[TomsSVX]

Originally Posted by Trevor

Set out below is a write up I prepared some time ago covering details including the resistor:-

THE DROPPING RESISTOR CIRCUIT.

It will be immediately apparent that the sudden on off pulse width modulated duty to which solenoid valve “A” is subject, tends to cause what could be called a hammering of the valve seat, even though this is largely reduced/damped by the controlled fluid flow.

The dropping resistor introduces a second series of current pulses applied in parallel with the control signal. These shorter pulses are applied during the off cycles and are timed to check the travel of the armature as it reaches the closed position, thus reducing both shock and noise. These secondary parallel signals in effect, “round off” the closing period and reduce the closing shock.

It will be appreciated that increasing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, has two outcomes. Firstly the relative electrical off time is increased, thus increasing the line pressure and therefore makes shifts more abrupt. Importantly as an undesirable second issue, shock loads applied to the valve are increased.

It is a recognized fact that the line pressure control solenoid is the first to fail, due to having to fulfill by far the most arduous duty. Failure is usually mechanical resulting in the valve seat not closing properly and as a result line pressure is markedly reduced. The end results are drastic, especially in respect of transmission friction surfaces.

The resistor should measure between 9 and 15 ohms to be within specifications. The usual is about 12 ohms.


You are doing the absolutely correct thing by driving in third when in traffic etc. In fact this will reduce hunting between gears, as fourth/overdrive will not become involved immediately light transmission loading is available.

Glad to have ya back Trevor

Tom