Hi All,
I have a MAN TGS which is jamming the trailer brakes on, when empty just slightly touching the brake the trailer will lock up.
Trailer is fine on our volvo so its nothing on the trailer.
The compressor was pumping oil which caused the exhaust brake and air drier to fail which have been replaced, so something else may be full of oil.
I have replaced the compressor and trailer control valve which has helped slightly but still not good.
If i put a pressure gauge on the brake suzzi coil, when you touch the brake pedal it sends a large spike down the hose then settles as per normal.
If ever this has happened to me. I lower the air suspension on both the trailer and unit, and let it reset itself. It’s worked more times than not and not just with MAN tractor units
What age is the trailer as it sounds like it could be an ABS lead fault as if it’s an EBS trailer it shouldn’t be using the air signal from the yellow line unless the trailer EBS has faulted out.
bowers340:
Hi All,
I have a MAN TGS which is jamming the trailer brakes on, when empty just slightly touching the brake the trailer will lock up.
Trailer is fine on our volvo so its nothing on the trailer.
The compressor was pumping oil which caused the exhaust brake and air drier to fail which have been replaced, so something else may be full of oil.
I have replaced the compressor and trailer control valve which has helped slightly but still not good.
If i put a pressure gauge on the brake suzzi coil, when you touch the brake pedal it sends a large spike down the hose then settles as per normal.
What would cause the burst of air?
Anyone has this before?
Cheers,
Nick
My 2014 26 480 TGX has just had a recon compressor and it does the same when empty , Zb’ing pain in the arris [emoji49] it’s done it so far on a 6 month old SDC a 10 year old Lawrence David and a 4 year old SDC which was serviced yesterday
Does the trailer EBS/ABS warning light in the cab go through its self check when the ignition is switched on ? It is very easy to fail to notice that this is not working.
What is the unit like solo? Does this have sharp brakes but simply doesn’t lock up because of the ABS? You have already replaced the unit’s trailer control valve so that should eliminate a broken spring in that valve causing the trailer brakes to be fierce. Reconnect your pressure gauges to a unit brake chamber service port and to the yellow line and repeat the test to see if you get a spike of pressure on both gauges. Do this with ignition on and again with it off. A spike of pressure originating from the footbrake valve - which you haven’t renewed - should show on both gauges. Ignition on/off should tell you whether the fault is electrical or pneumatic. A spike only at the yellow line should eliminate the footbrake valve.
Hi All,
The trailer is much older than the truck and doesnt have ABS or EBS but i have tried the trailer on our 2006 Volvo Fm and 2008 Isuzu prime movers and it is perfect.
The MAN is perfect without the trailer on.
I will have to get the pressure gauges again and try it with the key off.
Im pretty sure its not the foot valve, because if you put the exhaust brake on 2 or 3 it locks up the trailer wheels in between down shifting.
blue estate:
My 2014 26 480 TGX has just had a recon compressor and it does the same when empty , Zb’ing pain in the arris [emoji49] it’s done it so far on a 6 month old SDC a 10 year old Lawrence David and a 4 year old SDC which was serviced yesterday
I have a mate that works for a large company with lots of MAN’s and he reckons half of them do it and the others are perfect.
Dont forget on a mdoern truck/trailer combo when you press the brake pedal the trailer brakes will be applied before the air even gets to the trailer relay valve, you are in effect braking by wire and the air side is purely a back up.
Trickydick:
Dont forget on a mdoern truck/trailer combo when you press the brake pedal the trailer brakes will be applied before the air even gets to the trailer relay valve, you are in effect braking by wire and the air side is purely a back up.
Its not an ABS/EBS Trailer so its relying on air.
I fitted a wabco load proportioning valve and it seems much better, still not perfect tho
That picture seems to show taps in the trailer suzie lines; they were outlawed years ago. Without checking I would have said that fitting a load proportioning valve as an addition would probably be a notifiable alteration, the vehicle was not type approved with one fitted. So the trailer is pre ABS, does it not have a load sensor valve then? Is it even on air suspension?
Isuzu tractor unit seemed odd when I first read it, are we even talking about operation in the UK?
cav551:
That picture seems to show taps in the trailer suzie lines; they were outlawed years ago. Without checking I would have said that fitting a load proportioning valve as an addition would probably be a notifiable alteration, the vehicle was not type approved with one fitted. So the trailer is pre ABS, does it not have a load sensor valve then? Is it even on air suspension?
Isuzu tractor unit seemed odd when I first read it, are we even talking about operation in the UK?
Hi,
I’m in Australia.
Taps are still on every single prime mover over here. Only trailers manufacturered after 2015 need to have abs/ebs or load proportioning valve.
The company I brought the valve off said they have fitted close to 50 of these this year alone to late model euro trucks towing older trailers.
The trailer I have is on airbag, is there another valve I could be using on that as well?
Cheers,
Nick
It is very hard to comment without knowing the contruction and use regulationes which apply to the vehicle combination nor the actual specification of the braking system fitted by the manufacturer for the Australian market. It is very likely different in some way to the European spec. AFAIK a USA spec tractor unit used to include a bobtail valve, manually operated from the cab and selected to reduce brake pressure when running solo. The trailer spec could be something completely different to the European normal, modern trailers’ EBS systems take into account whether drum or disc brakes are fitted.
In this country you would be subject to an immediate movement prohibition with those taps fitted and a subsequent full annual vehicle roadworthiness test. The fitment of the load proportioning valve as shown and described worries me, I cannot see how this valve can relate its output to the weight imposed on the trailer axles. All it can do is deliver a reduced pressure to that which supplies it. Even if its control pressure was taken from the unit’s drive axle chamber pressure it would still not have any relationship to the load (mass) imposed on the trailer axles. Many (50) years ago pressure regulating valves were fitted in the trailer circuits on the tractor unit, but certainly not recently.
If your problem is not a mechanical issue with the trailer brakes, then it is excessive air pressure delivered to the trailer brake chambers in relation to the bogie load. The brake balance between unit and trailer has long been a problem with a history of different solutions. From waht you say it appears that the trailer does not itself have any means of regulating the air pressure at the chambers in relation to the axle load. The best advise I can give you is to contact the makers of the air brake equipment fitted to the trailer for help.
I realise this does not answer why two other units do not lock up the trailer brakes, which is why from the information given I had suspected the footbrake valve was not acting progressively in relation to the effort exerted by the driver’s foot - actually a common fault. However you seem to have eliminated that possibility.
To give an example of how things can go seriously wrong between vehicle markets and specifications I will relate the story of what happened locally in 1986. An unladen artic went out of control when the driver applied the exhaust brake in a busy urban situation. It turned out that the German made unit applied the trailer brakes when the exhaust brake was operated (the Dauerbremse system), the trailer brakes locked up and the trailer mounted the pavement. Tragically this was at school chucking out time and three primary school children were killed.
Edit: add link to Commercial Motor article banning the system mentioned .
