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Home made ARB's


hagarep

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With my car effectively off the road, due to broken head studs (and winter) I needed a reason to spend my evenings in the garage instead of in front of the TV. 

As I recently added a lathe and bandsaw to the garage toy list I figured it is a good time to make my own RSR style ARB's. Nothing too fancy, just cherry picking the bits I like from all of the available aftermarket options, but at a fraction of the price. I have plenty of Aluminium T6061 stock and have ordered 7/8" EN19T (4130 Cro Mo) bar which measures 22.25mm metric and cost £68 delivered. I still need to decide some measurements and where to connect to rear suspension, either the original locations on the trailing arms or the toe adjusters on the spring plates, but look forward to figuring it all out and will try to document everything on here with pics, in case anyone is interested.

In the meantime, here is a rough idea of how the rears will look, mocked up using www.tinkercad.com 

 

 

Rear ARB.jpg

First parts to be made, nylon bushes for the rear ARB.

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Still got to dial out the run-out on my cheapy Clarke pillar drill. I think the Mitutoyo run-out gauge, magnetic stand and flat-walled transfer punch cost almost as much as the drill :lol: 🙄

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All material pretty much in now. Milling and turning have begun. Still need to decide on M8 or M10 rod ends for the link rods. I also need to find dimensions for the three bolts used to mount the front bar to the inner wings.

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  • 3 weeks later...

Been a few design changes since I began. I originally wanted to use M8 rod ends, but when they arrived I thought they looked a bit weedy. Then I managed to find more photos plus diagrams of kits from Tarett and EB, which included hardware specs.

Tarett use an M10 rod end with M8 inserts for the bottom of the link. This meant my adjustable aluminium arms needed to go from 20 to 25 mm wide, which meant ordering more material, redesigning the arm in CAD and re-machining the bar end square an extra 5mm. For the top of the link, I have used threaded hex bar and machined a ring which will accept the original Porsche 1977 nylon cup that fits on to the ball joint on the trailing arm. I just need to TIG them together. From the photo you can see the alignment is not great, which is why I assume all of the kits you can buy use the rear toe adjuster bolt. I shall finish one link and rough one arm out so it clamps to the bar, then make a final decision.

Just a little warning. I was shocked to discover, my original rear ARB mounts, which have already cracked and been welded and braced, were significantly bent inwards towards the centre of the car. Obviously not an issue when you have rubber/poly bushes. But a big problem when you using 2-3mm of nylon bearing. I used the bar, bolted tight into each side, one after the other, to bend the brackets straight. Definitely going to buy some upgrade rear mounts and weld them in. Anyone doing significant track days should check their brackets too.

Jason.

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  • 3 weeks later...

Checking alignment of moment arm to original pick up point on semi trailing arm and clearance around mounting bracket. Arm design needs further tweeks and the square hole was finished with file, but not to an acceptable standard, so need to improve machining and buy longer slot drill. Al least i can cut the bar to exact length and machine the square now.

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Finished the rear links now. M10 nylon lined rod end (with 8mm inserts) and  home made pieces which take the original Porsche bushes. Just need some half nuts to lock them togther.

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  • 1 month later...

Scraped the first bar and arm, due to poor quality and fit. Improved quality with a digital level and adjustable stand for the long bar to ensure machine is parallel. Also re-levelled workbench, mill base, slide, vice and upright.

Finally, increased the size of the square to aid machining the hole and bought a long 5mm slot drill. Just needed minimal use of a square file in the corners for the test bar to fit. Ready to redo the bar now.

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  • 1 month later...

Scraped the first bar and arm, due to poor quality and fit. Improved quality with a digital level and adjustable stand for the long bar to ensure machine is parallel. Also re-levelled workbench, mill base, slide, vice and upright.

Finally, increased the size of the square to aid machining the hole and bought a long 5mm slot drill. Just needed minimal use of a square file in the corners for the test bar to fit. Ready to redo the bar now.

First trial fit of the complete bar. Not perfect but good enough for now. A light sandblasting and then off for plating.

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So, ARB still work in progress, workshop much improved! I'm joking, I admire your skills and patience, I'd have simply bought one a while back.

Keep going, Chris.

 

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  • 3 weeks later...
Posted (edited)
On 07/05/2021 at 10:41, Diesel76 said:

looks great, any thoughts on a small batch run? I have a 76 911S without a rear ARB so looking at options. Cheers

It takes a lot of time with the equipment i have and i have just bought a motorbike project, so i am unlikely to make any more this year. Mind you I still need to make the front one yet. I worry my quality isn’t up to the standard of Elephant or Tarett!

Thanks very much for the interest though. I will think about it.

Edited by hagarep
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Absolutely fed up trying to get these bushes in to the link rods. They usually end up damaged. Decided to make new links that can clamp around them! Back to the anodisers again!

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Are you using a male plug to support the bush as you press it in ?

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I heat the bushes to press them in as it is almost impossible without, but be careful not to apply too much!

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I tried boiling water, oven on low and heat gun to soften them.

I tried pressing the bush directly and pressing with a 9mm deep socket in the middle. Using a vice and a hydraulic press. I even added a bevelled edge to links.

Eventually, I ended up with two rough and damaged bushes in the links, which I could not then fit to the rear trailing arms.

I think it's a combination of slightly harder than original bushes from Matt and the links that I fabricated. I tried an old Porsche bush in the new links to test them and had no issue, but even though the dimensions match the originals I am sure they are the main problem.

Anyway, I can now pop a new bush straight on the trailing arms and clamp the link around it. Pics to follow next week, when they've been anodised and fitted.

Jason

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