Searching for the source of an unexpected transmission fluid leak - Transmission Digest

Searching for the source of an unexpected transmission fluid leak

As the installer was pumping fluid into the transmission from the right side of the vehicle, he was having a difficult time getting it full.

A 2018 Camaro SS with a 6.2L engine powering an 8L90 transmission comes into King Transmission Company in Elmhurst, Illinois, with a limited slip transmission problem. It would initially slip during launch followed by a no-move condition. The fluid level was found to be very low; yet there were no signs of leaking anywhere by the transmission.

Once technicians pulled and inspected the unit, as expected, damage from low fluid conditions was present. Max Dease rebuilt the transmission, and into the vehicle it went.

As the installer was pumping fluid into the transmission from the right side of the vehicle, he was having a difficult time getting it full. So, he continued to pump far more fluid into the transmission than what it typically calls for. Suddenly, fluid started pouring out of the rear differential area all over the floor. He stopped pumping the fluid and looked to see how this could be. What he found was a very unexpected sight: transmission fluid pouring out of the vent of the rear differential (seen in Figure 1).

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Figure 1.

If you look at the cooling line flange bolted to the transmission (Figure 2), you will notice that the front line goes to the radiator to cool the transmission fluid.

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Figure 2.

The rear cooler return line, however, goes to the rear differential. When it is traced to the differential (Figure 3), there is another cooler line alongside it which comes from the cooler in the radiator (Figures 4 and 5).

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Figure 3.
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Figure 4.
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Figure 5.

A limited slip differential is used in this vehicle which generates some heat. Inside this assembly is an oil cooler used to cool down the differential fluid as it flows. This warmer transmission fluid is then returned to the transmission.

It became apparent that this cooler assembly inside the differential ruptured, although it was not clear how. Could the diff be on its way out, damaging the cooler; or did the cooler just rupture?

There are no parts to rebuild this differential, so a whole new assembly needed to be purchased to make the repair. We wanted to get inside this differential to see what this cooling system looked like and why it was damaged, but the core charge was $1,000. This gave the shop owner a thousand reasons why we couldn’t open it up.

Needless to say, with the cooler being ruptured, it allowed transmission fluid to be pumped directly into the differential until it blew out of the vent, essentially emptying the transmission of fluid. The differential has a fluid fill and drain plug in it (see Figure 6). When the fluid fill plug was removed, quarts of transmission fluid poured out of it.

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Figure 6.

So, here we have a limited slip differential causing a limited slip transmission condition. Just when you thought you had seen it all.

Read more stories from our Technically Speaking column series here.

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