Stopping a Differential Leak

I recently had oil leaking from the differential on two of my vehicles, dripping from the pinion seal. Both are older vehicles, a high-mileage 1987 Ford F-150 and a 1978 Lincoln.

So, I thought I would try one of the many oil stop-leak products available, in hopes this type of chemical would re-condition the pinion seal. However, I couldn’t find any stop-leak that was recommended for use in a differential. Rather, the ones I examined were intended for use in either automatic transmissions or engines. Regardless, I thought this type of chemical might still work on a pinion seal, if I got the right “mix.” So, I experimented as follows:

I added approximately 5 fluid oz. of automatic transmission stop-leak to my differential and put 50-60 miles on the vehicle then repeated this process. After more than 100 miles, the leak persisted with no change.

Perhaps I didn’t add enough of this chemical, but I was concerned about thinning out the gear oil too much and impairing the differential’s lubrication.

So, I thought I would try something unorthodox, like applying the stop-leak full strength externally, directly on the seal. I did remove all sand and grit from the seal with brake cleaner first, then sprayed it down with the stop-leak from a pump oil can. My choice of stop-leak was Trans-X, although I suppose most brands would contain similar chemicals.

The first such “treatment” reduced the leaks considerably, but it took several more applications, about 100 miles apart, for the leaks to stop. The ’78 Lincoln required a longer treatment period due, I suppose, to its age.

This method has worked well on both of my vehicles, and they have been leakfree for many thousands of miles now.

In fact, I recently checked the differential on my Lincoln and it was still full after clocking another 4000 miles since the last time I checked.

Frederick Holser Dayton, Nevada