You all have been kind enough to explain to me how the gears work in a truck compared with a car (forget about it they’re automatic).
I wonder if you could now explain how the brakes work?
Having just passed my Theory test, and practical training starting in 5 weeks, I’ve heard about Air brakes, Exhaust retarder brakes and Jake breaks but haven’t a clue how to operate them. Is there a pedal? a switch?
Are hydraulic brakes used in an HGV? check the level daily?
Air brakes - is there a spring holding the brake pads to the brake discs like a parking brake, that is stopped from operating by the air pressure?
Why are there Emergency, Service and Auxiliarly air lines?
Many thanks.
Brake pedal same as a car
Air brakes - the flow of air keeps the brakes off and when you press the brake pedal it stops that air flow and operates the brakes
The harder you press the brake pedal the less air there is keeping the brakes off
Just like a car - the harder you press the harder the brakes work
Loose all your air in the air tanks and the brakes lock on which is why there is a warning buzzer for low air
ROG:
Brake pedal same as a car
Air brakes - the flow of air keeps the brakes off and when you press the brake pedal it stops that air flow and operates the brakes
The harder you press the brake pedal the less air there is keeping the brakes off
Just like a car - the harder you press the harder the brakes work
Loose all your air in the air tanks and the brakes lock on which is why there is a warning buzzer for low air
The first line is correct,
The hand brake/parking brake uses a spring to apply the brake, air holds the brake off when the lever is off.
The foot brake or service brake uses air pressure regulated by the amount you press the pedal, sent to brake chambers (think of it like a piston) to apply the brakes, the harder you press, the more pressure goes to the chambers, pressing the pads against the disk harder (shoes and drums also available).
Newer trucks are partly electronically sensed on the foot pedal,but still use air as well.
There are other components in the system but this is basically how it works.
The brake system is split into two parts as a fail safe, this is why you cant release the parking brake until there is enough air pressure, to work the foot brake. Or if you lost all the air pressure the brakes would come on with the springs.
Exhaust brakes/retarder/jake will usually have a switch to turn on/off/amount of braking, but can be set to work simultaneously with the brake pedal.
Some trucks mostly 7.5t and less may have hydraulic brakes, or air over hydraulic so there will be fluid to check the level of (sometimes two reservoirs)
Awesome thank you both! @pig pen , @ROG
Somewhat related. I have seen HGVs on downhill motorways braking! Why? I would have thought they would all be frustrated by the speed limiter. Is it because of the tachograph would catch them speeding? Or are they genuinely worried about the truck getting out of control?
stu675:
Awesome thank you both! @pig pen , @ROG
Somewhat related. I have seen HGVs on downhill motorways braking! Why? I would have thought they would all be frustrated by the speed limiter. Is it because of the tachograph would catch them speeding? Or are they genuinely worried about the truck getting out of control?
On the tacho it will have a limit set in to it say 90 or 92km/h if you travel over that limit for a certain length of time it will record as an over speed, while you are under then actual legal speed limit, some firms might get excited over an overspeed (read driver shortage problems 
) Old analog tachos had it as well, but it was just a light that came on/not recorded.
If your running at 56mph, on a downhill you`ll be over 60mph in no time if your heavy, maybe the drivers are just keeping it legal.
As a newbie also training up, I also had the same questions in my mind.
So, where would one use a retarder? Coming down on M62 from saddlworth towards Manchester? Would that be a spot for an artic to be using the retarder?
Muddy K:
As a newbie also training up, I also had the same questions in my mind.So, where would one use a retarder? Coming down on M62 from saddlworth towards Manchester? Would that be a spot for an artic to be using the retarder?
I dont know what the official trainers line on this would be/even if you would use it on test.
They can be used anywhere you need to slow down or keep your speed in check, and would be my first choice before the footbrake (except emergency’s). On older trucks you would use these to save your proper brakes for when you needed them. Even with a modern truck, with plenty of observation and forward planning use of these auxiliary brakes with give a smooth and fuel efficient drive, while reducing the wear on the main brakes.
Ask you trainer, if you dont need them for test, dont give yourself extra to worry about (although the truck may have them set to auto so they come on when you lift off the throttle or lightly touch the brake pedal), pass you test and let the real learning start
You tend to use engine brakes/retarders when loaded and going downhill.
There is a technical difference between an engine brake and a retarder.
A retarder works on the transmission directly and applies a load to slow the vehicle (either hydraulic or electromagnetic), whereas an engine brake relies upon creating a back-pressure in the engine which works through the transmission, acting as a braking force.
There is a further difference between a jake brake and an exhaust brake. I think most European trucks use exhaust brakes, which rely on exhaust back-pressure, whereas a jake brake is a separate piece of equipment attached to the engine.
In summary:
Engine brakes:
- Jake
- Exhaust
Driveline:
- Retarder
Auto trucks will generally select lower gears automatically when exhaust/engine/retarder is used. Don’t go downhill relying only on service brakes. They will get hot and will become less efficient to the point of fade and even failure. Plus they will.wear out quicker.
