Help - van has become unstable

[MikeMc]

At the weekend I visited the C&CC site at Cannock Chase but had a bit of a mare on the journey. My twin-axle had 2 minor snaking incidents on the M6 and felt as if it was buffeting the car around a lot more than I have ever felt before. The loading has not changed but there are a couple of things that are different about this trip and I need any help/advice so I can identify the cause of this unstability. The first thing is van tyre pressure. My van (Elddis Sirroco) is ten months old and I thought I would check the tyres. The handbook states 44psi but when I went to each tyre they all had 36psi. So the first difference is that I pumped them up to 44. The second difference is that I changed my car from a Nissan Terrano to a Nissan Pathfinder and had to have a new Whitter tow bar fitted. So do tow balls need to be roughed up a bit before the hitch stabiliser works properly? The Pathfinder is a heaver car and the outfit should have been more stable. I think I might lower the tyre pressures before towing again and I might take some sandpaper to the towball too. Has this happened to anyone else ie a previously stable van becoming unstable?

BTW Cannock is a lovely site and in the snow my kids said it looked like Nania

 

[Del_374232870]

I dont know what the correct tyre pressure is for you tyres. On our Lunar Delta t/a max pressure is 36psi.

Regarding the tow ball, have you ensured that all paint was removed before hooking the van on for the 1st time, if not the pads may have become contaminated.

Whilst you say nothing has changed in the van, are you sure rthat there arent any heavy items which have inadvertently been placed behind the axle, also was the cassette toilet flush empty.

 

[MikeMc]

Flush was indeed empty as it was our first trip of the year so all water had been drained as part of the over wintering.

There is no paint on the towball, its brass and was brand new so unless whitter coat them in oil prior to fitting there should have been no comntaminates on it.

One more thing I checked the noseweight upon arrival with the built in gague and it was 95kg.

 

[RogerP]

Hi Mike

dont know if this is any help but is the towball height different. Also did you check you cars tyre pressures?

Pressures on my car deffinately make a difference.

Finally , knowing that part of the M6 are you sure it wasn't rutting in the carriageway. The section 9-10 north is dire , it throws the car about on its own. Just a thourght.

 

[stevieg330]

Hi Mike,

Last year I had a similar thing happen. My normally stable van became a real handful and I also had a couple of snakes along the M5 which was a bit scary as we had not experienced it before.

After a bit of investigation I put it down to the fact that the correct type pressure for my van is 62psi but on the tow in question both tyres were 55psi.

I now have a digital tyre pressure gauge and a good electric pump and make sure that the tyre pressures on both the van and the car are correct before each journey.

Since I have started doing this I have not had a problem even in some quite high winds.

Hope this helps

Steve

 

[MikeMc]

RogerP - You may be onto something here, I did notice when hitching that I had to raise the jockey wheel almost to its full extent - but I dont see there is much I can do to change the height???

It happened when going downhill on the slip road joining the M6 which had quite a good finish so dont think rutting is the problem.

Steve - a digital pressure gague has just been ordered from ebay, I will do an all round check of pressures.

 

[rob_jax]

Mike,

You say the tow-ball was new - and had a brass finish. Sorry to say, but that "brass" is a protective layer - and it needs to come off - a 200 grit sandpaper will do the job.

And tyre pressures - higher pressure (car and caravan) means that the tyre side-walls are stiffer and should resist sway more - not less

So this brings us to the height of the tow-ball - this will have some significant effect - particularly if the caravan isn't running "level"

Robert

 

[MikeMc]

rob_jax - thanks, did not know that - emery cloth just ordered ( I am determined to get to the bottom of this snaking ).

 

[Royston]

Hi Mike, not sure about the colour of your towball,has it a brass or black coating.

Reason for asking is that if you have a ALKO hitch then you require the towball to suite.

This towball has standard diameter of 50mm but the lenght of the towball neck is longer than standard, this allows the stabilser to articulate to the required 25 degrees ensuring correct operation.

The alko towball fitted to my car had a black coating.

As RogerP said its a must to have your rear car tyres pumped up to the requirement for towing.

Royston

 

[MikeMc]

rob_jax - I have just been out to the carpark and inspected several cars with whitter tow ball covers. You are right, theirs are a dull steel colours whereas mine looks like shiney brass (as is slippy to the touch). From checking the Whitter site it says that it is a resin finish and should be removed. This is the first time I have heard of this in over 5 years of caravaning, I would have thought whitter would have been shouting it from the rooftops and it would be mentioned a lot more in hints and tips style articles. Or maybe it is and I have just been unlucky to not have come across one yet. Anyway thanks for the advise, I am sure that is the problem because it was just like driving without a stabilizer.

Best Regards

Mike

 

[Del_374232870]

I would also check (and possibly change) the pads in the stabiliser as it is possible that they have been contamited if you towed without removing the coating.

