Rear Radius arm modifications

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Ride_on
Posts: 2232
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Rear Radius arm modifications

Post by Ride_on » 07 Apr 2017 11:10 pm

Those who know me will know that I am a bit obsessed with the rear axle alignment. This is the correct adjustment of the rear radius arm to make sure the camber is vertical on the axle and has no forward vector turning it into toe-in. I spend many years in my early 20s driving a 340 without doing this properly and had pretty horrid experiences going through puddles when the back end would do a nice wiggle at 60+.

The plan was to make a rod that could be adjusted (others have done this) by rotating, rather than somehow bending the suspension then clamping. This needs a left handed threaded rose joint and the same threaded nut/tube weld onto the rod, the other end is standard right thread rose joint. This can be straight and the rose joints take up the different angles.

I finally got a reasonably priced LH thread and matching bits (threaded tube and locknut) on ebay for a few quid (previously I would have had to buy boxes of nuts for £20).

Anyway to cut a long story short.. it didn't work..well not the way I wanted it to.

I got the rod welded and cleaned up and installed. Got the suspension supported at wheel height just under spring (trolley jack under the middle of axle causes it to rotate), and started to turn. Got my measurement to about 1 degree off flat (using camber gauge) and though well I must have 0. It started going down but much less than before and was getting stiffer to turn. I got to about 0.7 degree and the rod just bent suddenly.
IMG_2497s.jpg
Bent the arm while adjusting, (although trolley jack is supporting the axle at this point putting more pressure on the arm)
IMG_2497s.jpg (162.32 KiB) Viewed 945 times
Strangley the rod bent to almost the same dimension as the orginal part (had already prepared this with Dia's bushes).
IMG_2499s.jpg
Same dimension as original
IMG_2499s.jpg (253.4 KiB) Viewed 945 times
Back to the orignal part. I put a 360 sissor jack under the spring in front of the axle with a bit of wood and used that to bend the spring to the max adjustment. This gave about 3-4 deg off flat.
IMG_2500s.jpg
Jack the spring to get max adjustment
IMG_2500s.jpg (151.63 KiB) Viewed 945 times
IMG_2502s.jpg
Jacking spring
IMG_2502s.jpg (215.54 KiB) Viewed 944 times
I am sure the axle is designed to be flat, having precision measured it off the car, and something has gone wrong in the design/modification process (maybe the bend in the back of the spring added later). The rod cannot make the axle flat, its a 12mm rod trying to straighten a 10x200mm bar of steel. It can just manage a little bit for suspension movement, but not much more. Maybe you could put in 1 deg but suspension movement might then put it past it limit and bend it. The constant pressure will certainly dent the bush (not rose joints).

A correction might be possible by shimming the front of the axle against the spring, but I'm wondering would we notice the difference.

4/90 (ratio) x 2 (camber) = toe-in = <0.1 deg , however only a few degrees (say 5 or 6) more is noticeably bad.
Last edited by Ride_on on 08 Apr 2017 12:27 pm, edited 1 time in total.
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

Ride_on
Posts: 2232
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Re: Rear Radius arm modifications

Post by Ride_on » 08 Apr 2017 12:11 pm

Sorry put this in the wrong section
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

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