Post by fccool on May 15, 2021 11:59:46 GMT 10
I know I did this the wrong way around but I have gone too far into restoring my caravan to think about removing the chassis.
My chassis is a web truss type quite similar looking to the chassis found under a sunliner, so much I am certain it's from the same factory in Newcastle as the sunliner chassis.
The chassis didn't look so bad till I spent a couple of weekends poking, scraping, proding, wire wheel, cup brush, flap disc, flap wheel, sanding and acid.
The chassis was one galvanized and then gone ever a few times with cold gal or maybe even just silver frosing brushed on, the chassis has now been quite thoroughly and painfully stripped with a cup brush on a grinder and different size wire wheels, flap wheels and flap discs and then scrubbed with phosphoric acid, rinsed, dried with metho before being painted with aldi metal car enamel with a penetrol additive that is not only supposed to penetrate rusted surfaces but also allow paint to bond to galvanized surfaces
Since I have no idea what I am doing when it comes to caravans I thought I might do some research on how to deal with this type of chassis, from this type of chassis and how it works, unfortunately there is next to no information on the internet about a web truss chassis like those in sunliner thrisftmaster and gypsy but from what I gathered it was aircraft technology superior in strength and low weight to a conventional beam chassis, it was often a extra cost option or standard on more expensive models.
The design was much slower to manufacture and required higher skilled workers to build compared to conventional chassis and due to this became less common.
Perhaps the factory making them closed up or stoped making the web truss design after manufacturers like sunliner and gypsy closed up.
Looking into tube Webb truss design the tube should probably be sealed air tight, in some aircraft manufacturing air was expelled or burned from inside the tube to prevent corrosion as the end of a truss cord tube was sealed.
Web truss tube space frames were often used in the construction of aircraft for maximum strength and minimal weight.
It was also common for the tube used in aircraft to be coated inside with a rust preventative such as linseed oil.
Someone times a tube had a screw or removable end cap that allowed more linseed oil to be put into the tube.
A well sealed tube from vintage aircraft is often found to still be like new inside if cut open.
Not all welds were completely air tight Wich could allow air into the tube.
By taping fittings into the tube a pressure test could be done to work out if a weld leaks.
Chords can rust inside due to condensation, air and water.
On a caravan the greatest stress point is where the draw bar is attached to the front crossmember.
I'm m not sure what the crossmembers are like on sunliner but on my gypsy there is only a 1x1" box running across the bottom edge where the wall meets the floor, above this is the floorboard and above the floorboard is the bottom of the wood caravan body frame.
The crossmembers are not very heavy duty, you can see they were really trying to minimize weight and it has me a little bit worried since I have found a fair bit of rust around.
My first thoughts were to mig in new patches and pieces.
But from alot of what I have read you should not be welding around the draw bar since the heat from the weld will change the tensile of the metal and cuase a crack.
I am not really finding anything anywhere on the internet about repairing a web truss caravan chassis like those found on gypsy and sunliner.
A web truss design could possibly differ becuase of the spread of stress point.
attached the front crossmember is two parallel top truss chords joined by overlapping, at this point a gusset plate was used below the front crossmember attaching the top chords to the bottom parallel truss chord, the bottom chord is one contionuos tube from the tow ball hitch to the suspension while the top stops under the front crossmember box and overlaps the top parallel chord that runs from the crossmember to a upright chord attached to the torsion axle tube mounting plate at the end of the parallel truss,a angular truss starts behind the axle with the bottom chord rising closer to the floor towards the rear
I have found rust holes at each corner of the caravan chassis floor frame in the outermost 3" of the rear most crossmember where the back wall meats the floor and the front wall meats the floor.
The floor boards look imaculate, maybe they have some asbestos in them making them indestructible.
There is some heavy pitting that has eaten into the metal mainly in the lower cross tube between the parrallel truss rails.
While the rear rails only support the rear of the frame the front crossmember box is also welded to a truss chord that goes across the front and attaches to the lower chords of the drawer bar.
I have thought of a few ways to tackle this but then after spending a couple of weeks under the caravan I moved the stuff I had holding up the front of the draw bar so I could clean up the coupling area and now with acsess to the front of the draw bar I started cleaning up underneath and found flakey rust on top of the lower chords where the top and bottom draw bar chords are attached to each other under the coupling.
As bad as this sounds it looked like you could quite well tow the van for years without a issues even though it would not pass a rego inspection, but then I sat there thinking about all the what if's with visions of my car being totalled and everyone killed in a one mile radius all my fault die to my carelessness and neglect and I ended up welding up the holes with the mig turned down fairly low and then braced between the inside join between the upper and lower cord where they meet each other under the coupling with some rod the same thickness as the rod used in the original truss braces with a bit more heat.
