allright- based on that I'm assuming it's a drag race only setup. If I'm wrong, say so, I'll 'adjust' any further posts to suit what the combo is! Do you mind if I ask what engine and gearbox it is running? I'm suspecting a ca or sr, or heck, maybe an fj (there's been a few quick utes with a turbo fj20 motor)

Anyway - some updated comments based on what you've shared:

detroit locker - pretty solid, fairly consistent, and were a good option for when you needed it to unlock to turn corners (for parking lots or whatever) but lock solid under power. I'd probably suggest going to a full spool if it is drag racing only - it's a touch lighter (marginally less inertia so a potentially quicker et, if you can hook it up) and it's locked alway, no guesswork, no moving parts, so to speak.

Next - the adjustable shocks and rear springs. You'll have to get someone to film it launching from side on, in particular watching the rear half of the car. It is very much a possibility that the suspension is bottoming out at the rear under a hard launch. When the shocks work like they are supposed to they give a smooth progressive 'loading' helping the weight transfer and downforce, but if it bottoms out, it hits the 'end' of travel and is a shock load, and will break traction a lot easier.

So you might very well need to increase the bump resistance/stiffness of the shocks. On that front be careful, I don't know your specific shocker model/type but SOME adjustable shocks are pre-set for bump and are really only adjustable for rebound. That combo is great and works for a lot of entry level circuit racing (as a general statement, and no doubt there are big exceptions to that) but it isn't so good for drag racing, where it's the bump resistance you need to tweak on the rear shocks at least.

So if it is bottoming out hard, increase the bump resistance in the shocks (if it can be done) and see how it goes. If it _still_ bottoms out, you will have to look at stiffer rate springs. and then lighten the shock bump setting and re-test, increasing if necessary.

It's _also_ possible if it still has the ute springs in there, that it's not 'bottoming out' as such, but that the shock _is_ coming in when the springs it the over-rider spring (the extra leaf on the utes, that comes into play if there's enough weight in the back to compress the suspension, and it increases the spring load from that point onward). So if that over-rider (I forget what it's more commonly called in datto 1200 circles, anyone?) spring is there, consider swapping it out and re-testing.

You might get to the point that you have that ute leaf removed, but instead of that causing the shockloading, it now bottoms out. If that is the case, get your hands on a spare set of leaves (or get a couple of pieces from a spring place that fit) and try sandwiching in an extra leaf, but this time one that plays it's part from the very start.

Alternately you could just modify the rear leaf shackle, and extend it, and bolt the rear leaf onto a lower hole (one that you have extended and drilled, a bit like in the datsun competition suspension pdf document available for download on the site). You'd be doing it for different reasons, but by doing that it is an easy way to lift the rear ride height, improve the rear suspension geometry (at least as far as hard launches go) and it would place it an inch or two higher which means it's got to squat back a lot harder before it bottoms out (if bottoming out was the problem of course)

Since it's drag racing - I'd _definitely_ go for more weight in the rear. I mentioned putting it as far back as possible. If you were to manage to put it (hypothetically) 2 metres behind the rear wheels, then for every kilo added at that point, it'd quite likely be the equivalent of 2-3 kilos of downforce added over the rear wheels. Think of the rear axle as a sort of 'centre' to a see-saw, and if you put weight far out the back, that weight is added to the centre, -plus a similar amount is unloaded from the front wheels and transferred to the rears, without actually moving the motor etc rearward.

OK so we've mentioned moving it back as far as possible. One of the 'prime' locations, due to it being 'right' at the back - is the rear bumper. If you have enough spare time, you could strip the inside of the bumper (if it is chromed) and then melt down and 'solder' some lead in there (I'd probably encase it - one easy way to do so is to weld a mesh grille along it's length, tilt it so the 'back' of hte bumper is at the bottom like a big bathtub with a mesh cover over it, melt the lead through, using soldering fluid (possibly called flux elsewhere?) and it'll mostly attach to the bumper itself, but even if it doesn't, once it solidifies, it'll be a solid lump and won't be able to get back the other way through the holes in the mesh/grille.

The beauty of that (if you then paint it - maybe matt black on the outside) is that it is essentially 'hidden' so the vehicle appears unchanged, in that respect at least. You could even look at the option of simply bolting on the weighted bumper for drag strip days, and a 'proper' one for street driving (where you likely wouldn't be pushing the car to the limit anyway, so it'll have more than enough traction for street appropriate driving)

Another thing you could do is (and I can't believe I'm saying this) is to add a wing of some sort to the rear, with as much overhang/rearward positioning as possible. This could (if the wing profile suits the combo) provide a bit of downforce at higher speed, which would be a good thing if you are running drag tyres with lower pressure at the rear, and front suspension setup that suits rearward weight transfer etc etc. But you could also find a way to include weight in that wing, which would overhang the rear and have even more leverage than weight added at the bumper.

You 'could' always just use a far more aggressive wing further forward, of far more weight positioned over the axle centreline. BUt of course, that weight has to be accelerated, and that wing will cause some aerodynamic drag. So in both cases, the further back you put them, the more leverage they have, and so you'll need less weight or less wind resistance to get the same job done.

