Dual Axle Suspension Help

[Needmorerum]

Righto all you guru's out there. I've got some problems with my suspension on my big boat. It is a standard Tinka trailer, dual axle obviously, and the springs keep inverting. I've got a number of pictures below showing what they are doing.
What I am asking, is, if possible, can I get some of you guys that have the same set up to put some photo's up of how yours is set up, and give me some ideas.
This only happens when I go over a driveway that puts the springs at full travel. I can take a stab in the dark at what the remedy is, but, installing anti-inversion plates at this stage shouldn't be necessary. I would have thought that this could be set up to work as it should.
Any help would be appreciated.

Corry

[Needmorerum]

This photo shows the centre pivot point of the two springs.

[Needmorerum]

Again, from a different angle.

[Needmorerum]

The other side. Does the same.

[Needmorerum]

From further back. Shows the rear shackle and the front hanger.

[Needmorerum]

As you can see in some of the photo's, there are other options for where the pivot points are, in the centre and at the front.
I have changed the centre pivot point to the top hole, and the front pivot point to the botton hole.
As the photo below shows, this makes the upper part of the centre pivot shackle very close to the trailer chassis. How this goes on the road I don't know at this stage, I will have a look over the weekend.
The centre shackle sits good when it is not inverted and travelling normal. It only inverts when I have to take the trailer over a sharp driveway. And this is most times it is out. It is getting to be a pain in the but putting trolley jacks under the shackles to try and put them back to normal each time.
The trailer is only 18 months old and I'm know this shouldn't be happening.

Corry

[blaze]

Hi Corry
My thoughts are that the rocker arm is to short, maybe if ya run the tape over it and posted the measurement some one could measure there rocker
cheers
blaze

[Needmorerum]

Done,
Rocker arm is 250mm from centre to centre.

Front and rear spring is 740mm centre to centre, as set up in the last photo.

And, spring shackle length is 90mm.

Hope this assists.

Corry

[Big_Kev]

The center post is set high to give clearance.
When traveling over terain that makes for full travel and obviously past the point it is inverting. The pics show that.
Perhaps stopper plates welded to the rocker box to prevent the rocker box traveling so far will correct the problem and you will get one wheel lift into the air when traveling accross the gutter.

[NQCairns]

Dunno might help,to me it looks as if your springs are shot, they may have simply relaxed to a point that each individual spring no longer has the weight bearing capacity it had when in spec.
Pull the rig onto level ground and take notice of how far past vertical the hangers are, they will tell a story pretty quick if it is the case.
I built myself a single axle trailer not long ago and opted for the heaviest springs available to suit. These springs with a partly gutted boat without engine have already relaxed to a point where I am unhappy with them and the trailer has not moved from the spot where the springs were fitted, they were good brand ones also or so I thought.
nq

[Needmorerum]

So what your saying Reel Hard, is that when the centre of the rocker arm is at the lower pivot point, this is to raise the suspension. So where I have put it won't hurt, it just won't give as much clearance. Maybe I should put the front pivot point of the front spring back to the upper point. I'm not after long travel, I just need it to be able to negotiate a driveway once a trip. The rest of the time is on normal roads.
I wouldn't have thought I would need to weld on any stopper plates (anti-inversion plates). Is there anyone that has these fitted. The driveways that cause the springs to invert are most of the servo driveways. It isn't just the 'extreme' ones.

Comon' surely someone out there has a dual axle set up similar that can post some photo's.

Corry

[jimnbob]

Corry

A couple of questions.

Is the pivot point of the centre rocker mid length? ie 125mm from the rear spring pin to the pivot point.

Secondly, what is the front spring centre to centre distance when it is supporting the weight of the wheel and axle load. I assume the 740mm measurement is taken with a jack under the axle and the shackle loose. To measure this distance jack the trailer and lift the front trailer wheel. If your front spring is too "bendy" and shortening the centre to centre distance, this could be allowing the shackle to 'reverse'. The solution may be to move the front spring mount backwards say 20mm thus stopping the pivot bar and shackle steightening.

Jim

[FLATHEAD1]

Bolt the spring to the rocker arm and move the shackle to the other end (fixed end of the trailer).

