Trouble is engineers are pushing everything too the limit with their designs to get maximum proformence and lowest cost, so something is going to give.
We didn’t have these problems running at 38 tons, so maybe 44 tons is just too much.
miketdt:
Trouble is engineers are pushing everything too the limit with their designs to get maximum proformence and lowest cost, so something is going to give.
We didn’t have these problems running at 38 tons, so maybe 44 tons is just too much.
more a problem of specifying correctly when ordering equipment
Belgians have been running at 44 tons for years
The Dutch run at 55 and in some Scaninavian countries 60 tons is normal
newmercman:
Truck racing is the only comparison, unless there’s something else lorries are used for that I don’t know about & I never said that it was an option for road going vehicles, the point was, that as Britpete said, they need better cooling to prevent discs cracking, the brake component manufacturers must be aware of this as they are heavily involved in the truck racing scene & came up with the water cooling idea.Also a truck loaded to 44t will be overloaded going down the Katzanbach & having driven that road many times, surely it wouldn’t need a single brake application if driven correctly? Proper use of the exhaust/engine brake/retarder would mean that the discs stayed cool all the way down
They need better cooling granted, any make of steel or alloy used to generate friction will get hot, the surrounding mountings will get hot, the bearings and the tyres will get hot, pouring water on the hot metal will only cause the water to get hot. Modern materials using ceramics can cope with temperature better, but at a much higher cost.
Any vented disc or better still a cross drilled floating disc will dissipate heat faster than a solid cast iron assembly.
You are spot on about the descent of a hill not needing brake application if driven correctly, however the modern way of driving is borne out by the modern trainers mantra. “Brakes to Slow, Gears to Go”
It isn’t my way of driving. I was taught to go down the hill in the same gear as I would need to get up it. This and using a retarder / Jake brake would keep the speed down without touching any service brakes.
I have used the same method in my 44tonne intermodal truck both up and down the Cats Back without incident, or cracked discs 
I have however had overheating problems with a water cooled Voith propshaft mounted retarder which resulted in turning on the cab heater in mid summer.
And drums did crack regularly but were much harder to spot with twin rims. You don’t see so many brake backplates in the road nowadays either. 
OK so you can run the cats back with an intermodal at 44t 
I think the watercooling starts as soon as the brake is applied so they don’t get too hot in the 1st place rather than cooling an already hot disc, surely that would guarantee cracking?
My current truck has drums, they’re about the same size as the ones on a mk1 ■■■■■■, we only run at 36t on 5 axles, which is good because they are useless, if i used the brakes to stop from 60mph in a short space they get hot enough to start smelling, luckily I have a Jake & apart from emergencies that’s pretty much all I use, when I approach a traffic light, which is not that often, I hit the Jake, go down through the box & try to keep rolling so I don’t notice the poor performance as much, I had to adapt my driving style dramatically to compensate, luckily I’ve been driving for a while & been over the mountains a few times so I’m used to crap brakes & going down hills in a low gear using the engine braking, but before I left the UK I had disc brakes on all 6 axles & because of their resistance to fade & superior performance I tended not to use the engine braking as much as I used to when I had crappy brakes. this leads me to my original conclusion that brakes are used more often & more heavily than we did when we had drums & that increased use is a major factor in cracking discs.
depablo:
Calipers seizing and severe cracks on discs is really down to poor maintenance.
Tell me about it, I’ve had the truck just 12 months, bought it s/h off a Merc dealer who had supplied it originaly with an R&M package.
Without wishing to stir, disagree or anything like that, but a lot of the trouble is down to how they are maintained and driven. I had a set of discs last 4 1/2 years, and the pads did almost 4 years. A lot of that time I was pulling tankers which is hard on steer axle brakes.
The disca will get really hot and then cool several times a day and that causes radiation cracking. These cracks are normal enough and will eventually crack through if you don’t keep an eye on them. Travelling in rain affects it, in dust or anything else. They all crack but they will shatter if they go too far and that is very bad news. You g=have to keep an eye on them but they are, in general, as durable as drums. The main difference is that a drum can be copletely shagged and they would not be able to see it, whereas a disc brake is visable so an easy target.
