Ugly Ash

Hey all, just finished boxing a set of trailing arms for pvk308, he seems pretty happy with them, so I thought I would go through the process and explain what I did. feel free to add any comments as you see fit.

first, I measured the arms for fit, with the suspension under load, I did this to work out clearances for the boxing:


first, I measured the distance from the end of the arm to the spring location on the commodore.



to back this up, I also measured the spring diameter.



Steve wanted the arms as solid as he could get them, so I checked the spacing between the spring and the rubber mount so I could put a brace between them.

__________________
need some parts for a BBC:

• fuel pump (VERY important)
• some nice rocker covers

also need a rachet shifter to suit (thinking about a pro stick or similar)

Ugly Ash

now that the arms are out of the car, you need to make sure that they are not already twisted (this set was in good nick) and then make a template to compliment your measurements:



make sure the arms are okay before you modify them



here, I used paper to get my templates basic shape. because the arms are dirty, you can just put the paper over and rub over the paper, it will mark out the shape for you!

if you are going to leave the handbrake cable clip, you will need to cut around it, you can also weld to it later anyway.

after marking the template out properly ( I used a compass and drawing implements) cut it out and mark it onto the steel plate you are using. be sure to mark them the way that best utilises the material ( leaves the most usable waste piece)



here I use engineers chalk to mark where I need to cut.

I then used a guilutine to rough-cut to shape, I then used a plasma cutter to gain the shape I was after for the spring relief.



use an angle grinder with a flap-disc to clean up the edges.

__________________
need some parts for a BBC:

• fuel pump (VERY important)
• some nice rocker covers

also need a rachet shifter to suit (thinking about a pro stick or similar)

Ugly Ash

place the cut boxing onto the arms, with the commo arms, clamp them in place, as they have a fair curve in them. when they are in the right placement, use the chalk again and mark any pieces that need to be cut way for better fitment.



remember, it as better to cut stuff off than to have to add it on, so make your template 'generous'.



for this modification, Steve wanted braces internally as well. these are made from 20x20 RHS overkill if you ask me, but that is what he wanted.



these were then TIG welded in place.

I then gave them a coat of zinc paint before stitch-welding the boxing in place.

* do not fully weld the boxing as it may put too much heat into the arm and distort it, it may also weaken the metal*

__________________
need some parts for a BBC:

• fuel pump (VERY important)
• some nice rocker covers

also need a rachet shifter to suit (thinking about a pro stick or similar)

Ugly Ash

now that the boxing has been stitch-welded, I made a brace between the rear rubber mount and the spring, just to brace this part, as it may become a weak point.

I then pressed new front rubbers in and gave them a coat of paint.



these shots aren't very good, I will post beter ones later, but you can get what they look like!



this shot shows the brace at the rear of the arm, it just holds the bits together and ensures there are no weak points.

__________________
need some parts for a BBC:

• fuel pump (VERY important)
• some nice rocker covers

also need a rachet shifter to suit (thinking about a pro stick or similar)

Ugly Ash

now that your arms are fully boxed and braced, the power is going to want to go somewhere else and is going to look for the weakest point to escape, this may not be your rear tyres.

the next point you need to look at is the body mounts for the trailing arms, we will look into this now:

please never weld these in place!! the weld, other than sticking this stuff together, can create a weak point in the joint (heat affected zone) which can be prone to cracking, especially under the loads created by a 10 second machine).

the mounts can be supported by bolting them to the floor.

most body mounts are rivetted to the floorpan, so are not that strong, using bolts will increase the strength in this area without compromising the body structure through welding.



bolts can be situated here...



and here. and same on the other side:



here...



and here!!

the floorpan of the car should not be trusted to take this torque pressure alone. on the other side of the floorpan, make sure the bolts are secured to a plate ( around 6mm for over-engineering) that covers the entire area. this should ensure that your new super heavy-duty trailing arms don't rip the guts out of your pride and joy.

this is my way of doing things... if you have any questions or comments please feel free to contribute, we are all learners, every day, so I am happy to learn from you all.

if you wish to get something like this done, feel free to pm me and we can discuss from there.

thanks for looking.
Ash.

__________________
need some parts for a BBC:

• fuel pump (VERY important)
• some nice rocker covers

also need a rachet shifter to suit (thinking about a pro stick or similar)