Alfa Pages

[RFlower]

There is a string about these started 19/01/04, but I'm wondering if everyone who lowers their suspension considers the effect on the valve adjustment.

If the equaliser is not adjusted for the new suspension height, the valve will operate as if the car is more heavily laden than it really is, possibly causing rear wheel locking under heavy braking. The valve and operating rod may also be damaged, as I have found on my 33, on which I have just replaced original suspension (it was lowered 35mm when I got it).

Of course this assumes the valve is not stuck in, which seems to be the usual case for 33's. This results in full pressure to the rear brakes at all times. Possibly makes the car more fun to drive?

Regarding operation of the valve when cornering, I believe the geometry is arranged so that the valve position is not affected by body roll, but to prove this you need a model (maybe on a computer if you are clever) and also to know the position of the rear roll centres, which also depend on the spring heights and rates.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)

[Peter D]

Yes, you have to reset the valve setting as prescribed, when fitting new lower springs.

You can also just move it a little and doing it again and again, until the brake balance just shifts from rear bias to front bias so that the front wheels lock up first (testing on a dry road with good friction).

That is the way to optain the best possible braking rate, because then you compensate for the actual friction of both the front and rear brake pads/linings and are not depending on the theoretical values on which the prescribed settings are based.

Peter (DK)

[Eddie W]

Hi Dick, from my understanding of suspension the roll centre is determined by the geometry(beam axle and panhard) not spring rates and heights which would determine the c of g axis. Others may have a more in depth knowledge.
Regards Eddie
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A LITTLE FURTHER A LITTLE FASTER

[RFlower]

Basically, yes, but springs, and also anti roll bars have a small effect, the roll centre height varies slightly between full bump and full droop of wheels.

I'm quoting from "Racing & Sports Car Chassis Design" - Mike Costin & David Phipps, don't pretend to know so much myself! I consulted this when I was trying to work out what that valve did on cornering, as I could not believe that Alfa designed the layout so rear wheels would lock up in one direction and have less braking in the other.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)

[Eddie W]

Hi Dick, an old book but a good one , on a beam axle the roll centre is (I think ) determined by the height of the Panhard at the axle end, It's a long time since I read the book. I think the action of the limiter valve is determined by where it attaches to the axle which is a fairly nuetral position.
Regards Eddie
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A LITTLE FURTHER A LITTLE FASTER

[lesthegringo]

Gents, before you condemn your balance /proportioning valve, you need to understand whether or not it really is stuck.

At rest, the stirrup, which is what sits on the sprung bar connected to the panhard rod, is fully up, or in. It is held there by two internal springs, which push two pistons, one for each side.

When you press the brake pedal, the two pistons are pushed downwards against the pressure of the internal springs and the external spring bar. While the pistons are moving, they absorb the pressure that would be applied to the rear brakes. Once the pistons have moved sufficiently down to push the stirrup against the spring bar, the pistons then encounter resistance and start exerting force on the rear brakes. The height that the rear axle is at will determine how much upward force is applied to the spring bar, and therefore determine how far the piston will travel before the rear brakes receive full pressure.

From that it can be seen that a heavier rear end, or a lowered rear end, will bring the rear brakes into play earlier in the proceedings. The spring bar can be adjusted (bent!) to compensate.

The way to check the valve is to get someone to stand on the brakes with the back of the car lifted up - you should be able to see the stirrup move. Whatever, they are not actually that expensive to replace, just a real bastard to get get to.

Some notes:

The four hydraulic lines that it connects with are arranged with different thread sizes to minimise the chance of connecting it incorrectly. There will be a need for two spannner sizes, and access is very poor.

The area is very often exactly in the right position to accumulate all the mud and crap that the rear left wheel throws up, so you'll have to go in there with a stiff brush first.

Remove the preload mechanism first, and then lower the spring bar, as not only will this make it easier for the valve to be removed, it will also give better access.

The 33 valve is a dual circuit one, and proportions the two circuits simultaneously. The AlfaSud valve is single circiut, and works on both rears. The dual circuit valve can be retrofitted to the AlfaSud, along with all the rest of the 33 hydraulic lines.

Les