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MG MGF Technical - Spongy Brakes

I have a one year old VVC (my third MGF) and I am having braking problems, when I had the car serviced the garage told me that they had re-adjusted the brakes as much as they could and they seemed to be a lot better. Previous to this it was touch and go as to whether the car would stop in time under heavy brakin - I don't do this too much but it's good to know that your car will stop before it's too late.

Any ideas why the brakes keep deteriorating or how I can improve their performance?

alison howe

Hi Alison

It sounds as though you have a frustrating problem- and one that may have more than one cause.

The deteriorating performance.

If you do alot of town driving you will be using the brakes frequently, but lightly. The side effect of this kind of use is that the pads and discs 'glaze' with brake dust. Effectively you end up with two polished surfaces rubbing against each other when you apply the brakes rather than the usual high friction material against metal!

Two solutions- one is to occasionally burn off the glaze by finding an empty road and doing a couple of emergency stops. The brakes will be far better after this. [Alternatively, you can take some emery paper and re-key the friction surfaces] The other solution is to change the pads to a compound that produces less dust- EBC pads are thought to be good for this purpose. Additionally, Brown & Gammons sell grooved brake discs that aid the clearence of dust from the friction surfaces- whether the cost for you to have this modification is worth it though is arguable.

The 'Sponginess' of the pedal

Old DOT3 brake fluid absorbs water, and its performance deteriorates. The change frequency on the MGF's service schedule is perhaps a little too long, but on an 18 month old car, this shouldn't really be a factor yet. There could be air in the braking circuit- and I presume that the garage has attempted to bleed the brakes to improve pedal feel. If the problem persists it may be that there is still some trapped air... bleeding brakes can be a frustratng process!
The other culprit for spongy brakes are the flexible hoses that have some 'give' in them. Many people have choosen to address this by fitting far more rigid 'Braided hoses' to firm up the pedal feel. I can't comment on this- yet. ;o)

I'd try de-glazing the pads and discs first before spending any more money, and see what change there is.


Rob Bell

There are some odd references here Alison. You mention that the 'garage' had adjusted the brakes? I find that quite an interesting statement when you have discs all round. The only adjustment that is potentially possible is within the mechanical linkages of the handbrake system which shouldn't have any bearing on the hydraulic side which is pure footbrake.

The question that this raises is... Was there a difference in the number of 'clicks' that the handbrake moves from before the latest work to now? If there was more than about 5 'clicks' before or now then this indicates there is a little slack in the system. If this is allowing the rear pistons to withdraw between braking applications then this will show up in the form of a longer first press of the brake pedal and if the pedal is released and pressed again the pedal travel will be felt to be shorter.

You indicate that the pedal is spongy so I presume that this has been previously reported and an attempt to rectify has been made by the garage before this last visit. I also presume that you are comparing this cars brakes with the previous two Fs you've had. Correct?

A spongy pedal is usually indicating air is in the system and if an attempt to remove it by normal bleeding has failed then a form of pressure bleeding may be needed to remove any well lodged air bubbles.

A spongy of softening pedal during heavy braking indicates that there is water in the brake fluid at a level that is boiling in the calipers creating vapour locks which become compressible and so the pedal feel softens and the pedal will sink. The brakes will have to get pretty hot to start this though.

The other common source of spongy brakes, and a sinking pedal under a steady pressure whilst stationary is a faulty master cylinder seal or seals. If after proper and extensive bleeding the situation persists then I would be starting to look quite hard at the brake master cylinder.

Connected to the brake master cylinder is the way it mounts to the car. It is on a crossover bar and has a quite flexible method of mounting to the body. I would also suggest that you have someone check out the security of the actual brake master and servo under the bonnet whilst someone actually operates the brakes. It may be better to have another car without the problem alongside to provide a good and accurate comparison.

If there is a problem with the friction surfaces then this tends to give a 'solid' and 'dead' feel to the pedal, with there being little actual retardation for the effort that is being applied.

The base line is that you have the experience to be able to make very valid conclusions and there clearly is a problem with your car. Being as this is suych a safety related area I would suggest that you may be best advised to seek the help of an alternative dealer, with a known track record, to provide a second opiunion. If the problem has been one that has been reported to a dealer as a fault within the first 12 months and the warranty has now expired then this fault will still be treated as a warranty fault as it is ongoing.

Roger Parker


I've just had my car returned from it's 48k mile service, and am alarmed to discover that there is pronounced slack in the initial pedal movement, and displays some of the 'pump' phenomenon that you mentioned (pump the pedal, the weight improves).

I was worried about air in the system (confirmed after chatting with Scarlet last night- cheers mate!). Would you agree with this or is it some other problem?

Unfortunately I need to get this sorted before Sunday as it is due to be thoroughly thrashed in a Sprint...

Thanks for any advice

Rob Bell

Rob, did you have the brake fluid replaced at the service? Spongy brakes usually means that there is air in the system. You could try bleeding them and see if any air bubbles come out. I'll only take a couple of minutes. Start with the rear off side one first as its the furthest away from the reservoir and keep topping it up. If there is air present do the rear nearside then front off side, then front near side.
Hope this helps and good luck on Sunday.

Thanks for support John!

Yes, I did have the system replaced- pads (EBC green stuff), discs (standard) and planned to have braided hoses, but the things didn't fit (nuts!!!). So new brake fluid too.

I have spoken to the garage voicing my concern regarding potential air in the system- and have been told that it is part of the bedding in process. This is not an explaination I believe frankly, but will try and put on some miles on the car to see if there is any change. Otherwise on Saturday, I'll go to the Halfords car park (the only flat ground near me) and by a bleeding kit from said store and bleed the system myself! And if air does come out...