 

[Hamer_5041128]

Mike,

You stated you had to wind your jockey wheel right up to get it on the towball. Is your twin axle towing nose up. If so this will definitly affect stability. It is essential that your caravan tows level or slightly nose down. You can fit a drop plate between the tow bar and the towball. If you get a drop plate with 2 or 3 hole positions you should be able to get your caravan just right.

Hamer

 

[Garfield]

I passed a Pathfinder a few weeks back towing a big T/A and it's a long time since I saw anything so tail down, the rear wheels were up into the arches and the fronts hanging down, Perhaps he had bags of sand in the boot but perhaps the Pathfinders suspension is a little soft for towing, I would expect such a big, heavy car towing a twin axle to be stable without any stabiliser.

 

[ProfJohnL]

This thread just goes to show that good weight ratios do not guarantee a stable outfit.

Mikes problem is complex. He has changed quite a number of factors each of which will affect stability to some extent, but in combination may be more detrimental to the whole.

Factors such as, height of hitch and thus angle of attack for the airflow, distance between rear wheels and hitch, tyre pressure, suspensions etc - the list is quite long and is unlikely to be full resolved by correspondence on this forum - though hopefully a few pointers already mentioned by other co respondents may help.

With regards to tyre pressures, it is important to have the tyres inflated to the correct pressure for the duty they are to perform. Both under and over inflation are dangerous conditions and may lead to instability, and premature failure of the tyres.

I have to observe that the accuracy of domestic pressure gauges is always going to be suspect for two reasons.

Even in the best professional laboratory grade pressure gauges, there are many factors that affect the quality of the readings. Usually there is a set up procedure that is designed to minimise errors in the actual readings. Domestic gauges often have no set up procedures, and they are not calibrated. As a result consumer tyre pressure gauges can easily have errors of up to +-10%

Digital gauges are no better, in fact they can be worse as the have two conversions to make first from the pressure to an electrical signal, then the signal has to be digitised. This is two of many sources of errors that can be introduced.

Digital is not necessarily more accurate; it is just easier to read.

 

[stevieg330]

Hi,

With regard to the accuracy of digital gauges, in my experience they are far more accurate than the mechanical ones on the forecourts.

I have compared my gauge (which is supposed to be accurate to 1 psi) with some of the newer forecourt ones and also the gauge on my pump and everytime it is the same, so as far as I am concerned they are pretty accurate and IMHO it is certainly worth using one.

Regards

Steve

 

[rob_jax]

Hi Mike,

In continuation:

1. After you've removed the "brass" coating with a light rub from the sand-paper, you'll probably have already introduced a small amount of contamination (resin) onto the caravan tow-coupling friction pads.

If it's nice weather at the weekend, you may want to look at the surface of the friction pads (which means lying on the ground) and see if there's any resin transfer. But as they'll both be a brownish colour, you may just want to give the pads a light sand - just a few rubs - and try to maintain the existing shape of the pad surface. Basically don't rub too hard !

2. But I'm more concerned about the nose-up attitude you've described for the caravan.

Car tow-bars are designed (EC94/20) so that the centre of the tow-ball is at a height of 385mm (plus/minus 35mm) when laden. And caravan manufacturers (or rather the chassis builder) will aim for that height when building the caravan chassis.

It might be worth measuring the height of the tow-ball (centre), have someone who weighs about 75 kg sit on the boot lip to load the car suspension, and if it's widely different from 385mm - then you may want to consider a drop plate.

Robert

 

[mickk]

Hi Mike

Do not know if you have solved your stabillity problem yet but I once towed a large twin wheeled trail loaded with diving kit & two inflatable boats, which was very unstable when I towed it with my Granada I found that two of the wheels were only just making contact with the road, which caused a very violent snaking which dragged the car right across two lanes, (this is what caused the unstable towing) I lowered the towball so that all wheels made better contact, never had a problem again, so its worth checking your ball height, best of luck sorting yours out.

Mick K.

 

[MikeMc]

Thanks for all the suggestions, I will be trying them all once it stops raining. I was booking my van in for it's first service so I asked the service manager about this problem. He said that 44psi is way too high and they only ever put in between 32 and 34 on twins of that weight (this is Leisure Sales in Brereton). I pointed out that the manual said 44 but he just said that the more pressure the more the van would bounce around. He adviced reducing back to 34 (which I think is what they were before I raised them to the manual value). He also said that the only coating he thought needed removing was the black one, but it would not hurt to remove the brass one (so I will).

 

[ProfJohnL]

Hi,

With regard to the accuracy of digital gauges, in my experience they are far more accurate than the mechanical ones on the forecourts.

