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MG MGF Technical - MOT Advisory Sheet

Hi Guys,

Just thought I would pick your brains on a few things on my mot advisory sheet!

Having just had "Nearside front suspension joint has excessive play in a lower suspension ball joint" fixed....would it be not unreasonable not to expect to get "Nearside lower suspension arm has slight play in pin/bush"? Or would these be completely seperate things?

Also my service brake has only just met the required efficiency (55%) what is there that could be adjusted for this? The pads are about 3 weeks old...would they be properly run in yet?

And finally...Front tyres 185/55/15, rear tyres 205/50/15 is this saying that's wrong? If so I wonder when it went wrong as I have only ever replaced like for like since I've had it. And if it is wrong is it a major problem?

Cheers,

Dan
Dan Wavell

Tyre sizes are correct - show them the handbook!

Brake pads will take a while to bed in. Has the brake fluid been changed?
Blue Pocket Rocket

Thought those tyre sizes were right...shame I didn't notice them on the sheet while I was there then I would've questioned him!

Nope..haven't changed the brake fluid. Should I have done?
Dan Wavell

If you don't know when it was last changed then I would change it. Should be changed every two years. I would also recommend you use DOT5.1 which is only slightly more expensive than DOT4 but has a greater boiling point and better tolerance against water absorbtion.
Blue Pocket Rocket

Hi Dan,

Good advice from BPR, fresh fluid could well show an improvement. If your car has ABS check carefully that whatever fluid you use is confirmed to be suitable for ABS systems - some are not.

The braking efficiency of 55% is overall, i.e. you could have one side biting well and the other side hardly biting, but overall the braking force is justabout sufficient. Worth asking for a breakdown of the individual figures, that would highlight which end/side is the weakest performer. IMHO this information ought to be supplied on the test sheet, but VOSA appear to think differently...

If the parking brake performance was good but the rear service brake efficiency only OK, that does point to the fluid as prime suspect.

Does it specify which end the 'slight play' is? Sounds like they could be be referring to the rear, do you have compliance washers fitted?
Mike Hankin

Thanks guys

There is also weaker than usual performance from the parking brake, but I'd put this downt to the handbrake needing adjusting as I hadn't done this since replacing the pads and disks 12months ago, and one of the calipers about 6 months ago.

Think I'll get on and replace the fluid, but also call the garage to ask for a breakdown of the results to see if an issue can be pin pointed.

Having looked back at the advisory sheet, the suspension "slight play" is definately on the nearside front. What are compliance washers? I'm guessing I don't have them if they are not standard!

It's a vvc btw so yes I do have ABS.
Dan Wavell

Take a look at the inside surface of the disks to see if the pad contact covers the expected area. Every time I've had brake problems it's been caused by the pad not contacting the disk, leaving large rusty areas. I've had a car fail the MOT for incorrect brake balance side to side. If the MOT check has been carried out correctly they should find this imbalance, 70% max I believe.
Ken Waring

Won't be brake fluid, that would show as 'excessive travel in brake pedal'. That said, it ought to be changed every 2 years anyway.

55% is real sh*tty performance if overall, the handbrake auto-adjusts so maybe you have another stuck caliper.

There are a number of places there can be play, why did they change the lower joint, I've just had the wishbone replaced for rust (and it is an inergral part with the balljoint). most of the shock and effort goes thru the top joint, which is much easier to change. also there might be play in the wheel bearing.

The tie rid bushes are at the rear, if you look for a link from the rear suspension forwards to the body you will find a bush the size of your fist, there is a little space either side of the bush in the tie rod 'sandwitch', this is where you squeze the compliance washers in, if you see play here then the bush is really shot, the complance washers should only stop play at heavy load on the road.
Will Munns

urgh....quite confused now!

Think I will ignore the suspension for now as seems to drive fine! But the brakes I would like to sort out.

The disks and pads on the back are about 1 year old so I don't think there is a problem there. Will check the other caliper ASAP as don't want a stuck caliper destroying another brake disk.

On the front the disks are a little rusty on the inside around the middle, and the pads I think are wearing into this....would that be enough to cause that low a level of braking effciency?
Dan Wavell

The rear calipers usually suffer seizure of the handbrake mechanism without affecting the service braking efficiency, so I'd be surprised if you have another kaput caliper. That caliper is particularly sensitive to correct procedure when fitting new pads, two pitfalls are (1) failing to get the locating lug on the pad backplate into one of the inserts on the piston face (the pad then sits at an angle won't make full contact), and (2) not pumping the footbrake before putting on the handbrake (that'll reduce the effectiveness of the self-adjuster).
There was a post a while ago from someone who had failed the MOT on rear brake performance having fitted new discs and pads, but repeating the fitting process more carefully brought them back up to pass level.

Rust on any part of the pad/disc contact area means only part of the pad is contacting the disc, so efficiency will drop proportionally. Best solution would be new discs & pads; the reason it is recommended to renew both pads and discs at the same time is to help reduce this occurring. Depending on how worn they are already you may be able to have the discs re-faced, but the price of standard discs is so low you'd probably not see a saving.

Bear in mind also that with single-pot calipers the biggest clue as to what is going on will be on the inside face of the disc, where the piston is. What you see on the more easily visible outer face may not tell the whole story.
Mike Hankin

Depends how big the rust area is and if it should be contacting the pad. If it's just a 3/4 mm wide near the centre of the hub that's normal and is usually where there is no contact with the pad.

Maybe we have a terminology problem. "Inside surface of the disk" = the surface facing away from the wheel, only visble with the wheel off or with a mirror or from under the car. Take a look.
Ken Waring

This thread was discussed between 14/08/2006 and 15/08/2006

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