Gears, whether in an auto or manual truck should be used to control descent on hills and when stopping.
Brakes are better now than in days of yore, but they will still overheat. Smaller wheels also have smaller brakes and less airflow, so will be more likely to heat up.
Driving a lightly loaded truck on flatish roads, you will “get away with” using only the foot brake, but it is a really bad habit to get into.
Some trucks using only the retarder/exhaust brake/whatever will apply the brake lights when the retarding device is operated, irrespective of whether the brake pedal is touched or not.
Thankfully i drive a vehicle which doesn’t apply the brake lights unless the brake pedal is pressed, you can be on the retarder alone in whatever gear is suitable for a mile or more going down a long descent holding speed without the brake lights showing once.
With other makes (typically Scania) the brake lights will have been on the whole time when in all probability no reduction in speed will have happened, should the driver suddenly have to apply the brakes sharply those behind have got used to seeing the brake lights on continually so their attention won’t be suddenly alerted, that’s why i prefer the type that only puts the brake lights on when a proper or more sudden reduction in speed is likely.
As Franglais speaks of, lorry driving is completely different to car driving, a driver should not use the brakes alone to reduce or maintain speed, every large vehicle will be fitted with a speed retarding device of some sort, most become more efficient higher up the rev band, when you apply the exhaust brake or whatever on many vehicles the ‘efficient band’ on the rev counter shifts up around 1000 revs, the vehicle telling you that the new green band is where the retarding device is most efficient.
ie many lorries the driving green preferred band will be in the 1000/1400 rpm banding, if you apply the retarding device that green efficient band shifts up to something like 2000/2200 rpm, meaning the retarder will provide more effort in the revs highlighted…but be aware often that green band upper limit is only 200rpm short of the red band, revs you shouldn’t subject the engine to, so keep an eye on things as hills steepen because you may need to apply some gentle braking to assist the retarding device.
Many retarding devices have 1 to 3 settings, progressively more efficient (and more audible) as you increase the setting, when you apply the brake pedal if the auto ■■■■■■ is on then the vehicle normally auto applies full ■■■■■■ and if the auto gearbox is in auto will auto change down.
The driver can instead select just the retarding device without braking, again it will normally apply full ■■■■■■ and change down automatically, you may be able and usually can reduce the effort by selecting a lower retarder setting, whether in auto or using manual gear override, variations of this because all makes have their own versions of how this works.
I should add here, be aware some retarders are really good, be aware of using maximum ■■■■■■ even if in auto ■■■■■■ setting when empty, an auto down change several gears on a wet road with a highly efficient retarder can and will lock the drive axle, this is a bad thing, so be aware of what setting the retarder is in ***
Some older designs have one setting only and no automatic retarding, but most of these will have been retired from typical fleets by now.
Learn your vehicle and what it can and can’t do for you is the best way forward whatever you drive, one size doesn’t fit all here.
Truck makers didn’t spend £millions designing this type of system into their products for a joke, only for some clot who should have stuck to driving Vauxhall Corsas to suggest ‘‘brakes to slow gears to go’’ is how lorries should be driven, ie on the brakes.
Its not efficient its not professional it causes excess brake heat and wear and its plain wrong.
there, thats clear as mud innit 
*** doesn’t matter how long you’ve been doing this job such things can still catch you out.
About 13 years ago i was between decent jobs and did a bit of agency, one freezing morning jumped into the VolvoFM i was using that day, ages since i’d driven one, my regular agency ru saw me leave the depot empty so sailed out along the quiet industrial estate road, slowing up for the first roundabout i hadn’t realised the auto retarder was in maximum setting, which on a Volvo provides serious retarding.
Just before the roundabout braking really gently (black ice) the gearbox suddenly dropped about 3 gears and the full retarder auto applied…cue one locked drive axle just entering said roundabout with a jack knife already starting, not good, dunno how but managed somehow to get the thing straightened up again and all was well, and no i said bugger all about it at the time 
Bear in mind i’d been driving lorries (obviously not well enough) for more than 30 years at this point but the combination of things caught me out, so use my example so it doesn’t happen to you.
Not the original poster but posting anyway to say thanks. Really informative thread.
HGV moving parts are turning out to work nothing like I thought they would.
Tim T:
Not the original poster but posting anyway to say thanks. Really informative thread.HGV moving parts are turning out to work nothing like I thought they would.
+1.
As someone learning to become a HGV driver, I really do think that the brakes and the working hours are what I find I need to spend more time on.
Many thanks for the info people. (Sorry for the thread hijack)
Muddy K:
As a newbie also training up, I also had the same questions in my mind.So, where would one use a retarder? Coming down on M62 from saddlworth towards Manchester? Would that be a spot for an artic to be using the retarder?
I do just that every night on that stretch, that way, you don’t get brake fade on the service brakes, and lose control.
Ken.