It is generally the linings freezing to the drums and we release them with a universal spanner… The valves tend to be ok because we have good air dryers.
My point was more, to begin with at least, that drums can be in as poor a state as a disc but it is visually difficult to see if they are. I would be more concerned about VOSA getting this into their heads that discs are an easy target. I always kept my eye on them- always- but I could still have probably had some oik with a grudge against trucks saying they were unsafe and what position would I be in to argue?
If the OP is saying that they always find something wrong with his firms vehicles then I would hope he will keep track of how many of these prohibitions are for discs, and maybe even keep a track of the inspectors names so that it can be compared. If VOSA have them on the hitlist, like they did with Tony M then it will be something to behold I reckon. Maybe pictures of these cracks should be taken.
gave me a pg9 a fortnight ago for an 8" tread peel, i said to the guy would he lift it as i had a tyre fitter out and he replaced tyre in 20 minutes, the vosa guy said no, you can take it back to the yard though but it must go to an approved testing station.
still, my company will insist on the cheapest of retreads.
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.
That modern day training idea of using the brakes to slow gears to go has to be one of the things which says it all about those who are out there banging on about safety in the theory books but have’nt got a clue when it comes to driving something properly.I’m with the same gear to go down it (or maybe even a few lower for luck) as I’d need to get up it fraternity and stuff the ‘experts’.Exhaust brakes have always seemed to provide reasonable retardation to me if you keep the revs as high as possible but sometimes a few dabs of the brakes are needed to keep those revs within limits?.The old Jacobs is in an even better league but it’s rare to see one fitted on the European engines ?.Having said all of that does’nt the idea of using engine braking on long descents to save the brakes make the argument for using double drive axles instead of 6x2 even stronger than just the traction advantage under power bearing in mind the retardation forces transmitted to the road through just one axle and one set of wheels in the case of a 6x2? especially in wet slippery conditions.But it looks like maybe the problem has more to do with modern day driving ideas than engineering maybe?.
There are arguments against twin drive, too. In Europe, drive axles are 11.5 tonne rated, although I thought they were 9.5 tonne on twin, now I think of it. This would give you way too much tolerance so neckweights would have to be higher to compensate.
The main worry is that, with double drive, you would have more chance of losing traction on one or more wheels as the distribution would be different.
I wonder about disc brakes. I am a great advocate of them- the ones I had were excellent- but they are easy enough to destroy. I remember taking a fridge from Lee Mill to Exeter for test and the mechanic told me to give the brakes a caning down Telegraph Hill to warm them up for the test. Sorry, but I can’t help but think that is a bad way to start out.
bobthedog:
There are arguments against twin drive, too. In Europe, drive axles are 11.5 tonne rated, although I thought they were 9.5 tonne on twin, now I think of it. This would give you way too much tolerance so neckweights would have to be higher to compensate.
The main worry is that, with double drive, you would have more chance of losing traction on one or more wheels as the distribution would be different.
I wonder about disc brakes. I am a great advocate of them- the ones I had were excellent- but they are easy enough to destroy. I remember taking a fridge from Lee Mill to Exeter for test and the mechanic told me to give the brakes a caning down Telegraph Hill to warm them up for the test. Sorry, but I can’t help but think that is a bad way to start out.
I’m not so sure about the weight distribution on 6x4 versus 6x2 being that much on an issue.That undriven axle on the 6x2 configuration seems like wasted traction potential if it’s loaded to it’s max and I think that it already takes more traction from the driven axle than the slight reduction needed to share it out equally between the two driven axles of a 6x4 would?.I I think they tried to get round the issue of traction on 6X2 by using the lift facility under load (on lifting tag axles) to put more load onto the drive axle when it lost grip and it was made illegal to do it after a while?.But they’ve been using units like Kenworths with double drive for years on European work even at the old 38 Tonne limit and it’s my guess that their drivers found the double drive set up an advantage in traction and engine braking?.As for giving the brakes a caning I’ve always looked on brakes as you’ve only got one set and when they’ve gone they’re gone and they don’t come back and I think that’s why they’ve got those massive great sandpits on the downhill side of the road on most of the big Alpine passes with the signs telling drivers these are your last hope if you need them.
