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Testing Brakes before test

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Testing Brakes before test

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roundeyefat

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Jul 7, 2012
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Hi Folks,

I ran this by blu73 (moderator), in case it was inappropriate.

With my own car recently, the brakes seemed fine, but there was an imbalance of 48 percent between the two rear wheels.
Blah, blah, check this and that, but no good, so retest required.

With my background in engineering, it seemed apparent that mechanics have no scientific way to check the balance of the brakes, apart from physically replacing every element of the system.

Since then, I've made a method to at least test my own, and any other small car with four stud for holding on the wheel. (built in allowance for various P.c.d.'s{pitch circle diameter}).

If I could, (maybe I can or can't), replicate this system at an affordable price, would anyone buy it?
One local genius uses his concrete yard to test brakes - he uses an observer (wife), to see if each wheel lock and skids - with black evidence on his white concrete. Apart from that, he has nothing handy, by way of a test.

So the question again is;
If I could, (maybe I can or can't), replicate this system at an affordable price (to a mechanic), would anyone buy it?

What would be an affordable/cost effective price?
Thanks
 
we must all be thick then,what we do is lift and secure vehicle,engine running leave handbrake off check rotation of wheel is smooth,get person in car to press footbrake wheel should lock we grab wheel with 2 hands and force rotation,no turn ok,check other side ,ohh wheel does not lock problem [needs looking at],wheel locks ok.
next is handbrake function ,one click at a time count how many until wheel locks on both wheels,if more than 2 clicks one cable is moving more.
it is easy to find the problem as with an imbalance you are going to have to remove wheels and drums to check what lining is left,cylinders not seized or leaking and handbrake lever back to rest,as in letting off adjustment on handbrake,maybe just needs a good rub down and removal of dust and rub down surface of drums and shoes with rough emery paper,readjust manually road test to bed in again using handbrake also and repeat the test.
all used by my 1 finger typing(y):D
 
@ dirtyhands
Sure this is problem; grabbing the wheel with your two hands and trying to rotate it or not, is solely dependent on your physical strength.
How much torque do you estimate, that you can produce, with your method?

My mechanic does the same method, and look where it got me? another full retest.

Since my "issue", I dived into the maths of the problem, and can tell you with some certainty that Hercules would not be able to produce enough torque by grabbing the wheel, to break the holding force of my worst wheel - let alone my "good wheel". This is maths and physics - something we are bound to, for the moment.

My mechanic is 32 years in the game - because of my job, I meet different mechanics weekly and I survey them. They all have the same techniques, but none of them are physically strong enough or heavy enough (they don't know this though), to definitively say that a car will pass the test, based on "their test" - they can guess based on experience, and it works most of the time by "accident", and the mass replacement of parts.

My car must surely be at the lower end of the weight spectrum (punto), and you might agree that the braking force must increase as the weight of the car increases.

With the greatest of respect, can you tell me that you can produce enough torque to overcome 1.4kilonewtons - the force returned by my previous nct (irish version of mot).

Balance. Both wheels (brakes) can be balanced, and have bad brakes at the same time, as you know. So the test requires that both wheels are balanced within a certain range, but hold above a particular torque for a particular car.

With your manual check, you can tell if both wheels are balanced, within a range that you do not know.
With your manual check/test, you can tell if either wheel is poor, but below a value that you can't estimate (maybe you can, and didn't say).

Thanks - as I am here for constructive criticism and feed back.
 
@ custard;

The market, if there is one, would be the mechanics, and not the car owner.

Picture this scenario.

  • My brother lives fifty miles from an NCT (mot) centre.

