Tow Itch wrote: I understand some bits of this but there are some issues that are beyond me please feel free to ccorrect me as I err.
This whole thing is a steep learning curve for me so I am very grateful for everyone's thoughts.
Tow Itch wrote: The coupling is an AL-KO delta coupling and though I cant read mine. I believe it's rated from a lower mass to a maximum of 700Kg
I am replacing the coupling with an Al-Ko with a built in stabilizer rated at 200kg-3000kg so that should be ok.
Tow Itch wrote: The Indespension suspension units are 500Kg units of the Knott type brakes (not AL-KO)
See the picture below. The Knott brakes are adjusted by a bolt not the star adjuster of AL-KO types. Yes I know if you look the whole axle is of a Knott type but it's the only photo I could find.
I want to both sort out the ride height and increase the weight capacity. If I stick with Indespension then I can replace the Indespension 500kg units with either 750kg or 1000kg units. There are a few issues.
a) 750kg units are available with 2 wheel bolt patterns, one is the same as the 500kg and the other the same as the 1000kg. I like the idea of moving to larger wheels to help with the weight capacity and also the ride height so the heavier duty wheel bolt pattern of the 750/1000kg units apppeals.
b) I would want to move the mounting forward so that the axle is in the same place. At the same time I would want to insert spacers to move the mounting down to increase the ride height.
c) Having read one thread where someone noticed that the suspension units had always been misaligned I have a slight preference for a system which comes with a full axle so that I know the wheels will definitely be parallel.
If I used the Indespension units my idea would be to get 2 of the 6 bolt mounting plates from Indespension per side. I would weld 2 lengths of 50mm box section running longitudinally between the two sets of bolt holes of the top plate and then weld the bottom plate onto the same box sections but offset forward enough to compensate for the longer swing arm of the suspension unit. (the cramped space between the box sections for welding the inside joints is the key challenge with this idea).
It is a bit like the solution Bilbo did but instead of having a single beam running across the Dandy and spacing the mounting plates vertically I would space the mounting plates with 2 short box sections per side each running forwards then the plates can be offset from each other without blocking any of the bolt holes.
The result would be that the axle would be in the same vertical place when unladen despite the longer arm. But it would be a bit lower to correct the ride height.
Tow Itch wrote: The spring or energy store I have never understood. I don't know if its an old Indespension design it doesn't look like their current energy store. It looks more like a Knott or Bradley item. Anyone know for certain?
I hadn't thought the energy store. You are right, if I decide to go beyond 750kg am going to have to look at upgrading this to the same weight capacity as everything else. H'mm that makes sticking to a 750kg limit more attractive.
Tow Itch wrote: I spoke to Ian at Riva about 750Kg suspension to see if he had any reservations. Be it frame strength or whatever, but no despite being less than happy about many mods he sees he has no issues about 750Kg suspension.
I have emailed him about the issue and whether he would be interested in doing the work, I have had no reply yet.
Tow Itch wrote: The dimensions of the different sized units are shown here.
With off the top of the head maths the 500Kg unit has the axle 54mm behind the centre line of the suspension.
The 750Kg unit is 80mm. So that is a difference of 26mm. The difference in the width of the mounting holes is 19mm so quite where the writer got a difference of 50mm from I don't know. I would check these dimensions against ones supplied by Indespension or whoever you use.
I have only done the detailed calculations for the Al-Ko solution so far. Basically I started with a cardboard cut out of the wheel that covered the full space needed through the whole suspension movement. That confirmed that providing I dropped the axle by 55mm I was ok. In fact due to the size of the Al-Ko unit it has to drop by more than this (or the suspension mountings end up almost in the caravan :-) That is ok as it contributes to the levelling of the Dandy. When I lined it all up it was just a fortunate co-incidence that the rear of the Al-Ko mounting could re-use the rear hole of the existing mounting, so all I need to do is create a new front mounting.
Tow Itch wrote: So I'd check the upper mass on the coupling if it is 700Kg then that's the limit but I'm going off a non Dandy AL-KO unit I've never been able to read my coupling.
If your thinking of going to 900Kg you will almost certainly be looking at a new coupling.
Coupling is fine as I was changing that anyway. The energy store is what I had forgotten.
Tow Itch wrote: If your considering new wheels and you may have to be looking at a new coupling then I'd say look at all the options.
You can look at whatever combination of coupling,suspension and wheel suit you.
There are a lot of options aren't there!
I feel reasonably comfortable narrowing it down to Indespension (easy sell because that is what is currently fitted) and Al-Ko (because it seems to me to be the industry standard for Caravans so again an easier sell).
Tow Itch wrote: I might give Riva a call to see how Ian feels about you upping to 900Kg
Agreed. Maybe email isn't his thing. I am still interested in him doing the work as I don't have lots of time. Plus I still need to get someone to issue a new trailer plate with the new weight capacities on it and he is the obvious person to do that.
Tow Itch wrote: If your going to go to a high enough mass and keep the dandy long enough then you can choose your features all that constrains is the cost. Sealed for life bearings, self adjusting brakes and even electronic stability systems or just as simple a mod as changing the PCD to one that suits your choice of wheel.
I can easily get carried away with fancy ideas :-) However, I also want to be able to get this done reasonably quickly so will try to resist the temptation to built the ultimate chassis.