Bking:
Reason tag or lift axle runs slightly warmer is because it is not in ABS loop.
You cannot put an axle that is some times up and sometimes down into the ABS programme,The lift axle always gets full supply pressure so takes on a higher braking load,
If you look you will see that the lift axle has no ABS sensors.
It does have ABS sensors on the tag axle
So you have a system that relies on wheel speed pulse but all of a sudden you stop sending a pulse from a lift axle because the wheels are not rotating and then what happens?
The ABS then goes into fail safe and shuts down.
WTF you talking about.
Jesus another “expert”
Depends on the sophistication the system but it is fairly straightforward for most current systems to be programmed to ignore the abs sensor signal on one axle as long as the system knows it is not in contact with the road.
Own Account Driver:
Could the skipping be the ABS cycling?
Quite possibly … I handnt thought of that … I assumed it was a load issue
It will quite likely be a load sensing issue if the ABS is cycling with no good reason. It will be air at too high pressure being sent to the chamber that causes the wheel to lock and the ABS to cycle. The air will generally be at too high pressure when the ECU thinks the axle is heavier than it really is.
It could also be the drive axle isn’t putting enough brake effort in and working the tag brakes too hard but more likely load sensing if the skipping is indeed the ABS cycling. As I say though without dealer level diagnostics it might be quite tricky but you could measure the air pressures, loaded and empty, in the brake lines and air bags and it would at least give you an idea what’s going on and a roller brake test wouldn’t harm.
If there’s a problem with it not correctly measuring the suspension air pressure, and therefore load, it could be quite pricey. I’d ■■■■ it and see a bit and see if you start wearing pads excessively on the tag. EBS can do all sorts of clever dickery in altering the brake pressures to try and even up pad wear which all depends on the individual system.
Yes I’m thinking this too … air at too high pressure to the tag chambers… The dash shows pad wear percentage and the tag pads are lower but Ive only just started monitoring it so not sure where they are in relation to drive axle. It was the only slightly warmer running temp that gave it away, then the skip on wet roads.
The brake test at MOT didn’t reveal anything ? which surprised me, but when you think about … why would it ?, they were still operating effectively, just not in sync with the drive axle. There is a sensor on top of the airbags on the tag axle which I think the dealer is suggesting changing, but I didnt want to throw cash at it randomly without a bit more thought on probable cause, worried that it may be an ECU problem, and Ive had a couple of bad experiences with this dealer doing some shoddy work before now, who are inclined to swap out parts ‘just to see’ if it sorts it. I think you may be right though, and the faster solution is to do some pressure tests, I’d have to test both axles simultaneously somehow I’d imagine to show the variance
Own Account Driver:
Could the skipping be the ABS cycling?
Has the axle been relined lately were oe pads used were discs good,how did the old pads wear ,there are some pretty ■■■■■■ aftermarket pads ,tried some on the dafs a few times and they cooked the caliper bellows ,oe pads sorted it. The volvos are the same seen some pad metals nearly thru to the discs after a months wear with ■■■■ pads .
It will quite likely be a load sensing issue if the ABS is cycling with no good reason. It will be air at too high pressure being sent to the chamber that causes the wheel to lock and the ABS to cycle. The air will generally be at too high pressure when the ECU thinks the axle is heavier than it really is.
It could also be the drive axle isn’t putting enough brake effort in and working the tag brakes too hard but more likely load sensing if the skipping is indeed the ABS cycling. As I say though without dealer level diagnostics it might be quite tricky but you could measure the air pressures, loaded and empty, in the brake lines and air bags and it would at least give you an idea what’s going on and a roller brake test wouldn’t harm.
If there’s a problem with it not correctly measuring the suspension air pressure, and therefore load, it could be quite pricey. I’d ■■■■ it and see a bit and see if you start wearing pads excessively on the tag. EBS can do all sorts of clever dickery in altering the brake pressures to try and even up pad wear which all depends on the individual system.
Yes I’m thinking this too … air at too high pressure to the tag chambers… The dash shows pad wear percentage and the tag pads are lower but Ive only just started monitoring it so not sure where they are in relation to drive axle. It was the only slightly warmer running temp that gave it away, then the skip on wet roads.
