Stupid question about truck brakes

[Youngsod]

This probably shows me up as the mechanical incompetent I really am, but can I ask a question about truck brakes?

I know trailers have air brakes, but does the tractor unit have air brakes too or are they hydraulically activated? 

I've been spending too much time watching Outback Truckers, plus I've been reading Train wreck : the forensics of rail disasters by George Bibel and there's an entire chapter in that related to train air brakes. I genuinely didn't grasp how complicated driving a train was.

[Saabnut]

Tractor units have air brakes as well. Some medium duty trucks have air over hydraulic systems which is basically a hybrid

[twosmoke300]

Air over hydraulics are a recipe for biting the steering wheel / head butting the windscreen

[sutty2006]

99.9% of commercial trucks are Air operated brakes. I think Iveco use air over hydrolic on their 7.5tonners but over that weight it’s all Air. Park brake chambers are spring loaded and are released using air. This avoids situations where the vehicle looses its air due to a leak in the system and rolls off down the road. Always mechanical over air on park. Service brake uses air. 

[wuvvum]

3 hours ago, Youngsod said:

I've been reading Train wreck : the forensics of rail disasters by George Bibel and there's an entire chapter in that related to train air brakes. I genuinely didn't grasp how complicated driving a train was.

The braking systems on American freight trains are ridiculously complex to operate.  That's partly because it's a 19th-century system which has had extra bits tagged on over the centuries in an attempt to bring it up to modern requirements, rather than doing what they should have done and junking the whole bastard thing and starting again with a modern design which can actually bring a train to a stop in less than 15 miles and doesn't require a PhD in mechanical engineering to operate.

[bigstraight6]

I much prefer to drive lorries with full air, when you get behind the wheel of a lighter lorry with air/hydraulic they don’t feel like they want to stop.

[Youngsod]

It's totally nuts how complicated it is just to work the sodding brakes, never mind the problems of bunching and stringing and the like. I really did not realise just how complicated it is.

 

[Youngsod]

Next stupid question, how much different is it learning to drive with air brakes? Am I right in thinking that the air pressure is used to release the brakes, so if pressure is lost the brakes come on?

[wuvvum]

That's only the case for the parking brake.  The service brake is applied by air pressure.  They vary quite a bit - the Leyland Roadrunner I had was incredibly sharp, the Iveco Eurocargo less so, and the D Series made you wonder whether you were ever going to stop.

Edit: and yes, if you lose air pressure completely, the parking brake will come on, which can be interesting if it happens at 56mph on the motorway.

[bigstraight6]

2 minutes ago, Youngsod said:

Next stupid question, how much different is it learning to drive with air brakes? Am I right in thinking that the air pressure is used to release the brakes, so if pressure is lost the brakes come on?

Air brakes can stop a 44 ton artic sharpish if needed, on older units with a tired air compressor you need to rev the engine to build up air to release the brakes.

[Zelandeth]

11 minutes ago, Youngsod said:

Next stupid question, how much different is it learning to drive with air brakes? Am I right in thinking that the air pressure is used to release the brakes, so if pressure is lost the brakes come on?

It *feels* very different.  My experience is all with buses, but I can't imagine a truck will feel that different.

The biggest difference is that all of the modulation is based on the pressure you apply to the pedal more than how far you press it... generally there is very little actual travel, much like in a hydraulic Citroen.  It initially feels like you're standing on a brick.

Depends a lot on the vehicle, but some sir brakes can be really snatchy (especially at low speeds) and make pulling up smoothly a challenge.

Worst I've ever come across were on a Volvo B7LA bendy bus (Y11ROT if memory serves).  Press the pedal, nothing. Press harder, nothing.  Press far harder, nothing.  Near enough stand on it, nothing. Press 0.0000001% harder, bounce your forehead off the windscreen.  The moment you relaxed your foot even slightly the thing would then spring back off the mark alarmingly quickly (auto box, which will do about 7mph at idle if you let it).  It's the one bus I never managed to get to grips with driving smoothly.  Most of them I'd usually get to grips with eventually...that one just defied all attempts to make it behave...so you ended up with comedy bouncing every time you tried to come to a halt.  Driving in traffic was bloody painful.

The only other thing I remember being a little unnerving initially was that if you do brake sharply, there's a fraction of a second delay before the brakes respond... it's infinitesimally brief, but it's there and enough to be unnerving the first time!

[Mally]

1 hour ago, sutty2006 said:

99.9% of commercial trucks are Air operated brakes. I think Iveco use air over hydrolic on their 7.5tonners but over that weight it’s all Air. Park brake chambers are spring loaded and are released using air. This avoids situations where the vehicle looses its air due to a leak in the system and rolls off down the road. Always mechanical over air on park. Service brake uses air. 

I have a story from the distant past. I'm not sure if this can still happen.

Trucker friend one day backed his cab up to an artic trailer, jumped on the back and plugged the airlines in.

When he did this, air went into the trailer lines releasing the trailer brakes.

Unfortunately he had not set the park brake on the truck, after he coupled up.

Yard was on a slope, the whole unit rolled forward.

