I’m not disputing any of that, Wheel Nut. But the fact of the matter is that the main cause of jacknife is the unit braking harder than the trailer, and using an exhaust brake/retarder is exactly that. So, as in ROG’s example above, when you add slippery conditions into the equation you’re asking for trouble.
As for air brakes being too sharp, that’s just crap, it’s down to the driver how hard he puts his boot on the pedal. It’s the same as people claiming they can’t reverse smoothly in an auto, entirely down to lack of skill.
Better to brake all wheels rather than just one axle when the conditions make it already more likely that you will have a problem.
Lucy:
Exhaust brake/retarder/jake brake OFF on an artic when it’s slippy. The guys who drive in US will tell you otherwise, but that’s because they still have delay on their air brakes over there where we don’t, so it’s the better option for a quick reaction for them. For us it’s simply unnecessarily lethal.
rubbish. exhaust brakes can’t lock up your wheels. a foot brake can. if you press your foot brake in a jacknife you just make it worse, if you use your exhaust brake/retarder you remain in the jacknife without the situation getting worse.
you need plenty of power to pull youself out of the [zb], but don’t floor it. don’t follow too closely to the vehicle in front. take it easy.
Sorry Phil, the part I’ve made red is simply untrue.
Using an exhaust brake definitely CAN lock the rear wheels and CAN cause a skid.
limeyphil:
the worst thing the fella wants is bad advice.
Lucy:
Better not to cause it in the first place by using an exhaust brake, eh Phil?
i wouldn’t expect that to be possible.
Downhill, slippery surface, slight curve, highish revs - exhaust brake enaged - unit slows - trailer don’t so starts to overtake the unit - have I got that about right Lucy
I’d agree with what you wrote ROG, but if the trailer is badly loaded and a little light on the pin, then the situation is even worse.
It’s the heavier mass of the trailer that tries to keep going in a straight line, because the tractor can’t supply enough steering force to overcome the inertia of the trailer. The tractor then jacknifes if its drive axle tyres have little grip.
T-Lad:
Think you do farms don’t you if i remember . Get phone numbers of farmer to come pull you out with tratter if you do get stuck
Further to that; ring farmer before arrival, check the farm lane is clear, more important than the main road as you well know. Also ensure he puts his tractor somewhere where he CAN pull you out; no good having it stuck behind you!
Most of the dairy boys round here are pretty good, if the road’s impassable they’ll ring us to tell us rather than have the lorry stuck halfway down the lane. Then again they don’t want us (feed delivery) blocking the way for the tanker boys!
limeyphil:
well i don’t mind being corrected, but i’ve never come across an exhaust brake that will lock up the back wheels.
Hi Phil, an exhaust brake doesn’t normally lock the wheels, but it will in the situation I described above.
limeyphil:
it slows the engine. nothing to do with the drive wheels.
Consider the process that you need to follow when ‘bump’ starting a car that has a manual gearbox…
Ignition on, engage 2nd gear, clutch pedal depressed, gather some speed then dump the clutch… the engine springs into life.
The force needed to turn the engine over came from the the fact that the drive axle tyres could grip the road. The force required to turn over the engine was transmitted via the wheels, driveshafts/propshaft, clutch, flywheel and finally the crankshaft. It’s the same route that the force normally takes to drive the vehicle along, but when bump starting, the force just goes in the opposite direction.
limeyphil:
well i don’t mind being corrected, but i’ve never come across an exhaust brake that will lock up the back wheels.
a few years ago, i was driving a scania 92 17 tonne rigid, middle of winter, Mid Wales 2 day run, on day 1, we were in the Malvern Hills and then going further into Wales, well, we was travelling down a steep snow covered hill, single carriage way, i was going down on the exhaust brake, and i can tell you, it DID lock the wheels and the truck went sideways
I have got a jake on my motor have driven on ice and snow many times in the 8 years i’ve been in her and belive me you can lock the drive up with the jake on slippery surfaces plus was always told not to engage difflock unless drive is stopped
First, I don’t have any more delay or lag on my US built truck than I did on my euro trucks. We have relay valves just the same as you do.
