Midlift Axle Wheelspin

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
21

Mazzer2:

WhiteDog:
I’d have to disagree with few of the above posts…

I drive a 68 plate R450, 6x2. Company policy we must drop midlift axle when coupling with a trailer. After I hooked up and was pulling away, I did as I always do, and press the button to lift the mid lift. Sometimes is says something like “Tag axle overload” and it won’t lift. This time the axle lifted.

However this particular time I had access to a weight bridge, so I thought I’ll weight the thing… steering axle is permitted at 8000kg, but was sitting around 8300kg, drive axle was permitted at 10000kg, was sitting about 10222kg. I put the axle down and went through again… all well with in the legal permitted weights.

Reasoning always lift the midlift, guy from Scania was out with me, told me always lift it if it will, reduces drag and makes for better fuel efficiency.

But if the lift axle had been configured to your vehicles axle weights then it would have dropped 10,000kg limit on a drive axle is not the normal setting usually it is 11500kg so for whatever reason your company have specced the vehicle to that weight and then not set up the lift axle to match. The irony being is that the company probably watch the fuel figures and are quick to blame the driver for not getting good results yet company policy increases drag, wear and fuel consumption.

Our 4x2 drive axle is 11500kg.

Don’t know much about the inner workings of it all. Just stating my case from few weeks back, I was grossly over weight on axles, and never knew it as I was reliant on the truck to work out it’s weights. :open_mouth: :open_mouth: :open_mouth:

22

idrive:

Quite right, I should say I will leave it well alone and stop pushing buttons until I know how it works…
It’s pretty rare that I’ve driven 6x2 and only twice used the axle.
Once on a Renault the axle was down already and I couldn’t get it to go up. It was wheelspinning everywhere and I thought it was me not doing something right. Was a fully loaded fridge and I now know (think?) from above that it was down for a reason and not up to me.
Second time was the other day in a MAN with the decker. I convinced myself that it needed the axle down as it felt so heavy and the ride was so terrible. I now know (think?) from above that if it needed to be down, it would be.
Still a lot to learn though obviously.

When you say “dump the midlift air”, what does that mean exactly?
[/quote]
^^^ sod me made i right pigs ear of that quote :blush:

There’s usually two axle lift switches fitted to most 6x2 mid lift artics.
1 is the standard lift button, basically pressing this lifts the mid lift completely and permanently if the weights inposed on the tractor unit are compatible, ie lightly loaded, pres it again to lower the axle.

The other is the weight transfer button, the label looks like an umbrella over two axles.
The drive and mid lift axles will be sprung with air bags, when you press the weight transfer button the air pressure in the mid lift air bags is ‘‘dumped’’ or drained fully, this leaves the axle sitting there just about floating carrying minimal weight, the weight that was imposed on the mid lift is shared between the drive and steer axle, but as the drive axle is closer to the mid lift it takes the lions share of the weight increase…not only does this increase traction on slippery surfaces, it makes maneuvering much easier and is gentler on the unit tyres and suspension on tight turns, you often see drivers who give a monkeys dump the mid lift air and the subsequent raising of the mid lift axle once off the public road and onto private premises.

Now on some vehicles, mainly MAN and DAF, after about 30 seconds the mid lift axle will lift off the ground completely, but remember this is not perma lifting because the driver request was weight transfer (dumping the mid lift air), this happy state of affairs will usually remain until either you press the weight transfer button again to re-inflate the mid lift air bags, or you drive over about 20mph when the re-inflation and dropping the axle back down again if it lifted happens automatically.

Some vehicles may not have any form of axle weight transfer, last Iveco i drove the driver had no weight transfer button and i’m fairly sure newer Mercs don’t either, but happy to be put right if anyone knows better about those as i haven’t driven a Iveco for 10 years and only have to suffer a Merc once in a blue moon…and if i never drove either make again as long as i live that would be fine if the last examples were anything to go by :unamused:

As for lots to learn, everything bloody changes about every 5 years, so even when you’re an old ■■■■ like some others here… :laughing: …you and the rest of us will still be learning the job :sunglasses:

23

Juddian:

idrive:

Quite right, I should say I will leave it well alone and stop pushing buttons until I know how it works…
It’s pretty rare that I’ve driven 6x2 and only twice used the axle.
Once on a Renault the axle was down already and I couldn’t get it to go up. It was wheelspinning everywhere and I thought it was me not doing something right. Was a fully loaded fridge and I now know (think?) from above that it was down for a reason and not up to me.
Second time was the other day in a MAN with the decker. I convinced myself that it needed the axle down as it felt so heavy and the ride was so terrible. I now know (think?) from above that if it needed to be down, it would be.
Still a lot to learn though obviously.

When you say “dump the midlift air”, what does that mean exactly?

