Fitting Super Pro rear trailing arm to chassis bushes

[Filbee]

The two big washers that go either side of the bush have a chamfer on one side of the centre hole. Can anyone tell me which way round the chamfered side of the hole needs to face please?

Unfortunately there are no instructions included and I couldn't find anything else on here or the wider t'interweb that shows which way round they should go 

I assume the chamfer will need to face the bush, but I wanted to check before I get stuck in tomorrow!

 

[uninformed]

There is a radius on the end of the pin section of trailing arm where it steps up in dia. Face the chamfer to this. There is also a crush tube inside the bush, you want the flat face of the washers hitting this to be correct length/preload when torqued up. (So full surface area of crush tube is in contact with washer.)

The chamfer to nut doesn’t do anything or matter due to the surface area of the nut, it’s just there because they mass produce one washer to suit. 

[Filbee]

Thanks, that makes sense.

I don't think there's a radius on the pin end of my trailing arms as they are Gwyn Lewis heavy duty ones, but I'll check when I take them off.

[uninformed]

2 hours ago, Filbee said:

Thanks, that makes sense.

I don't think there's a radius on the pin end of my trailing arms as they are Gwyn Lewis heavy duty ones, but I'll check when I take them off.

Looking at his website, my guess is he is using standard factory arms and sleeving a tube over them. If that’s the case they should still have the radius where the pin steps up to the main outer diameter of the original arm. 

 

 

[Filbee]

1 hour ago, uninformed said:

Looking at his website, my guess is he is using standard factory arms and sleeving a tube over them. If that’s the case they should still have the radius where the pin steps up to the main outer diameter of the original arm. 

 

 

These are the ones I have

https://gwynlewis4x4.co.uk/product/rear-trailing-arms-defender-disco1-rrc-standard-heavy-duty/

They are the same outer diameter as the standard ones, but with thicker tubing. If you zoom in on the pictures, it looks like the pin end has a square shoulder. The super heavy duty ones do seem to have a rounded shoulder.

I'll fit the washers as you describe anyway 👍

 

[uninformed]

44 minutes ago, Filbee said:

These are the ones I have

https://gwynlewis4x4.co.uk/product/rear-trailing-arms-defender-disco1-rrc-standard-heavy-duty/

They are the same outer diameter as the standard ones, but with thicker tubing. If you zoom in on the pictures, it looks like the pin end has a square shoulder. The super heavy duty ones do seem to have a rounded shoulder.

I'll fit the washers as you describe anyway 👍

 

Again I’ll take a guess. He is using the ends off factory arms and replacing the main tube between the friction welds.

If he is getting the pin ends made they should have a radius where I described, if not it’s poor machining and design. 
 

but like you say either way fit the washers and have fun 👍

[Filbee]

Well that's the bushes fitted!

It wasn't to bad a job. The worst part was removing the three bolts that held the bushes to the chassis on each side. Because they are quite long, the exposed threads get corroded and so it got progressively harder to undo them until the nut finally cleared the threads.

I left the wheels on and didn't jack the chassis or axle. I stuck an axle stand under the chassis just in case but there was no need. 

I fitted the big washers a per Uninformed's suggestion, with the chamfer facing outwards, and as it happens, the factory bushes also have a chamfer on the large washers, facing outwards. Good call!

For anyone interested, the factory arms have a square shoulder where the diameter steps down for the pin, so the Gywn Lewis arms are exactly the same as the factory arms apart from having thicker walled tubes and arc welded ends (not friction welded like the OEM ones).

After having a good look at the Gywn Lewis arms, I'd be surprised if he does use the ends off old factory arms. They look like they might be plugged into the tubes and the threads look too clean to be from a used arm.

Anyway, it all looks good now and I'm looking forward to a test run tomorrow 👍

Edited November 6, 2021 by Filbee

[uninformed]

Maybe different batches or changes. The factory trailing arms changed a few times over the years from the original RRC through all the various vehicles. 
 

Mine 6 definitely have a small radius. It’s not big but can be seen and felt if you offer the washer up with fingers. It rocks a bit if the chamfer is not facing it.

I did notice the plug weld on the GL arms which does mean they are longer than the LR item.  I was surprised to see his comments on his web page regarding the friction weld. Friction welds are very good and I confirmed this by building a test rig and bending to destruction the ends of factory arms. 
 

[Filbee]

20 minutes ago, uninformed said:

 

I did notice the plug weld on the GL arms which does mean they are longer than the LR item.
 

They are exactly the same length as the LR ones. I put them side by side to check.

The only difference visually between them is the welding. That's it. Same length, same diameter tubes, same diameter pin and shank.

[uninformed]

2 hours ago, Filbee said:

They are exactly the same length as the LR ones. I put them side by side to check.

The only difference visually between them is the welding. That's it. Same length, same diameter tubes, same diameter pin and shank.

I was referring to the solid pin end , it looks longer on the GW for it to go inside the tube for the plug weld. 

[Filbee]

23 hours ago, uninformed said:

Mine definitely have a small radius. It’s not big but can be seen and felt if you offer the washer up with fingers. It rocks a bit if the chamfer is not facing it.

 

I checked my original radius arms in the daylight today and they do have a small radius where the pin meets the shoulder as you described. It's only a couple of mm tall but it's definitely there. This matches the chamfer on the factory bushes.  I guess it maybe to ensure the pin stays centred on the bush? 

[uninformed]

1 hour ago, Filbee said:

I checked my original radius arms in the daylight today and they do have a small radius where the pin meets the shoulder as you described. It's only a couple of mm tall but it's definitely there. This matches the chamfer on the factory bushes.  I guess it maybe to ensure the pin stays centred on the bush? 

Given the length of the bush, centring one end isn’t going to do much. The crush tube is not a terrible fit and fit for purpose. The radius is there to form a smooth transition between diameters. If it’s a square corner it creates a stress riser where failure can start (crack propagation). The trailing arm will see tension and compression forces (braking and acceleration) but will also see bending forces when it articulates up and down. 
 

That radius transition is especially important for bending. A good example is the nice radius on the stub axles.