On a ■■■■■■■ the injectors are shut by a cross head when the jake is in operation,I don’t think this happens on a CRAP (CAT) 
not sure about modern engines though 
Wheel Nut:
Its a simple butterfly valve like a carburettor choke that slows the air getting past, its just back pressure that slows the vehicle or in the case of a DAF stops the engine.It is not linked to the gearbox, axle cooling system or anything else, it sits in the exhaust manifold, the higher the engine revs the more efficient it is.
I beg to differ regarding the exhaust brake not being connected to anything else.
Of course it is. It’s "connected"to everything, or it would have no effect at all on the progress of the vehicle. The Instant that you lift your foot off the accelerator, instead of the engine working to turn the wheels, the inertia of the vehicle is working to turn the engine, (provided that the vehicle is in gear and the clutch is engaged) , the effect of any system apart from the wheel brakes depends entirely on that connection. So, from the friction of the tyres with the road, all the way to friction between the clutch components, everything requires to be connected for any of these systems to have any effect on the progress of the whole vehicle.
I was out in a Scania once with a foot operated engine brake. I used it and it dumped all of the air out of the suspension seat. Apart from that it was a great vehicle.
Franglais:
Roymondo:
Most of us use the exhaust brake - but can anyone explain the physics and the mechanism involved?Regular brakes are easy enough - moving disc/drum brought into contact with brake pads/linings, resulting in friction which directly converts the rotational energy into heat, which is in turn dissipated to the air. But what are the Physics and mechanics of an exhaust brake?
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Disambiguation needed.
Do you really mean an exhaust brake? A simple block on the exhaust pipe to increase back pressure a little and give slightly more engine braking.
Or a form of engine braking? Valves are used to turn the engine into an air compressor.
Or a retarder? A fluid brake on the rear of the gearbox, that turns rotational energy into heat.
Or even (unlikely today on trucks) an electrical retarder?
Dunno really - our fleet consists almost entirely of 65 plate bog standard fleet-spec MAN units and rigids. Almost certainly one of the first two options. I note that on some of the units (and one or two of the rigids) pressing the button on the stalk achieves little more than a down-change and a different noise from the engine/exhaust while in others these effects are accompanied by a noticeable deceleration. I was really just wanting to understand the mechanical goings-on.
Always use the auxilliary brake whatever its design, regard that as the primary brake for slowing the vehicle and the service brakes for bringing the vehicle to a final halt or emergencies.
Most modern vehicles the green band on the rev counter changes when exhauster is operating, from a green band of say 1000 to 1500 rpm it changes to 2000 to 2200 rpm (taking MAN’s as an example) for best/preferred engine braking performance, it sounds cruel utilising such high revs but that’s what the maker intended.
I too know drivers who switch auto retarding off and use brakes only (don’t be silly no downchanges, BTSGTG all on the brakes it’s the modern way y’know 
), wonder how they’d have got on back in the days of drums all round and manual adjusters 
Juddian:
Always use the auxilliary brake whatever its design, regard that as the primary brake for slowing the vehicle and the service brakes for bringing the vehicle to a final halt or emergencies.Most modern vehicles the green band on the rev counter changes when exhauster is operating, from a green band of say 1000 to 1500 rpm it changes to 2000 to 2200 rpm (taking MAN’s as an example) for best/preferred engine braking performance, it sounds cruel utilising such high revs but that’s what the maker intended.
I too know drivers who switch auto retarding off and use brakes only (don’t be silly no downchanges, BTSGTG all on the brakes it’s the modern way y’know
Exhaust brakes need a low gear and as close to the red line as possible to be effective.They usually work ok when used properly.Anything below the red is the engine’s usable rev range the green is all about the best fuel efficiency.
Think of what happens if you park your car on a steep incline… Don’t many of us habitually leave the car in either 1st gear or reverse in case the handbrake fails? Why a low gear? - Because the force required to crank the engine via an uncontrolled (downhill lunge, in this case…) - is much more than if you left it in 4th - that’s why. You don’t “bump start” in 1st neither, of course for the same reason. 2nd or 3rd is needed. If you tried to bump it in 1st, you’d probably lock the wheels, because 1st gear is where that high torque that’ll stop you dead would be, with engine switched off in this example of course. You might also go down a 1:4 gradient like Porlock Hill in 1st or 2nd as well, if you don’t want to be pumping your footbrake like you’re trying to inflate a tyre…
If you inhibit the exhaust of an engine, the entire engine bulk moving parts - acts as a brake. I consider an “Exhaust Brake” or “Engine Brake” to be one and the same thing btw, although I’ve heard some say that they are merely similar, and operate in different ways…
The heavier crank needed to turn over that engine - would increase the effectiveness of that engine brake.
