Prescribed areas

Corrosion and prescribed areas.

The Mot Tester’s manual,appendix C describes a prescribed  area.

“Certain areas of the vehicle structure are particularly important for the safety of a vehicle. Particular attention must be paid to these areas during an inspection.

These areas are:
· The load bearing parts of the vehicle to which thetestable items defined in Sections 2, 3 and 5 of the Inspection Manual are mounted, and
any load bearing or supporting structure or supporting panelling within 30cm of the mounting location.”

Sections 2,3 and 5  refer to steering and suspension, brakes and seatbelts.

Excessive corrosion is described as

· The corrosion has caused a hole in the metal, or

· it is weakened to the extent that by finger and thumb pressure it does not feel sound, or
· finger and thumb pressure or use of the  Corrosion Assessment Tool causes a hole.

Some corrosion may actually fall into 2 different categories such as this sill on a Nissan Micra, the corrosion falls within the seat belt mounting area and the rear suspension mounting area.

Therefore on the vt30 failure notice the same corrosion will be referenced as 2 reasons for rejection, seatbelts and suspension although only one repair is actually needed.

pitted brake discs, again

When a vehicle is not used for a lengthy period, one of the first things to suffer are the brake discs, the surface becomes rusty and pitted. The following images came from the rear of a peugeot 306 that had been left idle for 3 months.

Although the pitting in this image doesn’t look severe enough to fail on the mot, it caused no imbalance, but it did cause severe judder when the brakes were tested in the rolling road brake tester.

When inspecting the  discs after replacement the reason was immediately clear, the disc on the drivers side at the rear had patches that had corroded to a greater extent than others thus leading to fluctuation in the braking effort on that wheel.

When the brake on this wheel was tested it felt as if the the rear wheel was egg shaped.

If for some reason you are unable to use the vehicle for an extended period, it’s worth moving it a couple of yards weekly just to clean the surface of the disc of the build up of surface corrosion.

 

 

More on brakes

Corroded brake pipes Two more examples of brake pipe corrosion, oddly enough both from BMWs and both on the offside rear of the car. The first on a 02 BMW M3  As can be clearly seen the corrosion has penetrated deep enough and caused the steel to begin to flake away. The following example was on a W reg BMW 320d  The rust hasn’t penetrated to any extent into the steel, a quick rub down with a bit of steel wool and a coating of oil or grease will prevent needing replacement for another couple of Mots. BMWs do seem more prone to corrosion of the brake pipes on the offside rear than anywhere else.

Brake pads and seized calipers

A Nissan Micra failed the test with a brake binding on the offside front wheel, although the wheel was able to rotate by hand  it needed a fair amount of effort to move it. When we removed the wheel to undertake the repair we found one of the pads almost down to the metal and the other only slightly worn.

The outer pad was seized in the pad carrier and was constantly applied to the disc leading to uneven wear of the pads, surprisingly this didn’t cause any imbalance when the brakes were tested in the roller brake tester. However the caliper on the nearside was actually sticking  where it slides on pins. Thus the seizure on one side balanced out the seizure on the other.

Had the outer pad been visible with the wheel in place then the brakes would have failed owing to being worn below 1.5mm. The view from underneath told a completely false story as regards the pad wear. Had the brakes not failed because of the binding in perhaps less than a month the outer pad would have been grinding on the disc.

Lighting

This weekend I had the unfortunate experience of having to follow a Ford Transit tipper with a few lighting problems.

I followed the vehicle for approximately 1/2 mile, unsurprisingly,  not one of the rear lights worked. The lighting faults already visible would, if listed individually fill one vt30 page.

The driver of this vehicle would probably be one of the  people that ask “Why aren’t you catching criminals, rather than hassling drivers? ” when he’s eventually stopped by the police.

If only the police had more time to concentrate on drivers like him.

Brake pad wear limit.

And limitations of the Mot inspection.

Nowadays we’re seeing more vehicles at Mot time that haven’t had a service in the previous 12 months, the customer using the Mot inspection as a “service”. Unfortunately this can lead to problems as on an Mot test we’re not permitted to dismantle anything to check any items not visible.

Twice recently I’ve advised brake pads wearing thin, but not able to fail the item as the parts of the brake pads visible were not less than 1.5mm thick . Most manufacturer’s service limits are at 3mm for brake pads. In both cases the pads not visible were below 1.5mm, in one case the brake pad was touching and scoring the disc.

In this case both pads are just below 1.5mm, however the pads from the inner side of the caliper have worn lower and one was scoring the disc.

In many cases the condition of brake pads can only be truly assessed with the wheels removed, rather than relying on the tester being able to peer past a wheel trim or through small holes in the wheel rim.

With wheels removed  the condition of all the brake pads can be checked.

In this case the slight pitting of the outer face of the disc indicated problems in that the outer pad wasn’t moving and being pressed onto the face of the disc, the caliper was sticking and allowed the inner pad to wear down to score the disc. In this case the caliper was only functioning at approx 50% of it’s efficiency and had to be replaced.  In fact this particular vehicle had had an advisory that the pads were wearing thin at it’s last mot, had they been replaced then the caliper may have been able to be lubricated and thus saved the expense of replacement.

Suspension components

A couple of items this week, quite common nowadays is a broken coil spring, this one  found on the front of a Ford Fiesta.

However also found was a broken anti roll bar link, on the other side of the vehicle

It’s possible the link broke away at the balljoint  (highlighted in yellow) owing to the coil spring being broken leading to a mismatch in spring rates between the two sides.

Circled in red is the point where the wiring for the ABS sensor has become entangled around the anti-roll bar, a few more miles and maybe it would lead to the sensor wire becoming broken leading to more expense.