I had SAF discs on the tank and they barely did 2 years. When I changed the pads I had to change the discs. But even so, they were better by far. Not sure I would be too comfortable having discs here.
Blimey Rob, they lasted well, my Stralis’s used to eat through front pads in 6 months, the rears were changed at the same time, although they still had a bit of life in them & the 2nd steer barely had any wear, the pads I used were pretty soft, that’s why they didn’t last too long & I never had any disc problems, my oldest was an 04 & I got rid of them at the end of 07 before I came here, I used to change the pads myself, much easier job than a reline with drums, cheaper too
Other factors could be harder pads generating more heat, after all it’s heat that is causing the problem, the kinetic energy from the momentum of the vehicle is transferred to heat energy when using the brakes to slow or stop the vehicle, the more energy taken out of the vehicle means more heat, so scientifically that makes the most sense (until an expert comes along) or maybe there are just a bad batch of discs about 
I’m sticking with my original theory though, it makes the most sense to me, my drivers were all older blokes who never had the luxury of being able to stop on a sixpence so weren’t so hard on the brakes, much like a tanker driver, you & I never had any problems & that was on Renaults (you) & Ivecos (me) & we all know they’re not the strongest of lorries 
Exactly, they weren’t hard on brakes. Make all the difference.
I got pulled for an inspection at dover once- middle of the night, the tank had a crack and was dripping grape juice so I had to lie and say it had got into the tank laggind and was just dripping from there. The inspector asked me when I had last changed the discs and pads and I admitted I never had. He was amazed and told me as much when I said how long they had been in there.
Hard pads will make a difference, and Petes assertion about the quality of the steel is valid too.
What do you reckon though, Mark? With Jakes like ours, and with the roads here, how do you reckon discs would be? It is only the clogging with snow factor that bothers me really. I can’t see them adhering to the discs because they cool away from the pad unlike drums, but I reckon they will get clogged up with ice easier than drums in real snow.
I don’t know Rob, the ice build up on the caliper would be a concern, they run higher pressures than drums, but as you know from driving on it, ice is pretty strong stuff! I don’t think they’d hold up well to all the salt they use in the states, the gravel roads wouldn’t do them any favours either, yes I would like the increased braking performance for emergencies, but I reckon they’d be a real headache over here, I reckon you’d have a lot of compatability issues with the amount of trailers over here it would take 20yrs before they all ended up on discs, so you’d end up knocking the unit brakes out in no time, think I’ll stick with my old timer methods & listen to the Jake popping & cracking 
what would be nice is to hear from the members who live and work
say in Scandinavia , Russia, and all points around this direction as they
would be having the same type of weather, in Siberia not,
many years ago;MAN sold a large amount of vehicles to the the firm working
on the gas pipeline and they were all fitted with the magiurus deutz
air cooled engine not sure what type of brake system,they would be able perhaps to give some good info if the vehicles /trailers were fitted with disc brakes,
we do not hear from our Scandinavia partners any complaints about
disc having problems■■?
Big Joe:
Tell me about it, I’ve had the truck just 12 months, bought it s/h off a Merc dealer who had supplied it originaly with an R&M package.
Anyone on here who has an R&M package is living a dream if they think workshop foreman will authorise repairs on a worn component. It basically has to be worn to excess beyond the limits of VOSA before the component will be replaced.
This is how R&M packages remain competative, cutting back on quality. Bring back the in-house repair shop and fleet engineer who took a pride in their work and their reputation.
limeyphil:
‘… i got 2 prohibitions … they accepted that it wasn’t the sort of thing a driver is likely to spot … they have never given one of ours a clean bill of health…’
That’s a bit scary - but this post (from the current “Tesco ■■■■■” thread) suggests that some blokes there (?) are getting grief/leant upon/the push* for blanking obvious defects - which is, as I understand it, drivers not being arsed or encouraged to observe the law that nobbled you:
Stanley Mitchell:
‘…@ Fradley … “defect freaks” certainly do not last …’
I suppose it’s a case of not getting proper snags confused with ‘seat cover faded’ type nonsense…
- You choose: We’re all aware that it’s too easy to scarper-off home without defecting the wagon - but I’m reckoning jacking colleagues with snags that one can’t be bothered with aint big or clever…
The argument about disc v drums has been going for a long time. Around the world scientists have been trying hard to find a material that can achieve all the requirements of weight, cost, braking performance, resistance to cracks and long life.
