Fel-Pro BS 40644 Rear Engine Main Seal Set

I started noticing oil droplets on my driveway and the transmission appeared wet in oil but it was not red so I knew it was engine oil. Sure enough, the rear seal had a small crack. I used a jack to support the transmission while a buddy removed the old seal and installed the new one. This seal is super easy to install with the tool it includes, slides great and it definitely seals great. I've had the seal for 7 months now I believe, and it is working perfectly! No oil leaks!

Had transmission out and was an easy replacement of a rear main seal with this quality one.

Perfect fit

For such an important install that really needs to be done right the first time, there’s surprisingly little documentation or illustration available. My vehicle is a 2000 F-150, 5.4L 2V, and the pictures tell most of the story.Updated: Nov 5, 2025 – Still No Leaks!1. PTFE SealClean the crank thoroughly with alcohol before installation. This is a PTFE lip seal (no spring)—it must be installed dry, with no oil or grease on the inner surface. Some light grease or RTV can be applied only to the outer edge to help it seat, but not on the sealing surface itself. The inner lip contains a Teflon layer that bonds to the crank after initial startup.2. Seal Flaring ToolThe plastic “cup” tool is used to gently stretch the inner lip during installation. As you slide the seal over the hump and off the flaring tool, it will relax and conform to the crank. Skipping this step risks the lip folding backward toward the flywheel, which will cause leaks.3. Installation DetailsI installed the seal flush with the outside of the cover, about ¼ inch back from the flywheel. The original setup had an additional factory “slinger” seal, but it’s generally not needed when using the updated design—the new seal’s smaller outer lip already helps block debris.I removed the aluminum housing to access both the slinger and rear main seal (probably overkill, but it made extraction easier). When reinstalling the cover, there was no gasket, so I used RTV. Some tutorials show people installing the seal into the cover before reattaching it to the engine, but that approach didn’t make sense to me since the plate requires RTV and careful alignment.Tool Tip:I picked up a 4" PVC cleanout plug from Lowe’s to press in the seal—it worked perfectly. Here’s a similar product:Genova 71840 PVC Threaded Plug on Amazon

Well I didn’t have this part on my radar. It was suggested that other customers bought this part with the clutch kit I ordered. This was another part I could replace while I had the transmission dropped. I never installed this part before. Thank God for YouTube. It was an exact fix.