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Revision as of 23:34, 12 November 2012

Lowering the car makes it handle transitions better and reduces aerodynamic resistance. And it looks cool.

1 Overview
2 Reduced Travel
3 Front
4 Rear Suspension
- 4.1 Lowering Blocks
- 4.2 Flipping

Overview

Common ways to lower the 1200:

Fit ready-made lowering front coil springs or lower the spring perch
Re-arch the rear leaf springs or fit lowering blocks.

These and more advanced lowering methods are discussed below.

NOTE:

We accept no responsibility for damage to your self, others personally or property. YOU take the risk of working on your car and should follow all safe and accepted work practices.

Springs are under tension. Follow your repair manual for the safe procedure for removing and reinstalling springs.

Reduced Travel

Lowering leaves less room for the suspension travel. This means the suspension is more likely to bottom-out on bumps. So for maximum comfort and load-carrying capacity, do not lower the vehicle.

When lowering 1 inch, reduced travel is not much of a problem. When lowering 2 inches, reducing the length of the Bump Stops will restore some travel.

A stiffer spring rate will reduce the occurrence of bottoming out, and will make for a more sporting ride but at the cost of additional harshness.

When lowering more than 2":

Modify the Bump Stops
Struts should be shortened. See Shortening struts
Coil springs should be tied for postive capture (see below)
Rear Shock Aborber need to be replaced with shorter unit
- Lowering with blocks does not affect the shock placement so no worries. Exception: Sedan shock mounting.

Front

Using shorter springs can lower the car further, as can precisely cutting a small portion of the coil. Another alternative is to lower the spring perch.

With extreme lowering (more than 2 inches), steps must be taken to keep the spring from falling out of the lower seat at full suspension droop. The end coils of the spring must be securely wired to strapped to both the top and bottom seats.

Lowering Springs

The best, but most expensive way, to lower the front is to fit custom spring, of a certain length and rate. King Springs is popular vendor for 1200. Also Nissan Competition made lowering springs.

See main article: Lowering Springs

Lowering the spring perch

You can carefully cut the lower spring perch and position it lower.

See main article: Fastening Spring Seats

METHOD 1: The perch can be re-welded in the new position.

METHOD 2: The perch can use commercial-grade shaft collars to fix it.

METHOD 2: Threaded sleeves can be fitted to the strut tube, along with a threaded ring. The spring perch is placed above the ring. This can be adjusted after installation to suit height.

Cut Springs

Since Datsun 1200 springs are constant rate, cutting them does not change the spring rate. They are 90 lbs/in, regardless of how many inches long you make them.

Variable rate springs will become stiffer if you cut the loose end, or softer if you cut the tight end:

Bottom: 1200 springs (constant-rate)

Cut Springs Yourself, or Pay a Professional?

If you need extra stiff springs, or want to carefully match the springs to an intended result, you can't go wrong by working with a professional, reputable spring company. Since their business is springs, they presumably won't make stupid mistakes like cut the springs too far

Coil Spring Swap Candidates

B110 uses 110mm O.D. diameter coils 100mm I.D. B210 & B310 rates are only 1% to 2% higher than rate of B110 -- but they are longer.

280ZX rear coil springs fit in the front of the B110, cut to suitable length, are a good way to get firmer springs -- just right for a sporting street 1200.

S130 1983 280ZX
 Front 150mm coils
  127 lb/in
  S130: 12.1" long (white/yellow)
  GS130: 12.4" long (white/white)
  S130J: 12.8" long (red/blue)
 Rear 100mm coils
  126 lb/in
  S130: 14.5" long
  GS130: 14.8" long (also S130J)

Since 280Z rear coils are 100mm, they would be good for extra-firm upgrade. Cut them down more than 2 inches to use in the 1200.

B110 stock coils: 13.3" long

S30 1975 280Z 100mm front & 100mm rear
 front GS30: 8.5 coils @ 115 lb/in (16.7" long)
 front S30 : 9.5 coils @ 103 lb/in (16.0" long)
 rear coils: 8.5 coils @ 198 lb/in (15.4" long)

Roll Center Spacers

When Lowering the front suspension, if going ultra-low, strut spacers (roll center adapters) are used. They are intended to correct the lower arm angle when the vehicle height is dropped, to correct the roll centre.

See main article: Roll Center Adjusters

Rear Suspension

Lowering blocks are the low-buck solution, but using modified springs is a better way. The spring eyes can be "reversed" or the leaf(s) can be flattened (re-arched).

discussion: reverse eye leaf suspension
discussion: Lowering rear end of a 1200

Here's what they do in USA and Japan, from "best/most expensive" to "less expensive"

Fit special-design lowering springs
Re-arch the leaf springs
fit lowering blocks
Flip main leaf

Lowering Blocks

See main article: Lowering Blocks

Flipping

One way to lower the rear is to add another spring to your rear leaf spring pack and reverse one onto the top of the pack, while flipping it. This should lower and stiffen the rear end slightly.

To flip the rear leaf springs:

up the car, take off the wheels

Make sure you use axle stands on the rear chasis and another pair on the rear axle assembly so it doesnt drop to the ground.
Unbolt the U bolts from the rear axle, spring pack and then un bolt the front 3 mounts for the leaves. Unbolt the rear bolts and remove the spring pack
Now using G clamps, compress the spring pack and unbolt the center locating bolt. Then slowly undo G clamps releasing the spring pack to individual leaves
Flip the 2nd bottom spring onto the top of the pack and added another longer 2nd bottom leaf.
Using a long screw driver through the center locating holes, loosely repacking them then doing them up tight and slowly with the G clamps again till completely compressed. USe the screw driver tho keep the leaves aligned. Once compressed, re insert the center securing bolt and tighten.
Re installation is reverse procedure of removal