What else - you could also look at the rear tyre pressure. I'd need to know specifically which brand/model/spec tyre you are using (and I'm not suggesting I know them all off the top of my head, but I'd need to look up whether they are radial or not, most likely yes, and their construction more generally). What I'm getting at is that usually - unless they are specifically designed for drag racing (some circuit racing, but generally they don't run quite as low in pressure as drag oriented slicks or semi slicks) - well for a lot of tyres (all 'real' street radials ) lowering the tyre pressure won't increase grip. It can actually reduce it. If they are a proper drag racing tyre, the sidewalls are made to flex (a lot) and they also will run at lower pressure without the contact patch being screwed up to the extreme. They act as a cushion (like the shock settings nad the springs too) to allow the weight/downforce to be smoothly increased/maximised for max traction and no shock loading. SO if they are drag tyres (and manufacturers generally specify these things if you enquire) certainly also play with the rear tyre pressures too. IF they are street tyres (i.e. anything from a true street tyre and also including 'some' of the tyres that are treaded and are referred to as 'street legal' but are really competition tyres made to be 'legal' in racing classes that specify a treaded or street tyre of some sort), try going a bit higher in pressure. Sometimes (esp if the tread has lots of tiny blocks, but almost never if the tread has huge tread blocks with only a few token grooves to make em look street) the higher pressure helps make the blocks more stable so they won't (for want of better term) roll or squirm and then lose grip.

Similarly - a lot of street tyres (and less so the competition ones) grip ok at modest temperatures but their grip falls off when they get warm. So unlike race compounds that tend to have a heat range where they work best that is a little higher, they (the non competition tyres) can get worse at similar temp. Why I'm mentioning this as well, is that the seemingly 'compulsory' burnout to heat the tyres just before the 1/4 mile run - well on some tyres it can actually worsen their grip. You can't always 'drive around' the water puddles where the burnouts are started in drag racing, but if you can, without getting the tyres wet, then try it. If you _can't_ get around it, then give them a quick blast, and move forward the instant they start to spin, continuing the burnout just a little longer to get rid of any water, but stop well short of the hardcore burnouts most high end drag cars with drag tyres do.

And on related note - also get someone to record the launch focussing on the rear tyres. It might possibly be (if they are drag tyres, and the pressure is low enough the the rim itself is bottoming out on the tyre (or coming close to it). I haven't seen that (that I can recall) but I think it is at least possible, and without knowing specifically what tyres and what pressures you run, and thousand other thing, obviously it's something that needs to be at least investigated (to whatever extent is necessary to totally rule it out)

If you check google, look for the phrase 'match bash' - they were drag cars from circa the 1960s. they had more or less conventional bodys (gutted out) - but they'd cut the guards, inner guards/wheeltubs and alter spring/suspension. They moved the rear axle forward,
by a fair bit (probably 15cm or more). Shifting it forward is like shifting the car body rearward - so that extra rear downforce/loading thing - or another variation that achieves the same thing. Likewise, they moved the front wheel centreline forward (so even more of the weight is carried on the rears). Obviously I'm not suggesting you move the rear axle centreline forward - it's major major work. But you _can_ alter the front (by a small margin, but hey, every little bit helps). Essentially if you had/made/fitted some adjustable caster bars (also called tension rods), you could then adjust them to provide more positive caster (which is achieved by moving the wheel/steering assembly forwards). The extra caster will improve stability, esp at higher speed (also make the steering heavier, but there's no such thing as a free lunch). And since hte front wheels are moved forward, the rears take up more weight. You obviously can't move it a mile forward - maybe a few centimetres. Even if you could move it way forward theoretically - it is putting the control arm on a bigger angle, front to back, and this puts a hell of a lot more strain on the control arm bush. And even with a mdest forward shift of the front wheels, they'll hit the bottom/corner on each guard just in front of the wheels (esp so if it has bigger tyres on the front). Trimming the front guard is easy enough to do, so get whatever front caster increase you can.

I've mentioned all this stuff as most of it could be done without spending millions - it'll mostly just take time and perseverence/methodical testing.

Depending on the motor type and fitment, you can also look into altering the firewall and trans tunnel and shifting the engine rearward.

Last thought (for now!) - I have no idea what the budget is, but if it's not a huge no-go - well if it is currently a manual transmission, swapping to an auto (with appropriate upgrades and a torque convertor spec/stall rpm to suit it well) makes for much more consistent and harder launches. You can even do stuff like have a switch/sensor that runs less boost (or less nitrous, or even less ignition timing) until a certain road speed, or whilst in first gear, or a 2-3 second delay after launching - whatever is most useful.

For anything more specific - we'd need more details on the exact specs - including rear suspension bushes, how the caltracs are set up, specific motor and box, and the power output - both hp and rpm it makes it at. Torque figures. Or even better - any scans of a dyno run with it or anything? Which diff (detroit locker came out for the ford 9", but there are other diffs out there with that type of lockup device)??

