Home built independent suspension?

[GeoTracker90]

Just wondering if any one has successfully designed and built their own independent trailer suspension? Looking through my trailer supply catalogs I can buy the spindles with the brake flanges and I'm tempted to try my hand at this.

I know that AT has their kit available, but it is a lot of fun to design and build my own stuff. In another post I shared the following picture of a trailer frame that I was modeling, but I thought I would start a thread specific to the suspension. If I try to go this route then I'll probably be looking at using air bags as well.

What are your thoughts guys?

 

[cowboy4x4]

At's arms are adjustable.....If it were me I would buys an axle that is straight NOT. the kind with the bow in it.mount it where you want make sure it it straight, add your arms, air bags then cut the center section out of the axle. JMO.

 

[WhereTheHellIsJames?]

Cool... another Rhino user. NURBS rocks!:jumping:

As far as the trailer goes, I don't think that it would be all that difficult, and I've actually entertained the idea of building my own as well. However, I have a little different idea about the suspension from the days where I was building racecars,but that'll wait 'till another post.

Words of advice from someone in the trailer business (hoggdavis.com):

Measure twice, weld once.

Make sure that you do all the math. The last thing that you want is to throw a bunch of money at a project that works crummy when you're done.

Also, I'd maybe do a stress analysis with whatever CAD program you're going to use for the final drawings. Figure out where your weak spots will be, and make sure you beef 'em up a bit.

Get creative- There are a lot of different ways that the suspensions for trailers made for off-road use can be improved upon.

Again... Do the math before fab (looks like you have this under control so far), and measure again and again before melting steel. Think "Alignment"!


Good luck with it, and make sure to keep us all posted on your progress. :26_7_2:

 

[UK4X4]

mmm stress analysis....that'll be fun..........

D = P x l^3 / 48EI

for those who like math..........me I'd go by experience.....

Now the arms would be only around 18"-20" Long...so 1/8" wall would be fine....if not overkill as there are two.

with one or two braces between the arms

looking at the design, from a fabricating view point, I'd miss out the cut and bend on the inner piece and go at an angle from the bushing to the spindle.

the inner mount really only limits the twisting of the outside bushing, the spindles available on the web are usually only 8" long, unless you do the mount and cut method....expencive in parts.......

But if you know of long spindles as per your design let me know....I'll be doing something similar soon.....basic frame is done and I'm working on the upper boxes right now
whilst I juggle the suspension plans....trailing arms or the more standard triangular yoke hinged from the center of the trailer.

Another thing I'm looking at is replacable spindles......as its a wear part long term...

spindle mounting inside a 1/4' thick 2" tube and bolted through.

a plate wrap welded from the arms around the tube and back on the arms would make a stronger joint than an angled butt weld.......especially if making in the garage rather than a factory angle cut ....ie I know I'll have weak points if I just butt weld

I guess your talking about using these too, as the bushings ?

http://www.ruffstuffspecialties.com/catalog/bushed-sleeve-p-148.html

 

[Martyn]

The difficult thing about trailing arms is that each weld makes the tubing bend in a given direction. Once all the welds are completed you pray it's all square. You pray it's square even when the assembly is clamped on a welding table in a template.

Adding to the issue is getting the spindle welded into the tube at 90' to vertical and horizontal. Did I mention that nasty internal seam on the tubing that needs to be addressed?

We have a 15 - 20 % rejection rate on trailing arms. And before anyone asks we dont sell the rejects.

 

[Photog]

Find an old IRS VW Beatle, and use the rear suspension from it. You could buy one of the aftermarket torsion tubes to save weight. All the suspension parts mount to the torsion tube. Then fabricate the shock mounts, and you are good to go.

All of the parts are available in the aftermarket, and you wouldn't need to find an old VW. These parts are much lighter weight also.

Shouldn't have any alignment issues either.

Just an idea, since you are still in the design phase.

Either way, it should be a fun project.

 

[Grim Reaper]

Find an old IRS VW Beatle, and use the rear suspension from it. You could buy one of the aftermarket torsion tubes to save weight. All the suspension parts mount to the torsion tube. Then fabricate the shock mounts, and you are good to go.

All of the parts are available in the aftermarket, and you wouldn't need to find an old VW. These parts are much lighter weight also.

Shouldn't have any alignment issues either.

Just an idea, since you are still in the design phase.

Either way, it should be a fun project.

Now thats an original idea!

70'sType 2 (bus) and Type 4's (wagon and fast back) are coil rear suspension. They have the coil buckets in the A-Arm. Easy to convert to air bags.

 

[MossMan]

The difficult thing about trailing arms is that each weld makes the tubing bend in a given direction. Once all the welds are completed you pray it's all square. You pray it's square even when the assembly is clamped on a welding table in a template.

Adding to the issue is getting the spindle welded into the tube at 90' to vertical and horizontal. Did I mention that nasty internal seam on the tubing that needs to be addressed?

We have a 15 - 20 % rejection rate on trailing arms. And before anyone asks we dont sell the rejects.

I've been thinking about this too and that's my biggest concern. You would have to have a very good jig for setting all this up. If not you'd be going through a lot of tires and bearings.

 

[mjm]

Can the alignment issues be addressed by fabricating with a single tube at the bottom (as in axle) and another where it connects to the frame? The tubes could be cut after everything is welded up. A good jig will still be needed.

Good luck!

 

[Rezarf <><]

Welding relatively thin material, like .125" wall tubing for instance, will warp, no matter how hard you try to keep it in place. From what I have read, controlling the warping is the hardest part of any suspension fabrication as it jacks around everything that started out square.