Problem solved.

Cheers
FLATHEAD1

[NQCairns]

Flathead - that is a great call [smiley=thumbsup.gif] when looking at it now it looks like someone put it together wrong, even butchered by compressing the cantilever :o

[Big_Kev]

So what your saying Reel Hard, is that when the centre of the rocker arm is at the lower pivot point, this is to raise the suspension. So where I have put it won't hurt, it just won't give as much clearance. Corry

YES.

Putting the ROCKER pivot point closer to the chassis will limit the travel of the rocker the same as adding the stop blocks like I earlier said.
But the trailer will carry the boat closer to the ground, and you may find that the arse of the boat will hit the driveways.

Therefore if needed to locate the rocker in the lower pivot point to keep the travel height higher, stoppers to limit rocker travel will be needed.

This will prevent spring over center.

What is needed to be acheived is
STOP THE ROCKER TRAVELING TO THE POINT WHERE THE SHACKLE AND ROCKER STRAIGHTEN AND GO OVER CENTER.

A floor jack under the back axel will lift the trailer and recreate the same affect as is happening on the driveway.
Doing this will allow to determine where to place the stopper.

When in place and towing the trailer you will see the front axel lift in the air when going over a driveway and all weight go on the one axel. (Just like a semi trailer does.)
Slow travel over driveways when this occurs is recomended.

Disclaimer-
Any modifcation to the trailer should be carried out by the manufacturer of such trailer and certified by an engineer.


Cheers Reel Hard.

[aido]

here's my setup...

http://users.tpg.com.au/adessaix/springs.JPG

when i go over gutters, 1 axle suspends in mid air like reel hard says.

the end of the pivot plate with the hanger link is fwd.

[Needmorerum]

aido, I would have thought that the shackle at the front of the rocker arm should be down, that is with the spring under the rocker arm, not above.

I am going to take FLATHEAD1's advice and move the shackle to the other end, so it is not at the rocker arm. This makes good sense when you sit back and think about it.

Corry

PS. Will probably do this over the weekend if the weather doesn't allow me to get out, if not, I will do it next week. Will post up how it goes.

[SeaSaw]

Corry,

My centre rocker arm is set up the same way as Aido's with the spring above the rocker arm and the hanger is on the front spring side.

The front end of the front sping is connected straight onto the bracket on the trailer frame, while the rear end on the rear spring is connected via another hanger.

Yours looks all backwards to me. Good luck

Mark

[Big_Kev]

I am going to take FLATHEAD1's advice and move the shackle to the other end, so it is not at the rocker arm. This makes good sense when you sit back and think about it.

Corry


I think this will cause bump steer, and you will loose the lot at speed.

[Needmorerum]

I think this will cause bump steer, and you will loose the lot at speed.


Can you explain what 'bump steer' is?
I'm not sure which way to go now. I had a look at a new Dunbier trailer today, they have dual slipper springs. I've been looking at every dual axle trailer I go past and none of them seem to be the same.
Still open to hear/see how others are set up. Will hold of changing anything for now.

Corry

[Big_Kev]

Putting a moving point at the front of the leading spring/axel as well as at the rear of the axel will cause a change the angle of the axle across the chassis when only one wheel hits a bump.
Thus causing the trailer to steer itself when it hits a bump.
Can be dangerous as the trailer re-acts and then steers the other way.
Might cause the trailer to fishtail and turn the whole show around.

Have you contacted the manufacturer yet, or gone back to the dealer for a solution?
They should be only to willing to offer advice.
I recomend you contact the manufacturer for advice before you do any modification, even take the trailer to them and explain what the problem is.

[Needmorerum]

Typically, the dealer that supplied the trailer, has now closed down.
Searching the web, I have come across the below photo. The link to this site is http://www.industrialsprings.com.au/ies1007.htm.
What is the perception of this setup? Having both shackles on the rocker arm. Would this cause 'bump steer' on the rear axle.

Corry

[Big_Kev]

The rear spring has a pivot fixed solid to the chassis.
Also note the difference of e and f. ie;the springs can be installed the wrong way around.

[Big_Kev]

.

[Cheech]

I wish there was just one way. Now I am wondering if mine is right.

