Tandem axle travel

[Stuart]

I’m setting up my trailer with new tandem rocker suspension and two new axles. My BMT will weigh the best part of 3t and my springs, which are ratted to 5t however; I have taken a couple of leaves out. If ts to stiff I can remove one more leaf if need be. What I don’t know is how much travel I should allow for between the axles and the bottom of the trailer? I have worked out 165mm travel should be enough and of course I wont know exactly until the springs are under it and the full load applied. I want to calculate it as close as possible so I don’t have to drag them both out again and weld more spacers. So how much travel, 165 or more?

Stu

[SunnyCoastMark]

Geeze mate - haven't you got that trailer sorted yet? - Rocker Springs don't have a lot a vertical travel (unlike slippers). Because they are fixed at both ends - they can only mave so far vertically (that's up & down). As they are loaded - both wheels will move in towards the centre and slightly up. On larger Car Carriers that we build - up to 4.5t - we have slideaway ramp cradles between the axle and chassis and the axle never hits. Sometimes with as little as 90mm of clearance.

......and weren't you using IRS axles?

Are you home today?

Mark

[johncar]

Hi Stu, If it's of any help my trailer (Belco) is built to 4 tonne, uses Vehicle Components suspension. They are 7 leaf, 8mm x 60mm leaf, fixed at the outer ends and rocker in the centre. The axles with full average load at 3.04T sees the rear axle with only about 50mm below the chassis, front axle has a little more. Now that did concern me a little when I bought it but after quite a few miles it surprisingly doesn't seem to be a problem. But I would like to see a bit more clearance just the same. I think if I was flogging the thing off road it would need more but not likely I will be doing that, everywhere I go is on the black stuff. Hopefully no big potholes.

[Stuart]

Mark,

Im home today mate, O and I know what verticaly means, didnt think I came across that stupid. I did have IRS but as one side snapped it planted the seed of doubt in my mind. One of the managers at Alko was so arrogant and full of him self I told him were to go and I went with the rocker suspension. Good to see nepotism is alive and well in Alko.I might allow 100mm to maybe 130mm travel.

[Out-Station]

My belco has 70mm, just got a new one built for the old mans 609 stabi, it has 60mm of travel, they work on an absolute min of 50mm in the belco shop (i don't recon there sto much science behind that, its just whats worked for em). I recon if you were getting any more than 50mm travel on a tandem rocker setup then you need to stick a leaf back in anyway, springs only designed to do so much work.

Scott

[SunnyCoastMark]

Stu,
Didn't see your reply until now - just got back home. 100-130mm travel will be plenty.
What are you doing to keep the rockers from siezing up?

Mark

[Stuart]

I think I will allow 100mm travel for these bad boys.

Mark, I have purchased greasable bolts for every moving part along with bushes for the spring hangers.
I have made the actual rocker arm from solid 50mm square bar and drilled the three holes myself, time consuming that’s for certain. The main rocker bolt is 5/8 or ¾ can’t remember.
I also machined some nylon bushes to fit between the metal to metal sections of the springs and spring hangers. May not be needed but it cant hurt.

[EdBerg]

Due to a slight screw up on mine when I was building it, I ended up only having 50mm between the guard and the top of the tyre,

When I noticed it I intended to raise them but thought I would see how it went as it would be a pain to have to raise them.

The boat with trailer weighs in at 3.2ton so far, (another 200kg to go) and the axles are 2 x 1800kg rated each with rocker style springs, and I thought that surely the rubber will scrape the guards underneath as I leave my driveway, but so far nothing, I have done about 100km on it so far and not a mark underneath. So obviously they don't move all that much.

Cheers

Ed.

[SunnyCoastMark]

Hey Stu,
You probably have this sussed already, but just in case:- Be careful with where you position your front and rear spring hangers. - too far apart and the springs will be prone to inverting. Too close together and the rocker box/shackle plates will wear a nice hole in your chassis side mambers or at the very least - be constantly banging away.

Mark

[Stuart]

Thanks mate, I have that sussed. Im going to mount the axles and springs on there own cradle then roll it under the trailer. Im going to have the axles and springs adjustable foward and back so I can fine tune it if need be, besides that If I need to remove it I will be able to. It will be attached by bolts for the most part and maybe some stich welds.