  • The general practice around here, is that you run your car through the test to identify any issues - they reckon its cheaper.
  • The mechanic goes through the list and must "fix" the brakes.
  • He does as dirtyhands (example only) does, and everything is fine.
  • The retest fails, because of imbalance - My brother must drive 100 miles to discover this.
  • The mechanic looks again, and changes a few more parts. He's conscious that the money is rising, and won't change everything.
  • It doesn't happen often, but issues like mine arise - the "usual suspects" are not the suspects.
  • Another test - another failure. Embarrassing, for the mechanic and expensive for the brother.
  • Mechanic rings around, and advice from the brethren, will lead to another part being replaced. Mechanic, cannot test definitively, and wants to fall out with the customer.
  • The money/cost rises.
My "solution", is that the mechanic will know, that each wheel will pass the test, before he sends it in, for the retest. First time, every time.


In this country, Ireland, you may have to go through a full test again - apart from the higher cost, there is every likelihood , that an old car will return a whole new set of issues, instead of automatically getting a year of certification - if only he was sure that the brakes were good enough
 
Doesn't the imbalance test constantly measure the imbalance as the pedal is pressed, so throughout the brake range. Struggling to think of any way to measure the imbalance the same way without rollers. If it was just with the brakes in one set force you could just use a big torque wrench and measure the total force needed to move each wheel.

Might be wrong though, i suppose you know this if you're looking into it?
 
@ maddogmorg

You're warm!!
Only that there are a few problems with using a torque wrench.

But the bigger question; Do you see the point of measuring/knowing, whether ones brakes are holding , or not?
And if there is a point, would anyone buy it?
 
@ dave

You're right - its the first thing that people think of - usually the only alternative, which might suggest something.
I wonder what they'd do if there wasn't a kwikfit locally?

  1. Replace parts, en masse
  2. Open a kwikfit outlet, locally.
  3. Resort to the "concrete test", mentioned above - while crossing the fingers.
  4. Loosen the oil bung, in the hope that "the patient" suffers a catastrophic event, before the next test:)
Bring the car back to kwikfit, after you change part by part. It happens, I'm sure.


Everything is fine when you're not in recession. Buy a new car, or get finance for it.
The economists (Ireland) will tell you that wages are "sticky" - we're overpaid.
My counterpart in Germany is paid 300 euros less per week. And we're paying off our debts, just like the customer/car owner.
So, every time you go to the mechanic and he can't solve something, both the mechanic and the customer, feel the pressure like never before.


My intention, if it works out, is to produce a tool/system, for something under 120 euros. Is it worth it?
You could spend/waste an hour alone, going to and from kwikfit. How much an hour is the implied free service? The mechanics time, is not free (usually).


The mechanic could get my brother (example), to bring in the car to kwikfit. Its still not free.


In the future, cheap cars like the punto (example), might have in-built pressure sensors, but thats a while away.


Until then, would a tool be a waste of money - something selling for 120 euros?
 
I think if you can do it, go for it.
Levy Roots made a sauce, took it to 5 business persons and bam, millionaires.
Good luck to you.
Ta
 
no i am not hercules but my point was if footbrake is applied wheel should not turn,if it turns on one side there is a problem,it works for us with limited resources,i know money is tight over here,you can still do everything and get a cranky tester having a bad day,nothing is 100% as if they want it to fail they will find something no matter how stupid.:devil:
 
The concreat test of which you speak is most probably the best and most obvious solution and although archaic it does the job,

If you thing that in the test centre the torque that the car is braking against is being exerted by the rollers making contact with the tyres, then to fail on a balance issue one brake is locking before the other side, using a concreat or Tarmac surface is going to be able to exert similar forces on the tyre and therefore the braking system.

What you need to do is establish the extent of the imbalance so you need to find the point that both brakes are able to lock.

Now your talking about diagnosing the fault without spending money, on a basic braking system you have discs > pads > brake calliper > hoses (abs pump if fitted) > master cylinder. If one side is under performing and you've changed the discs and pads you're happy the calliper is in good working order then it's basically a hose/pipe problem or a knackered master cylinder.

