What is this part?

[Mertz]

I was trying to remove my old brake lines from the rear end junction block. I ended up braking off the hollow nut that holds it on. I was surprised that it is hollow and even more surprised that it has some brass steel wool like material in it. What is this used for?

Thanks

[Plymouthy Adams]

vent for the axle......it vents the axle while it also is the fastener for the T-block for the brake lines...

[Mertz]

Why does the axle need to be vented?  I will need to clean it off to see how it vents. Are they still available somewhere?  I would like to keep every as original as possible. 

[David A.]

I’m no expert, but I would assume if the housing was sealed, as the temperature increased, so would the pressure. It could eventually push oil out the seals, or worst case I guess it could possibly blow out the entire seal. 

[Mertz]

I have never seen one before on any of my old cars and trucks. I would think that the volume in the axle would be adequate to handle any pressure changes and the level of the oil would be low enough not to cause hydraulic pressure on the seal. Having said that I’m not really sure why a back up seal is required on the backing plate. When I took mine apart both seals had failed and I had grease all over the brake shoes and backing plate. 

[Plymouthy Adams]

why did you bother to ask what this part was.......it is evident even after being told what it is you still are in disbelief....while often not pictured in the IPB it is covered in the diagnosis section under causes for possible leakage....

[Eneto-55]

I suspect that most people, when they see them, they just think it's a bolt.  I'm pretty sure that all differentials have them.  (Don't have a 'modern' car with rear wheel drive anymore - my wife just likes FWD, so I cannot go out & look, to verify this for myself.)

[Tooljunkie]

Yup, its a vent.imagine running your truck down the highway, boat on trailer behind you, pressure builds, excess air pressure bleeds off through seals. You launch boat with a hot diff. Seals work best keeping oil in,so would suck water in in a heartbeat. 
 

Many diff leaks caused by a plugged vent. 

[Mertz]

It’s always good to learn something new. As I mentioned I have never seen one before but suspected something was different with this bolt because of the cap on top. I will be replacing it with the vent either with a new bolt or making something to create the vent. Thanks for all the help.

[Young Ed]

1 hour ago, Tooljunkie said:

Yup, its a vent.imagine running your truck down the highway, boat on trailer behind you, pressure builds, excess air pressure bleeds off through seals. You launch boat with a hot diff. Seals work best keeping oil in,so would suck water in in a heartbeat. 
 

Many diff leaks caused by a plugged vent. 

That's why some trucks have a hose that goes up to a frame mounted vent- keeps it even more out of the water if going off-road or your boat launch example

[Mertz]

Can you tell me where the transmission vent is?  I need to make sure it is clear before putting it back in. 

[Plymouthy Adams]

unless I have overlooked a port, it is vented through the input shaft cover.....there is special provision provided for the oil to return to the tranny should any make its way from the front bearing....

[greg g]

Other makes didn't have them because they didn't hire highly qualified engineers like Walter P Chrysler did.  They are common these days on 4wd drive setups which have extension tubes on the to keep water out when fording streams.

[Mertz]

I found the part on line and it is listed for 40’s thru 70’s mopars. 

[chrysler1941]

Plymouthy Adams is correct, called housing vent assembly part 3-02-20

 

@greg g funny comment but Cadillac had it back before 1937. Se attached from shop manual