This is what I wanted to read

Thanks Feral!

To determine your spring rates, Remove springs from your struts then set the car at the desired ride height using a trolley jack. Lower the car and check the amount of available travel before fouling occurs or end of travel is reached. Write down the bump travel. Raise the car fully till the arms are at full droop and measure the total suspension travel.

Belgian Roadster The front corner weights on your car should be approx 250 kgs (550 lbs). Designing the suspension for a maximum load of 2.5G's for club/road use The maximum load is 550 *2.5=1375 lbs.
Divide this maximum load by the amount of travel available and you get the rate in lbs/inch that will provide the load on the springs to fully limit travel with 2.5 G's.
If your car has 4" travel then 1375/4" = 345 lb/inch springs.
For 6" travel 1375/6" = 229 lb/inch springs.
This gives the spring rate to use.

The length of the spring to use depends on the position of the spring platform and is a secondary consideration after the necessary rate has been determined. The spring must remain captive on both platforms at full droop. This can be adjusted by limiting droop travel or fitting tender springs if only short springs are available in the required rate.

If using premium quality shocks the valving rates are determined by the spring rate and the corner weight and usually do not require further adjustment for normal use. On race cars the adjustemt is needed to take account of varying race conditions such as wet tracks.

For other brands that have double adjustable functions you must select a shock that has a suitable range of adjustment in both the bump and rebound for that application. Often adjustables ( and some double adjustables) sold over the counter are not suitable for the application. At best some single adjustables have pathetic low, intermediate or high shaft velocity valving and are not much more than jazzed up tap valves. In shocks you usually get what you pay for.

The shock stroke should exceed the total suspension travel. Droop can be limited by fitting internal bump stops in the shocks if required.
My 2 cents worth

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As you can see, I'm not alone

Taking about availability of Datsun parts not only in Belgium but in nearly hole Europe, it is = 0
All Datsun and Toyotas have been sold to Africa regardless of rust, engine damage, missing parts. Africa took it all.
Only way to get a Datsun is buy one where they are still running for exemple PORTUGAL. You can compare it a bit to California, US. Much sun, few humidity, no salt against snow. Even better are cars from the isle of Madeira. That is were I bought my 2 B110 2door and 1 510 4door.

So if you need much parts for a conversion/swap you take it from another cars you bought before or you just buy a new ones.

You're right I had 910 still as NOS in my warehouse.

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This Is a fine description of what I was worried about. If the ride height is not good, if I have to lower the car a bit more.....what happens to my spring?....not enough preload! As I will work with height ajustable spring perches

I could use a helper spring to give enough preload at full suspension travel. But before using a helper, you have to choose the right main spring. That is what all this topic is about.

And don't forget I will use a SR20DET, so a 1200 aftermarket sport spring will compress to much under the more weight of the SR20DET. At least that is what I suppose.
Butr at least I know now that I have to start with 240Z shocks.
It seems that Tokico Illuminas are preferable to the Koni's as I read on the 510 mailing list.
Thanks to all,
Chris
To all 910 strut user keep the forum updated about your experience

Ill be doing more or less the same. A mate of mine used asimilar set up , only he welded threaded pipe to the strut, and had two big nuts underneath the bottom spring cup to make the height adjustable. Then he had hillman avenger stationwagon rear coils either cut or compressed( I'll have to ask him) . Adjustable strut tops, 310lower arms modified to give adjustable camber, and he had cut and welded some 310 steering arms to alter the ackerman. When the time comes I'll hit him up for more info. But anyway that car had demon handling.

I am also using 910 front struts, I was recommended these by people in the car industry that use to run 1200's in rallys. I have carried out modifications upon recommended strategies. 310 sterring arms and bottom ball joints (which increase track width by 25mm) OE bottom arms, radius rods and top strut support. New 910 shocks and compressed 910 springs lowered to set camber but using original spring rate.

But heres the biggy, I have yet to complete this task which will happen one vehicle is reassembled with full vehicle weight, so I can neither confirm or deny whether this setup IS successful.

Damon

Ok, you are "fixed" on using these 910 struts. These were on the 1980's Bluebirds here in Australia. This is part of your problem. I don't know of anyone else using these struts in their 1200. Does this not set off alarm bells for you?

