Installing Tokico 280Z HP Springs in a 240Z

[johnc]

A member here called me on this recommendation. I've had this in my head and done it a couple times for customers at my shop but I never wrote it down. Here it is:

 

Stock 1970 through 1972 Datsun 240Z US Spring Specs

 

Left Front: 14.750" free length, 83 lb. in. rate.

Right front: 15.250" free length, 83 lb. in. rate.

Rear: 14.500" free length, 104 lb. in. rate.

 

The installed SPRING STACK HEIGHT under load (meaning installed and sitting on the ground with two 150lb. people in the seats, no fuel on board) is:

 

Left Front - 8" @ 562 lbs.

Right Front – 8” @ 604 lbs.

Rear – 8.4" @ 635 lbs.

 

Tokico Datsun 280Z HP Spring Specs

 

Front (5022-F): 11.250” free length, 185 lb. in rate, 8 free coils.

Rear (5022-R): 12" free length, 200 lb. in. rate, 9 free coils.

 

Installation Math (using the load information from the FSM)

 

To achieve a stock 8” installed spring stack height on the left front of the car the Tokico front spring needs to compress 3.25”. Given the 562 lb load in the example we get a 3” compression so the left front spring needs to have 1/4 coil removed to get to the 8” stock installed height (assuming a 1" drop in stack height for each coil removed).

 

To achieve a stock 8” installed spring stack height on the right front of the car the Tokico front spring needs to compress 3.25”. Given the 604 lb load in the example we get a 3.25” compression so the right front does not need any coils removed to get to the 8” stock installed spring stack height.

 

To achieve a stock 8.4” installed spring stack height at the rear of the car the Tokico rear springs need to compress 3.6”. Given the 635 lb load in the example we get a 3.175”compression. The rear springs need to be have 1/2 coil removed to get to the 8.4” stock spring installed installed height (assuming a .93" drop in stack height for each coil removed).

 

Quickie math: Take the installed spring stack height measurement and divide it by the number of complete coils in the spring. That should give you a basic idea of how much additional drop in stack height you get when one complete coil is cut.

 

Caveats

 

All of the above is for an “idealized/perfectly original” 240Z. Your car is not! I strongly suggest you put the Tokico springs on the car, loosely assemble the top insulator to the shock and then loosely assembly the insulator and suspension in the car. When I mean loosely I don’t mean finger tight. I mean snug things up with a wrench but don’t torque to spec. DO NOT DRIVE THE CAR IN THIS CONDITION. Just set the car on the ground and roll it back and forth, jump up and down on the door sills, anything non-driving to get the springs to settle.

 

At this point check the installed spring stack height and check your ride height. Then do the math and figure how much you'll need to cut.

 

Cutting the Springs

 

Its best to do off the car after doing some math and checking against the figures above. As far as cutting is concerned, it doesn't matter whether you cut from the top or the bottom of the spring.

 

If you want to try it on the car, you might be able to:

 

1. Jack up one end of the car so the suspension hangs free. Put the car on strong and secure jackstands. Don’t be a dumbshit, do this safely.

 

2. The Tokico spring will be loose and you should be able to pull it out at the bottom enough to get a cutoff wheel or hacksaw in there to make the cut. You'll want to cut at the bottom on the rears to make sure you don't nick the shock shaft if you screw up while cutting at the top. Its better to cut the fronts at the top so wrap the shock shaft to protect it from sparks and any clumsiness you're born with.

 

3. You don't have to make a perfectly perpendicular cut on the spring. Remember, its made from spring steel so its very hard and will take some time with a hacksaw. Buy extra blades. With a cutoff wheel buy some extra wheels. Don't use heat (torch or plasma cutter).

 

Once you have the ride height where you want it be sure to properly assemble the suspension and torque everything to spec. Again, don't be a dumbshit. Do this right, check your work, and be careful.

Edited September 16, 2010 by johnc

[hoov100]

Do you know what the OD the springs are?

[johnc]

The factory front springs are 4.35" OD and the rears are 3.94" OD.

[240Z_Master]

Reading this over roughly...I gathered that this method was for Tokico 280Z springs into a 240Z for stock ride height?

[johnc]

Reading this over roughly...I gathered that this method was for Tokico 280Z springs into a 240Z for stock ride height?

 

Yes.

[jbryan]

I found this post and I am actually trying to install 240z struts with a one inch drop into a 280z '78. Can this be done or will it be too short?

 

Thanks,

 

JohnB

[johnc]

I found this post and I am actually trying to install 240z struts with a one inch drop into a 280z '78. Can this be done or will it be too short?

 

Thanks,

 

JohnB

 

Search man and please don't post off topic in stickies or FAQs.