It looks like maybe it wasn't moisture getting into the tube and sitting on the bottom but condensation inside the top of the lower chord tube or a build up of dirt at some stage holding moisture ontop of the tube hidden below the coupling holding moisture on the outside of the tube.when I purchased the caravan the rear wind up stands were removed and the previous owner had just fitted a brand new jockey wheel, I'm guessing this could have spent years outside resting on either its draw bar or bum.
One tube has a big rust hole at the end I have left open to fit my my inspection camera inside before I cap it off, the plan then was to drill holes at the end of the truss chords and tap them for screws so I have acsess to spray penetrol rust preventative inside the chords.
At first I had planned to ad another lighter angular truss below the drawbar extending about 10" past the front crossmember like seen on more modern caravans were a truss is added under the box A frame but then I worried out heat affecting the metal in high stress sections of the lower draw bar chord, I wanted to make up for any strength loss from corrosion and I am still not sure enough if welding to the bottom cord will do more bad than good so I haven't done that yet.
Being a newby to caravans and trailers I'm not sure how critical strength is in what areas apart from laying underneath trying to think how heavy braking, fast acceleration, cornering and rough roads put strains, pushing, pulling, twisting and shocking , I drive trucks for a living and know where to find cracks in some different design truck trailers with a draw bar and had to have gussetts and plates welded in but this thing is only probably 700kg, 1100 loaded up, the axle is much closer to the draw bar than a truck trailer and forces are probably more up and down than just pushing down.
Also on a truck trailer dray bbar you might have about 8" of height in a beam, you might notice a 1" crack and it might not go much further for a week or two, but 1" on a truss cord is just about the hole cord broken and double the stress now on the top cord, the way the truss frame looks it cleverly makes alot of strength that would be hard to break becuase each part of the frame is helping to make it rigid but if one of those parts failed it could become pretty weak and if two close by sections failed it could start going bad pretty quick but looking at the caravan draw bar for a while and then looking at the basic design of our larger modern box trailer I am now wondering how the hell do box trailers or conventional a frames survive with their primitive basic design.
Another consideration is how these are used today compared to how they were used in the 1950s-60s.
We see old black & white photos of these things in remote areas, in the bush, on corrugated dirt tracks, on beaches and the windy hills, long dirt roads on mostly unsealed Wich makes you think they would have had to be built quite durable and to think these days to get to those areas people need to use specail caravans with a big heavy chassis, 6 stud off road wheels and specail off road raised suspension towed behind 4wd vehicles with a 3500kg towing capacity and heavy duty chassis with anti lock braking , computer controlled stability control and braking Wich still seem to end up smashed to pieces on the side of the highway every week.
Thinking these old vans were towed from Sydney to gold coast in the 1950s usually sitting on wild angles by underpowered cars with small drum brakes and narrow cross ply tires, sometimes cable operated brakes and a non synchro 3 speed gearbox , how did they even do a whole return trip without dieing?
But the thing about today is the highway traffic is moving at 110kph, truck trailers are much larger and make more wind and move along at 100 kph on the flat, down hill and uphill. the highways now are flatter, smoother straighter with more lanes but this also means you have vehicles passing at high speed for pretty much your whole trip from Sydney to gold coast instead of stuck behind you.
So I guess a caravan these days needs to handle and stay together at high speed or you are dead and with high wind for longer periods, the old trips of driving through towns and stopping, stretching the legs are no longer, even if we try it is now easy to leave Newcastle and forget to stop, before you know it your in coffs harbour these days you fill up at a service center and drive for 500 kilometers in under 5 hours. A vehicle moving slow on the highway is a dangerous object in the path of alot of high speed traffic.
Also these days even classics tow cars might be upgraded with larger engines, bigger boosted disc brakes etc giving them more sudden stopping and acceleration and stiffer suspension, this too I assume could affect stress on the caravan.
One thing I have been thinking is if it is better to stick to he old highways, the problem here is that they are poorly serviced once they are bypassed, some towns the road of the old highway seems to be more pothole than road.
Would this be harder or more dangerous than the new freeway it was replaced by?
So if you read this far and are still here I guess what I am asking here is if you have or had a web truss type chassis in a caravan like a sunliner or gypsy, did you ever find major rust? and how did you deal with it without replacing the chassis and how did the repairs hold up? How did you maintain it?
What is the longest or hardest trip you did with it and we're there any issues with cracks, welds or torsion suspension?