Bearing this in mind there is no way of diagnosing this using rolling roads braking hard on concreat or any other system that exerts torque on the wheels/hubs
From an engineering point of view you need to see what force the calliper is able to exert on both sides, if imbalances then you need to be able to measure the fluid pressure on both sides, consider air entry into the sealed system. if the calliper forces are equal then you need to look at the braking surfaces discs and pads.

I can't see any logical need to spend money on a mechanical solution to what can be achieve in a car park. However if you really needed to! you take a length of box section weld on end of it to a steel wheel centre bolt it to the hub with the car supported have some one stand on the brakes while you stand on the other end of the metal bar, how much force can you exert then? The longer the bar the bigger the force the fatter the bastard the bigger the force, probably more than a rolling road can achieve? My weight on the end of a pole 6 feet from the centre of the hub would equal about 1000ft/lb of torque? And that's gonna cost a lot less than €120

It's also worth bearing in mind that permanent 4wd vehicles in the uk are often brake tested in the car park with a decelerometer as a rolling road would damage the 4wd system.
 
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Yes Andy,

So, we can deduce your weight.
What is the cost of getting a wheel rim and welding a bar to it - and do so for cars with different p.c.d.'s (pitch circle diameters) for its wheel studs, be they three, four or five - and the calculation element is not present/not simplified.

With the concrete test, you don't really know anything other than the wheels are locking - maybe this is good enough, most of the time.

I do agree that even the rolling road will not diagnose the exact problem either - my point, is that the mechanic must keep going before the test, to be satisfied (needs definition) that the car will pass.

If the car doesn't pass the test, and the mechanic is sure that it is fine for the values, then he can argue his case like never before. He'd have tested it, himself.

Yes I know how these test centers can return false results - because the local one sends in their rollers to the likes of me, and I've seen first hand, how the bearings were collapsed - they usually don't collapse instantly, and this roller would have returned false reading for some time. In one case, the roller shaft had to be built-up, meaning that it dodgy for a long time (these are relatively slow-moving, as things go).
With the visual inspections, there will always be subjective errors - I get it.

But if my good wheel has a test centre reading of 1.4kilonewtons, then the mechanic has a starting point. The bad wheel must be improved, up to whatever the balance percentage allowance is. With the proposed system, he can be confident in himself, to his customer and to the test center personnel - his argument will be based on simple maths; a simpler process than the test centre machinery (given the errors they can produce, briefly mentioned above). How much is confidence worth, compared to the red face that my mechanic had, when the car failed?

A car park test can look great, but is hardly a calculation, is it. As most agree, it can be enough, but can be lacking also.
 
And good luck to anyone, hoping to find a dry car park in this country, the way the weather is :) Another unreliable variable.
The concrete around here, is as wet as the day it was poured - though if you could mark it, the test is somewhat better.

And thanks again for everyone's input.
 
So, you're telling me that there is no portable version of a rolling road?

I might be simplifying this too much but with modern tech, is it not a case of attaching a decellerometer to each wheel & noting the results of stopping from a set speed?
2 units, one on each side (testing both backs or both fronts), should give roughly the same result (?) each time the vehicle is braked.


Just had a vision of some mech driving down the road with a pair of smartphones strapped to the wheels :-D
 
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Hi sludgeguts,

I'd imagine that the cheapest way, would be to have a sensor(s) built into the car when it is made - volumes, etc., as mentioned earlier.

There is probably a million ways to do anything, or to get things done - and that's why I'm here.
Sticking with a decelerometer; the one at http://www.jhmbuttco.com/acatalog/Shop_Brake_Meters_473.html seems expensive enough, but I'd still say that anything like that, would be worth it, cost wise.

Or say the one at http://www.brake-tester.co.uk/brakecheck-faqs.php - quote :
"
Q. What will the BrakeCheck tell me?
A. BrakeCheck will report how good all your brakes are at once. The decelerometer will also measure a pull left or right, this measurement will help identify individual wheels, a stopping distance and speed at braking is also reported."
Immediately above, I'd say, is a general statement - and that one would have to be able to interpret the various measurements that it (device) takes.
How do we imagine that these things work? I don't have one, but would think that there is a limit as to how a small portable device can analise its environment - and thinking that you'd have to perform numerous tests and calculate something from the results?