It’s not just the cost benefit that has dictated their introduction. There is a definite benefit in reducing accidents too as this American study shows (must have been fun for the drivers involved).
www-nrd.nhtsa.dot.gov/pdf/esv/es … 0290-O.pdf
“Based on the results presented here, the hypothesis that a brake system that provides a shorter stopping distance in an emergency braking event would reduce crashes and fatalities is valid. The type of braking system had no statistical effect on driver behaviour prior to braking. The experiment used a validated virtual environment with high fidelity and showed systematically within a reasonable statistical confidence that professional drivers using either enhanced or disc brake systems were able to avoid many collisions.
In an extreme emergency braking event at high speed, drivers using the disc brake system avoided collisions better or had reduced collision severity than those using the enhanced brake system.”
Remember that the job of any braking system is to convert the kinetic energy of the vehicle into heat.
For an object that is moving the kinetic energy equals one half times the mass of the object times the square of the speed of the object. (In symbols: EK = (1/2)mv2) The answer is in Joules:
One joule in everyday life is approximately:
- the energy required to lift a small apple one meter straight up.
- the energy released when that same apple falls one meter to the ground.
- the energy released as heat by a person at rest, every hundredth of a second.
- the energy required to heat one gram of dry, cool air by 1 degree Celsius.
- one hundredth of the energy a person can receive by drinking a drop of beer.
- the kinetic energy of an adult human moving at a speed of about a handspan every second.
- the kinetic energy of a tennis ball moving at 14 miles per hour.[1]
So a 44 tonne truck at 80Kph would have 550,000,000,000 joules of energy which all has to be converted to heat in order to bring it to a halt.
This is an extract from a Japanese study into materials.
“Braking by disc brakes consists of a process in which the brake pads are pressed against a rotating rotor to convert the vehicle’s kinetic energy into thermal energy before releasing it into the air. Extremely hot heat spots at temperatures (approximately 750 °C) are caused in a very shallow layer under the friction surface of the rotor. Due to the consequent local temperature gradients, the friction surface of the rotor undergoes compressive yield accompanied by plastic deformation. When the rotor subsequently cools down, it undergoes residual tensile stress generated in these spots. Repetition of this thermal stress cycle causes heat cracks to initiate in the friction surface.
The rotor comes under not only the above-mentioned local temperature gradient but also the temperature gradient that occurs between the friction surface average temperature (some 500 °C) and the rotor inside temperature. In contrast to the local temperature gradient, this surface/inside temperature gradient is a macroscopic or average temperature gradient. Repeated thermal stress caused by this average temperature gradient has an effect of propagating heat cracks. The thermal stress caused by local temperature gradients is presumed to be much greater than that caused by the average temperature gradient. As reported in past research, heat cracks initiate at a very early stage of brake application. The life of a rotor, therefore, is considered to be governed by the propagation life of heat cracks after they have initiated.”
The point is that disc brakes are better in almost all respects than drums. Engineers are solving the cracking problem and surely we all welcome anything that improves road safety.
That is what I was wondering, Pete, since Volvo are Swedish. And those were similar concerns, Mark.
Fascinating subject. I’m fairly new to the trucking world and this is completely new to me.
It troubles me that this problem could land you in trouble despite it pretty much being out of the drivers ability to detect during daily checks, without putting the vehicle over an inspection pit, and leaves me wondering who’s going to “monitor” the cracks in the disks when most of the firms I’ve driven for have chosen against on-site mechanics in favour of dealership servicing. I’m usually pretty sharp eyed with regards to the condition of a vehicles mechanical devices due to having a background in mechanical engineering, and I’m fairly sure that over the past couple of years I haven’t seen a cracked disk on any vehicle I’ve driven or had access to, although I haven’t specifically been looking for cracks.
