Banner Vehicles July 2019

Transmission Fluid Levels

When did you last check the oil level in your gearbox?

Gearbox Dipstick The Fluid level in both Automatic and Manual Transmissions is incredibly important. There is no such level as low; it just has to be full. If you let your transmission get even 500 ml low of fluid you run the risk of major transmission damage. Running low fluid levels in transmissions is totally unforgiving. We have seen so many transmissions with damage from low fluid levels over many years of dismantling, rebuilding and selling both Automatic and Manual gearboxes for Fords and Holden’s.(Note some transmissions are not fitted with dip sticks so you will need to ask your garage to check the level).

Here is some research information we found that backs up what we know already:

Gearbox dipstick showing low fluid level1.    LOW FLUID LEVELS

“The testing of the transmission was carried out under controlled conditions at 500 ml below the recommended oil levels or approximately 12 mm bellow the pan rail. The pressure in the transmission was monitored and in this condition the gearbox was completely unstable. It was jumping from very low pressure to beyond the maximum of 300 PSI. When you changed gears, particularly on the 2-3, 3-4 and reverse gear this condition became even worse. You could easily see how after doing this you could do a lot of damage to the condition of your transmission”.

Transmission Pressure Guage “In the case of the low pressure coming from the low fluid levels the result was obvious with major friction burns, however at the same time the pressure spikes could just as easily break parts inside the transmission and push out snap rings causing serious damage or sudden failure”. 


Adding Transmission Oil“Tests done by over filling the transmission with too much fluid was however unlike the lower fluid level test above. Although you would imagine the results would be similar. Adding about 500 ml over the full line did not seem to have any notable effect on the transmission performance.

However adding 1-2 Litres over the full line began to have pressures resembling the low fluid scenario with the pressure dropping and spiking erratically and of course the fluid began quickly to resemble the appearance of the low fluid transmission with lots of air bubbles and since a transmission is not that different from a brake system the result was similar.

You cannot have stable hydraulic pressure with air in the fluid. The air created in the low fluid scenario is a result of the filter becoming uncovered and the pump pulling air into the system. This results in crazy pressure readings and with the over filling this occurred because the internal rotational assemblies in the transmission were acting a lot like a blender and churning air into the fluid more rapidly than it could bubble out.

The lesson here from the testing is that a slight over filling is OK but drastic over filling or under filling is no good at all”.

The whole point of this, is that the fluid level is of major importance with all transmissions.

Installing a TransmissionThere is no such thing as a little low. A little low means you just took years off the life of your transmission or it may be too late. 
All transmissions should always be kept at the top of the crosshatch level when they are warm running in park or neutral. You must always be aware of the manufacturers correct fluid quantity for any transmission you are installing. Get this wrong and you are in for some major issues. If you are doing the job or you have asked an installer to fit your transmission get the oil levels right every time. It is important also to check the oil level once you have installed the transmission the following day.

Ideally it would be good if there were a way to assure the transmission fluid was equal to the pan rail level as not all modern transmissions have dipsticks.

Another thing that should be addressed is the aftermarket and stock deep pans. Always carefully read the pan manufacturers instructions. While regardless of the pan type the dip stick (if fitted) will still read the level correctly. If you for instance use a deep pan with the wrong filter bear in mind that manufacturers like General Motors actually use the bottom of the pan to hold the filter up in place. True the little seal feels tight holding it in the pump but it can work its way out and drop into the pan when used this way. This will result in the transmission acting like its low on fluid even when its not. At the same time if you place a filter that’s too tall for your pan combination it will crack in the neck area and again cause the symptom of low fluid.

It is worth mentioning this because you see this with some people changing pans and not being aware of the filter differences and requirements. So always make sure you are using the correct type of filter for the pan you are installing. Also note when installing a transmission. If you do not provide even support across the pan, you can bend the pan and damage the filter causing the same set of symptoms.
Advanced for Ford & Holden

If you are fitting a replacement transmission and you are not sure what all this means, then it’s worth talking to one of our Ford & Holden parts specialists. Even if they can’t help, Reg our transmission expert is sure to be able to give you some sound advice.


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