Having been in extreme conditions I will say that I always use the jake on maximum. If you are slowing using the jake you hear if you are sliding instantly via engine noise and can dab your foot on the throttle or clutch just to cut the jake off and you will regain traction immediately.
While many jacknife incidents do occur when the tractor loses grip, more are caused by the trailer swinging around when the brakes do not release quickly enough, which is the same there as it is here. ABS is a waste of time in the snow as once all the wheels have locked it cannot detect that the vehicle is still moving so doesn’t release. That is when most get in trouble, not because the drive axle has locked up.
The main thing to remember in adverse conditions is pretty much as Mark, Rikki and some others have said. Do NOTHING RADICAL!
Think ahead and drive as if you really do not know what is ahead of you, regardless of what you can see. Treat the brake as an emergency attachment and steer as if you have all the time in the world. If you drive thinking that you are in no hurry then you will be fine.
While many jacknife incidents do occur when the tractor loses grip, more are caused by the trailer swinging around when the brakes do not release quickly enough, which is the same there as it is here. ABS is a waste of time in the snow as once all the wheels have locked it cannot detect that the vehicle is still moving so doesn’t release. That is when most get in trouble, not because the drive axle has locked up.
That’s not jacknife then is it? It’s trailer swing. Different incident with different causes.
I’m going to have to go off and search for the post claiming there was still delay on airbrakes over there now, 'cos I could have sworn blind it was you that made it, although obviously not.
bobthedog:
Engine braking is gentler than air, and you get immediate notice if you are sliding, because the engine noise will let you know. Also, the tractor will kick a little instead of the trailer coming around you. With the pedal, the first notice you might have is the bang when the trailer swings into you. The jake is instant when it releases, and you can go from braking to accelerating to pull yourself out of mischief in a split second. The 1/2 second lag on air brakes is enough time to go from a potential problem to a real problem. On the winter roads, the footbrake is virtually ignored until you get to shunting somewhere. When I first started going up north, I hit the snowbanks more than once by dabbing the pedal.
P’raps make your mind up before wading in further, eh Bob?
All I can say is that folks must be very fortunate, they have never picked a ferry trailer up with snatching brakes or had a slow releasing cam. I can regulate my retarder. I cannot always be so certain that the hired / ferry trailers are in perfect order.
Obviously on this thread, it comes down to personal choice, a ham fisted user of a retarder will lock up his drive axle. so will anyone who is ham fisted with a footvalve.
Past experience tells me to use all the tools I have at my disposal, not just a one size fits all solution.
I was once told by an instructor never to use the front brake on a motorcycle. I ignore that advice too.
In ice or snow, do everything slower, do it smoothly and give yourself more time.
An instructor told you never to use the front brake on a bike?
That certainly comes into the category of advice to be ignored completely - while at the same time wondering if the instructor has ever ridden a bike or given any serious thought to the physics of stopping it.
I remember going that road from the M8 at Bathgate across to linthgow in really bad conditions, hitting that gorge can’t rememebr its name steep decent putting on the exhaust brake and felt trailer start to go a bit.
Disengaged it and used brakes lightly.
Was a pant filling moment, love to say it down to skill nothing happening but was more down to luck and blind panic, lesson learned though to be wary of the exhaust brake and it use.
MartinC:
That certainly comes into the category of advice to be ignored completely - while at the same time wondering if the instructor has ever ridden a bike or given any serious thought to the physics of stopping it.
I mind when i was a courier got knocked off by a taxi broke the front brake lever off had to drive back to Croydon from central London with no front brake. Was scary how easilly if you had to brake hard the back wheel would lock up. Someone walk out in front of me slammed on the back brakes locked up the back wheel again was luck never slammed into them.
Wheel Nut:
Past experience tells me to use all the tools I have at my disposal, not just a one size fits all solution.
Great line
Having a ‘play’ with each of those tools and considering what the possible consequences might be in different situations is another key factor
As for those possible consequences, well, that’s where discussions like this come into their own
Lucy is absolutely right. It can get really seriously slippery here, I’ve done two winters now and there have been several times when just the exhaust brake was enough to instantly break traction on the drive axle, even on the lowest setting .