He panicked, jumped off the back and tried to open the door and press the brakes. It crashed into a fence doing considerable damage.

Had  he unplugged the air line that he just plugged in it would have stopped instantly.

 

 

[sutty2006]

3 minutes ago, Mally said:

 

Had  he unplugged the air line that he just plugged in it would have stopped instantly.

 

 

Yep, if he’d managed to drop the lines back off it would have stopped. This is a common problem with drivers especially new ones or drivers just in a rush. Brake goes on every time I connect to our test trailer. 
 

 

[sutty2006]

41 minutes ago, Youngsod said:

Next stupid question, how much different is it learning to drive with air brakes? Am I right in thinking that the air pressure is used to release the brakes, so if pressure is lost the brakes come on?

I’ve been manoeuvring trucks for the last 16 years and in the last 2 I’ve had my class 2 licence. They’re easy to drive especially new ones. I’ve only ever done one emergency stop in a rigid 26 ton van transporter after spotting a stranded motor on a dual carriageway with no hard shoulder...... standing on those brakes made it almost stand on end. It’s expecting the poor fucker behind to slam into you that was my biggest worry. 

[Barry Cade]

7.5 tonner can be one or the other. My iveco has normal hydraulic brakes which are OK, but has a normal mechanical handbrake, same as a bmw or volvo with little shoes inside the rear disc. Can be interesting when you're pulling a car with the winch and the truck is coming to meet it rather than the truck pulling the car. My old roadrunner had air brakes, and you either crashed or went through the windscreen if it wasn't loaded. 

[MJK 24]

2 hours ago, sutty2006 said:

99.9% of commercial trucks are Air operated brakes. I think Iveco use air over hydrolic on their 7.5tonners but over that weight it’s all Air. Park brake chambers are spring loaded and are released using air. This avoids situations where the vehicle looses its air due to a leak in the system and rolls off down the road. Always mechanical over air on park. Service brake uses air. 

If you lose air, the brakes are on full.  They’re fail safe.  They don’t and can’t release without air pressure being built up. 

[Zelandeth]

1 hour ago, sutty2006 said:

...standing on those brakes made it almost stand on end. It’s expecting the poor fucker behind to slam into you that was my biggest worry. 

Yep.

First time the trainer had me out in this beastie...

...Which by the way is unexpectedly an absolute joy to drive...I was specifically instructed when the road was clear to do an emergency stop so I was familiar with how the vehicle would behave.

My brain to this day still has some trouble reconciling the fact that it's possible to bring something that big and heavy to halt so quickly.  The driver's seat in this is thankfully fitted with a three point belt, or I'd have most likely come to rest about half a mile down the road from the bus.  Even with the seatbelt, the deceleration was still honestly painful.

Speaking of, I can now confirm that the B7LA I was referring to earlier is Y148ROT.

One of very few buses I've driven that I honestly didn't like!  I quite enjoyed the bendies, even though the whole experience of driving a vehicle where the engine is in the trailer is a little strange at first...that particular one however just had something far wrong with the braking system I feel.  The B7LAs First had all seemed to have hair-trigger brakes, but that one was an order of magnitude worse.

[Andy F]

Probably a stupid question, but do the rear most or middle wheels drive those bendy buses?

[wuvvum]

1 hour ago, Barry Cade said:

My old roadrunner had air brakes, and you either crashed or went through the windscreen if it wasn't loaded. 

Glad it wasn't just mine then...

[sutty2006]

11 minutes ago, Andy F said:

Probably a stupid question, but do the rear most or middle wheels drive those bendy buses?

Engine is in the back. Rear wheels are driven. The rest is witchcraft 

[Zelandeth]

2 hours ago, Andy F said:

Probably a stupid question, but do the rear most or middle wheels drive those bendy buses?

The engine is hung right out the back, rear wheels are driven.

The results on an even vaguely slushy road in the winter is predictable...

It's downright creepy as in the cab you honestly can barely even hear the engine...

Some of the larger coaches used a conventional front/mid engined coach with an unpowered trailer...Know Stagecoach Bluebird had a couple of them, but sadly I never had a chance to travel on one. 

I believe the reason for having the "trailer" powered was something to do with driver licensing rules...if the front part was powered it was classed as a vehicle & trailer so you'd need a D+E licence...whereas if the trailer pushes the front it's not considered a trailer so you can drive it on a normal category D licence. 

[Spiny Norman]

4 hours ago, MJK 24 said:

If you lose air, the brakes are on full.  They’re fail safe.  They don’t and can’t release without air pressure being built up. 

Since when has this been the case, does anyone know?

Reason I ask is I can vaguely remember a bit of pre-internet folklore in Glasgow which claimed this type of fail-safe air brakes came about in the early 70s after a tipper truck's brakes failed going down a very steep hill in Glasgow city centre causing it to smash into a stationers shop in Sauchiehall Street killing someone in the shop.
 

[sutty2006]

8 hours ago, Spiny Norman said:

Since when has this been the case, does anyone know?

