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Small-diameter springs can be fitted to the Datsun 1200, replacing the stock front coilover springs. In the rear coil springs can supplement the leaf springs. One advantage of aftermarket coilovers is that many spring rates are available for customizing.
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Overview
Stock Datsun 1200 struts are coilovers from the factory, but with fixed, large diameter springs. You have the option to convert them to adjustable spring height and/or small-spring configuration. Advantages include:
- Adjustable spring height, for lowering, raising, or for adjusting the ride height
- If using small-diameter springs, you gain:
- Many spring rates are available for customizing
- more room to move the strut inward for extra negative Camber
- about 15 mm more room for taller-than-stock tires (stock size tires fit under the spring portion)
Adjustable Ride Height
Adjustable spring height is used for lowering, raising, or for adjusting the ride height: The lower spring seat is replaced with 1) threaded collar that fits over the strut tube and 2) threaded spring stop which can be rotated to raise or lower it
Alternatively you can use a simple seat stop (non-threaded), which is adjustable if you use a commercial-grade shaft clamp (see Fastening Spring Seats).
Stock lower seat VS threaded adjustable seat
Adjustable spring seat with stock springs
- Moving the adjuster nut will lower or raise the car. It will not change the spring rate
- How much adjustment range you'll have depends on the length of the threaded adjuster collar
- Coilovers do not change the extended length. That is set by the strut (length of strut tube and the stroke of the piston)
- Coilvers do not change the compressed length. That is set by the strut housing and the bump stop
Extra-long threaded collar
Spring Rates
Choose your spring rates for coilovers like you would for any spring. Coilover springs are available in many different rates from soft to rock firm.
See main article: Spring Rates
Coilover Kits
Kit can be used for Φ45 stut tube such as Corolla KP61, EP71, AW11, YZ Sports: 48511-YZ502, etc.
Ground Control has fully adjustable Coilovers kits for the Datsun 1200 and other models, for $199 USD a pair.
NOTE that the kit does not include the struts themselves, just the spring seats & coils.
Coilover kit from Ground Control on Datsun struts
Discussion: stiffer suspension
Paradise Racing has front coilovers for Datsun 1200: Part Number DATF $175. Their softest spring rate (250 pounds) is suitable for racing.
Non-Kits
Instead of buying a kit, you can modify Datsun struts to accept standard 2-1/4 inch coils. You can buy the springs and spring seats separately.
My threaded sleeves are 125mm long. They are placed 172mm up from the hub casting.
45mm stock struts Sleeve length: 125 mm Strut length: 393 mm from top of hub casting Sleeve starts: 172 mm up from hub casting
Front
The main advantage of moving to small-diameter coilover springs is that many rates and lengths are available. With the stock large-diameter size, only a few off-the-shelf springs are available such as the King Lowering Springs (lowers a 1200 30mm) and choices of longer springs. By converting to small-diameter springs, the full range of pre-made springs are available by rate and length, for example, Eibach's line of 2.25" springs.
The other advantage of small-diameter springs on the front is that you can move the strut top further inwards to gain additional negative camber when using camber tops. With the stock springs, only a little adjustment is possible before the spring hits the inside of the strut tower. With small springs, much adjustment is possible.
* Stock springs: 100mm (4") I.D. * Small-dia. springs: 2.25" I.D.
See: Camber Tops
Smaller springs can also give slightly more room for taller-than-stock tires (stock size tires fit under the spring portion). The stock springs are 110 mm O.D. while small springs are typically 2.25" (~77mm O.D.) which will gain an extra 15mm or so closer to the strut tube, allowing for wider wheels, even those with less offset(for that "dish" look).
The Datsun 1200 strut housing is 45 mm diameter (many other Datsun are 50.8 mm).
Stock strut inserts have a 17mm stroke.
The better coilovers actually have the thread for the top cap on the inside of the threaded sleeves. This way you just have to cut the strut to the length you want and then weld the threaded sleeves on and the cap screws into the top of the sleeve. They also have a turned step on the inside of them where the threaded sleeve rests on the top of the strut body. This way no load is supported simply by a weld.
Remember that the stock spring rate is 91 pounds/inch, so 250 pound springs will result in a very stiff ride, suitable for track racing with a lowered car. Not recommended for bumpy surfaces such as public streets or off-pavement racing. For street use, consider 175 pounds the upper limit.
Rear
Coilovers can be easily fitted to the rear of sedans (and less easily to coupes). Some modifications to the shock tower are needed.
One idea is to remove all the leaf springs except the main leaf. The main leaf is left to control placement of the axle housing. The coilovers handle most of the weight of the rear suspension.
Paradise Racing has rear coilovers for Datsun 1200: Part Number DATNAR $349 for non-adjustable, and DATR $499 for 12-position (soft to firm) units. Their softest spring rate (250 pounds) is suitable for racing.
KONI sells 42mm Inside Diameter and 50mm I.D. threaded sleeves for coilover use. They use 2-1/4 inch (57mm) I.D. springs. KONI 80-series are 42mm O.D. shocks, while 30-, 82- and 87-series is 50mm O.D.
generic coilovers
SPAX on dattodude sedan:
Spring Seats
You can buy the spring seats separately from the springs. Since most "kits" are only available in high spring-rate (stiff) springs, not suitable for streets 1200s, this give you the flexibility to mix and match.
Threaded Seats
A coilover 'kit' typically comes with a threaded tube and nut-type seat that can be screwed higher or lower. They typically come in 2-1/4 inch size for 2-1/4" springs.
You can buy these separately and use with your own spring choice.
BMW Spring Seats
Instead of buying new, 2" diameter expensive springs, re-use your existing ones by using BMW removable spring seats.
BMW sports option rear coilovers have a glued on lower spring seat that can be tapped off, the ID is the same size as the datsun OD so can be slid over the Datsun 1200 strut and welded on. They come in late 70s-80s 320i, probably in a lot of other BMW models too.
The BWM spring has a flat bottom, for use use the the BMW seat. However, the top of the spring is the same as the Datsun spring so it fits the 1200 top seat perfect. These BMW springs are around 200 lb/in, suitable for racing 1200s.
Do they work with the stock 1200 springs?
reference: removable spring seat
Fastening the Spring Seat
Traditionally, spring seats are welded to the strut body. Or, some Datsun fans use a Shaft Collar instead of welding the bottom perch. Both methods allow adjustment on-car after installation.
See main article: Fastening Spring Seats
Base Height Coilovers
Most coilover kits installed on Datsuns use a normal height adjustment mechanism which pre-loads the spring to adjust the ride height. But there is a more advanced system called 'Base height adjustable'.
To install a 'base height' adjustable kit, you cut your standard strut tube down to about 2" long and weld on an internally threaded sleeve. The fully threaded coilover unit then screws into the sleeve, and a lock ring secures it in place at the desired height. The coilover unit also features a conventional adjustable spring platform further up the body - this allows for independent spring pre-load and ride height settings.
The problem with conventional coilovers is if you set your car up on corner weight scales, the passenger side will be lighter, so you jack the weight from side to side side/front to back/diagonal etc to correct it - except then the spring pre-load is uneven and so too is the droop characteristics. Base height adjustables offer the solution here as ride height and spring pre-load are independent set.