MOT fail on wheelbearing

My BMW 528 has just failed on 'excessive play in front wheel bearing' It's not noisy and doesn't show in driving. Having looked at the various MOT sites I can't find a definition of 'excessive play'. So what is it?

My SD1 workshop manual gives the amount of free play they specify - but it has adjustable taper bearings.

So is it *any* free play detected by hand?

Reply to
Dave Plowman (News)
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Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

Tester's opinion.

Reply to
Adrian

Have you jacked it up and given it a wobble, Dave? Is it one of those wot can be adjusted up a bit?

Si

Reply to
Mungo "Two Sheds" Toadfoot

Nope, at least that's not what I was taught on my MOT testers course last year. However 'excessive' is so vague that you'll probably get nowhere complaining. Our instructor was of the opinion that 'excessive' meant the wheel was likely to fall off in the next few weeks, his favourite saying was if the vehicle managed to drive to the MOT station it should probably pass. It's all about minimum standards and not servicing standards.

John

Reply to
John Greystrong

John Greystrong ( snipped-for-privacy@ntlworld.com) gurgled happily, sounding much like they were saying :

Where's he work? I think I need to go see him.

Reply to
Adrian

His opinion was there was should be a lot more pass and advise. Too many testers are using standards that they would on a car they were servicing rather than the minimum standards set by VOSA.

John

Reply to
John Greystrong

same advise i got as well, we need to take off our servicing hat & put our MOT hat on, we need to issue more PANDA's, but not on some of the bag's of s**te ive seen come through lately !!

Reply to
reg

============== The new computerised Test Certificate (VT20) has a box entitled "Advisory Notice Issued". It seems clear that the intention is to offer advice about potential problems rather than failing cars on minor defects. I think that slight play in a wheel bearing should come under this heading.

Another interesting item in the investigation section is that concerning accident damage. Mine showed up as having serious accident damage but the only actual damage has been a dented nearside wing. I think that this is likely to generate some heated arguments about what constitutes 'serious damage' especially as it is likely to affect the resale value of a car.

Cic.

Reply to
Cicero

the " serious" accident marker is only viewable on the VT40 ( checklist) top right corner, its to aid the tester, to alert him to any damage serious or not, the customer doesn't receive this checklist & its not printed on any other paperwork that the customer receives. in fact I had one today with a serious damage marker, I talked to the customer about it & the only damaged the car had sustained was a front end bump, I guess its all interested parties i.e. insurance companies, dvla all talking together now, which in one respect is good.

Reply to
reg

and dont forget you can go here

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all the details in thats required and it will show the pass, fail oradvises that were issued to the vehicle your inquiring about.

Reply to
reg

When new, non adjustable wheel bearings have virtually no play. It usually takes many thousands of miles before any play becomes easily noticed. It could be argued that at that point the bearing should be replaced. I would to agree with that, even though the bearing could last for many more thousands of miles before it actually started to break up. Maybe the examiner thaught the same.

Ball bearing races, like the non adjustable types fitted to many front axles, indeed ball bearings, do not tolerate any noticeable play, unlike the taper roller bearings fitted to an SD1. Taper roller bearings have a greater contact area, so can take heavier loads, and easily cope with play or preloading, which would overstress a ball bearing. Mike.

Reply to
Mike G

Interesting that no one has given a definitive answer - like 3mm movement at the top of the wheel or whatever.

My experience of worn wheel bearings is they go noisy first - but can still pass an MOT. Not that they're quiet but have too much play - unless adjustable. Any sites that give definitive guidelines?

Reply to
Dave Plowman (News)

Maybe there isn't one. It's hard to define a small amount of play that might just be felt, but is too small to be accurately measured. A very little play might be the only guideline given to MOT inspectors for ball race front wheel bearings. In that case it would depend on the examiners judgement, but how much is very little? You say it failed on 'excessive play' but how much play has the wheel bearing actually got?

As for a noisy bearing, that should be a fail every time IMO. It's the first sign of a bearing breaking up.

Of course you could always try taking it somewhere else. :-) Mike.