Both mine are facing the same way. Front of front spring is fixed and back is sliding. This back end is straight on to the centre swing. ie there are no short upright extensions. Then the back spring is fixed direct to the other side of the centre swing. And the back of the back is sliding and that is straight to the trailer.

Cheech

[Needmorerum]

I think I've opened up a big can of worms here. Would it be possible to ask those that have dual set ups, to take a piccy of them and throw them up. I wouldn't mind comparing some of the options.

Corry

[dnej]

I phoned my mate who is in the business.

NB. Both ends of each spring, should have a pivot point, and the short part of the spring should be towards the centre .

He said that when the springs drop down, generally extending the length of the central pivot point bar, will stop providing room for the shackle to swing down.

The springs in other words are to far apart in the middle . There should not be room for them to get through the space created by the hanger, and the end of the spring pivot.
Hope this helps
David

[Needmorerum]

David, I get the part where he suggests that both the short ends of the springs shoudl be in the middle, but where are the shackles. In the middle on the rocker arm, or at the chassis ends, or the front one at the rocker arm, and the back one at the chassis?

Corry

[dnej]

Corry, hope this helps.
David

[searaider]

Corry ,
I hate to say it but I think some has had your suspension of and reinstalled it backwards .
I have just had a look at my 2 year old Tinka classic & it has the same set up as aido & SeaSaw . I took some photo's I hope this helps .

Peter
Searaider 2

First Photo is looking from the front looking towards the back of the trailer .

[blaze]

Hi David
I believe thats what i suggested at the start of the thread
cheers
blaze

[searaider]

2nd Photo ,
Front of the trailer is on the right hand side

Peter
Searaider 2

[searaider]

3rd at the back of the trailer

Peter
Searaider 2

[dnej]

Blaze,
Yes, thats the reason I phoned the professional guy, as I thought you were correct.
The arc the shackle travels through, cannot be the size of the shackle , else it will travel around that arc every time.
Your suggestion fixes the problem, as the springs are to far away from the pivot point.
Did you draw down my sketch?
Those last lot of photos are great
Regards David

[Kerry]

One term that comes to mind is "AAF" ;)

Cheers, Kerry.

[Big_Kev]

Searaiders looks the goods.
Have you tried it with the shackle over the rocker Corry?

[SeaSaw]

Peter, I wish mine were in as good condition as yours. #I think I am almost due for a new set of springs.

Here is a picture of my front wheel.

[SeaSaw]

and here is the rear wheel. This is the same set up as Peter's (Searaider) but shown from underneath the trailer.

Cheers,
Mark

[searaider]

Hi Mark SeaSaw ,
Thats a good ider of the photo from underneath the boat ,
it shows the relation of the short & long section of the spring .
At least you can fit under your boat ;D
Looks like you will be up for a new set of springs shortly .

Peter
Searaider 2

[Needmorerum]

One term that comes to mind is "AAF" #;)

Cheers, Kerry.


Sorry Kerry, not into the phonetics of webtalk, so I have no idea what you are saying.

Peter, thanks for the photo's. Identical trailer to mine. Will change mine around this weekend, for the last time.

All, I hope no-one thought I was doubting them at all. Was just chasing as much clarification as possible before I go mooring the boat at the marina for a day while I go changing things around again.

Thanks for the input from everyone, it has been outstanding.

Corry

[Kerry]

Ar.. About Face :-X

Cheers, Kerry.

[Danf]

Bumping this thread along. I wouldn't mind getting some views on tandem axle suspensions. There are quite a few variations to the "load sharing setup" which I am interested in.
I am looking at 5 leaf 720 mm eye to eye springs, tandem load sharing setup. I have attached a couple of photos of different designs.
Basically, one type that has a center rocker with one set on shackles on it for the the front spring. The other shackles are on the rear eye of the rear spring.
This setup has springs with center bolts, making the distance between axles around 960mm.

The other setup, has a center rocker with both sets of shackles on it. The front of the forward springs and rear of the rear springs are bolted directly to the hangers.
The springs center bolts are off center, making the distance between axles around 870mm.

I have 13inch wheels, and I think that 960 mm between axles is a too much.

??????
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