Leaving tubes in and cutting them out might help a little, but any of the "warping load" that is carried by that peice has the potential to come loose as soon as you cut away the material.

Leafs and shocks... or AT airbags/trailing arms, are the only logical choices for me.

I'd love to see someone try it though, and see if they can do it within an acceptable spec.

 

[ntsqd]

The VW bug isn't a great donor as it's IRS is part of the pan, but the T3 Variants use a removable rear subframe that could make a nice unit. I've considered building a buggy trailer out of one.

Some method of adjusting toe needs to be designed in. There are "rod ends" that use a urethane bushing instead of a ball. Most frequently seen on street rods.

 

[UK4X4]

I think you also have to understand the accuracy of chassis on vehicles.

on the average rangerover chassis they can easily be 3/8" to 1/2" out over the length......especially diagonals...

The rear wheels have no real adjustment because its not important....the front wheels yes as they steer the vehicle.

On a trailer it would make little or no diference if the wheels were miss aligned by 3/8" or more.

Tire wear at that amount would be negligable if not completely unseen....

especially when you consider the amount of miles you'd complete....

I started with a shop bought frame and it was easily 1/2" out on the diagonals
and still tracked fine.

I'm working to about 1/8" tolerance on the frame of my new one.....

The upper body was built matched to the frame.

Movement during welding is normal...and way worse on small wall tubing, the heavier wall you get the less movement you'll have.

And also small tack welds done first....beat the item into shape and then final weld the construction is an easy 'garage method' of getting less movement.

If you just completly weld one side....by the time you turn it over.....its changed shape...wether you clamped it down or not.

Front suspensions and alignment is highly important....and the manufacturers know they can't weld the parts to a sufficient tolarance...hence the in built adjustment in the design.

 

[Martyn]

I think you also have to understand the accuracy of chassis on vehicles.

on the average rangerover chassis they can easily be 3/8" to 1/2" out over the length......especially diagonals...

The rear wheels have no real adjustment because its not important....the front wheels yes as they steer the vehicle.

On a trailer it would make little or no diference if the wheels were miss aligned by 3/8" or more.

Tire wear at that amount would be negligable if not completely unseen....

especially when you consider the amount of miles you'd complete....

I started with a shop bought frame and it was easily 1/2" out on the diagonals
and still tracked fine.

I'm working to about 1/8" tolerance on the frame of my new one.....

The upper body was built matched to the frame.

Movement during welding is normal...and way worse on small wall tubing, the heavier wall you get the less movement you'll have.

And also small tack welds done first....beat the item into shape and then final weld the construction is an easy 'garage method' of getting less movement.

If you just completly weld one side....by the time you turn it over.....its changed shape...wether you clamped it down or not.

Front suspensions and alignment is highly important....and the manufacturers know they can't weld the parts to a sufficient tolarance...hence the in built adjustment in the design.

We designed a fully adjustable suspension for toe in and camber as we found that the slight variations in geometry resulted in different handling characteristics.

I'm thinking it's something we see due to the volume of trailers we manufacture, and our ability to test drive each one, and compare one with another.

I don't think that non adjustability is a deal breaker by any means, but we did find it sufficient enough to incorporate adjustment into our design.

 

[UK4X4]

"We designed a fully adjustable suspension for toe in and camber as we found that the slight variations in geometry resulted in different handling characteristics.

I'm thinking it's something we see due to the volume of trailers we manufacture, and our ability to test drive each one, and compare one with another."

Thats why you have a superior product......


its not required but to improve handling the adjustment is there.

The only vehicle I've personally worked on that had adjustable rear suspension systemns were Porsche 944, and 911's

 

[Grim Reaper]

I think you also have to understand the accuracy of chassis on vehicles.

on the average rangerover chassis they can easily be 3/8" to 1/2" out over the length......especially diagonals...

The rear wheels have no real adjustment because its not important....the front wheels yes as they steer the vehicle.

On a trailer it would make little or no diference if the wheels were miss aligned by 3/8" or more.

Tire wear at that amount would be negligable if not completely unseen....

especially when you consider the amount of miles you'd complete....

I started with a shop bought frame and it was easily 1/2" out on the diagonals
and still tracked fine.

I'm working to about 1/8" tolerance on the frame of my new one.....

The upper body was built matched to the frame.

Movement during welding is normal...and way worse on small wall tubing, the heavier wall you get the less movement you'll have.

And also small tack welds done first....beat the item into shape and then final weld the construction is an easy 'garage method' of getting less movement.

If you just completly weld one side....by the time you turn it over.....its changed shape...wether you clamped it down or not.

Front suspensions and alignment is highly important....and the manufacturers know they can't weld the parts to a sufficient tolarance...hence the in built adjustment in the design.

It really is amazing just how much cars are off.

My buddy use to work For SAAB in warranty parts testing in Atlanta. SAAB had to buy a convertible back from a customer. They could not get the top to work correctly. It took two people to get the top to latch and then the windows didn't seal.

They finally got all the body dimensions and started measuring. The body at the top of the door opening was over 1/2 wide and out of tolerance. The car was actually bowed up in the middle. The Top was out the opposite direction. Top and windows down you could not tell with your eye the car was off at all.

SAAB used it as a shop car for a while and never put the top up on it. At the end of the model year I watched my buddy cut that brand new car up and throw it into a scrap metal dumpster after he harvested everything he could off it. He ended up taking the complete electrical system and putting it on a couple sheets of plywood to use for training.