Thus, if you are running downhill with a load on, you’ll find that a tractor with a no-guts engine that feels like it can’t pull the skin off a rice pudding - will have a lousy exhaust brake, whilst a chunky-engined decent truck that pulls like a locomotive - will have a far more effective engine brake, even with a decent load on.
If memory serves, the Actros was one of the worst engine brakes I can remember of combinations I’ve driven fully laden, but those day cabs that one uses for supermarket work - are not much cop neither.
I can’t say I’m familiar with all the side-brand models of tractor out there, but if I had to pick a truck make that I reckon has a pretty decent engine brake on it - I’d have to say “Volvo”. 
Juddian:
Always use the auxilliary brake whatever its design, regard that as the primary brake for slowing the vehicle and the service brakes for bringing the vehicle to a final halt or emergencies.Most modern vehicles the green band on the rev counter changes when exhauster is operating, from a green band of say 1000 to 1500 rpm it changes to 2000 to 2200 rpm (taking MAN’s as an example) for best/preferred engine braking performance, it sounds cruel utilising such high revs but that’s what the maker intended.
I too know drivers who switch auto retarding off and use brakes only (don’t be silly no downchanges, BTSGTG all on the brakes it’s the modern way y’know
I drove back in the time of mechanical slack adjusters and such. People that switch off auto retarding in icy conditions have their head screwed on and are aware of the possible consequences of not doing so. That is why the switch is there in the first place.
Winseer:
Think of what happens if you park your car on a steep incline… Don’t many of us habitually leave the car in either 1st gear or reverse in case the handbrake fails? Why a low gear? - Because the force required to crank the engine via an uncontrolled (downhill lunge, in this case…) - is much more than if you left it in 4th - that’s why. You don’t “bump start” in 1st neither, of course for the same reason. 2nd or 3rd is needed. If you tried to bump it in 1st, you’d probably lock the wheels, because 1st gear is where that high torque that’ll stop you dead would be, with engine switched off in this example of course. You might also go down a 1:4 gradient like Porlock Hill in 1st or 2nd as well, if you don’t want to be pumping your footbrake like you’re trying to inflate a tyre…If you inhibit the exhaust of an engine, the entire engine bulk moving parts - acts as a brake. I consider an “Exhaust Brake” or “Engine Brake” to be one and the same thing btw, although I’ve heard some say that they are merely similar, and operate in different ways…
The heavier crank needed to turn over that engine - would increase the effectiveness of that engine brake.
Thus, if you are running downhill with a load on, you’ll find that a tractor with a no-guts engine that feels like it can’t pull the skin off a rice pudding - will have a lousy exhaust brake, whilst a chunky-engined decent truck that pulls like a locomotive - will have a far more effective engine brake, even with a decent load on.If memory serves, the Actros was one of the worst engine brakes I can remember of combinations I’ve driven fully laden, but those day cabs that one uses for supermarket work - are not much cop neither.
I can’t say I’m familiar with all the side-brand models of tractor out there, but if I had to pick a truck make that I reckon has a pretty decent engine brake on it - I’d have to say “Volvo”.
Rubbish!
Apart from perhaps the last paragraph.
CLOVER50:
Juddian:
Always use the auxilliary brake whatever its design, regard that as the primary brake for slowing the vehicle and the service brakes for bringing the vehicle to a final halt or emergencies.Most modern vehicles the green band on the rev counter changes when exhauster is operating, from a green band of say 1000 to 1500 rpm it changes to 2000 to 2200 rpm (taking MAN’s as an example) for best/preferred engine braking performance, it sounds cruel utilising such high revs but that’s what the maker intended.
I too know drivers who switch auto retarding off and use brakes only (don’t be silly no downchanges, BTSGTG all on the brakes it’s the modern way y’know
I drove back in the time of mechanical slack adjusters and such. People that switch off auto retarding in icy conditions have their head screwed on and are aware of the possible consequences of not doing so. That is why the switch is there in the first place.
In very slippery conditions it is probably a good idea to switch off auxiliary braking, as it only brakes one axle, unless the vehicle is double drive. Modern ABS systems disable auxiliary brakes instantly if traction is lost though
Old John:
Winseer:
Think of what happens if you park your car on a steep incline… Don’t many of us habitually leave the car in either 1st gear or reverse in case the handbrake fails? Why a low gear? - Because the force required to crank the engine via an uncontrolled (downhill lunge, in this case…) - is much more than if you left it in 4th - that’s why. You don’t “bump start” in 1st neither, of course for the same reason. 2nd or 3rd is needed. If you tried to bump it in 1st, you’d probably lock the wheels, because 1st gear is where that high torque that’ll stop you dead would be, with engine switched off in this example of course. You might also go down a 1:4 gradient like Porlock Hill in 1st or 2nd as well, if you don’t want to be pumping your footbrake like you’re trying to inflate a tyre…If you inhibit the exhaust of an engine, the entire engine bulk moving parts - acts as a brake. I consider an “Exhaust Brake” or “Engine Brake” to be one and the same thing btw, although I’ve heard some say that they are merely similar, and operate in different ways…
The heavier crank needed to turn over that engine - would increase the effectiveness of that engine brake.
