'd be surpised if the brakes were that hot, though I was coming down a hill when it started.

For social acception the preferred driving style. Towards both the public and the passenger.

BUT…….

Not towards the car’s bracking system.

Anticipating and using your brake pedal only is a relaxed stype results in layers of brake dust, squealing noises when applying the pedal, and a restriced ability to brake in , the unlikely, case you have to! Also a short and firm braking will result in a lower temperature increase of the braking system.
In contrast to my daily cars, I treat my MG’s in a sporty way(as the car is adapted to that style of driving) sorry for my co-driver, but like me she is keen on a rollercoaster every now and then.

[JeremyC]

Massive bleeding session (best part of a litre of fluid, at leasts I have new fluid now) on Saturday, initialyl unsuccessful with the pedal method but then my cheap Amazon vacuum pump arrived and I achieved a firm pedal.

24 very hard stops at an Autosolo on Sunday and it's still OK.

However, I defnitely need a servo brace. I'd value input on the various designs available. Thanks.

[Notanumber]

It will be great if flushing the fluid through has resolved it.
What front brakes do you have by the way; the standard sliding calipers or the optional 4 pot AP Racing type ?

I fitted a servo brace recently. It was very tough to bolt into place, seemed hard work to get the holes to line up. Then I realised that's because the metal of that part of the bulkhead had become stretched from years of braking - so a good illustration of exactly why a servo brace is a good idea to have.
It's worth doing. It won't completely transform the braking but it will improve pedal feel and remove that spongyness from the bulkhead flexing.

[RobboMC]

A servo brace will not transform your braking, until the day arrives
when the firewall cracks and falls to bits and you have no brakes at all.

Then it will become a transformative alteration.

In my view it's a must have for all cars.

Unfortunately here down under it involves decommissioning of the air conditioning system
and I've never got around to re-commissioning as I will need a new compressor to get it going again properly.

Agree about needing 1 litre of brake fluid, if it's the once in 2 years fluid change you might get away with just 1/2 a litre,
but for a full flush out of really old fluid, or to change to a different fluid, then a full litre is needed.