The brake test at MOT didn’t reveal anything ? which surprised me, but when you think about … why would it ?, they were still operating effectively, just not in sync with the drive axle. There is a sensor on top of the airbags on the tag axle which I think the dealer is suggesting changing, but I didnt want to throw cash at it randomly without a bit more thought on probable cause, worried that it may be an ECU problem, and Ive had a couple of bad experiences with this dealer doing some shoddy work before now, who are inclined to swap out parts ‘just to see’ if it sorts it. I think you may be right though, and the faster solution is to do some pressure tests, I’d have to test both axles simultaneously somehow I’d imagine to show the variance
Bking:
Reason tag or lift axle runs slightly warmer is because it is not in ABS loop.
You cannot put an axle that is some times up and sometimes down into the ABS programme,The lift axle always gets full supply pressure so takes on a higher braking load,
If you look you will see that the lift axle has no ABS sensors.
Ok Ive taken the plunge and gambled too busy to fanny about with dealers ATM, so Ive ordered an airbag pressure sensor from Dingbro which is £50 cheaper than the stealer … looks a bit like its a Wabco EBS set up on this motor. I’ll report back on how I get on for the benefit of others on the forum. As always with electrickery … you wonder, without test gear where to look ?. Apart from the auto level and load transfer I mentioned at the top of the thread, it also has the ability to auto drop the tag depending on load, or deny a lift up , if the load is too much, so clearly there is a ‘brain’ that is well aware of the loads on the axles. When traction is poor for load transfer, a switch on the dash increases pressure in the drive axle air bags and the dash displays a read out of the tonneage loaded on each, so there is a bit of tech going on here undoubtedly.
Someone asked earlier about the axle load limits, the tag is rated at 8.5 tonnes, and the drive is 11.5, so even with the 8 … (not a 9 tonner) loaded in the promo shot earlier as cav551 asked the load was still fine had it been moved
I deliberately placed an 8 tonne load over both axles today, and there was no discernible difference in hub temps after arriving at site, which suggests the drive axle was more balanced due to the higher load, so, it would appear the fault is only evident on a smaller load on both axles, where the leccy bits have to work out the pressure variance, and clearly if they cant then the fault is evident,
which is why Ive plumped for the sensor on the tag just now. I was minded to swap it with the one on the drive to see if there was a fault on the drive axle, but the dash shows no EBS fault as it is ? so wondered about the effectiveness of that and the time taken to do it. will keep you posted …
Once you get up to higher weights the impact of the load sensing on brake pressures falls away as it gets towards full tank pressure. This is because the possibility of locking up gets much less.
I’m pretty sure the sensor will probably fix it. The dealer should have in theory been able to test the sensor by checking what the ecu thinks the pressure is against the actual pressure measured but it wouldn’t be worth their labour against the cost of the sensor.
At that price it’s not worth trying to swap the tag and the drive sensors.
On EBS, depending on sophistication levels. It measures, axle load, individual wheel speed, and brake pad thickness plus the speed and force of the pedal application and churns all the info together in its electronic brain and instaneously deciding what air pressure to apply to each individual brake chamber. Even something wrong with the brake pad wear sensors can trigger problems that can’t be ignored in some systems.
The only thing that worries me with it being the sensor is, if it is, I would expect really very pronounced symptoms on the tag locking up when the truck is driven empty.
Own Account Driver:
The only thing that worries me with it being the sensor is, if it is, I would expect really very pronounced symptoms on the tag locking up when the truck is driven empty.
Agreed … but I know what load she will take before the tag drops, and so I usually drop it anyway, and never usually run with it dropped when empty because a: its a rougher ride and b: thats the reason for the lift to exist when empty, so always run lifted. However … after I discovered this issue last week, I tried a run with it down when empty, and it was skipping quite badly under sharper braking. I normally drive quite conservatively leaving ample braking distance, so hadnt noticed it at all , until someone cut me up the other day and I had to brake more sharply when the problem became evident. Anyway that’s the new sensor on tonight, see how it goes
Bking:
Reason tag or lift axle runs slightly warmer is because it is not in ABS loop.
You cannot put an axle that is some times up and sometimes down into the ABS programme,The lift axle always gets full supply pressure so takes on a higher braking load,
If you look you will see that the lift axle has no ABS sensors.
Bking:
Reason tag or lift axle runs slightly warmer is because it is not in ABS loop.
You cannot put an axle that is some times up and sometimes down into the ABS programme,The lift axle always gets full supply pressure so takes on a higher braking load,
If you look you will see that the lift axle has no ABS sensors.
wrong again !!!
Thats a pad wear sensor!!!
Remind me not to bring a truck to you if it needs new pads.
