Rear Lower Trailing Arm-Axle Housing Separation: parallel measurements

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey all,

After performing full articulation measurements on the lower trailing arm-axle housing separation on the rear of the 120....

http://www.pradopoint.com/showthread...n-on-Prado-120

....I had to perform some parallel measurements to find the true trailing arm binding limits on the rear end.

This is because in parallel everything binds at shorter shock open lengths compared to when the axle housing is fully articulated.

Here are my new measurements;



With a horizontal axle, the lower trailing arm will bind at approximately 700mm shock open length. Fully articulated it won't bind until around 800mm.

This shows that if you are not running a swaybar then you can run rear shocks out to an open length of 700mm before binding occurs.

The offset lower trailing arms from Superior really then only become necessary in two possible cases; i) for those running without swaybars and running shocks with open length longer than 700mm, which is not very many folks, and ii) to allow longer than 30mm extended swaybar links to increase the open length at which the swaybar will bind.

It's the same story for the upper trailing arms, the PS arm won't bind on the fuel tank until an open length of 740mm, so offset upper trailing arms would never really be necessary.

Best

Mark

[Joshy Member Find all posts View Profile Close Joshy]

Looks like you've spent some time working on all this data Mark! Great work. Its certainly taking a lot of the work out of it for me looking at new shocks. Any idea on how many more mm the superior lca's will allow the sway bars to be lengthened? I imagine it would only be guessing without having them or at least the measurements of them. I'd just be curious how much more length it would allow and then how much longer of an open shock it would allow before limiting travel.

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Looks like you've spent some time working on all this data Mark! Great work. Its certainly taking a lot of the work out of it for me looking at new shocks. Any idea on how many more mm the superior lca's will allow the sway bars to be lengthened? I imagine it would only be guessing without having them or at least the measurements of them. I'd just be curious how much more length it would allow and then how much longer of an open shock it would allow before limiting travel.

Hey Joshy,

All I can tell you at the moment is the link binds on the trailing arm about 240mm behind the front chassis rail bush. As it's a long distance from the bush, I'm guessing you might score at least 10mm more vertical displacement with the offset Superior arms. Most of the offset on the Superior arms is close to the rear bush on the axle, not so much up near where the link binds, but if you got an additional 10mm, that means you can run your extended links out to 40mm longer than factory, which means your sway bar will bind at 615 + 40 = 655mm, which would allow you to run the Superior 650mm shocks and make sure they top out before the sway bar binds.

I confirmed today that my 30mm longer links push the sway bar binding open length out to 645mm. The factory setup binds at 615mm, so this means you get all the extra 30mm on the extension back, 615 + 30 = 645mm.

I've definitely spent a lot of time making measurements on the rear end this week, bloody hard yakka in my tiny cramped garage with the Prado jacked way up in the air!

Best

Mark

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Any idea on how many more mm the superior lca's will allow the sway bars to be lengthened? I imagine it would only be guessing without having them or at least the measurements of them. I'd just be curious how much more length it would allow and then how much longer of an open shock it would allow before limiting travel.

Hey again Joshy,

Today I got my hands on some Superior lower trailing arms, and compared them to the factory trailing arm dimensions.

At the point at which the sway bar link binds on the trailing arm, about 240mm behind the front bush, I measured 12mm extra vertical displacement on the Superior arms. I was comparing them by lying the Superior arms over a 1:1 schematic I made of the factory arms, so I would say 10mm within error.

This is good news, it means if you run the Superior arms, you can extend the links by 30 + 10 = 40mm total.

This means the sway bar will bind at 615 + 40 = 655mm, and you can then run an open length shock = 650mm which tops out before the sway bar binds.

Most shocks out in the 650mm range are 395-650mm, a typical 10" shock.

395mm is very close to the factory axle-bumpstop bind at 405mm. Further, the initial 10mm of the factory bumpstops with the gap in them are easily torn off, meaning that only about 40mm of the bumpstop is doing the work.

The factory closed length is 356mm. The bumpstop is 50mm thick, which means closed length + bumpstop safety margin = closed length of the shock, in this case 356 + 50 = 406mm, right on the 405mm I measure.

You must account for 100% compression of the bumpstop, for example if the car is airborne and lands with a hard hit that does a big compression on the bumpstop. I would only be accounting for the 40mm of useable bumpstop.

This means that any shock with a closed length longer than 405 - 40 = 365mm must use a spacer to prevent bottoming out the shock.

If you run a shock with for example a 380mm closed length, then you need to space it by 40 - (395-380) = 25mm.

If you run a 395-650mm shock, then you need to space the bumpstop by 40 - (395-395) = 40mm. You must also extend the sway bar links by 40mm.

Note that I'm using a bumpstop-axle binding closed length of 395mm, which ignores the first 10mm of the bumpstop which is not useable, ie, 405-10 = 395mm.

With a 40mm bumpstop spacer, this will give you useable travel of 650-(395+40) = 215mm, pretty much the same as what I have with the unspaced 618-405 = 213mm travel I'm running now using a 365-618mm shock.

This is pretty much the limit of geometry including the swaybar.

Best

Mark