Front Page


What's On


A technical article by Brian Richards

Oil Seals Can be Directional!

I needed to replace a rear gearbox seal last week and picked up a new seal from David Clark. It is a National (7038 SA) seal that has a flange on the outer diameter so that when the seal is fitted, the flange sits square on the end of the housing. It is a nice looking double lip seal and David reckons they are the best. The rear gearbox seal is the same size as the front engine seal and I nearly used one I had, but elected to get this one from David. He fixes Triumphs for a living so I figure he only uses ones that work and I only wanted to fix this once. 

When I removed the old rear oil seal to see if I could see why it was leaking, I noted it was a front seal and as such was guaranteed to leak. Now I had fitted this seal so it was my problem. I had not taken a good look at it before fitting. This has led me to take pen to paper. 

Seals come in a variety of configurations, double lip, single lip, spring tensioned, Viton, Teflon, etc but did you know they can also be directional! You can get bi-directional, clockwise and anticlockwise. The best ones are directional. How do you tell??? Well when you look at the lip that runs on the shaft, it will be plain (bi-directional), or have small grooves that act like an oil scroll (directional).

The one below is a BI-DIRECTIONAL seal.
ie. it will operate correctly when running in either direction.


The front seal needs a seal that is clockwise from the front of the engine but the gearbox needs one that is anti-clockwise from the front of the engine. I can guarantee a good directional front seal will leak a lot when used as a rear gearbox seal!

The one below is a UNI-DIRECTIONAL front crankshaft seal.
ie. it will ONLY operate correctly when the shaft running in a CLOCKWISE direction.


Most of the seals you will fit will be for a shaft that runs in a clockwise direction AS ABOVE. The only exception is the rear gearbox/OD seal. Most of the seals will also be bi-directional as they are the narrow style. As best as I can remember, the only directional seals used on the TR are the front engine, rear gearbox/OD and diff pinion seal.

So - the one at the rear of the GEARBOX should look like this (ANTI CLOCKWISE).

The lesson here is that if you get a seal from the Register, they will be correct for the purpose they were ordered. If you get one from the local bearing shop, they may not be. Not that they are not a quality seal, just that they are not suitable for the job. Always check, regardless of where you get it from. It is the old measure twice, cut once rule.

ALSO - for more information, read this article courtesy of "SEALING AUSTRALIA"

Brian Richards