MOT brake test, how does it work?

[dieselnutjob]

Yesterday the 604 failed the handbrake test as the handbrake scored 14% "efficiency". The pass is 16%.

 

What is it 14% of? Is it the weight that's on the rollers? Are they weight sensative?

 

If so then emptying the boot and removing the spare wheel etc would reduce the weight and increase % figure. I am just guessing though.

 

The thing is that RWD pugs always have a crap handbrake, it just doesn't seem to meet modern standards. Is there some kind of VOSA exception for cars that were crap from new?

[alf892]

Check adjustment.....

 

If not just pull harder...........or (nicely) ask the tester too

[dieselnutjob]

I think I found the answer to my question here:-

 

http://www.motuk.co.uk/manual_370.htm

"Class 4, the ATL system has a facility to automatically weigh the vehicle and the presented weight will be used for the brake efficiency calculations."

 

So if I empty the boot making it lighter then the same brake force will result in a higher percentage reading

 

It's a self adjusting system that seems to be working. If it wasn't adjusting the handbrake lever would come up higher and the foot brake would have dead travel.

[alf892]

Just to check.......have a quick look at the mechanism with the handbrake on. For max efficiency the included angle between the cable and operating should be 90 degrees.

 

If everyting is new is could be just a question of bedding in.

 

Comment about pulling harder was not meant to be facetious.....there is no figure for the 'pull' applied.......and you don't need much more to pass!

[michael1703]

My station uses decelerometers on anything older, take it somewhere that uses one if you cant get a good reading

[Pete-M]

That may be an idea. Tell 'em the ol' 604 has a limited slip diff and they'll use the decelerometer normally...

[dieselnutjob]

by my calculation to get an increase of 2% in "efficiency" I have to reduce the weight on the back axle by 2% which only about 11kg. Loosing the spare wheel,jack and the collection of spare parts will probably do it.

[scaryoldcortina]

Losing weight to pass a brake test will only work if the station is an ATL (automated test lane) - ordinary brake rollers don't weigh the car - the weight is either supplied bu the computer (VSI) or inputted manually from the kerb weight of the vehicle (VIN plate or supplied info from the presenter) If you have neither of these, efficiency is determined with a decelerometer instead.

 

It's one thing to say "pull harder" but another in practice - you often find cases where more effort at the lever doesn't increase the resistance at the wheels. We are taught to apply steady pressure until it reads a pass (and no further) or to stop when max effort at wheels is reached to avoid damaging the vehicle.

 

I would recommend having another go at the handbrake - did the tester give you any idea why it is low? You can often tell what is up from the readings, but the overall % figure on the fail doesn't help too much. For example, if you got (say) 140 NS and 160 OS on the footbrake, but only 120 NS and 60 OS on the handbrake I'd be suspecting the OS handbrake cable to be siezed. Low readings on both footbrake and handbrake is probably shoe/drum related. Either way, even a "crap" design should make way more than 16%. Try getting a Mk4 zephyr through a test on handbrake! It weighs two tonnes, has disks and pre-historic calipers, an umbrella lever and is single circuit (so needs to make 25%).

[dieselnutjob]

No he didn't give me any indication

He just said that as the rear pads were brand new that they might need a bit of abuse to get them to "bed in"

Maybe I should try and work some oil into the cables before retest as well

Also, maybe if it passes on everything else he might try a bit harder. As the car had already failed by the time he tried the handbrake there wasn't much incentive to really go for it.

[simmo]

On the rear brakes are the little arms that come out of the back of calipers all the way back when the handbrake is off? If they are partually on you may get the bit extra you need by letting off the cable adjustment then make sure the arms are as far back as possible apply the foot brake hard a few times with the engine running this can get a tadge more adjustment on the internal mechanism. Can't remember doing this on a 604 but have had it work on 504s with rear discs.

[Albert Ross]

Think yourself lucky. I have ONE handbrake drum that has to make 25% of 1700kg..... I have drums all round and NO servo. But hey, that's Land Rovers built prior to 1985 for you.

[dieselnutjob]

On the rear brakes are the little arms that come out of the back of calipers all the way back when the handbrake is off? If they are partually on you may get the bit extra you need by letting off the cable adjustment then make sure the arms are as far back as possible apply the foot brake hard a few times with the engine running this can get a tadge more adjustment on the internal mechanism. Can't remember doing this on a 604 but have had it work on 504s with rear discs.

 

I can't be a 100% sure, but this appears to have helped.