Did you add any weight to the van, extra gas bottles, spare wheels etc? Did it cause issues?
My chassis is a web truss type quite similar looking to the chassis found under a sunliner, so much I am certain it's from the same factory in Newcastle as the sunliner chassis.
The chassis didn't look so bad till I spent a couple of weekends poking, scraping, proding, wire wheel, cup brush, flap disc, flap wheel, sanding and acid.
The chassis was one galvanized and then gone ever a few times with cold gal or maybe even just silver frosing brushed on, the chassis has now been quite thoroughly and painfully stripped with a cup brush on a grinder and different size wire wheels, flap wheels and flap discs and then scrubbed with phosphoric acid, rinsed, dried with metho before being painted with aldi metal car enamel with a penetrol additive that is not only supposed to penetrate rusted surfaces but also allow paint to bond to galvanized surfaces
Since I have no idea what I am doing when it comes to caravans I thought I might do some research on how to deal with this type of chassis, from this type of chassis and how it works, unfortunately there is next to no information on the internet about a web truss chassis like those in sunliner thrisftmaster and gypsy but from what I gathered it was aircraft technology superior in strength and low weight to a conventional beam chassis, it was often a extra cost option or standard on more expensive models.
The design was much slower to manufacture and required higher skilled workers to build compared to conventional chassis and due to this became less common.
Perhaps the factory making them closed up or stoped making the web truss design after manufacturers like sunliner and gypsy closed up.
Looking into tube Webb truss design the tube should probably be sealed air tight, in some aircraft manufacturing air was expelled or burned from inside the tube to prevent corrosion as the end of a truss cord tube was sealed.
Web truss tube space frames were often used in the construction of aircraft for maximum strength and minimal weight.
It was also common for the tube used in aircraft to be coated inside with a rust preventative such as linseed oil.
Someone times a tube had a screw or removable end cap that allowed more linseed oil to be put into the tube.
A well sealed tube from vintage aircraft is often found to still be like new inside if cut open.
Not all welds were completely air tight Wich could allow air into the tube.
By taping fittings into the tube a pressure test could be done to work out if a weld leaks.
Chords can rust inside due to condensation, air and water.
On a caravan the greatest stress point is where the draw bar is attached to the front crossmember.
I'm m not sure what the crossmembers are like on sunliner but on my gypsy there is only a 1x1" box running across the bottom edge where the wall meets the floor, above this is the floorboard and above the floorboard is the bottom of the wood caravan body frame.
The crossmembers are not very heavy duty, you can see they were really trying to minimize weight and it has me a little bit worried since I have found a fair bit of rust around.
My first thoughts were to mig in new patches and pieces.
But from alot of what I have read you should not be welding around the draw bar since the heat from the weld will change the tensile of the metal and cuase a crack.
I am not really finding anything anywhere on the internet about repairing a web truss caravan chassis like those found on gypsy and sunliner.
A web truss design could possibly differ becuase of the spread of stress point.
attached the front crossmember is two parallel top truss chords joined by overlapping, at this point a gusset plate was used below the front crossmember attaching the top chords to the bottom parallel truss chord, the bottom chord is one contionuos tube from the tow ball hitch to the suspension while the top stops under the front crossmember box and overlaps the top parallel chord that runs from the crossmember to a upright chord attached to the torsion axle tube mounting plate at the end of the parallel truss,a angular truss starts behind the axle with the bottom chord rising closer to the floor towards the rear
I have found rust holes at each corner of the caravan chassis floor frame in the outermost 3" of the rear most crossmember where the back wall meats the floor and the front wall meats the floor.
The floor boards look imaculate, maybe they have some asbestos in them making them indestructible.
There is some heavy pitting that has eaten into the metal mainly in the lower cross tube between the parrallel truss rails.
While the rear rails only support the rear of the frame the front crossmember box is also welded to a truss chord that goes across the front and attaches to the lower chords of the drawer bar.
I have thought of a few ways to tackle this but then after spending a couple of weeks under the caravan I moved the stuff I had holding up the front of the draw bar so I could clean up the coupling area and now with acsess to the front of the draw bar I started cleaning up underneath and found flakey rust on top of the lower chords where the top and bottom draw bar chords are attached to each other under the coupling.
As bad as this sounds it looked like you could quite well tow the van for years without a issues even though it would not pass a rego inspection, but then I sat there thinking about all the what if's with visions of my car being totalled and everyone killed in a one mile radius all my fault die to my carelessness and neglect and I ended up welding up the holes with the mig turned down fairly low and then braced between the inside join between the upper and lower cord where they meet each other under the coupling with some rod the same thickness as the rod used in the original truss braces with a bit more heat.
