question AEC Militant MKI MOT Brake/Efficiency Test Readings

Good day Gents,

I was looking over my recent MOT Certificate from April 2016, I was a bit baffled about the figures on the brake test as per attached picture. I would be grateful if someone can explain the figures. I thought maybe I should take the time to remove the four rear wheels and brake drums to check the condition of the shoes, and adjust/change as necessary.

Also after the test I discovered that the low air warning buzzer in the cab had been disconnected (At the air tank). I was thinking maybe the whole brake test had been carried out whilst Milly had insufficient air pressure.

I will have a go at removing the low air sensor on the bottom of the air tank (60 PSI) and see if I can be cleaned & freed off, as I have had no joy in finding a new one. (Anyone done this?)

Once again Gents many thanks in advance, Happy New Year to you all.

Hutch3674

See Annex 3 Brake Test Calculations (page 11) for the explanation:-

http://www.gea.co.uk/docs/264.pdf

Hi Hutch,

The WWW. page recommended by Matchfuzee does a very good technical description of the procedure on how to test and how the calculations are worked out, but it doesn't really explain how to read the results page, which if you are not familiar with them they can be difficult to understand.

Briefly it goes like this. Brake effort is what the brakes actually achieved at test. Service or footbrake at the top, axle one being the front, 2 and 3 are middle and rear. Then parking brake underneath, middle and rear axles.

Imbalance is the difference between the readings across each axle. A big imbalance will make the vehicle pull to one side. Brake fluctuation will show any ovality of the brake drum.

The figures on the right of the page show the standards the vehicle must achieve. E.G. The maximum imbalance permitted is 30%

I would suggest it is unlikely that your test would have been carried out with less than sufficient air pressure. The VOSA Examiner will normally give the driver time to replenish air pressure in between each axle test.

Should you check and adjust your brakes? I would if it were mine. The Off Side 3rd axle reading is much higher than the other 3 rear axle readings. Not only is a 28% imbalance across the axle very close to failure, but on a Militant the brake effort between the 2nd and 3rd axle should be considered, and yours is bad on the off side.

If you need it I can send you a "how to" sheet for adjusting the rear brakes it's not that complicated but you do need to do it in the right sequence.

Any chance you could post that "how to" for the rest of us Knocker owners please Rob??

Hi Rob,

many thanks again, and I would really appreciate the help sheet (Idiot's guide) to adjust the brakes. I have until 25 April to rectify and improve on last years results.

I am also looking forward to getting into the brake drums and improving the overall efficiency of Milly.

Thanks a Million again, a happy man Hutch3674

Hi Hutch,

 

The WWW. page recommended by Matchfuzee does a very good technical description of the procedure on how to test and how the calculations are worked out, but it doesn't really explain how to read the results page, which if you are not familiar with them they can be difficult to understand.

 

Briefly it goes like this. Brake effort is what the brakes actually achieved at test. Service or footbrake at the top, axle one being the front, 2 and 3 are middle and rear. Then parking brake underneath, middle and rear axles.

 

Imbalance is the difference between the readings across each axle. A big imbalance will make the vehicle pull to one side. Brake fluctuation will show any ovality of the brake drum.

 

The figures on the right of the page show the standards the vehicle must achieve. E.G. The maximum imbalance permitted is 30%

 

I would suggest it is unlikely that your test would have been carried out with less than sufficient air pressure. The VOSA Examiner will normally give the driver time to replenish air pressure in between each axle test.

 

Should you check and adjust your brakes? I would if it were mine. The Off Side 3rd axle reading is much higher than the other 3 rear axle readings. Not only is a 28% imbalance across the axle very close to failure, but on a Militant the brake effort between the 2nd and 3rd axle should be considered, and yours is bad on the off side.

 

If you need it I can send you a "how to" sheet for adjusting the rear brakes it's not that complicated but you do need to do it in the right sequence.

