Castor

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Current revision

Checking castor (also spelled caster) is part of Alignment for proper tyre wear or to change handling characteristics.

Increased Caster

More caster will improve on-center "feel" and make the car track better. In other words, it will go straight ahead with hands off wheel -- without wandering. This will make the steering effort heavier, but the 1200 is arguably too light in this area to start with, so no worries.

More caster will also give the car a negative camber change while cornering, which is desirable.

Increase caster up to 3 degrees for a street 1200. Use at least 2 degrees for good tracking. Stock specification is as low as 0 degrees 20 minutes, which makes the 1200 wander on the road.

Increase caster up to 4 degrees for racing. The tension rods may be modified to provide an increase in caster.

As always after modifying the front suspension, the Toe-in must be re-adjusted to retain correct wheel alignment.

• To increase caster, shave the Tension Rod bushings and pull the wheels forward (see below#Modified Bushings)
• OR, use standard length bushings, and shorten the rod pull-through (see below #Datsun Competition)
• Do NOT cut the threads longer

• To decrease caster, insert spacers (washers) on the tension rod

• Another way to use adjustable radius rods. See main article: Custom Caster Rods
• OR, fit adjustable Strut Tops: See Strut_Tops#Camber_Tops

See discussion Negative Camber (Page 3, for caster)

Datsun Competition

Datsun 1200 Competition Suspension Manual

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Tension Rod and Bushing Modification

High speed stability can be enhanced by increasing the caster. On a Datsun 1200, this is accomplished by remachining the tension rods .600 of an inch as shown in Fig. 17. This shortens the rod and pulls the bottom of the strut forward to obtain approximately 4° of additional caster.

diagram

The stock tension rod rubber bushings are too soft for competitive use. Replace them with two Balkamp (NAPA) motor mount rubbers, part number 3-5121. The Balkamp rubber bushings have an outside diameter of 1.5-inches and a thickness of .850 inch. The only modification needed is to enlarge the center hole for 3/8-inch to 5/8-inch (Fig. 18). When installing the rubber bushings on the modified tension rods, use all the stock washers and spacer sleeve.

Modified Bushings

Datsun 1200 came with very antiquated Wheel alignment settings. They didn't drive very straight even when new. A little more caster will fix that!

Discussion: Moar Castor

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Cut the Tension Rod rubber bushings in half, and shorten the metal spacer and put it back together. It will pull the wheels forward just enough to track well, with no wandering. Even with hands off the wheel it will drive straight.

1. Park on a level surface and measure the toe-in. Mine was right on spec, 3mm closer at front of tire compared to rear of tire (or 4mm measured from tread centerline, but as you can see I measured closer to the hub)
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I used the long stick to go clear across the car and measured front tape to rear tape.

2. Remove the Tension Rod (castor rod). Undo the front nut, then the two bolts on the LCA, then pull it out.
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3. Cut rubber bushings in half. Cut the metal spacer tube down from 42mm to 18mm. Stock used bushings were 21mm thick.
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Alternatively, 1978-1981 R30 uncut bushings may be used

• 27.3 mm long
• 40.5 mm diameter outer
• 22.2 mm inside diameter

4. Insert back through the Tension Rod Bracket and tighten bolts to specification. Remember this is suspension parts, you life depends on them, so do not weaken the fasteners by overtightening. 5.5 to 6.5 kg-m (40 to 47 ft-lb)
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5. Re-measure the Toe-in, and if out of spec (4-6mm) then evenly rotate the side-rod ends until Toe-in is correct.

Enjoy driving.

• Before: two hands gripping the steering wheel, making frequent steering adjustments on straight roads
• After: two hands lightly holding the steering wheel, making occasional steering adjustment