Problem solved ! Guess I owe that one to the stealer this time Was running with a 2.5 tonne load over the axles and she was braking smoothly at any pressure, all for something the size of a 27mm Nut … that still cost £100 … So in my final analysis, I could be wrong but, when I bought this chassis, (to load plant) I was told I could load anything up the rear without any problems, but I also designed the body for it and had my reservations, so fitted jack legs to aid support over the rear axles when loading heavier kit. Those have now been done away with due to ram seal failures and as we dont load anything heavier than 8 tonne any more, but I wonder if its that extra weight appearing from the tail, thats caused high pressure in the airbags, leading to sensor failure ?
Anyway still think the Scania is a decent yoke, and it works as hard today as it did 10 years ago and is my second one to own. I dont suppose brake system maintenance on this motor is any worse than any other, and at least theres commonality of some parts, such as the brake calipers, which you can refurb yourself with a scania kit, although sided, are common across all three axles so that means theres a pad wear sensor and an ABS sensor on each axle … just a wee note for Bking
Bking:
Reason tag or lift axle runs slightly warmer is because it is not in ABS loop.
You cannot put an axle that is some times up and sometimes down into the ABS programme,The lift axle always gets full supply pressure so takes on a higher braking load,
If you look you will see that the lift axle has no ABS sensors.
It does have ABS sensors on the tag axle
So you have a system that relies on wheel speed pulse but all of a sudden you stop sending a pulse from a lift axle because the wheels are not rotating and then what happens?
The ABS then goes into fail safe and shuts down.
WTF you talking about.
Jesus another “expert”
Depends on the sophistication the system but it is fairly straightforward for most current systems to be programmed to ignore the abs sensor signal on one axle as long as the system knows it is not in contact with the road.
Name one? Haldex dont produce one but no doubt you know better.
FlatbedFlyer:
It does have ABS sensors on the tag axle
So you have a system that relies on wheel speed pulse but all of a sudden you stop sending a pulse from a lift axle because the wheels are not rotating and then what happens?
The ABS then goes into fail safe and shuts down.
WTF you talking about.
Jesus another “expert”
Depends on the sophistication the system but it is fairly straightforward for most current systems to be programmed to ignore the abs sensor signal on one axle as long as the system knows it is not in contact with the road.
Name one? Haldex dont produce one but no doubt you know better.
Er, well the OP’s truck and the one someone posted a photo of, for a start.
coiler:
Volvo use a Knorr Bremse EBS system, and that uses abs sensors on the midlift.
1.5.1.1.8 Lifting axle control In conjunction with a WABCO lift axle control valve the EBS controls the lifting axle automatically as a function of the current axle load.
I replaced an abs sensor on a midlift axle on a Volvo yesterday, was going to get a picture of it but I’ve not worked out how to put pictures on this forum.
norb:
Keep up bking ,after all it is 2017 ,technology moves on .DAF also have EBS and the lift axle of the new XF CF FTG models …
The day DAF produce an ABS system I will platt fog.
I never said DAF produced an ABS system …Please keep up bking ,we are talking about EBS ,and like most manufacturers ,they get their electronic systems from 3rd parties ie WABCO ,KNORR BREMSE…
Please read what people have written before you reply …And I will apologise first for any spelling mistakes And a happy new year to yourself
too busy to fanny about with dealers ATM, so Ive ordered an airbag pressure sensor from Dingbro which is £50 cheaper than the stealer … looks a bit like its a Wabco EBS set up on this motor. I’ll report back on how I get on for the benefit of others on the forum. As always with electrickery … you wonder, without test gear where to look ?. Apart from the auto level and load transfer I mentioned at the top of the thread, it also has the ability to auto drop the tag depending on load, or deny a lift up , if the load is too much, so clearly there is a ‘brain’ that is well aware of the loads on the axles. When traction is poor for load transfer, a switch on the dash increases pressure in the drive axle air bags and the dash displays a read out of the tonneage loaded on each, so there is a bit of tech going on here undoubtedly.
… So in my final analysis, I could be wrong but, when I bought this chassis, (to load plant) I was told I could load anything up the rear without any problems, but I also designed the body for it and had my reservations, so fitted jack legs to aid support over the rear axles when loading heavier kit. Those have now been done away with due to ram seal failures and as we dont load anything heavier than 8 tonne any more, but I wonder if its that extra weight appearing from the tail, thats caused high pressure in the airbags, leading to sensor failure ?
