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Replacing the internal automatic transmission fluid filter...


Take the pan off the bottom of the automatic transmission every 24 months or 40,000 kilometres (24,000 miles), whichever comes first (ie. every second change of the fluid), in order to inspect the inside of the transmission and to replace the relatively ineffective, internal, strainer-type, fluid filter.  Note that this fluid filter inside the automatic transmission only needs to be replaced every twenty-four months as a result of the use of the high-quality, external, magnetic filter being replaced every six months.  Because the external filter is capturing the majority of the particulate contaminants, the internal filter takes much longer to fill up with these contaminants.

Even if you perform the work yourself every twenty-four months of taking the pan off and replacing the internal filter, itís a good idea to take the vehicle to an automatic transmission specialist afterwards at this time who can check over the automatic transmission for any problems and make any other adjustments that need to be made.  If those adjustments are internal, itís probably best to leave it to the specialist to take the pan off and change the internal filter.  After you get the vehicle back, you can continue with draining and refilling the transmission an additional two to three times as you see fit since the specialist is only likely to drain and refill the transmission once.

If you do the work yourself, here are some important points to observe when removing and refitting the transmission pan and internal filter:

  • Be sure to use a new washer when refitting the transmission drain plug after draining all the fluid out of the transmission for the last time.
  • Loosen the pan bolts in a crisscross manner.
  • Support the pan with your hand as you remove the final few bolts and try to keep it level as you remove the pan to minimise the spillage of the last remaining fluid in the pan.
  • Refer to the workshop manual for your particular vehicle to see if it indicates that the bolts that secure the internal filter are of different lengths.  In any case, record the positions of the bolts removed when removing the internal filter.
  • Refer to the workshop manual for your particular vehicle for the tightening torque specifications for the bolts that retain the internal filter and the bolts that retain the pan.  In all likelihood, the torques specified are less than 10 foot pounds (13.5 Newton metres).  For this reason, if you are doing this work yourself, itís strongly recommended that you purchase a torque wrench which is capable of accurately tightening to such low torques.

    A 1/2Ē drive torque wrench suitable for tightening heavier duty fasteners such as wheel nuts will generally only tighten accurately down to 10 foot pounds (13.5 Newton metres) but not less as is needed in this case.

    Kincrome make an excellent 3/8Ē drive micrometer torque wrench with a range of about 1.5 to 17.7 foot pounds which is the same as 2 to 24 Newton metres (Nm) since 1 foot pound is equal to 1.356 Nm.  (Note also that 1 foot pound is equal to 12 inch pounds since inch pounds are often used to refer to the range of micrometer torque wrenches.)

    Itís important to tighten the internal filter bolts and the pan bolts to the correct torque with a micrometer torque wrench to prevent transmission damage or maladjustment from over-tightening the filter bolts and to prevent fluid leakage from over-tightening the pan bolts.
  • Inspect the replacement internal filter before fitting it to make sure that itís clean and that thereís no foreign matter or contaminants on it because sometimes the quality of these new internal filters leaves a lot to be desired.  If the internal filter isnít clean and there is foreign matter or contaminants on it, do NOT fit it to the transmission.  Either clean it or replace it with another one from your local automotive parts shop as I had to do once.  Automatic transmissions contain precision-engineered components and the fitting of dirty or poor-quality parts will impede the performance of the transmission and quite possibly necessitate expensive, inconvenient and frustrating repairs.
  • Refit the bolts to secure the replacement internal filter in the same positions from which they were removed, as recorded above (unless theyíre all the same length and identical bolts in which case their positions donít matter or unless theyíve previously been fitted incorrectly in which case they should be refitted in the configuration that the workshop manual specifies).  Tighten the bolts in a crisscross pattern progressively in stages with a micrometer torque wrench to the torque specified in the workshop manual for your particular vehicle.
  • Ensure that the gasket surfaces of the automatic transmission and the pan are spotlessly clean.  Under no circumstances should you use any metal implement to clean these surfaces.  Such a metal implement could easily score and damage these surfaces which are meant to provide a perfect seal with the pan gasket in order to prevent fluid leaks.  Only use blunt, plastic implements to remove stubborn material such as old pan gasket from these surfaces.  You can also use kerosene with a clean, lint-free cloth as a degreaser to clean these surfaces.
  • Fit a new pan gasket, fit the pan and fit the pan bolts in a crisscross pattern to retain the pan just finger-tight for now at this stage of checking the seal of the pan gasket.

    If the gasket surfaces on the pan and transmission are flat, true and in good condition, there should be no need to use any type of sealant on the pan gasket.  If you think that you do need to use sealant, check carefully with your mechanic or local automotive parts shop for the type of sealant to use.  Personally, I would avoid using sealant on the pan gasket.  If the gasket surface on the pan is not flat and not true, therefore risking fluid leaks when the pan is installed, I would go so far as to purchase a new, genuine pan supplied by the manufacturer of your vehicle (which is flat and true) rather than use sealant on the pan gasket.  The interior workings of the automatic transmission are much better off without possible contamination from sealant on the pan gasket.
  • Tighten the pan bolts in a crisscross pattern progressively in stages to the torque specified in the workshop manual for your particular vehicle using a micrometer torque wrench.  This progressive tightening in stages ensures that the pan gasket is compressed evenly across the entire pan to minimise the possibility of fluid leaks.  The use of a micrometer torque wrench to tighten the pan bolts to the specified torque also ensures that the pan bolts are not over-tightened which can lead to the pan gasket being over-compressed and pinched so that the transmission leaks fluid.

    Note that even when you tighten the pan bolts correctly in this crisscross, progressive manner to the specified torque, the transmission may still leak some fluid initially after you refill it, until the pan gasket, which is often make of cork and is therefore porous, is saturated with fluid and swells up to provide a better seal with the transmission and pan.


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Copyright 2016 Andrew Mackinnon.  All rights reserved.