Reply to
Mike G

Oh dear, I think we need a wheel bearing 101 here. Most wheel bearings on modern cars, especially fwd cars, are not ball bearings but taper roller bearings whether they be the "torque them up to 150 ft lbs plus" type or the "hand tighten them and stick a split pin through the axle" type. Neither type run with any preload.

The difference is that the torque them up type have two sets of rollers facing opposite ways in each sealed unit with a factory fitted shim between the inner races which sets the free play. When you heave on that socket bar with a length of scaffold pole over it you aren't tightening the bearings at all, you're just transmitting the clamping force through the front bearing and its shim down the axle to the back bearing unit, through its shim and on to the rear of the hub. The free play in each bearing is factory set by its shim and when the wheel starts to rock the only cure is a new bearing. The double sealed type generally have to be press fitted into the wheel hub.

The hand tighten type of bearing is also a taper roller but with only one set of rollers in each unit. The rollers will come staked into a plastic or metal cage on the inner cone and the outer cone will be a separate piece. You tighten those to maybe 20 ft lbs while rotating the wheel and then back off a tad until the split pin fits through the axle into the nearest hole in the nut cage. That gives the bearing its free play which the sealed double type gets from its internal shim. You can regrease and readjust these to eliminate wheel rock provided the rollers and cones are still in good condition. You can ignore any car specific tightening specs as being gospel because the aim is only to get a small amount of free play and there are many ways to achieve this.

Ball bearings are now pretty rare. You'll generally only find them on a live rear axle on an old rwd car like Capris and Escorts. They will also be lightly hand tightened like the single taper roller type.

Modern FWD cars will normally have sealed shimmed double taper roller units on the front and single adjustable taper roller units on the back. Modern RWD cars will tend to be the reverse. However there are no strict rules and a designer can put either type in at either end.

So both types of taper roller bearings and also ball bearings will have the same amount of free play at the wheel rim when they are new and properly adjusted. This free play is minimal. A couple of mm at most, ideally less. Ideally the free play will be as close to zero as possible while still allowing the bearing some slack which it needs to operate correctly without overheating. 'NO' type of wheel bearing has preloading even if you think it must have because you have to do the hub nut up very tight. Any bearing that started life with a heavy preload would burn itself out in no time flat.

So on to the MOT requirements. A bad bearing will usually give itself away by displaying roughness or rumbling as you turn the wheel. Free play doesn't necessarily mean the bearing is bad unless it's a double sealed type. Even then it could be a good bearing with a shim that's a bit too thin. However to set a wheel rock limit would be nigh on impossible because of the different types of bearing and the variation in wheel rim diameters. It's something that has to be left to the tester's discretion and that means sometimes a good bearing will get failed and a bad one passed.

I hope this has dispelled some myths or misinformation about how bearings work. I know that a lot of people think that some types of bearing need a heavy preload whereas others need free play when in fact all types need free play. If only I knew as much about boilers as I do about cars (in joke for Mr P).

-- Dave Baker

Reply to
Dave Baker

Edit - a shim that's a bit too thick.

-- Dave Baker

Reply to
Dave Baker

I took my car to Kwikfit who found MOT, 7 faults.

I then took my car to a non-garage MOT centre that does no reapris.. no faults.

Worth trying a non-repair MOT centre?

Reply to
Zzzzzz......

I wasn't suggesting that front wheel bearings were fitted with preload, only that in some applications taper roller bearings are.

The same can apply when the wheel bearings are supplied as matched set of 2 side and thrust ball bearings, without a spacer by the bearing manufacturer. Such a pair of bearings are fitted to my Celica GT4 front axle. The 2 inner races are torqued together by the axle nut. with the outer races a press fit in the hub.

When you heave on that socket bar

The same as for when they are a pair of matched ball bearings without shim or spacer.

The free play in each bearing is factory set by its

At least we agree on that. :-) Mike.

Reply to
Mike G

Dave Plowman (News) ( snipped-for-privacy@davenoise.co.uk) gurgled happily, sounding much like they were saying :

Because there isn't one.

"Excessive" is in the tester's opinion.

Reply to
Adrian

Especially on blown bulbs, wiper blades, horns, broken numberplates etc etc.

Reply to
Conor

Always.

Reply to
Conor

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