Is the 910 strut assembly the best platform for your brakes and front suspension?

There are many reasons why people choose a strut for use in their Datto upgrade:
- Cost
- Availability
- Length
- Shock Absorber Availability
- Camber on Axle
- Availability/Cost of Brakes spare parts
- Ability to work with a known upgraded disk/caliper
- Availability of Springs to suit a 1200

I don't know what made you decide to use 910 struts. I can only think that you had them in your shed, and have chosen to use them based on Cost and Availability.

You have chosen a combination that has not been tried by other people. You will need to answer many of your questions through trial and error, and this will involve cost and mental pain.

By following the combination of parts used by others, you don't need to understand the complex science of suspension systems.

In Belgium do you have many "Wrecking Yards" with Datsun parts for sale? In Australia, we have them, and most have a good selection of parts to choose from.

If you have only a small number of choices in what spare parts are being used, then this will constrain the solution that any of us can provide.

When shortening the strut tube, you are making changes that will require some degree of trial and error.

1. Say you cut down the strut to suit a 240Z insert.
2. What length spring does a 240Z use?
3. What weight is that spring carrying? Too much for a 1200. For B110 diameter springs you can use the 240Z, 1200, 210, 310, A10 springs. All of these the same diameter (different length, different load capacity). There are also 2 diameters of strut tube. Smaller 1200 ones and the larger ones for L Series equipped models.

If you are to use the 910 struts, then the spring cups will need replacing. I recommend using stanza A10, cups. As they are the larger diameter, and cheap and easy to find.

The 1200 springs (even aftermarket sports springs) have enough travel to cope with the shorter 240Z inserts. So I'd recommend using aftermarket lowered sports 1200/120Y springs, Stanza Cups, 240Z inserts, and cut down your 910 struts to suit. Assemble the struts with the cups loose on the strut tube, push the cup up until it holds the spring in place with shock insert extended. With a texta, mark the spot where the cup is sitting on the strut tube. Disassemble the strut, move the cup 5-10mm up the strut further, to provide some spring preload, so it doesn't rattle around when the car gets airborne over speed humps. Tack the cups into place in 4 spots. Reassemble the struts, and drive up and down your driveway and see where the ride height has settled. If it's ok, remove the struts and complete the welds around the circumference of the cups, then refit and go for a decent drive.

Chris

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Please give me an exemple of what you calll a factory part for my 910 strut?

A bottoming spring or a bottoming shock is BOTH bad. Both will mean you risk bending the chassis.

You should have a rubber "bump stop" inside the coilover to prevent either the spring or shock from physically bottoming out.

As for spring rate, many springs have a progressive nature, to provide soft ride and protection against bottoming out under heavy spring compression.

Always have more spring than required, thats why you never see springs close to the same length as the stroke of the shock. For soft springs, the cup on the strut should be 5-10mm more than the sum of the diameters of the spring material from top to bottom. This means that the spring can never bottom out.

Then it's up to the shock to stop itself from bottoming out, and the spring strength to assist, given a maximum load scenario.

Seriously, you should just use factory parts, or someone elses tested solution, and all of these considerations aren't required.

Chris

The problem I have is with the stroke of both spring and shock insert. The stroke of spring should be shorter as the shock to prevent bottoming. At least that is what I think.
Once I have chosen a shock insert and I have cut the 910 strut, I can measure the stroke of this insert. I then know what free lenght the spring need to have. But how to be sure that the car will not drop to low?
For the spring rate I suppose I have to watch the spring rate for similar cars with the same engine. S14 or more NX with SR20?

As a starting point, try inserts out of a 4wd celica. They should be around 30mm shorter than the 910's

For the street, try 9-10 inch tall front springs, tack the lower spring platform in place, let it off the jack see if you end up with around 6 inches bump and 4 inches droop travel....
If not, grind the platform off the strut and move it accordingly until you do...
The spacer between the steering arm and the strut is only needed if your bottom arm ends up lower at the crossmember end. For road use, this arm can be 5-10mm lower at the outer (strut arm) end....
Spring rate....hmmm....I could only guess for road use, but say you put an extra full length leaf in the rear, try doubling the front spring rate....