It looks like maybe it wasn't moisture getting into the tube and sitting on the bottom but condensation inside the top of the lower chord tube or a build up of dirt at some stage holding moisture ontop of the tube hidden below the coupling holding moisture on the outside of the tube.when I purchased the caravan the rear wind up stands were removed and the previous owner had just fitted a brand new jockey wheel, I'm guessing this could have spent years outside resting on either its draw bar or bum.
One tube has a big rust hole at the end I have left open to fit my my inspection camera inside before I cap it off, the plan then was to drill holes at the end of the truss chords and tap them for screws so I have acsess to spray penetrol rust preventative inside the chords.
At first I had planned to ad another lighter angular truss below the drawbar extending about 10" past the front crossmember like seen on more modern caravans were a truss is added under the box A frame but then I worried out heat affecting the metal in high stress sections of the lower draw bar chord, I wanted to make up for any strength loss from corrosion and I am still not sure enough if welding to the bottom cord will do more bad than good so I haven't done that yet.
Being a newby to caravans and trailers I'm not sure how critical strength is in what areas apart from laying underneath trying to think how heavy braking, fast acceleration, cornering and rough roads put strains, pushing, pulling, twisting and shocking , I drive trucks for a living and know where to find cracks in some different design truck trailers with a draw bar and had to have gussetts and plates welded in but this thing is only probably 700kg, 1100 loaded up, the axle is much closer to the draw bar than a truck trailer and forces are probably more up and down than just pushing down.
Also on a truck trailer dray bbar you might have about 8" of height in a beam, you might notice a 1" crack and it might not go much further for a week or two, but 1" on a truss cord is just about the hole cord broken and double the stress now on the top cord, the way the truss frame looks it cleverly makes alot of strength that would be hard to break becuase each part of the frame is helping to make it rigid but if one of those parts failed it could become pretty weak and if two close by sections failed it could start going bad pretty quick but looking at the caravan draw bar for a while and then looking at the basic design of our larger modern box trailer I am now wondering how the hell do box trailers or conventional a frames survive with their primitive basic design.
Another consideration is how these are used today compared to how they were used in the 1950s-60s.
We see old black & white photos of these things in remote areas, in the bush, on corrugated dirt tracks, on beaches and the windy hills, long dirt roads on mostly unsealed Wich makes you think they would have had to be built quite durable and to think these days to get to those areas people need to use specail caravans with a big heavy chassis, 6 stud off road wheels and specail off road raised suspension towed behind 4wd vehicles with a 3500kg towing capacity and heavy duty chassis with anti lock braking , computer controlled stability control and braking Wich still seem to end up smashed to pieces on the side of the highway every week.
Thinking these old vans were towed from Sydney to gold coast in the 1950s usually sitting on wild angles by underpowered cars with small drum brakes and narrow cross ply tires, sometimes cable operated brakes and a non synchro 3 speed gearbox , how did they even do a whole return trip without dieing?
But the thing about today is the highway traffic is moving at 110kph, truck trailers are much larger and make more wind and move along at 100 kph on the flat, down hill and uphill. the highways now are flatter, smoother straighter with more lanes but this also means you have vehicles passing at high speed for pretty much your whole trip from Sydney to gold coast instead of stuck behind you.
So I guess a caravan these days needs to handle and stay together at high speed or you are dead and with high wind for longer periods, the old trips of driving through towns and stopping, stretching the legs are no longer, even if we try it is now easy to leave Newcastle and forget to stop, before you know it your in coffs harbour these days you fill up at a service center and drive for 500 kilometers in under 5 hours. A vehicle moving slow on the highway is a dangerous object in the path of alot of high speed traffic.
Also these days even classics tow cars might be upgraded with larger engines, bigger boosted disc brakes etc giving them more sudden stopping and acceleration and stiffer suspension, this too I assume could affect stress on the caravan.
One thing I have been thinking is if it is better to stick to he old highways, the problem here is that they are poorly serviced once they are bypassed, some towns the road of the old highway seems to be more pothole than road.
Would this be harder or more dangerous than the new freeway it was replaced by?
So if you read this far and are still here I guess what I am asking here is if you have or had a web truss type chassis in a caravan like a sunliner or gypsy, did you ever find major rust? and how did you deal with it without replacing the chassis and how did the repairs hold up? How did you maintain it?
What is the longest or hardest trip you did with it and we're there any issues with cracks, welds or torsion suspension?
Did you add any weight to the van, extra gas bottles, spare wheels etc? Did it cause issues?