buzz

[92SVXLS-LDC]

alright...
my car frequently makes a buzzing noise from the tranny, doesnt sound mechanical, however for a while i thought something was just vibrating...

if i'm in any gear besides neutral or park... say at a drive through (pretty noticeable there) it'll buzz, till i get goin a couple mph...

now explain this... when i was testing my new stereo, i had the shift lever all the way into position 1.. Car OFF, key to acc... just for testing, and i heard the buzzing again, with the car off!!! when i pushed it into neutral, it went away, car is still off... just accessory on...

what would this be? if i need to explain myself better just say so, i will try

[oab_au]

Originally Posted by 92SVXLS-LDC

alright...
my car frequently makes a buzzing noise from the tranny, doesnt sound mechanical, however for a while i thought something was just vibrating...

if i'm in any gear besides neutral or park... say at a drive through (pretty noticeable there) it'll buzz, till i get goin a couple mph...

now explain this... when i was testing my new stereo, i had the shift lever all the way into position 1.. Car OFF, key to acc... just for testing, and i heard the buzzing again, with the car off!!! when i pushed it into neutral, it went away, car is still off... just accessory on...

what would this be? if i need to explain myself better just say so, i will try

It is the solenoids in the gear box doing the buzzing, its normal.
You must have very good hearing, I have to stick my head under the car to hear them.
Harvey

[92SVXLS-LDC]

too loud, its not LOUD... but its not normal, i'm sure of it...
could they get louder if they're bad??

[Trevor]

Originally Posted by 92SVXLS-LDC

too loud, its not LOUD... but its not normal, i'm sure of it...
could they get louder if they're bad??

I have already written up something which will help you understand things.

DUTY SOLENOID VALVE "A".

This is a pulse width modulated duty solenoid valve, ( Sometimes known as a pulsoid). The device is incorporated in the SVX transmission control system in order to adjust line pressure in the following manner :-

The fluid line is provided with a bleed or bypass via an on/off device, in the form of an electrically operated valve. This solenoid valve is opened and closed repeatedly, in a rhythmical manner by a control current which is turned on and off by the transmission control unit (TCU) at a very fast rate. The valve is a normally closed device, and remains closed in the event of the loss off a control current.

After passing through this modulated solenoid valve, the continually interrupted pressure is in the form of a pulsed flow. When the peaks level off with the troughs, there is a resulting overall steady reduced pressure. The level of this pressure is adjusted by varying the on/off intervals. Most often the length of the on time is adjusted and the number of on/off pulses per second is kept constant. The usual rate is around 50 cycles per second.

The resulting adjusted output pressure is therefore delivered as a rapidly fluctuating stream. The system incorporates an expansion chamber as a smoothing element, which works as a sort of cushion. This device is usually in the form of a cylinder and piston or diaphragm, backed by a coil spring. In the SVX system the component is described as a Pressure Modifier Accumulator. The high pressure peaks in the stream press the piston outwards and become rounded off, while the low pressure troughs are filled in as a result of the piston moving inwards under spring pressure. The end result is a smoother level of pressure, such that controlled devices are not materially affected.

An increase in the volume of fluid controlled, is achieved by transferring the solenoid regulated pressure, to a pressure modifier valve and a regulator valve.

It should be clear that by “chopping” the fluid supply in an adjustable way, pressure control is achieved economically using a simple poppet type solenoid valve, with few mechanical or electrical complications. However the valve remains in a continuos cycling mode, which imposes rather arduous mechanical stresses.

THE DROPPING RESISTOR CIRCUIT.

It will be immediately apparent that a sudden on off cycle tends to cause what could be called a hammering of the valve seat, even though this is largely checked by the viscosity of 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 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. This arrangement can be made even more sophisticated and configured so as to soften the the opening cycle, as well as the closing of the valve.

It will be appreciated that reducing 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 a second issue, increased shock loads are applied to the valve.

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

It is a documented fact that the line pressure control solenoid is the first to fail due to having by far the most arduous duty to fulfill. 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 fault will not necessarily be registered as a fault code, as the armature of the valve can be in the fully closed position with the problem confined to a worn and faulty valve seat. In the event of an electrical fault, which will register, the valve being normally closed, will fail safe and result in maximum line pressure.

SOLENOID "C".

Also a pulse width modulated solenoid valve this device is arranged to adjust control pressure to the centre differential, or alternatively clutch actuating mechanism, according to model. Solenoid C operates along the same lines as solenoid A. However the duty is in no way as arduous as that involving constant control of line pressure and no parallel secondary circuit is incorporated.--------

You will see that lack of fluid or air in the system, could result in a solenoid making an excessive noise due to the normal damping factor being absent. There have been no reports of a resistor fault causing this problem, but a low resistance may do.

Now that you know what is involved, follow your nose.

[92SVXLS-LDC]

whoa, i'm lost...

[oab_au]

Originally Posted by 92SVXLS-LDC

whoa, i'm lost...

That makes two of us.

Harvey.

[-JJ-]

Before goin all to technical, check this out first....
This was the source of my intermittent "buzz", it may not be the cause of yours but its worth checking, to rule it out!



Good luck,
Jake