Thread: Suspension bushes

I had Rocky Mountain on mine when I bought it (78 SWB Game). The sag on the drivers side of those ended up at about 50mm before I replaced them with a set of Britpart ones. They lasted about 50km before the sag on the drivers side reached 75mm. I replaced them with another set of Britpart ones (warranty) and they also ended up sagging to 75mm (took a couple of weeks or so longer to do than the previous set). Then I went and bought some after market standard springs and modified them by removing some leaves and diamond cutting and chamfering the ends and while there is some sag it is no where near as bad and they are much more comfortable than the standard springs on the other Game. I have cold reset the fronts right and will get to doing the same on the back and I believe they will then sit nicely again.

One problem with Parabolics not often mentioned is that most spring companies will not reset them. The ones here in Brisbane I tried said that they break after resetting and they would not touch them. Not sure how true that is if they are done properly.

But I would not bother with Parabolics again. Though with the dollar so high against the euro at the moment there is always Heystee in Belgium, supposed to be the best you can buy. They also have disk brakes and power steering but it would certainly bust the $1000 import duty limits .

Cheers,

TimJ.

But funnily enough, Rocky Mountain and new after market set of leaf springs from a local supplier are about the same price, about $3-400 per axle last time I priced them. I like the idea of modifying stock spring sets, but you have to be able to buy a 'good' set of leaf springs in order to modify them. So, as my springs are sagged and pretty rigid, I'm thinking, why not try the parabolics, at least they will have 12 months warranty,(I don't know about mileage) but if I modify a set of new set of leaf springs, warranty gone! BUT, should it be necessary to modify a nrw set of springs to get an acceptable ride??, Buy the way, my shockies are in good order.

Looking forward to more discussion,

Regards, Jack

Originally Posted by jacknz

But funnily enough, Rocky Mountain and new after market set of leaf springs from a local supplier are about the same price, about $3-400 per axle last time I priced them. I like the idea of modifying stock spring sets, but you have to be able to buy a 'good' set of leaf springs in order to modify them. So, as my springs are sagged and pretty rigid, I'm thinking, why not try the parabolics, at least they will have 12 months warranty,(I don't know about mileage) but if I modify a set of new set of leaf springs, warranty gone! BUT, should it be necessary to modify a nrw set of springs to get an acceptable ride??, Buy the way, my shockies are in good order.

Looking forward to more discussion,

Regards, Jack

Your old, sagged springs are a much better starting point for modification than new springs, as long as they aren't pitted and swollen from rust.

The OEM steel used in landy springs is IME MUCH better quality than any of the aftermarket springs.

And the other problem with new springs, is that as far as I know, nobody is making them with the original thickness leaves - they use fewer, thicker leaves (except 109 rear, which are thicker anyway), which means that similar criticisms (although not as bad) can be made as the ones I made above about parabolics. This may be the reason that you have found the originals to be better rather than the steel quality - as the leaves are thinner, the same steel performs better.

John

Originally Posted by JDNSW

And the other problem with new springs, is that as far as I know, nobody is making them with the original thickness leaves - they use fewer, thicker leaves (except 109 rear, which are thicker anyway), which means that similar criticisms (although not as bad) can be made as the ones I made above about parabolics. This may be the reason that you have found the originals to be better rather than the steel quality - as the leaves are thinner, the same steel performs better.

John

You are correct in that the OEM leaves are as thin as 4.2 mm, yet modern spring steel is only readily available down to 5 mm. Which makes a big difference to stiffness. e.g. an OEM 9-leaf front spring made of 9x4.2-4.8 mm thick leaves is ~220 lb/in, whereas 9x5 mm leaves gives you ~450 lb/in!!!

However, I was talking about the hardness and fatigue resistance of the steel. When you drill and cut OEM leaves, you can tell they are a LOT harder, however they also are (IME) less prone to failure.

As for the thinner leaves - yes you are right that the interleaf streeses are less for thin leaves, therefore they should have more cycles to failure, however in practice I have found this not to be the case. I have never broken or seen broken a 7.1 mm thick (OEM 109" rear) leaf, yet I have broken and/or seen broken plenty of 5 mm (aftermarket) and 4.2-4.8 mm (OEM) leaves.

I was

If we consider two springs with the same maximum deflection and the same rate, the thinner leaved one will have, of course more leaves, and each leaf will have less strain. This means that everything else being equal, the thinner leaf is less likely to break (or sag). Of course, it would be too much to expect everything else to be equal, and I can see three reasons why the thinner leaves are more likely to break -

1. The 109 rear springs are rarely operated with their maximum load, and hence rarely get as much deflection as the thinner leaved springs do.

2. The surface layer of heat treatment represents a greater proportion of total thickness in the thinner leaves and localised defects in hardening are more likely to cause failure.

3. Similarly, wear or rust are much more significant for the thinner leaves.

Now I think about it, I agree with your observation of broken leaves, but I would add, most if not all I have seen have been in badly rusted or worn spring packs.

Worth noting that most of the length of the leaf in a parabolic spring is much thicker than the 7.1mm leaves on the 109 spring, so that the strain of the metal is much greater. Another point about parabolics - because of the greater strain, is it possible that they are more sensitive to surface damage, such as stone chips as crack initiators?

John