21 replies to this topic

[Dan]

It is water, promise. It's got a tiny bit of glycol added to stop it freezing up and some dye and flavour to stop you drinking the glycol but it is basically water. It's the dye you can't get rid of.

The displacer works like this:
The bottom of the displacer is a conical piston, this pushes upwards into a reservoir of fluid when the suspension is moved. At the top of the reservoir is a valve which leads to another small reservoir, connected to a pipe which travels to the rear displacer. The important bit is the valve (well the shape of the piston matters too, being conical it means there is an exponent value in the amount of fluid displaced for a given travel). The pressure on each side of the valve determines which way fluid will flow, into or out of the larger reservoir. If the pressure both sides is the same, no fluid will flow. So what you're saying is that if you try to lift both wheels the same amount at the same time then it will be impossible to move either. This wouldn't give a very nice ride and would soon damage the car. The really clever bit is that the valve and it's smaller reservoir are mounted inside a rubber cone spring. So if the pressure on the valve is equal both sides and there is no flow of fluid, the suspension movement can be taken up by the spring without increasing the line pressure in the hydro system. That's why the displacers are connected by flexible hoses rather than rigid ones, the whole system moves about. Alex Moulton's a clever chap, he knew that if there was nothing flexible in the system something would break.

Insert very old BMC drawing -

[Pavel]

Glycol! That's it!
That IS a clever piece of gadgetry to be honest, but what happens once the rubber spring perishes as it does in dry suspension systems? Or is that a rare occurence?

There we go, learn something new everyday!

[Jammy]

Quick question, I'm guessing dry subframes would need a fair bit of 'adapting' to allow use of hydro suspension?

[Pavel]

I believe so, the seats are different. Otherwise I couldve easily given you a bunch of hydro setups from here (got access to 2 for free, whether one is shot I don't know).

[mini1976]

Didnt this topic start cause someone wants to convert from hydro to dry. Maybe you guys could get together and swap

[Jammy]

Yea, I thought that, but I don't have a system to swap with. The hydro system would go on a future project.

[Dan]

When the displacer dries out, hardens, perishes or does any of the other wonderful things rubber can do to annoy you you need a new one. Which are no longer available. There's some new old stock ones lying about in various warehouses around the world but they could be just as dried out as the ones you're replacing since they've been sitting there for at least 25 years. So it's fair to say that very few hydro Mini's still perform as well as they did when new because rubber does wear out. This is something that Heritage really need to work on re-introducing.