I have compared my gauge (which is supposed to be accurate to 1 psi) with some of the newer forecourt ones and also the gauge on my pump and everytime it is the same, so as far as I am concerned they are pretty accurate and IMHO it is certainly worth using one.

Regards

Steve

Hello Steve,

When considering the accuracy of the forecourt air lines, I agree that there is so much variation that they could not be relied on. However things are changing.

I believe that most of the in handle versions have been removed, They were highly susceptible to abuse or damage and thus their accuracy could be easily compromised. Not only that the gauges were often small with coarse graduations which can easily lead to incorrect inflation pressures. Trading Standards have been involved in some cases and Insurance companies were not happy with being made liable if a tyre failure proven to be the result of incorrect inflation as a result of one of these inaccurate gauges at a forecourt they cover. Most gauges are now mounted in the lane side pump housing, and use a larger more readable dial. They are better protected and more easily calibrated.

As for your digital gauge, it seems you have one that is providing a consistent reading, but despite that you still do not know how accurate it is. +-1psi sounds good, but unless it is accompanied with a test certificate it is still potential out.

Digital displays are too often assumed to accurate i.e. closer to the truth because you can apparently easily differentiate between one count of the smallest digit.

By way of a parallel example, most domestic Digital Multi Meters will claim a DCV accuracy of between 1 and 3% yet a 4 digit display will resolve to 1count in 9,999 which is 0.01% of full scale. In practice at actual 1% accuracy the meter should only be read to the Two Most significant digits, the least two are not within the calibrated range. Also due to the rounding and non linearity errors the specification should also state +- 1 count on the least significant figure, The key word here is 'significant' figure which is the 0.9 not the 0.009.

My point is that simply because it is digital, does not mean it is accurate. I have to fair, and also point out that analogues are not accurate either. But the marketing boys often use the public gullibility and false belief that digital is always best.

Just keep an open mind about it.

 

[MikeMc]

I think I may have found the problem, I measured the height of the towball with a 75kg weight and it came to 480mm. There is provision to lower the ball by 2 inches so I will give that a try, hook up the van and re-measure.

So does anyone know if I can re-use the bolts and washers when I lower it or do I need to replace them - like the wheel nuts on the van.

 

[Guest]

I used mine again when I fitted a snake plate on my car (some years ago admittedly) but had no issues after

 

[Fibre]

Flush was indeed empty as it was our first trip of the year so all water had been drained as part of the over wintering.

There is no paint on the towball, its brass and was brand new so unless whitter coat them in oil prior to fitting there should have been no comntaminates on it.

One more thing I checked the noseweight upon arrival with the built in gague and it was 95kg.

That seems ODD to me -- the special tow ball for the Alko hitch is always painted Black... the Brassy looking ones are the ones for "normal" tow hitches.. and have a special anti rust paint which makes it look golden or brassy..

I would check that you have the correct Alko tow ball hook for your type of hitch.. and then If it does come with Black paint on -- clean all of this off.. and dry it.. Then check that your pads in the tow hitch haven't become contaminated with the brassy stuff -- have a look -- they shouldn't look golden.. If they do you will have to clean them -- or change them.. I would go for the latter..

Maurice

 

[Hazel_374324904]

Hi Mike

We too have had the exact same problem as you, we also have a very similar van, Eldiss Superstorm, very long and very heavy. Within 2 weeks of purchasing the van our car was written off (not our fault). We decided to buy a landrover discovery, during our first couple of outings it was windy and we were driving on the motorway, we had very bad snaking, something i had never experienced before. Fortunately my husband is very experienced and we arrived safetly. After speaking to several people we were told our black tow ball was the cause. I went to Mendip Caravans (Now, Discover) Weston super mare and explained the problem and that i needed to buy a new tow ball. the sales man commented that he had never heard of snaking due to a painted towbar and tried to suggest we had bought a vehicle not suitable for the vans weight!!! Fortunately the manager did know what i was talking about and sold me a towball. It was shiney silver. Its been fitted and we have just returned from a 300 mile trip mostly on the motorway with no trouble at all. However after reading all the other comments we will check the pads for residue. Good luck and thankyou for highlighting this problem.

Hazel

 

[MikeMc]

I rang a professional towbar fitter who said that the tow ball height should be between 16 and 20 inches. Mine was 21. He charged me

 

[ProfJohnL]

Mike,

Whilst I know that you have tried various things to improve the stability of your outfit, I am very concerned that you may be illegal by lowering the tyre pressures. The correct tyre pressures should be given by the vehicle manufacture, and if by using a different pressure (lower or higher) then the vehicle does not conform to its type approval.

If a vehicle is used on a public road in an unapproved configuration, it may be deemed to be none roadworthy, which is of course a prosecutable offence, and it will also jeopardise your insurance cover.

You should seek the advice of the caravan manufacture as to the correct tyre pressures for the caravan.