hi all,
it’s been a while since i’ve drove an auto, so cant remember, or even remember if i did know!
if you’re going down a hill that the exhaust brake can’t hold you back on, what happens at max revs? will it up shift into the next gear or would it over speed the engine?
cheers
in the volvo switch the veb to level three leave the box in A and the truck will hold you on most hills even at 44t
stevieboy308:
hi all,it’s been a while since i’ve drove an auto, so cant remember, or even remember if i did know!
if you’re going down a hill that the exhaust brake can’t hold you back on, what happens at max revs? will it up shift into the next gear or would it over speed the engine?
cheers
If you’re going down a hill in the correct gear ( at most no higher than the one you’d use to go up it ) that the exhaust brake alone won’t keep the engine speed down below the red line the last thing you’d want to do is upshift the thing thereby increasing road speed and cutting engine braking.The idea in that case is hold the gear and use a combination of exhaust brake and the brakes to keep the engine speed below the red line.
If you’ve got a proper engine brake (Jacobs) then it might hold the truck back with very little or no use of the foundation brakes…if all you’ve got is the flap in the exhaust pipe, no chance. but you need to get the revs into the blue for the full effect.
GasGas:
If you’ve got a proper engine brake (Jacobs) then it might hold the truck back with very little or no use of the foundation brakes…if all you’ve got is the flap in the exhaust pipe, no chance. but you need to get the revs into the blue for the full effect.
Wot he said, standard exhaust brake as much use as a chocolate teapot.
GasGas:
If you’ve got a proper engine brake (Jacobs) then it might hold the truck back with very little or no use of the foundation brakes…if all you’ve got is the flap in the exhaust pipe, no chance. but you need to get the revs into the blue for the full effect.
That’s some of the problem.The revs with an exhaust brake,or in fact any type of engine brake,need to be as close to the start of the red as possible.Which is all about using a low enough gear.
I frequently come down birdlip fully freighted without touching the brakes, the I shift and VEB combination works very well!
yeah i get all that, but i’m just interested to know, what does an auto box do i you run out of revs, shift up or over speed the engine?
the reason i ask is because i drive a tractor with a vario transmission and an exhaust brake, as said, to get the most out of the exhaust brake i need plenty of revs. on the flat if i pull back on the stick the transmission will rev the engine to 2500, max revs are 2600 and keep them around 2500 until i’ve stopped without using the foot brake. but when going down a hill if 2500rpm at the given speed can’t slow or maintain my speed, then the transmission won’t adjust to stop the engine from over speeding.
there’s no reason the tractor couldn’t adjust itself to sit at 2500rpm whilst the road speed increases the same way it does when the road speed decreases.
If the vehicle is in danger of overevving i think you have to take that into account and use the brakes to control the speed before it gets out of hand, if hills that steep i’d probably slip it into manual and take over anyway.
I get your point about what would it do if you left it to its own devices, but i can’t allow the vehicle to be overstressed despite my hatred of satans gearbox, so can’t be sure whether it as a self protection program.
stevieboy308:
yeah i get all that, but i’m just interested to know, what does an auto box do i you run out of revs, shift up or over speed the engine?the reason i ask is because i drive a tractor with a vario transmission and an exhaust brake, as said, to get the most out of the exhaust brake i need plenty of revs. on the flat if i pull back on the stick the transmission will rev the engine to 2500, max revs are 2600 and keep them around 2500 until i’ve stopped without using the foot brake. but when going down a hill if 2500rpm at the given speed can’t slow or maintain my speed, then the transmission won’t adjust to stop the engine from over speeding.
there’s no reason the tractor couldn’t adjust itself to sit at 2500rpm whilst the road speed increases the same way it does when the road speed decreases.
You don’t want the road speed to increase while under braking going down a hill.In the situation whereby the engine is overspeeding under engine braking with the exhaust brake on then you need to use the brakes to hold the road speed down.If you upshift it you’ll not only increase road speed you’ll also lose the engine braking effect and the effectiveness of the exhaust brake thereby putting more load on the brakes.