Many thanks MatchFuzee,

really appreciate your help

Hutch3674

See Annex 3 Brake Test Calculations (page 11) for the explanation:-

 

http://www.gea.co.uk/docs/264.pdf

Hutch, to add a little to Rob's comments, for a pre-1983 vehicle you do not need the low air warning buzzer, just a visual warning. If the examiner did the brake test they will have kept an eye on air pressure. If you were in the driver's seat, I'd expect you would have automatically kept an eye on the gauge?

Often in a large vehicle you will not notice a substantial brake imbalance when driving as the vehicle's momentum keeps it in a straight line, but it'll get you into trouble in an emergency situation.

Rob is the Militant expert and may know how these figures compare to other Militants, but I think I'd definitely be going right through the brakes inspecting and adjusting everything. You have the significant imbalance on axle 3 and across the axles as Rob suggests, but on a typical vehicle I'd also like to see that front axle imbalance below 10%.

Your service brake effort is also very low overall, only 3% above the minimum requirement; and unless I'm miscalculating, the tester has based the braking efficiency on your current all up weight rather than the design gross weight. By my calculation on a design gross weight basis those figures equate to an efficiency of under 25% - not great.

To add to Sean's reply, an inspection of the shoes might be wise because if there is any contamination on them, this would have to be addressed first.

Indeed. as Richard suggests, inspecting everything means inspecting everything. I know it's heavy work, but whip the drums off and have a look.

...............................................

 

Your service brake effort is also very low overall, only 3% above the minimum requirement; and unless I'm miscalculating, the tester has based the braking efficiency on your current all up weight rather than the design gross weight. By my calculation on a design gross weight basis those figures equate to an efficiency of under 25% - not great.

I'm pleased to see you came up with those figures. I did the same sums and decided not to publish in case I got shot down for mathematical errors. If I use Hutch's figures and the unladen weight of a Militant, I get 43% which would be a comfortable pass. Using the design weight, like you have, it fails.

As for being a Militant expert, I'm not sure about that one

If I use Hutch's figures and the unladen weight of a Militant, I get 43% which would be a comfortable pass.

Well, a pass. Given a 40% minimum and a reasonable expectation of 66%, I wouldn't say 43% was comfortable; under 25% considerably less so.

As for being a Militant expert, I'm not sure about that one

Well, you, Neil and Richard have considerably more experience of the dark and oily bits of Militants than I, so had you said those were typical figures I'd have deferred; but they don't seem adequate to me.

 

Well, you, Neil and Richard have considerably more experience of the dark and oily bits of Militants than I, so had you said those were typical figures I'd have deferred; but they don't seem adequate to me.

It was nearly 40 years ago when was working on these. We had stacks of them coming through the workshops, mostly for deep repairs and refurbishment, also I was regularly working on the Coles crane versions too. But I would have to set my mind back a bit ! I do remember our boss making us change engines through the front, which was a struggle, I did get to do one by taking the roof of though, much easier.

regards, Richard

I've been turning the cupboards out trying to find a brake test sheet for my timber tractor, it has had 2 voluntary tests since its restoration, but as yet I cant find either of them.

From memory I recall the rear brake figures were much higher than Hutch's readings. Somewhere in the 1200-1300kgf sort of area (11.76-12.74kN). Biggest difference is mine all locked out as well.

So yeah, I would agree with everybody else here. A good check over, service and adjustment is called for.

Bit of trivial info now.

Believe it or not, back in the day the official test involved the use of a standard house brick!! The brick would be stood upright on the cab floor, the vehicle would then be driven at ( I think) 10mph and an emergency stop performed. If the vehicle stopped in a straight line and the brick toppled over the brakes were deemed good enough.

From memory I recall the rear brake figures were much higher than Hutch's readings. Somewhere in the 1200-1300kgf sort of area (11.76-12.74kN). Biggest difference is mine all locked out as well.

That makes more sense. Apart from anything else, Hutch has two readings in the 10 - 12 kN range, which implies the rest are low and efforts of that order at least should be achievable all round.

Having said that, another quick calculation says that a true pass should be about 15 kN all round...

The brick would be stood upright on the cab floor, the vehicle would then be driven at ( I think) 10mph and an emergency stop performed. If the vehicle stopped in a straight line and the brick toppled over the brakes were deemed good enough.

Upright on end or upright on one long side?