Transmission Pan Gasket Leaks

Do you have a transmission fluid leak coming from the transmission pan gasket area after a new transmission fluid, pan gasket, and filter installation? Transmission pan gaskets typically never fail. One of the following scenarios is likely the root cause. This article will help troubleshoot a transmission fluid leak coming from the pan gasket. Following the information provided below during your new transmission pan gasket installation should ensure that you do not experience a premature transmission pan gasket leak. 

Thoroughly Cleaned Transmission Pan Gasket Mating Surfaces

The transmission pan gasket mating surfaces should be thoroughly cleaned and cleansed, free from corrosion, road debris, oils, solvents, and fluids allowing for a perfect dry fit and seal. When done improperly, the gasket area may weep or leak transmission fluid. It is also recommended to not scar the transmission pan gasket mating areas while using gasket scraping tools to clean the gasket mating surfaces. We have seen many gasket mating surfaces weep or leak as a result of imperfections in the transmission gasket mating surfaces as a result of aggressive gasket scraping tool use. Even the smallest of imperfections can cause a mild fluid leak.

Transmission Pan Gasket Alignment

If the gasket has not been properly aligned during installation it can begin to roll off it's intended gasket sealing/mating surface causing transmission fluid to weep or leak. If it is determined that this is the case, the transmission fluid should be drained from the transmission, the transmission pan should be removed, allowing for a thorough cleaning and cleansing of all gasket mating surfaces (as outlined above). Note that paper gaskets are typically not reusable.

Factory Torqued Transmission Pan Mounting Bolts

If the factory-intended transmission torque specifications are not confirmed and are over-torqued, this can cause an uneven load to the transmission pan gasket and subsequent leak. Rubber-style pan gaskets will bulge or roll off the intended gasket sealing mating surfaces causing a transmission pan gasket to weep or leak. Over-torquing or under-torquing a paper or metal gasket can result in either too much or too little pressure, allowing the transmission pan to unevenly compress the gasket, resulting in an improper seal.

Transmission Pan Mounting Bolt Torquing Sequence

Most gasket mounting requires a particular bolt torquing sequence. Depending on the style of transmission and the procedures set out by the manufacturer, the transmission pan mounting bolts have an order of how they should be tightened. This sequenced order of tightening the bolts allows the gasket to be evenly squeezed ensuring a proper seal. When done improperly this can cause the gasket to be compressed unevenly loading the pan and pan gasket mating surfaces resulting in a transmission fluid weep or leak.

Paper Style Transmission Pan Gasket

Confirm that the paper gasket has no kinks or creases. If a paper gasket is kinked or creased, this will cause an imperfect seal and can give the transmission fluid a small channel to weep or leak through.

Rubber Style Transmission Pan Gasket

New fully rubber transmission pan gaskets rarely ever leak prematurely. However, old and aged gaskets that have experienced thousands of heat cycles can cause the rubber to harden and shrink resulting in a distorted seal and subsequent leak. Most leaks from a rubber transmission pan gasket are the result of not thoroughly cleaning the transmission gasket seating and matting surfaces, gasket with pan misalignments, incorrect use of gasket spacer inserts, over-torquing the transmission pan mounting bolts, or the incorrect transmission pan tightening torquing sequence. It is possible that one or more bolts are not torqued evenly causing uneven load to the pan and pan gasket mating surfaces. 

Metal Style with Incorporated Rubber Transmission Pan Gasket

Confirm that the gasket has no kinks or creases. If it has been kinked or creased, this will cause an imperfect seal due to an uneven metal and rubber mating surface, resulting in a small channel to weep or leak through.

Use Caution When Unpackaging Transmission Pan Gasket

While unpackaging your new transmission pan gasket you will need to confirm that you didn’t damage any part of the gasket with a razor blade knife or kink the gasket. 

Even new transmission pan gaskets can leak if the above procedures and examinations weren't followed thoroughly. When performing your transmission filter and fluid change, take the extra time needed to do it right and prevent any premature transmission gasket leak issues.

Should RTV gasket maker or silicon sealants be used with transmission pan gasket installation?

In all cases using an RTV gasket maker or silicon gasket sealants with the transmission pan gasket is dependent on the factory's specific intended application.

If the transmission pan was originally assembled onto the transmission from the factory without RTV or without silicon gasket makers then no RTV sealants should be used.

Some transmission manufacturers will not use a transmission pan gasket but rather rely only on using RTV gasket-making compound to seal the transmission pan. If this is the case for your transmission then yes, an RTV gasket maker or silicone sealant can be used.

The key to a successfully sealed transmission pan is to reproduce the factory-like sealing conditions. This typically means the mating surfaces should be clean of old gasket materials, corrosion, and debris. This is typically best done with a plastic scraper-type tool. Ensure that the gasket mating surfaces are not scarred or gouged during tool use. To ensure the gasket mating surfaces are free from imperfections, feel the mating surfaces with your finger and remove them as needed. Also, just before installing the new transmission pan with the gasket, a light amount of acetone, brake cleaner, or lacquer thinner on a CLEAN RAG can be used to remove all oil residues. Do not spray any area of the transmission with any of these solvents. Once these areas are wiped clean allow the mating surfaces to dry for about 2-3 min from these solvents, and then install the pan, gasket, and gasket spacers. This will give the best sealing condition for a gasket-sealed transmission pan or an RTV-sealed transmission pan.