How do seals work?

Status
Not open for further replies.

Bonnewagon

Lost in the Labyrinth
Supporting Member
Sep 18, 2009
10,967
15,390
113
Queens, NY
I am replacing seals in a gearcase. If I had room to use two seals instead of only one, would that be better or worse? I know that there is often a spring inside the lip of the seal that helps the lip press against the shaft it is sealing to. It must rely on some of the fluid to lubricate the seal interface. I read that the open side of the seal faces the fluid and the fluid pressure pushes the seal against the shaft. So if I added a second seal, would that defeat the operation of the first seal? Or would one seal starve for lubrication? If I packed the cavity between the seals with grease would that work? Or would it be better because any fluid that got past the first seal would get stopped by the second seal? Or am I totally backwards on this?
 
I probably wouldn't use 2 spring lip seals in tandem or it may starve the outer one, as you point out, making all that extra work a moot point. If you've ever had to deal with lip seal grooves, whether on axles, or crank balancers or torque converters, etc., you know that eventually, lip seals will wear into the metal basically rendering the nominal seal used in that application useless. If you're spring lip seal is leaking and it's a problem getting it to seal, there's a reason other than not enough seals.

Spring-aided seals can be part of the issue with eating the seal surface over time, but they're also the beauty part of the equation. Many variables can come into play- speed, pressure, temperature, etc., so I'm going to be nebulous on this, but there are lip seals that aren't spring-aided, and they do well in very low pressure applications, like being vented on both sides, and in situations where maximum sealing isn't a huge concern. O-rings, E-rings, and labyrinth style seals and the like can do the job where bleedout may not be a huge concern and are more for static sealing conditions. But one of the cool things about the spring-aided seals is that they help seal even with conditions of in-tolerance run-out of the shaft so the slight pressure on the lip of the seal that the spring gives helps you leak less over time. The durometer of the materials in a spring seal are usually firmer than non-spring seals, so the spring helps keep good pressure on the seal to help prevent lip seal set issues and still seal even if there's slight reciprocating movement of the shaft. This helps the seal do its job in harsher environments for longer period of time.

Packing the void between 2 seals wouldn't be advisable, IMO, because there's a risk of the grease could just hold heat, and the grease closest around the shaft would start to liquify and whip up and perhaps cause swelling of the volume and raising internal pressure between the seals, and excess grease would go somewhere. Which probably wouldn't benefit you in any way.

There's likely a reason the engineers designed the gearcase to use the seals the way they did. If you use the wrong material or size, etc., it can cause you issues as well. Ensure the seal surface is flat and smooth with no pits and/or burrs. You don't want any rough surfaces to eat the seal. If the shaft is too far bent, then it won't matter how many seals you jam in there.

I would just ask the question to myself...how many single lip seals does my car use and need? Why am I only needing one seal on the harmonic balancer or torque converter, drive shaft yokes, etc.?

All this probably doesn't help you much on deciding, but it's just something I would consider.
 
  • Like
Reactions: Rktpwrd
Actually it does help. Good point about heat building up inside between the seals. The grease would expand, push out because the seal is facing the wrong way, and when it cooled,it would create a vacuum drawing dirt in from the outside. I do examine my shafts carefully, and if I find a groove, I fill it with Marine Tex and sand it down flush. That saves crankshaft dampers and companion flanges that have become very expensive to replace. Where I have used Jiffy-sleeves to fix grooves, they did not last as long as the Marine Tex repair. My whole concern was that the second seal would starve the first seal, rendering it useless.
 
I believe they sell double lip seals in basically every size, maybe they will have one for this application.
Most of the automotive seals are technically double-lipped already, but the outer seal is more like a dust/dirt/water shield for the main lip seal. Only one spring-aided lip and the other is just there. So, it really just depends on what you're wanting to do. Pick up say, a GM axle bearing seal and inspect it. You'll see what I mean. You don't want junk flying around under the car getting up in the seal areas and making the shaft act like sandpaper on the seal.

You can see the spring in this lip seal, and you can see the outer lip, which is at the bottom in the pic, does not have a spring.

s-l1600.jpg
 
  • Like
Reactions: Rktpwrd
With rubber lip seals I always heard to put a little grease or oil on them. Sometimes older style seals will have an outer felt seal to keep dirt away from the inner lip seal.

With spined or keyed shafts you will need to make a tin cylinder to protect the new seal from getting cut during install. Once the keyway or spines are past the seal you can pull the tin cylinder.
 
  • Like
Reactions: xylorex
This is the double lipped seal vs the single lipped seal. You would normally stack the two single seals back to back. One seal faces the oil, the other faces the water. I was able to insert the new style seal farther into the seal cavity and now it rides on fresh metal. Now I have room for the third old style seal. But I am now convinced that the seal inside would suffer from not being lubricated. Bad idea, time to back up and regroup. Thanks for all the replies.
1642886651898.png
1642886679794.png
 
Status
Not open for further replies.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot UMI Performance

Contact [email protected] for info on becoming a sponsor