How does a exhaust brake work, im talking in mechanical terms no how to pull a stalk 
Also what is the difference between a retarder and an exhaust brake.
You see i had a shot of a volvo i think it was a exhaust brake and it had 4-5 different levels and it was really effective on downhills. But on my current daf the exhaust brake is pish need to come down the gears to make it work effectively.
Just a flap in the exhaust pipe, that when closed, restricts the exhaust gas flow. If the exhaust canāt flow, the engine gets choked, resulting in more engine braking.
Then thereās the Jake brake engine brake, which alters the valve timing to turn the engine into a huge compressor. Makes a sound like a machine gun.
Or the torque converter type retarder that just squishes oil between gears to create drag on the transmission.
Or the electric engine brake, which is in effect a huge motor on the propshaft. This causes drag on the prop to ā ā ā ā ā ā the transmission.
I believe itās a throttle valve in the exhaust manifold which almost completely blocks the exhaust and causes the engine to compress the exhaust gases. The energy which goes into the compression is taken from the momentum of the vehicle, thus slowing you down. Iām not sure why the volvo ones are so much better though. It might be that the exhaust manifolds are stronger so they can deal with a higher level of compression, so the volvo valve closes the exhaust more (on max settings) than other makes versions do.
The best way to think of a retarder is like a big magnet, normally mounted between gearbox and drive axle. And when energized slows you down.
merc0447:
Also what is the difference between a retarder and an exhaust brake.
Exhaust brakes work as the others have described, retarders can work in different ways. I had a Scania with an oil motor retarder which was excellent. Basically, when you engaged it, it converted the drive axle into a pump, which pumped oil around a captive circuit. By increasing the retarder setting, a valve in that circuit was progressively closed, restricting the flow of oil, creating back-pressure and therefore rolling resistance in the drive axle.
Other retarders work by altering the inlet and exhaust valve timing, forcing the engine to compress air in the cylinders on the up-stroke which is then released when the piston reaches top dead centre.
Mechanic Dan:
The best way to think of a retarder is like a big magnet, normally mounted between gearbox and drive axle. And when energized slows you down.
Oh aye, Iāve seen a few Irish wagons with these type of retarders.
Wellā¦ A big magnet stuck on the back of the gearbox, I guess it was a retarder ā ā ? 
The Volvo has both an exhaust brake and an engine brake.
An exhaust brake is indeed a flap in the exhaust which restricts the flow of air out of the engine.
They arenāt very effective, even at high revs.
Without going into too much detail, on the compression stroke, the engine compresses air, ready to add diesel which then ignites and forces each piston down, giving power.
This takes effort, normally overcome by the power stroke, when the fuel is burnt, forcing the piston back down.
An engine brake works by cutting off the fuel and then releasing the compressed air at the top of the compression stroke, so that the engine has to work to pull the piston back down, as the exhaust and inlet vales are closed.
The resulting drag on both the compression and firing strokes is more than enough to slow a loaded vehicle down, alarmingly so sometimes if itās a solo tractor unit.
An engine brake with stages simply acts on an increasing number of the cylinders, depending on the stage selected.
A retarder is something different again and is normally mounted on the vehicle drive axle.
Mostly they are electro magnetic and slow the vehicle by making the axle work against a magnetic field.
Regards,
Nick
Ive got a Jake brake on my cat engined, Foden . Great sound 
and really effective too 
. and now thanks to trucknet i know how it works 
Oh yeah smarty pants. Are you allowed to use it on a night, in residential areas
It alters valve timing.
Intruiging, I didnāt realise Volvoās had the engine brake which works by venting the cylinder after the compression stroke. I was told that design was too loud for road use. Perhaps I was hearing some drivers diesel fumes 
we all know what the best use for retarders/exhaust brakes are don`t we??
apart from what the manufacturers intended.
I found out several years ago while doing agy work for āWilkosā
The run to Scarborough generally got the best results, as the road up to the store in the town centre was a narrow residential road lined with cars either side belonging to day trippers, so it seemed obligatory to switch on the exhaust brake as I drove along it, with the enevitable consequences. 
