No life (a.k.a. DattoMaster)  
Joined:
2008/10/10 22:02
From Melbourne Australia (and likely under the car)
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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.
Posted on: 2012/2/13 9:53
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Transfer