Watch this space!

Rob Bell

Rob, If you had new pads fitted they will need bedding in but they usually just feel as if you need longer to stop, ie not as sharp but I still suspect air in the system as they shouldn't feel spongy especially as you say there is some travel in the brake pedal before they go firm, plus you have to pump them. I'd go and bleed them for my own peace of mind.


Thanks John- I think I shall do exactly what you suggest.

Quick plea- has anyone got a copy of the workshop manual handy? I need some pictures of the brake calipers and hoses. Would someone be able to fax me a copy? Many thanks!


Rob Bell


you've said you had your brake pads replaced at 48K. Was this the first time you have them replaced ?
I ask that because my car has 30K miles and the brake pads still seem OK.
What's the average mileage to expect from OEM brakepads ?

now on 16" and looking forward to get your imput about EBC green stuff pads ....

Hi Fabrice

I suspect that pad life will very much depend on the driving environment and style of driving. I live in London, and whilst I don't use the brakes too often ;o) when I do, they get a good ol' shove. Hence, I'd be very lucky to see more than 25k miles from OE pads...

@ 30k miles, I'd say your pads are clse to being up for replacement. Are you thinking of Green stuff pads? Once I get the current pads bedded in I'll let you know what I think.


Rob Bell

Yes Rob, I'm thinking of Green stuff pads.
I'll watch this space to know what you're thinking about ...


Interesting scenario you have since with my car I have exactly the same for different reasons.

I have recently fitted EBC Green Stuff pads to the original discs and used them for a period to obtain back to back data to compare with the original pads. (Car has only 9k miles and the original discs and pads are still in the 'first flush of youth'! I expect a spongy pedal feel with new pads simply because the pads need about 250 miles to fully bed in before normal full pad to disc contact is achieved.

Once these pads were bedded and I have experienced them in use I removed both these and the original discs. I replaced the discs with a pair of development 280mm discs. The Green Stuff pads were refaced and refitted. Once again there was a distinct spongy feel to the pedal whilkt the pads and dics bedded to each other. This has nearly been achieved and the pedal has firmed up considerably. Brakes are more than pretty good as well, but more on that when I have some more miles!

One thing that is NOT present is the ability to 'pump up' the pedal. If this is present then this indicates that the pads are receeding further into the caliper than is normal. This then showing up with a longer first press of the pedal and a quick release and press down again showing up much less travle since the pistons have not had the opportunity to receed back into the caliper.

When you release the brake pedal the pistons and pads should receed just enough to provide clearance for the disc to pass without contact. If they go in further then this may indicate a loose/worn wheel bearing or slightly warped disc. Now specifically in your case I would suggest the possibility of the new disc not seating correctly on the hub. This may not be severe enough to feel in a pulsing brake pedal.

This is one reason why it is so important to ensure that the mating faces of both disc and hub are spotless. If not then a piece of debris can cuase the disc to sit skewed to the hub and then 'run out'. This run out will push the pads and piston further back within a few seconds from brake release.

When you get a chance remove wheels, turn to full left lock and look end onto the disc as you turn the hub. Lokk for any obvious run out. Do the same for the other side. Removal of the caliper and disc, cleaning of the hub and disc inner faces should rectify any run out.

I know that being Sat evening this is probably too late for this weekend, but any miles you do cover should see a steady firming up of the middle pedal.

BTW There is a mail with attachments in your work box.

Roger Parker

Thanks Rog- I'll check my e-mail!

I've been driving like a loon today using the brakes as often as possible to try and attempt an "accelerated" bedding-in of the new pads before tomorrow (and no, I haven't done any emergency brake manoevres yet ;o)
The result? Happy to report the pedal is feeling firmer, and even better, the pumping-up phenomena is reducing (odd eh?). I have 150 miles to travel tomorrow morning, so hopefully the brakes will be up to speed by the time I get to Curborough.


Rob Bell

> DIE Elektronik merkt sich bestimmt nichts, vergisst höchstens was ;-)

Cyril, fast richtig, meine ich:

Sie merkt sich interne Fehler und Sensorfehler.
Kann man mit Testbook wohl auslesen.


Hups, pasted to the wrong input field.
Sorry that happens if someones writes parallel to several boards.
Ahmm, a german language answer to MEMS storage.


Shame it was Mothers day. I was only 2.5 miles down the back lane from Curborough this afternoon - at mothers!! Family politics wouldn't wear, 'I'm just nipping down the road for a bar of chocolate'!!

Knowing how wet it was, I imagine tyre grip was a more pressing need today!

Roger Parker

It was wet and understeer was rife.

Rob's brakes certainly did something good as he did rather well.
2nd in class wasn't it Rob? :o)

Shame you couldn't have popped along 'for some chocolate' Rog.
Wet, but good fun for the spectators. Thankfully, no bad damage but quite
a few 'moments'.


I was a bit stunned- I walked away with a little momento (yup- 2nd in class :o))))

I think that the wet saved the brakes a bit, which was a very good thing as the journey up gave absolutely no opportunity to get the new pads and discs settled. Having said that they feel far better than the old worn discs/pads- and inspire far more confidence.

The winner of the day for me though was the tyres which have so much more feel and are wonderfully grippy yet progressive. Money well spent, IMO. Paul, get 'em fitted to the front ASAP!

Sorry you couldn't make it Rog- it was fun, a few acrobatics and nearly everyone got out of shape at some point. The most stunning 'off' I saw was by a midget which gracefully landed itself in a ditch with very minimal damage. Driver okay thankfully- just a bashed ego.


Rob Bell

This thread was discussed between 28/03/2000 and 03/04/2000

MG MGF Technical index

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