Thus, if you are running downhill with a load on, you’ll find that a tractor with a no-guts engine that feels like it can’t pull the skin off a rice pudding - will have a lousy exhaust brake, whilst a chunky-engined decent truck that pulls like a locomotive - will have a far more effective engine brake, even with a decent load on.If memory serves, the Actros was one of the worst engine brakes I can remember of combinations I’ve driven fully laden, but those day cabs that one uses for supermarket work - are not much cop neither.
I can’t say I’m familiar with all the side-brand models of tractor out there, but if I had to pick a truck make that I reckon has a pretty decent engine brake on it - I’d have to say “Volvo”.
[/quoteRubbish!
Apart from perhaps the last paragraph.
If you want to be an engineer here rather than a politician - you might like to add your own write-up with full explanations then, rather than just rubbish my musings for the sake of doing so…
You’ll need to give examples of supermarket tractors with very good exhaust brakes (that would prove me wrong) as well as the correct way to get an actros to slow down with 11 paper reels on it (nearing 44t gross) and of course a make of tractor that actually is better than the latest Volvo model - surely an easy goal for you there?
CLOVER50:
Juddian:
Always use the auxilliary brake whatever its design, regard that as the primary brake for slowing the vehicle and the service brakes for bringing the vehicle to a final halt or emergencies.Most modern vehicles the green band on the rev counter changes when exhauster is operating, from a green band of say 1000 to 1500 rpm it changes to 2000 to 2200 rpm (taking MAN’s as an example) for best/preferred engine braking performance, it sounds cruel utilising such high revs but that’s what the maker intended.
I too know drivers who switch auto retarding off and use brakes only (don’t be silly no downchanges, BTSGTG all on the brakes it’s the modern way y’know
I drove back in the time of mechanical slack adjusters and such. People that switch off auto retarding in icy conditions have their head screwed on and are aware of the possible consequences of not doing so. That is why the switch is there in the first place.
Even back in the dark ages they fitted Jake Braked vehicles with switches so you could chose how many cylinders were operational (in pairs), they trusted drivers to work out for themselves by seat of the pants feel the level of braking required, i would have thought any lorry driver worthy of the name would know at what point auxilliary braking the drive axle alone would be inadvisable.
As Old John mentions, if lock up is detected on modern electronically controlled auxilliary braking, it cuts out straight away.
I was talking about people who turn auxilliary braking off permamently when they are behind the wheel, one bod old enough to know better complaining about uncomfortable lurching when the vehicle selects a particulary low gear when autoretarding, too thick presumably to cancel the auto ■■■■■■ before that inevitable too low gear is selected, heaven forbid he might have to select his own gears to maximise retarding without involving a too low gear too soon 
Winseer:
Old John:
Winseer:
Think of what happens if you park your car on a steep incline… Don’t many of us habitually leave the car in either 1st gear or reverse in case the handbrake fails? Why a low gear? - Because the force required to crank the engine via an uncontrolled (downhill lunge, in this case…) - is much more than if you left it in 4th - that’s why. You don’t “bump start” in 1st neither, of course for the same reason. 2nd or 3rd is needed. If you tried to bump it in 1st, you’d probably lock the wheels, because 1st gear is where that high torque that’ll stop you dead would be, with engine switched off in this example of course. You might also go down a 1:4 gradient like Porlock Hill in 1st or 2nd as well, if you don’t want to be pumping your footbrake like you’re trying to inflate a tyre…If you inhibit the exhaust of an engine, the entire engine bulk moving parts - acts as a brake. I consider an “Exhaust Brake” or “Engine Brake” to be one and the same thing btw, although I’ve heard some say that they are merely similar, and operate in different ways…
The heavier crank needed to turn over that engine - would increase the effectiveness of that engine brake.
Thus, if you are running downhill with a load on, you’ll find that a tractor with a no-guts engine that feels like it can’t pull the skin off a rice pudding - will have a lousy exhaust brake, whilst a chunky-engined decent truck that pulls like a locomotive - will have a far more effective engine brake, even with a decent load on.If memory serves, the Actros was one of the worst engine brakes I can remember of combinations I’ve driven fully laden, but those day cabs that one uses for supermarket work - are not much cop neither.
I can’t say I’m familiar with all the side-brand models of tractor out there, but if I had to pick a truck make that I reckon has a pretty decent engine brake on it - I’d have to say “Volvo”.