Also in my early days there was a couple of streets in Norwich that had overnight (7am-6am??) weight limits, As I was delivering plastic tanks etc, Id usually over night outside the plumb centre, a it was my last drop on a monday, and they where ok with me parking outside, and the next morning I would head to another ind Est up the road for my 1st drop the next day. which meant lengthy either sneaking through the streets or a diversion around town. however these streets did have the āexcept for accessā added to weight limit signs, I did on occasion accidentally leave the exhaust brake on while going through these streets, again with the enevitable consequences.
Always wondered that when you use the exhaust/retarde brake, do your rear brake lights come on. stupid question you may think but its an answer to a question i have often wondered.
cieranc:
Mechanic Dan:
The best way to think of a retarder is like a big magnet, normally mounted between gearbox and drive axle. And when energized slows you down.Oh aye, Iāve seen a few Irish wagons with these type of retarders.
Wellā¦ A big magnet stuck on the back of the gearbox, I guess it was a retarder ā ā ?
No, that was a ā ā ā ā ā ā you saw.
manowar:
Intruiging, I didnāt realise Volvoās had the engine brake which works by venting the cylinder after the compression stroke. I was told that design was too loud for road use. Perhaps I was hearing some drivers diesel fumes
Yeah that type is a Jakobs brake (Jake Brake). I didnāt think they were allowed here either, for the noise reason. Even in America theres some states where their use is not permitted.
Iāll ask my mate Barrel, he works at the dealers.
merc0447:
How does a exhaust brake work, im talking in mechanical terms no how to pull a stalkit doesnt
Also what is the difference between a retarder and an exhaust brake.
300kg
You see i had a shot of a volvo i think it was a exhaust brake and it had 4-5 different levels and it was really effective on downhills. But on my current daf the exhaust brake is pish need to come down the gears to make it work effectively.
that is the idea
ā ā ā ā ā ā 00:
Always wondered that when you use the exhaust/retarde brake, do your rear brake lights come on. stupid question you may think but its an answer to a question i have often wondered.
I think I remember that the Volvo puts the brake lights on above a certain level of engine braking.
As to the āJake brakeā, I believe that is named after a manufacturer, a bit like a āHooverā is used to describe a vacuum cleaner, but that it is itself an engine brake.
The Volvo is fairly loud when the engine brake is at work.
Regards,
Nick
Sam Millar:
It alters valve timing.
How does it do that Sam, it would bend the valves
Two types, solenoids acting on the valves and tapered (3D) cams.
On the pistonās compression stroke, as the piston approaches TDC, the cam slides across onto a different profile, this shoves the exhaust valve open just enough to dump the pressurised air. Then slides the cam back to shut the exhaust valve.
When the piston is going back down, itās induction stroke, the injector is switched off so itās only drawing air, the cam moves again and the inlet valve stays shut, so the piston is pulling a vacuum. With the piston at the bottom of its stroke, the valve push open again to release the vacuum.
So the engine works hard to compress the air, then works hard to pull a vacuum = lots of engine braking.
In cars this is known as Variable Valve Timing and is used to provide both performance and economy in a sports car, the cam is pushed across over 5k rpm, off āeconomicalā profile and onto āraceā profile. Stay below 5k rpm and itās calm and economical, nail the throttle and it flies!
The other type has seperate solenoids acting on the valves to do the same thing.
Itās loud on my FM12 underlift, not 'cos of the engine brake though, thereās 2 feet of pipe off the turbo and straight into a vertical eminox, no silencers
ā ā ā ā ā ā 00:
Always wondered that when you use the exhaust/retarde brake, do your rear brake lights come on. stupid question you may think but its an answer to a question i have often wondered.
No stupid questions,only stupid answers.I hope this isnāt one 
No brake lights with an exhaust brake.Hydraulic retarders AFAIK donāt have that option.Telma electric retarders I think may have had that as an option.