If you have time and the equipment - it'd also help to see pics of the setup - the rear end from various angles, so the leaf pack, the diff/type, the caltracs (to see how precisely they are installed and adjusted)

It has a
Detroit locker
semi slicks
coilovers in front
Koni adjustables in rear
caltrac tramp rods

Thanks heaps guys for all ur help

LSD, semi slicks, shocks, springs, tramp bars, throttle control all could help this!

unbelievable that you would sit there and write a post covering so many bases when the original poster hasn't bothered to post much detail about the setup at all... a very patient man you must be....I love your passion for cars!

your a beast jmac! What he said

I'm going to look at this axle height vs front eye bolt height. You mean the bolt holding the front leaves to the chasis correct?

This is no 'trade secret' but there are good and bad tyres, each have combinations of longevity vs grip, vs sidewall ridgidity/compliance - and basically each tyre is made to emphasize whatever they think is most important for their users. So basically if you look at a more expensive, grippier tyre (that will wear out a lot quicker) you'll get a better result.

Driving style is a HUGE thing on something like a ute, which has less weight over teh rears (in general). If you do add any weight, add it right in the tailgate region, so it has more 'leverage' to create more downforce than if it was just over the axle centreline. But note that doing that also gives it more 'leverage' for hte rear to start to break loose during a hard corner when you accelerate mid corner or on corner exit. But on driving style specifically, you need to (at the expense of clutch life) slip the clutch off the line _ a fair bit _ as power goes up, so that there's rearward weight transfer (and the whole body doesn't have to actually tilt rearward a lot - weight transfer can happen without massive suspension movement). So that certainly helps.

The next thing is suspension setup - is there any chance it is lowered at the rear (maybe the front too, but the rear is the big deal for this one) ?? If it is lowered, two things can be big time bad news there. Firstly, if it uses lowering blocks, they space the axles away from the springs, and give them more 'leverage' and it's a lot easier to wind up the leaf springs in a layed down S shape, and that will lead to axle tramp, and a loss of grip..

And on top of that, if it is lowered by lwoering blocks, or reset springs (either way) and it has been lowered to the point that the axle centreline is level or even higher than the front spring eye bolt, then that is very bad for launch/traction.

THere's a little bit more to it than that but in very basic terms, if the axle centreline is lower than the front spring eye bolt, as the wheels push forward, the front of the leaf angles upward, and so it pushes forward AND tries to raise the car up (pivoting on the front spring eye bolt). It won't 'actually' raise the car up, it will just try to. Since it has rearward weight transfer at the same time, the car resists being raised, so what instead happens is it tranfers the force, and actually pushes the rear tyres down onto the road surface, increasing the downforce, and therefore the grip..

Not surprisingly, if it has been lowered far enough that the axle is level with or higher than the front eye bolt, it'll try and push the other way, and lower the car, or as before instead of lowering it as such, it'll REDUCE the amount of downforce on the rear tyres. And that might be exactly what is happening.

The next 'related' issue is the springs again. Over the years, due to the engine rotating/powering in one direction, it always has some twisting force acting on the diff/housing at full power, esp in the lower gears. This then raises the right rear under each hyard launch. Which is why non lsd diffs tend to always spin the right rear when you launch hard.

OK, so over the years that right rear leaf sees more stress/forces and will sag a little more than the left rear. So that means the right rear tyre is always having less downforce, so it won't grip off the line. And even with an lsd, you still have inconsistent grip left vs right and overall traction is not optimised.

You could put in new springs, hey no drama. BUT even with new springs with even heights, well that right rear is still going to lift on a hard launch. One of the tricks (and I haven't done it specifically on a 1200, but on plenty of other cars) is to swap the left and right rear springs from side to side. That way now the left rear has a little less downforce than the right when stationary. BUT when you launch hard, it lifts the right rear, and since the right was pushed down a little harder than the left to begin with, well when it lifts it, it ends up back to (or very close to) 'even stevens' left to right rear downforce, and launch potential is optimal.

With regard to the axle vs front leaf eye bolt heights, there's not any great way around it, you might need to raise the rear (though I admit I don't currently know what the rear is currently setup like, so I'm trying to cover all things it _might_ be). The other way would be to raise the front eye bolt location. That's not really doable easily on a datto, you'd have to move the springs inboard of the chassis rail section, so they could be located higher (and you'd oo inboard, not outboard, since this would also allow for larger rear wheel sizes.

If the heights of said pieces are ok, but it's still showing axle tramp, then traction bars are the go. There's a few articles on how to make and install them in general on the net, and there's also either a thread in the archives here, or on the datsun 1200 tech wiki pages.

cool, so its just the springs then

you got a big turbo giving a big power whack at once or reasonably smooth power delivery?

you trying to drive fast or do burnouts? you got open or lsd or locked diff?

the more you tell us the more we can help

there are your tyres hitting? what diff? what wheels? blah blah blah

It's got brand new Koni adjustable shocks

two options...

1. put the 500kg pay load in the back that the ute springs are designed for

2. put coupe/sedan springs in there that arn't designed for that


you probably have not put new shocks in either.... that is gonna make a massive difference too