Lotus Elan

Steering Rack Query

PostPost by: david.g.chapman » Thu Nov 16, 2017 12:31 pm

I have just removed my +2 steering rack to check the pinion pre-load, as I have a theory that this is important to minimise sensitivity to front wheel imbalance.

As expected, instead of 2lbs at 8 inches to turn the pinion, it's 10 oz at the straight ahead position, and 1lb 3 oz at the extremes of the rack.

OK, but I have a question about how you set up the preload correctly. Reading the workshop manual we have:

Para. 3
a) Fit the plunger and cap nut to the pinion housing. Tighten.the nut to eliminate all end float and, using feeler gauges, measure the clearance between the nut and housing as shown on Fig. 15. Remove the cap nut and plunger.
b) Make up a shim pack equal to the cap nut to housing clearance, plus .004 in
c) Pack the unit with grease and assemble the cap nut, shim pack, spring and plunger to the housing and tighten the cap nut.


So this sets the distance between the cap nut and the plunger, assuming that the spring rate of the spring is correct for the right preload. So if the spring is a bit tired, then the preload will be too light and there is no way to adjust it unless I replace the spring. Have I got that right?

Dave Chapman.
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PostPost by: Chancer » Thu Nov 16, 2017 3:00 pm

I dont think the rate of a spring changes when they become "tired" more that the free length decreases (for a compression spring) which might even theoretically increase the rate.

In a pre-loaded situation like the rack damper the pre-load will dissapear with only 4 though of length reduction or more importantly 4 thou of rack wear.

I fitted a new coil spring to my road car ? weeks ago as the old one had shed half a coil, the new ride height has settled a little already.
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PostPost by: david.g.chapman » Thu Nov 16, 2017 4:23 pm

Hmmm... OK.

The free length of the spring is 20mm, and the spring coils bind up at 12mm. I was using a washer between the cap nut and the spring previously to increase the preload.

I have calculated that with the washer in place the compression length of the spring is 15mm, so I have another 3mm until the spring binds up, if I want to increase the preload with another thicker washer, or by removing a shim.

I will take the rack apart completely, then clean up the plunger "saddle" and the back of the rack, then play about with washers and shims to try and get the preload about right (that's all of the weights from my wife's kitchen scales in a bag hanging off of a screwdriver!).

What fun!

Dave.
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