Reason I ask is I can vaguely remember a bit of pre-internet folklore in Glasgow which claimed this type of fail-safe air brakes came about in the early 70s after a tipper truck's brakes failed going down a very steep hill in Glasgow city centre causing it to smash into a stationers shop in Sauchiehall Street killing someone in the shop.
 

That could be more to do with brake fade maybe? I’m not sure when spring brake chambers were introduced but I recon they’ve been around a while. 
 

spring brake chambers can be released without air, using a 24mm socket and ratchet on the back of he chamber there is a bolt you undo to draw the spring tension which releases the brake. I remember going out to a broken down 7.5ton MAN that had driven over a tyre carcas on the M6. Ripped air line out of the nearside rear chamber and of course locked the brake on solid in the slow lane. When I arrived the highway wombles were still putting cones out. I slid underneath with my ratchet, wound the chamber off and got him off the motorway before the wombles had finished coning the lane off. Scary though. 

[bunglebus]

On my long, uncomfortable trips to Germany and back in my boss's 7.5 tonne Eurocargo, we would sometimes have to park in a residential area and weren't entirely sure if it was permissible to do so. To try and avoid it getting towed away, he used to release all the air out of the brakes so it would have to be running or have air connected from elsewhere to move it.

I only drove it once around the industrial estate, for some reason he preferred to pilot it everywhere despite me having a 7.5 tonne license (cos I'm old), so I was stuck on the co-pilot's seat for many miserable hours. You just can't get to sleep in one of these no matter how you try and contort yourself

[Youngsod]

1 hour ago, bunglebus said:

On my long, uncomfortable trips to Germany and back in my boss's 7.5 tonne Eurocargo, we would sometimes have to park in a residential area and weren't entirely sure if it was permissible to do so. To try and avoid it getting towed away, he used to release all the air out of the brakes so it would have to be running or have air connected from elsewhere to move it.

I only drove it once around the industrial estate, for some reason he preferred to pilot it everywhere despite me having a 7.5 tonne license (cos I'm old), so I was stuck on the co-pilot's seat for many miserable hours. You just can't get to sleep in one of these no matter how you try and contort yourself

See now you've touched upon another one of my sad life goals, to drive a 7 1/2 tonne truck.  A license from 1989 means there's all sorts of weird stuff that I can drive and that's top of the list. 

 

[warch]

Me too I’ve always regarded 7.5 ton lorries as a starter truck which have all the key truck features, forward control, convoluted gear change, big step up into the cab but aren’t so huge and scareh as an actual HGV

[spartacus]

You might struggle with that. 

I was explaining a few of the oddities of the driving licence and how I could drive a 7.5t vehicle to my daughter. Being 13 she had no idea what one was, so I told her I'd point one out on the journey to school, on main roads, in rush hour, between Chesterfield and Sheffield, a 12 mile journey.

Nope, not one.

I'd never really thought about it but obviously the change in licensing, amongst other things, has been the death of the 7.5 tonner. 

[Agila]

2 hours ago, Youngsod said:

See now you've touched upon another one of my sad life goals, to drive a 7 1/2 tonne truck.  A license from 1989 means there's all sorts of weird stuff that I can drive and that's top of the list. 

 

If you do want to give it a go I'd ring a proper driver training place up. Just tell them you would like to drive one and have a few hours lessons etc. I certainly wouldn't recommend just trying to hire one. You may find trying to hire one as a non business/commercial maybe difficult.

Treat them with the respect they deserve and you will be fine. Treat it as "just a big van" then you might have a bump.  That's speaking as class1 arctic driver for 15 years.

 

[wuvvum]

The good thing with 7.5-tonners is that they usually have a fairly straightforward gearbox - dogleg first on some of the older ones is about as weird as it gets (although you'd normally pull away in second in those anyway).  There's no splitters, range changes, two-speed axles or any of that jazz to worry about.

My first experience driving a 7.5-tonner was when I bought a Leyland Roadrunner off eBay whilst in an intoxicated state.  That was an experience - it had no seatbelts, pin-sharp brakes and it was bloody massive (nearly 30' long), and the first bit of my drive involved piloting it through the centre of Rotherham on a busy Saturday afternoon.  I survived though, and only went up on the kerb once - and once I got on the A1 it was a lovely old thing to trundle along in.

[Spurious]

Used to drive an 18 ton Renault and it was a dreadful bag of bolts. Only ever had my C and not the C+E. The brakes were shite, they would eventually work and work well but they had horrible modulation. I used to prefer the little DAFs which were much nicer to drive. 

Doesn't really matter now as I only need a C1 for the ambulance. Speaking of which we've Merc Sprinters in work and Fiat Ducatos. The Mercs have horrible brakes, they're really rubbish, push gently and nothing happens, push a bit more and nothing happens and you almost have to stand on the pedal for anything to happen. You get used to them eventually. Jump back into the Fiat and it's very car like, very modular with a progressive braking effort.

Jump into a Merc after driving Fiats, morn than once, especially downhill I've had a brown trouser moment especially on blue lights where I'm suddenly having to apply a lot more brakes than I'm used to. They also have a retarder on the Merc but I swear all it does is light up an indicator on the dash and nothing more.