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MG MGF Technical - Rear Brake Problems

Is it only me this has happened to ?

October last year, MGF went in for MOT, had to have both rear discs and pads replaced due to excessive corrosion on the discs, both had corroded badly on the inside surface, garage left old discs in boot for me to double check I was happy they couldn't be re-used.
Three weeks ago, car had to go back to garage, ( which I pass on my way to work ) as a very loud crack had occured slowing for a roundabout. The loud noise was the osr disc splitting !
I could understand it if it was the front disc, but the rear ? I wasn't going that fast ! Garage were brilliant as usual, they fitted new discs and pads for me FOC, and also while they had the car fitted the sub frame mounts I got off ebay for a small consideration.
They have never seen this before, anyone else?
Jay Smith

If the inside of the disc was corroded again it's a caliper problem. Get them to check if the anti rattle springs on the pads are binding in the caliper. Only applies to the inside pad as thats the only one that moves. Also can cause pad wedging both vertically and horizontally and therefore can bend the disc which may cause sufficient strees to crack same. The surface where the springs contact must be smooth. The corrosion happened on two cars of mine. The problem was poor quality casting. It's a poor design and applies to many cars that use this design without some kind of stainless steel shim for the anti rattle springs to contact. Siezed guide pins can cause similar effects.
Ken Waring

If the disc broke away from the bell I would imagine it is either a faulty disc which is pretty rare or too much side loading from the caliper pushing the disc one way or other rather than being clamped evenly from both sides.
Tony

Tony
In my case it wasn't a case of uneven clamping, it's an area of the disc on one side with no contact at all. This creates a bending moment about the clamping point. As you say side loading without a balancing reaction.
If the disc completely parted company with the bell I'd like to know who manufactured the disc. Eight/nine months bending the disc back and forth(IF that was the case) may well cause sufficient fatigue to cause this.

Ken Waring

Not heard this before - it sounds like a manufacturing fault. Would be interesting to find out whether the replacement parts fitted here were MG Rover or aftermarket pattern parts?
Rob Bell

Both sets of discs and pads were from a local XPart supplier, the split radiated from the centre of the disc out in an almost straight line. It made one hell of a bang when it went !
Jay Smith

It is worth contacting X-Part directly, if you haven't already done so - they'll be keen to identify whether this is a one-off or whether there is a large batch of faulty discs out there!!!
Rob Bell

Jay
Was the disc that split corroded on thje inside face?
Ken Waring

Ken
Having spoken to the garage today who replaced the discs for me, they do not remember any corrosion on the 'swept surface' of the disc, but minimal corrosion of the bell, and the edge of the disc.
I believe they have spoken to their supplier, who apparently, will not give them a straight answer, and is still looking into the matter !
I did ask if they still have the discs, as I would be interested to have a good look at them myself, but they have, unfortunatly, been disposed of.....
Being a bit cynical, I wonder if pattern parts are being 'pushed' as OE spec parts.

Are there any distinguishing marks on the discs, that will tell me ?
Jay Smith

Sorry I don't know. I've used a few pattern disc suppliers but only once had mild surface cracking. When you find it early it's not a problem.
Just shows you need to inspect everything fairly often.

What you've described sounds as if it might be a lack of thermal stress relief in the casting, maybe???
Ken Waring

Jay, I don't know is the answer. I haven't seen enough pattern parts to be able to tell - I've only ever used genuine Rover parts (the last sourced from X-Power months before they were liquidated in that tragic auction).

This is a genuine safety worry. I just hope that this was a one off rather than a manufacturing fault affecting a whole batch! :o(
Rob Bell

This thread was discussed between 15/07/2006 and 20/07/2006

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