[/quoteRubbish!
Apart from perhaps the last paragraph.
If you want to be an engineer here rather than a politician - you might like to add your own write-up with full explanations then, rather than just rubbish my musings for the sake of doing so…
You’ll need to give examples of supermarket tractors with very good exhaust brakes (that would prove me wrong) as well as the correct way to get an actros to slow down with 11 paper reels on it (nearing 44t gross) and of course a make of tractor that actually is better than the latest Volvo model - surely an easy goal for you there?
As you, by your own admission, don’t acknowledge that an engine brake and an exhaust brake are two very different things, i fear i would be wasting my time.
Also, you demonstrate a complete failure to understand the principle and effect of reverse gearing on slowing a moving vehicle.
However, if you scroll down through the comments on this topic, you should find one from me which i hope you will find illuminating and educational.
When you read it, then read it again, if there is anything you still don’t understand, I’ll try to help.
Chin up 
Just to add a jake is at its best when an engine has good oil pressure and the top end is set up properly.
youtube.com/watch?v=Hw13DrfR1i0
The noise gets you after a while plus it vibrates the exhaust manifold bolts loose and blows by the gaskets
Punchy Dan:
Just to add a jake is at its best when an engine has good oil pressure and the top end is set up properly.
I had a couple of 14ltr ■■■■■■■ back in the day, but neither had a Jake unfortunately.
I’ve had a couple of Volvos with the excellent engine brake, and the older of those, a series one FM, wouldn’t allow the use of the engine brake until the oil was warm. Close reading of the manual revealed that, if the brake was used in slippy conditions while the engine oil was too viscous, there was a possibility of inducing a skid, as the engine brake would take a little longer to disengage.
Cunning, the Swedes. (In some ways)
That’s right John the thick oil does not like small holes ,I normally do about 15 miles or 25 minutes before use although from leaving home in a morning I drop about 650 ft over 1 to 2 miles depending on which way I turn out the drive I can’t use it .
Punchy Dan:
That’s right John the thick oil does not like small holes ,I normally do about 15 miles or 25 minutes before use although from leaving home in a morning I drop about 650 ft over 1 to 2 miles depending on which way I turn out the drive I can’t use it .
650ft in 2 miles is a fair drop Dan, even by West Highland standards!
Father used to operate on the principle that, in his Parrot nose Dodge, “you go down in the gear you’d go up in” Things have moved on a bit though, thank goodness.
Old John:
Punchy Dan:
That’s right John the thick oil does not like small holes ,I normally do about 15 miles or 25 minutes before use although from leaving home in a morning I drop about 650 ft over 1 to 2 miles depending on which way I turn out the drive I can’t use it .650ft in 2 miles is a fair drop Dan, even by West Highland standards!
Father used to operate on the principle that, in his Parrot nose Dodge, “you go down in the gear you’d go up in” Things have moved on a bit though, thank goodness.
I mite be a little bit out on that but it’s just over 1000ft here and down hill all the way
No higher than 5 th gear loaded .yes he was about spot on its 4 th / high range in to 5th coming up so yes 
Old John:
Wheel Nut:
Its a simple butterfly valve like a carburettor choke that slows the air getting past, its just back pressure that slows the vehicle or in the case of a DAF stops the engine.It is not linked to the gearbox, axle cooling system or anything else, it sits in the exhaust manifold, the higher the engine revs the more efficient it is.
I beg to differ regarding the exhaust brake not being connected to anything else.
Of course it is. It’s "connected"to everything, or it would have no effect at all on the progress of the vehicle. The Instant that you lift your foot off the accelerator, instead of the engine working to turn the wheels, the inertia of the vehicle is working to turn the engine, (provided that the vehicle is in gear and the clutch is engaged) , the effect of any system apart from the wheel brakes depends entirely on that connection. So, from the friction of the tyres with the road, all the way to friction between the clutch components, everything requires to be connected for any of these systems to have any effect on the progress of the whole vehicle.
The OP asked about an Exhaust Brake, not an Engine Brake - VEB or Gearbox Retarder. You also had the option of the Telma type on coaches which were a magnetic force on the prop shaft.
Remember the Spanish trailers and
rigids with the glowing disc brake on the rear axle. It was a similar set up as a Vanwall race car. A disc brake on the tail shaft of the gearbox which slowed the engine and wheels together.
Comparing a gearbox retarder, Jacobs, VEB, or TELMA to an exhaust brake is akin to comparing a ratchet handbrake on a PSK to a wax thermostat.
A middle aged driver may remember the exhaust brake on a Volvo F7 - F10. A button on the floor and a switch on the dash. It was orange and had a safety catch on it.
Can you explain what it was for?
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