Carryfast:
stevieboy308:
yeah i get all that, but i’m just interested to know, what does an auto box do i you run out of revs, shift up or over speed the engine?the reason i ask is because i drive a tractor with a vario transmission and an exhaust brake, as said, to get the most out of the exhaust brake i need plenty of revs. on the flat if i pull back on the stick the transmission will rev the engine to 2500, max revs are 2600 and keep them around 2500 until i’ve stopped without using the foot brake. but when going down a hill if 2500rpm at the given speed can’t slow or maintain my speed, then the transmission won’t adjust to stop the engine from over speeding.
there’s no reason the tractor couldn’t adjust itself to sit at 2500rpm whilst the road speed increases the same way it does when the road speed decreases.
You don’t want the road speed to increase while under braking going down a hill.In the situation whereby the engine is overspeeding under engine braking with the exhaust brake on then you need to use the brakes to hold the road speed down.If you upshift it you’ll not only increase road speed you’ll also lose the engine braking effect and the effectiveness of the exhaust brake thereby putting more load on the brakes.
Trust me, I know how to come down a hill!!
You don’t need to come down every hill at a speed that the exhaust brake can hold it back and still not touch the foot brake. Tractor brakes are expensive to replace so I’m not planning on them needing to be replaced whilst I’m driving it.
There are plenty of hills I go down that i’ll knock x amount of speed off before the hill, then with the exhaust brake pressed I’ll let it run on so that i’ll reach my original speed as the hill levels out at the bottom.
But to do this, I’m constantly starring at the rev counter and nudging the transmission on, keeping an eye on the road speed as well as looking where I’m going. To me I should be able to pull back on the transmission to get maximum exhaust braking and the tractor should adjust the transmission to maintain the engine speed the same way it does on the flat, so I can look where I’m going whilst keeping an eye on the road speed.
One fella at work says there must be a legal thing, about it not speeding up whilst you’re not on the accelerator, so I thought I’d ask what auto’s do.
stevieboy308:
Carryfast:
stevieboy308:
yeah i get all that, but i’m just interested to know, what does an auto box do i you run out of revs, shift up or over speed the engine?the reason i ask is because i drive a tractor with a vario transmission and an exhaust brake, as said, to get the most out of the exhaust brake i need plenty of revs. on the flat if i pull back on the stick the transmission will rev the engine to 2500, max revs are 2600 and keep them around 2500 until i’ve stopped without using the foot brake. but when going down a hill if 2500rpm at the given speed can’t slow or maintain my speed, then the transmission won’t adjust to stop the engine from over speeding.
there’s no reason the tractor couldn’t adjust itself to sit at 2500rpm whilst the road speed increases the same way it does when the road speed decreases.
You don’t want the road speed to increase while under braking going down a hill.In the situation whereby the engine is overspeeding under engine braking with the exhaust brake on then you need to use the brakes to hold the road speed down.If you upshift it you’ll not only increase road speed you’ll also lose the engine braking effect and the effectiveness of the exhaust brake thereby putting more load on the brakes.
Trust me, I know how to come down a hill!!
You don’t need to come down every hill at a speed that the exhaust brake can hold it back and still not touch the foot brake. Tractor brakes are expensive to replace so I’m not planning on them needing to be replaced whilst I’m driving it.
There are plenty of hills I go down that i’ll knock x amount of speed off before the hill, then with the exhaust brake pressed I’ll let it run on so that i’ll reach my original speed as the hill levels out at the bottom.
But to do this, I’m constantly starring at the rev counter and nudging the transmission on, keeping an eye on the road speed as well as looking where I’m going. To me I should be able to pull back on the transmission to get maximum exhaust braking and the tractor should adjust the transmission to maintain the engine speed the same way it does on the flat, so I can look where I’m going whilst keeping an eye on the road speed.
One fella at work says there must be a legal thing, about it not speeding up whilst you’re not on the accelerator, so I thought I’d ask what auto’s do.
As GasGas mentioned several posts above, what you expect isn’t going to happen unless the lorry has a proper retarder or engine compression brake, if it only has an exhaust brake then the brakes are going to be needed to restrain overspeed/overrev whther you apply them or the lorry itself applies them.
Thinking sensibly even if you had a full Jacob or retarder there would come a point where even that wouldn’t be enough, indeed those who have used goood retarders, and Volvo’s 3 position effort is as good as most, will have had to turn them down to prevent drive axle lock up when lightly loaded or in slippery conditions.