It suprises me how much concern there seems to be from VOSA about this. Is this a new area which they’ve found they can target trucks and line their pockets with? Going by my experience, I’ve never even heard cracked disks being mentioned before from other drivers or colleagues. What I’d like to know is; how many incidents are there each year of brakes disintegrating due to cracks and how many accidents are caused by this fault? Sure, it’s not ideal having cracks in your disk but in my previous job in aviation, it wasn’t ideal finding cracks in the stringers of commercial airliners during inspections but so long as they weren’t excessive, they’d normally remain in place until the next major overhaul - an example of an industry with a far more advanced and realistic outlook on periodic maintenance.
If this is such a problem and such a major safety hazard, it’s pretty clear to me that disks, in their current design, are simply not up to the job of heat dissipation without fracture, therefore the Department Of Transport should never have allowed the design to be fitted to trucks in the first place - although that’s not to say that they’re any worse than drums. The problem is, it all comes down to price. It’s a cheap design, and that’s how it will remain. You could have a much better setup with multiple sets of disks per wheel and even enhance the brakes with forced airflow from cooling fans which take their power from the decelerating transmission. This’d keep the initial braking temperatures lower and could potentially eradicate cracking. Trouble is, it’d cost a packet and would add extra weight.
In the real world though, disks are now here to stay for quite a while to come. I’ve recently been put through quite a few VOSA “Daily vehicle check” videos as well as actual lessons by ex traffic officers on how to make certain ones vehicle is roadworthy and thus avoiding fines, but not once has cracked disks ever been mentioned to me. Maybe VOSA should send out a leaflet to all LGV drivers explaining the disks of cracked disks and how to check for them if the fault is so serious to other road users - as it clearly seems to be if they’re handing out prohibitions for it.
Not wanting to have a dig or digest from from the brake question BUT how can you not see a EIGHTNEEN INCH flat spot on a tyre ! 
I would imagine it was 18 cms as 18" would be into the tyre and it would have blown out long before it got that long. The question is how you wouldn’t hear it once you got rolling. It would be slapping on the road and you would feel it I reckon. Regardless, that is a bang to rights PG9 and nothing really can be said. But it is also a simple enough fix- call ATS out.
But the disc one is more worrying from a drivers perspective because it is suggestive. It suggests that it will become a favourite point for the inspectors to check. Because it is largely discretionary on the part of the inspector as to what constitutes and unsafe crack, it will be an easy way of getting in trouble, and once the ministry is on your back they are impossible to remove again. I had one of the SW TA inspectors after me because he didn’t wish to respect the law as much as enforce it and refused me a second weigh at a dynamic scale with a liquid tanker. Once he did that I refused to cooperate further and the whole thing was dropped by the then VI. He was furious about it,and he started after me for a while, but the second time he went after me for a nonsense vehicle fault, I wrote to the comissioner stating that I wanted to pursue his inspector for harrassment and that one got dropped as well.
Look at the firms getting in trouble with the VOSA bods now and I bet you will find that they will have an awful lot of cracked discs in the next few years.
Thanks Santa
I thought about the Scandinavian situation, after posting, perhaps it’s not an issue? after all our s cams get frozen solid & they still work ok, may even stop the trailer brakes getting frozen on when some ■■■■■■■■ doesn’t let them dry out before dropping the trailer, which would be nice
newmercman:
Thanks SantaI thought about the Scandinavian situation, after posting, perhaps it’s not an issue? after all our s cams get frozen solid & they still work ok, may even stop the trailer brakes getting frozen on when some [zb] doesn’t let them dry out before dropping the trailer, which would be nice
Frozen unloader valves and s cams are a whole new issue and a whole new thread about flat spotted tyres
Wheel Nut:
newmercman:
Thanks SantaI thought about the Scandinavian situation, after posting, perhaps it’s not an issue? after all our s cams get frozen solid & they still work ok, may even stop the trailer brakes getting frozen on when some [zb] doesn’t let them dry out before dropping the trailer, which would be nice
Frozen unloader valves and s cams are a whole new issue and a whole new thread about flat spotted tyres
Oh yeah, this one has been completely hijacked