^^^ sod me made i right pigs ear of that quote :blush:

There’s usually two axle lift switches fitted to most 6x2 mid lift artics.
1 is the standard lift button, basically pressing this lifts the mid lift completely and permanently if the weights inposed on the tractor unit are compatible, ie lightly loaded, pres it again to lower the axle.

The other is the weight transfer button, the label looks like an umbrella over two axles.
The drive and mid lift axles will be sprung with air bags, when you press the weight transfer button the air pressure in the mid lift air bags is ‘‘dumped’’ or drained fully, this leaves the axle sitting there just about floating carrying minimal weight, the weight that was imposed on the mid lift is shared between the drive and steer axle, but as the drive axle is closer to the mid lift it takes the lions share of the weight increase…not only does this increase traction on slippery surfaces, it makes maneuvering much easier and is gentler on the unit tyres and suspension on tight turns, you often see drivers who give a monkeys dump the mid lift air and the subsequent raising of the mid lift axle once off the public road and onto private premises.

Now on some vehicles, mainly MAN and DAF, after about 30 seconds the mid lift axle will lift off the ground completely, but remember this is not perma lifting because the driver request was weight transfer (dumping the mid lift air), this happy state of affairs will usually remain until either you press the weight transfer button again to re-inflate the mid lift air bags, or you drive over about 20mph when the re-inflation and dropping the axle back down again if it lifted happens automatically.

Some vehicles may not have any form of axle weight transfer, last Iveco i drove the driver had no weight transfer button and i’m fairly sure newer Mercs don’t either, but happy to be put right if anyone knows better about those as i haven’t driven a Iveco for 10 years and only have to suffer a Merc once in a blue moon…and if i never drove either make again as long as i live that would be fine if the last examples were anything to go by :unamused:

As for lots to learn, everything bloody changes about every 5 years, so even when you’re an old ■■■■ like some others here… [emoji38] …you and the rest of us will still be learning the job :sunglasses:
[/quote]
.
.

I believe some newer vehicles have an auto weight transfer as part of electronic traction control.
.
.I could be wrong?

24

Franglais wrote
‘‘I believe some newer vehicles have an auto weight transfer as part of electronic traction control.
.
.I could be wrong?’’
end quote.

Not one i’d heard about Franglais, but they’re desperate to take away any sort of control from the driver so wouldn’t surprise me, i understand our model of Actros’ have no weight transfer system, instead the transmission is supposed to ‘judder’ to help get you moving in slippery conditions, seems a lot of ■■■■■■■■ to me when the obvious answer is to shift some weight onto the drive axle but what do we know :unamused:

By the way old mate, did i ever let you know the outcome of the experiments re the draining of air from the trailer and lifting of the tractor unit (including dumping of tractor mid lift air)? i remember you asked just couldn’t remember if i ever gave the result.

At max wt properly loaded for stability (ie enough weight on the tractor so the dog’s wagging the tail, and not the too often seen out there, other way round) the drive axle weight was increased to around 15 tons, that would make a big difference to getting up a slippery hill if needed.

25

Juddian:
Franglais wrote
‘‘I believe some newer vehicles have an auto weight transfer as part of electronic traction control.
.
.I could be wrong?’’
end quote.

Not one i’d heard about Franglais, but they’re desperate to take away any sort of control from the driver so wouldn’t surprise me, i understand our model of Actros’ have no weight transfer system, instead the transmission is supposed to ‘judder’ to help get you moving in slippery conditions, seems a lot of ■■■■■■■■ to me when the obvious answer is to shift some weight onto the drive axle but what do we know :unamused:

By the way old mate, did i ever let you know the outcome of the experiments re the draining of air from the trailer and lifting of the tractor unit (including dumping of tractor mid lift air)? i remember you asked just couldn’t remember if i ever gave the result.

At max wt properly loaded for stability (ie enough weight on the tractor so the dog’s wagging the tail, and not the too often seen out there, other way round) the drive axle weight was increased to around 15 tons, that would make a big difference to getting up a slippery hill if needed.

Pretty sure you did.
One goid thing about getting older: my Altziemher is getting much stronger!

26

I have only driven a midlift on a handful of occasions, and, even using the weight transfer devices as they should be used, I couldn’t believe how utterly useless they are on anything other than flat, dry, warm tarmac…
I concluded therefore, that they are the work of the devil and should all be cut into small pieces, melted down, and reborn as tags.
Problem solved!

Seriously though, as others have said, there are many reasons for the poor grip phenomenon, and I would agree that if the axle does not drop automatically then you should leave it up. Unfortunately, as someone else has said, weight distribution on the trailer can also be a major factor, and if the load feels heavy, but the axle stays up, drive carefully as jack knifing is a hazard of this condition.

27

Thanks for the replies everyone, interesting stuff cheers