From the same page; "

Q. Is the brake tester connected to the vehicle?
A. There is no connection to the vehicle; this portable brake tester simply sits on the floor around the driver."
So I can leave this on the floor, and by reading the text, you'd imagine that it will test for pull, left and right? We can't doubt that its approved, and that that should be enough.
Star Trek and the advent of the Smart Phone, has us thinking that technology can do anything - you'd want to read the small print, or try it perhaps?


Maybe someone here, can fill us in as to precise nature of these decelerometers - apart from the cost even, I think that they're not as straight forward as they seem, in terms of analising results?


The first thing that hits me is how you can leave it on the floor (without fixing it), and test for left and right? Is one test enough? Can't it spin about a little, being lightweight and all
 
There are apps for smartphones that take advantage of the g-force sensors built into smartphones.
It'd be interesting to see if they are sensitive enough to detect one brake being less efficient than it's opposite - although are the results afected by road camber (the camber would (?) make a car veer off course under braking).
I presume the MOT allows a percentage variation across axles? & presumably this percentage is more than measurable by an app?
 
Yeah, they can be great.
They must be able to measure in a range of planes - front/back, left/right, and maybe a number of points in between? They might even do up/down, for all I know.

But they'd want to be able to do so, at the same time; else a number of tests would be needed?
And now I see this; http://mobiledeviceinsight.com/2011/12/sensors-in-smartphones/

Perhaps, it is stuff like the above that is in the decelerometer - a gyroscope as well?
 
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You can just hack into the OBDII port of new cars and look at the ABS wheel sensor data, brake hard till one or more of the wheels lock up and it should indicate which wheel is the problem, some systems also measure internal fluid pressures
 
Yes, that sort of thing, Andy.

Too late to retrofit a 99 Punto.

Flexible pipe should be in the motor factors today. If it is, then I should be able to hook up "my apparatus" to the car, and test before and after it is fitted - at least then, I'll know whether I have solved https://www.fiatforum.com/punto/304463-back-brakes-valves-99-punto.html , or whether I have to go ahead and replace the master cylinder as well.
I machined a bit of pipe to the same diameter as the hubs, so that a visual inspection of the "adjuster" system, can be made as well while someone is pumping the brakes - some mechanics are still saying that its an adjustment issue, in that they can be new and yet slip? At least with the pipe, we should be able to look at it "slipping", if that is the case.

@ AndyRKett and internal pressure;
It depends where on the system, the pressure is measured. If its not very close to the wheel, it wouldn't be conclusive.
In the case of the flexible pipe; none of the local mechanics buy the theory of an expanding flexible pipe, though I do in so far as it could behave like an inline accumulator.
What two mechanics propose re the flexi pipe, is that the internal lining of the pipe,
partly comes away from the steel or fabric support matrix, and that the hydraulic pressure actually causes the flexible pipe to "seal itself" - like the most basic non-return valve. When it is "put" to them, they agree that it will be difficult to actually "see" the damage - small bore pipe, big human eye and no pressure, when observed. The before and after, torque test, might be as good as it gets, unless I can slice the flexible pipe in some way.

If these mechanics are right, and you can't ignore experience (they've seen it before, two of them claim); then any pressure sensor which is earlier in the system, would detect that the pressure is fine - while it could be practically zero, after the blockage. Though, this would help to determine the health of the master cylinder, once the possibility of an expanding pipe (absorbing the pressure to a point, and before it fails), could be ruled out.

Calculations based on the ABS performance, would be a good thing.

The object, as always, is to establish that the changing of one part, makes a difference at all - and to test for some proof.
 
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