Thread: Longer rear trailing arms on a defender.

Longer arms will push the bottom of the diff backwards causing the balljoint angle to change thus reducing its movement, maybe not a lot and probably will have a greater affect on the rest of the suspension like shock mounts etc.

I can see possible confusion already.

MLD, when you say "all else remaining factory" you are still moving the chassis mount point, right?

If so, I don't see how loanrangie could be right? (Which is possibly a misunderstanding?)

Originally Posted by Judo

I can see possible confusion already.

MLD, when you say "all else remaining factory" you are still moving the chassis mount point, right?

If so, I don't see how loanrangie could be right? (Which is possibly a misunderstanding?)

If he didnt move the mounts which was one of his questions then he will have complications - this is how i read it.

I don't pretent to know anything about what I post below, but I'll throw a thought / an idiots observation into the ring:

I knocked this pic up to explain:


If we are talking longer trailing arms where you change the pivot point from Pivot 1 to Pivot 2,then the radius of the circle will be longer (this is the trailing arm length), and the length of the circumfrence of the circle that sits within this area of travel will be longer (this is the swing area of the axle). Compare the red line to the yellow line, yellow is stock, and red is the modified longer arm (not to scale or anything).
The area of the arc that fits within the limit of travel (bump stops / full droop) will have a depth of the chord of this arc / circle- this could be considered the forwards/backwards movement of the axle relative to the pivot. So the small ter the trailing arm, the more pronounced the forward backward movement of the axke centre relative to the pivot point.

So for the bushes flogging out, if you have a set travel height, then the longer the arm, the narrower the angle becomes at the pivot point, to see the given travel height. It would be possible to work out the angle using trig, but I forgot all that years ago!

As for your A frame being an issue, I guess it would come down to your resting height, and where this is relative to the respective red or yellow arc. As the axles move up and down (wheel travel up, wheel travel down) along their trailing arm arc, the secondary arc formed from the pivot of the A frame back out the the wheel will also come into effect causing the wheel to tuck (camber in) or camber out on its upward or downward movement respectively.

I guess you need to work out the angles that the standard A frame bushes will handle, then endure that your travel is within this operating angle.

If Service is not an issue the rose joints / johnny joints / heim joints would be the way to go. Because race car.

Sorry for the confusion.

All else remaining factory is:

A frame
standard location of the shock mounts (i run gwyn lewis shock mounts which are +2")
standard location of the coil
any other part in the suspension (excluding the trailing arm).

If the gigglepin trailing arms works with the factory A frame I will cut off the factory trailing arm chassis mounts and fabricate new chassis mounts to suit.

What I'm trying to ascertain is the relationship between the A frame length and the trailing arm length. Do they need to be relative in length to each other to work in harmony. When does it become outside the happy range.

The fall back is the TF johnny joint or the Raptor Johnny joint arms which both are a replacement for the factory length arms without modification of the mounts.
MLD

Mark, have you seen the Superior Engineering solution?
https://www.superiorengineering.com....?filter=84,355
This is listed in the discovery section. I think from memory the defender chassis mount differs in "rotation" in comparison to the disco mount. Maybe worth a look?

Thanks Mitch.

I think (and I'm no engineer) what is happening is when the axle drops at full extension the axle walks forward, couple that with the compression of the chassis bush and the drive from the rear tyres the trailing arm is being pushed forward through the chassis mount. My bushes are failing by separation of the bush material fore and aft of the plate that mounts to the chassis from the material that encases crush tube permitting the arm to push forward even farther. Visually I end up with a donut of bush material that provides little resistance to fore and aft movement of the arm. Once I get a weakness in the bush it destroys itself relatively quickly.

Your insights of the trailing arm arc is the reason why i'm contemplating the longer arms. I'm trying to grapple with the affect of longer arms on the A frame geometry. I am not smart enough to work what data is required for a 4 link calculator and less smart to make sense of the results.

Cammo - The Superior engineering arm was designed off a RRC which have a different bolt location/orientation to the defender, which results in the arm being twisted and out of plane to the axle. I understood SE were redesigning the arm to suit the defender.

Ta, MLD

Originally Posted by Toxic_Avenger

..................
So for the bushes flogging out, if you have a set travel height, then the longer the arm, the narrower the angle becomes at the pivot point........

Years ago in 4WD Monthly there was a guy who'd plonked a Def body on a RRC chassis.

He'd made f&r custom arms much longer than original. The chassis mounts for these were actually in the middle either side with just enough room to undo the nuts.

Thought it was quite clever.

DL