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        General >> Problems >> Front discs
        
(Message started by: jonnycab on Apr 21^st, 2006, 2:05am)

Title: Front discs
Post by jonnycab on Apr 21^st, 2006, 2:05am

In my old '95 Scorpio I once had a pair of 'Apec' discs fitted in the front. After about 2000 miles the brakes were wobbly on low speed braking. It turned out that the discs had warped. They were fitted by Kwik Fit & had a years warrantee. I took the car back & explained what had happened but they wouldn't honour the warantee......why...."cos it's a taxi mate, we don't guarantee brakes on taxi's"(they didn't say that when they fitted them). 'nuf said.
When I bought my latest Scorpio two months ago it needed new front discs & pads. I bought them from my local motor spares shop & they were 'Apec' (again). I didn't think anything of it until last week when my brakes started wobbling at low speed (after only doing 2000 miles).
The moral of the story is...if you are thinking of putting new front discs in then don't buy APEC!!!!

Title: Re: Front discs
Post by Chris Dean on Apr 21^st, 2006, 8:06am

I've just replaced the Front Disk & Pads. £100 for the lot from Ford.

Title: Re: Front discs
Post by sector-9 on Apr 21^st, 2006, 8:49pm

Discs warp when they're overheated. The most common cause of this is sitting in traffic with your foot on the brake (at lights, etc.) The hot shoes heat up that one part of the disc they're in contact with, whilst the rest of the disc is cooling off in the air. Vented discs are more prone than solids as the two halves are thinner and so heat up quicker.

To avoid warping discs, always use the handbrake if you're stopped for more than about 3 seconds (the back discs are usually solid and don't get anywhere near as hot so hardly ever warp).

Mind you, take off any signs of it being a taxi then take it back to Kwik-Fit. If they say it's a taxi then tell them it used to be but not since you've owned it!

Darren

Title: Re: Front discs
Post by jonnycab on Apr 22^nd, 2006, 10:43am

I think it is more than just coincidence that two pairs of Apec discs have warped at such a low mileage. I've never had any problem with any other make. Maybe the Apec discs just aren't up to the job in a heavy Scorpio.
P.S. I don't go to Kwik Fit anymore. Not since the first time about 5 years ago. They charged me a small fortune & then refused to honour the warantee (even though they said they were guaranteed at the point when I handed over the cash).

Title: Re: Front discs
Post by mr._floppy on Apr 22^nd, 2006, 5:35pm

Mmmm, that's a new one :-/, never thought of that, I think every driver of a automatic holds the car with the footbrake at the lights or similar hold ups.

There are other reasons for a wobbly steering wheel on braking, soft wishbone rubber bushes , dodgy track rod ends, worn steering rack to name but three.

Title: Re: Front discs
Post by sector-9 on Apr 22^nd, 2006, 8:49pm

Indeed. I don't think it's as bad once the discs, etc. have worn in a little, but according to a brake fault-finding chart (in a service centre), that is the cause. Well, the cause of warped discs at least.

The last automatic I had was a Rover Sterling - I always shifted it into neutral if I was going to be stopped for more than a few seconds. Of course, in heavy traffic the brakes don't get that hot (although they are being used a lot) simply because the vehicle tends to be moving slowly so has less kinetic energy to convert to heat.

Darren

Title: Re: Front discs
Post by jonnycab on Apr 23^rd, 2006, 12:58am

The first Scorpio I had with the 'Apec disc warping syndrome' was a 2.0 manuel. So that throws out the auto foot brake theory!!
Are Apec discs made in Eastern Europe perhaps?
As for sitting on the brakes at standstill, if a disc were to warp because of this then it must be made of inferior metal!!....Obviously Apec brakes were designed for lighter cars like Mondeos.. etc

Title: Re: Front discs
Post by sector-9 on Apr 23^rd, 2006, 1:08pm

It depends. Thin discs (we'll treat a ventilated one as two discs joined together by fins) heat up quicker than thick ones. They also lose heat faster to the surrounding air. If you hold a hot brake pad firmly against the disc then that part of the disc it is in contact with won't lose heat as fast as the rest of it (which is exposed to the air) - it may even heat up as it absorbs some of the heat energy in the pad. A thick disc needs more heat than a thin one so the pad will have less effect; also it is losing heat slower from exposed surfaces. As I've said, rear brakes don't tend to get as hot as front ones so usually they can be made smaller and solid rather than vented (or use drum brakes).

You can improve things by making the discs thicker (but this also adds weight and makes cooling slower), or evening out the heat being applied to the disc. In practice this means removing the pads as soon as the disc has stopped rotating. That, I'm afraid, is the law of physics. Having said that, the metal Apec uses may be less resistant to warping (but presumably chosen for other benefits such as being very hardwearing?)

My first 'real' car (a 1983 1.6 Sierra) had terribly warped discs when I bought it. I replaced them both and because I was only earning £2/hr I read up as much as I could on what causes them to warp - the replacements had cost me nearly a week's wages and I didn't fancy having to do them again. So far I've never had discs warp on a car I've owned. 8)

Darren