Currently driving an MAN (must have upset someone) fitted with satans autobox, if you press the autoretard button it will automatically downchange to a low a gear as possible as well as automatically apply the exhauster (fair effort for an exhaustbrake only), and keep downchanging as you slow up, invariably i switch the autoretard function off when it gets down to 7/8th as the next downchanges can be jerky, by then i’m usually planning a junction approach anyway so take over manually.
Going down steep motorway inclines i still have to gently brake to keep it below 60, it will downchange to 11th and sometimes 10th as it tries to slow but 58mph in 10th sees the revs high enough that by then i’m gently braking anyway.
[quote=“Juddian”
As GasGas mentioned several posts above, what you expect isn’t going to happen unless the lorry has a proper retarder or engine compression brake, if it only has an exhaust brake then the brakes are going to be needed to restrain overspeed/overrev whther you apply them or the lorry itself applies them.
Thinking sensibly even if you had a full Jacob or retarder there would come a point where even that wouldn’t be enough, indeed those who have used goood retarders, and Volvo’s 3 position effort is as good as most, will have had to turn them down to prevent drive axle lock up when lightly loaded or in slippery conditions.
[/quote]
Because I have only driven truck with just an exhaust brake, what and how do the others you have mentioned work?
Apologies for being thick 
stevieboy308:
‘… I’m constantly starring at the rev counter and nudging the transmission on, keeping an eye on the road speed …’
To differentiate between ‘normal’ driving and a downhill, on the latter I forget the roadspeed being a target and let mechanical sympathy become the priority.
I personally think the best retarder in the business is on the Scania. The engine brake on my Volvo is nowhere near as good. I never found a hill or weight that was too much for the Scania
Foxstein:
[quote=“Juddian”
Because I have only driven truck with just an exhaust brake, what and how do the others you have mentioned work?
Apologies for being thick
[/quote]
edit…^^^^^one day i’ll get this quoting thing right, promise… 
No apologies please and you’re far from thick, most modern fleet lorries have a standard exhaust brake which as you know make a noise and thats usually about its full contribution…
I luckily had a Jacob brake a lifetime ago on a 14 litre ■■■■■■■■ fantastic thing, running at the then maximum 38 (and a bit) tons seldom needed to use the vehicle brakes except to bring it to a final rest.
Nearest thing in effort i’ve since driven is Volvo’s 3 level engine brake, i’m not entirely sure how it works but judging by its efforts sound and vibration assume it operates in a similar way to the Jacob.
In both cases they operate (if so switched) automatically when you lift off throttle, Volvo if i recall correctly will also downshift automatically (i shift) whilst giving full ■■■■■■ if you flick the right button.
Switchlogic rates the Scania retarder and i must bow to his knowledge here as i’ve never driven one so fitted, the normal Scania exhauster you have to look see if the things switched on such is its dismal performance but its hardly alone in that.
Good old Wikipedia describes Jacob’s operation far better than i could, have a poke nose here…
en.wikipedia.org/wiki/Compressi … gine_brake
Course with modern teaching methods all this is old hat and apparently (according to some) should be consigned to history, brakes to slow gears to go is the current fashion……me? i’ll carry on trying me best to drive the things properly (failing miserably) using any auxilliary braking systems so fitted.
The Scania one is an oil based gearbox jobby. When running solo after pulling a heavy load you have to be careful you haven’t left stalk all the way down because as soon as you lift throttle it nearly puts you through the screen!
switchlogic:
The Scania one is an oil based gearbox jobby. When running solo after pulling a heavy load you have to be careful you haven’t left stalk all the way down because as soon as you lift throttle it nearly puts you through the screen!
:Lol: I’ve done that a few times!!! On mine it actually cuts out if its stopping too ferociously. It is an amazing accessory, the brake lights even come on when you use it because it is THAT good.
I’m surprised that nobody’s mentioned Telma yet, but maybe that’s because 1) nobody’s as old as me or 2) most operators dismissed it as being too heavy.
Any comments?
Retired Old ■■■■:
I’m surprised that nobody’s mentioned Telma yet, but maybe that’s because 1) nobody’s as old as me or 2) most operators dismissed it as being too heavy.
Any comments?
I’ve driven some old coaches with a Telma retarders. Weight obviously less of an issue. Didn’t Spain allow for the extra weight of a retarder in their weight limit years ago?