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MG MGF Technical - Brakes... again ;-(

Hi, folks,

I've haven't posted in a while, but I hope someone can help.

Some history: all calipers removed and cleaned, brake lines bled, new OEM discs and greenstuff pads during Christmas 2004. Everything (brake-wise) is fine from Christmas to October 2005 when I take the F off the road (company wheels). Apart from scooting her up and down the driveway once or twice a week since then to keep her turning over, she's effectively not moved in six months.

Enter the MOT, stage left. Driving the twenty odd miles to the centre, I'm a little concerned about my ability to stop :-( Now, I appreciate that braking is subjective... particularly when you've gotten used to a Megane which can stop on a tuppence. However, the MOT report states a 'braking effort' pass rate of 55%. The F scraped through with 59%. Something's amiss.

So...

o The pads need to bed-in again?
o One or more of the calipers are seized/semi-seized*.
o The servo's shot, bad vacuum?
o The pads are contaminated/glazed?
o The system needs to be rebled (though the pedal isn't spongy)?
o The fluid needs completely replaced?

* There was a negligable NS/OS difference in braking effort on the MOT report.

Oh, and she's ABS.

Any suggestions welcome.

Ta,
Col

PS She *did* the MOT btw ;-)
Colin McIlwaine


o The pads need to bed-in again?

nope, unless glazed

o One or more of the calipers are seized/semi-seized*.

this would show up as left/right diffrence

o The servo's shot, bad vacuum?

This would show up as hard pedal rather than poor braking

o The pads are contaminated/glazed?

Possibly, take them out and rub down with emery cloth

o The system needs to be rebled (though the pedal isn't spongy)?

Unlightly, very difficult to get air in a system you are not using!

o The fluid needs completely replaced?

in 6 months yes, you should do this every 2 years, but it won't be causing your problem.

It might be that the rubber is on the way out and you need fresh tyres, the ABS will hide this from you by not alowing the wheels to lock
Will Munns

Cheers for the responses Will!

I've been searching the archive in the meantime, and am leaning towards glazed pads... it's certainly the cheapest solution ;-)

Just for my own interest, can you maybe explain why a shot servo would result in a stiff pedal?

Oh, and she got new shoes all round for the MOT. I'm presuming I cannot get the ABS to kick in because I can't produce enough effort to get the wheels anywhere near a 'locked' state.

Hmmmmmm.
Col
Colin McIlwaine

You do not say whether it was garaged or left on the drive for the discs to rust.
Whichever, it sounds like rust on the pad faces which will clear itself over a few miles.
Geoff F.
G. Farthing

the servo is an 'assist', if it fails then the failure is in the assist, not in the braking per-se, the upshot is that the engine does not help apply the pressure for you, so the brakes feel stiff because you are doing all the work.

Try a couple of high speed long stops 60->10->60->10 to see if this clears the pads.
Will Munns

Thanks Will re: servo.

Well, stripped out the EBC pads (front only) last night and the faces were like *glass*. Threw in a spare set of Halfrauds...

Performed the high speed emergency stop, locked the front wheels (joy!) and felt the ABS kick in briefly before I came abruptly to a halt.

Interesting that occasional low-speed driving/braking produces this effect (as Rob describes here ->

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=archiveth&subject=69&subjectar=69&thread=2000032811524416411

)

Thanks again,
Col

Colin McIlwaine

This thread was discussed between 18/04/2006 and 19/04/2006

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