Same breather can for both motor and gearbox?

[Brian C]

Wasn't sure which forum this question best belongs in, so trying here in Engines.

I currently have a breather can which collects the gas venting from my valve covers. It's right next to the gearbox at the back of the car and I'd like to add a vent line from my gearbox as well. The gearbox currently has a breather cap but mist sprays all over the gearbox, so I want to run a line to a can.

The question is, should I use a separate breather can for the trans, or would it be OK to weld on another bung onto the existing can? It's simpler, cheaper, and a weight savings to boot. The only potential downside I could think of is engine gases somehow making their way into the trans case, but I don't know if there'd ever be enough pressure from the engine gasses to force air back through the trans line, especially considering there is a big mesh breather on top!

 

[Randy V]

I see nothing wrong with it unless you were wanting to cycle the oil back into the engine or gearbox.

 

[Jac Mac]

Probably more important to make sure none of them are placed where oil that is being flung off rockers, pushrods or gears in the transaxle is aimed at the catch tank hoses. Personally I'd prefere seperate tanks, less mess to clean if you have a head gasket or other issue where coolant can get into the transaxle as well.

 

[Brian C]

Thanks guys, went ahead and added a bung and plumbed them all in together. After 300 miles, there was only a few drops of oil in the can, so I don't think fluids mixing would be an issue.

 

[Bob Putnam]

I'm curious... Is there a baffle (or something equivalent) in the gearbox cover in front of the breather hose inlet?

 

[Brian C]

Hi Bob. No, there isn’t. So some small amount of splash does reach the hole and had soaked my breather cap I had previously, which then leads to heavy misting on the gearbox exterior.

I’ll probably add a filtered/screened AN fitting at that joint to provide some kind of fluid guard.

 

[Andrew Robertson]

I was getting so much oil throw-off from the ring gear on my inverted 930 transaxle (which uses the original drain plug hole - now on top - to plumb to the catch can) that I run the can drain straight back into the filler hole on the side of the trans. The catch can is basically an air separator that sees a constant minor flow. Obviously in that situation nothing from the engine can be introduced.

 

[Scott]

I was getting so much oil throw-off from the ring gear on my inverted 930 transaxle

My Albins specifies 100 – 150mm of vertical run as close to the transaxle as practical. My assumption is that this greatly reduces the amount of oil that makes it to the breather. My plan is to put a 180-degree bend in an aluminum tube for the vertical section so that the oil has to push up before returning down to flow into the breather. The breather can be above or below the transaxle vent out so long as none of the horizontal sections have a dip that would trap fluid.

 

[Brian C]

My Albins specifies 100 – 150mm of vertical run as close to the transaxle as practical. My assumption is that this greatly reduces the amount of oil that makes it to the breather. My plan is to put a 180-degree bend in an aluminum tube for the vertical section so that the oil has to push up before returning down to flow into the breather. The breather can be above or below the transaxle vent out so long as none of the horizontal sections have a dip that would trap fluid.

That's a good idea!

I'll drain the can in a few months and assess how much fluid is actually making it into the line. My guess is it don't be much at all. The stack of fittings on top of the housing are already 3" high.

 

[Randy V]

My Albins specifies 100 – 150mm of vertical run as close to the transaxle as practical. My assumption is that this greatly reduces the amount of oil that makes it to the breather. My plan is to put a 180-degree bend in an aluminum tube for the vertical section so that the oil has to push up before returning down to flow into the breather. The breather can be above or below the transaxle vent out so long as none of the horizontal sections have a dip that would trap fluid.

Like you, I generally try to run a 180° Up-hill loop in the breather hose in order to accomplish much the same thing. That which makes it to the breather can be cycled back through, or recycled altogether..

 

[BenL]

Could check valves be added to the breather hoses to prevent fluids being pulled out of the catch tank?

 

[Scott]

Could check valves be added to the breather hoses to prevent fluids being pulled out of the catch tank?

Ben, the vertical 180-degree run is to mitigate the amount of oil that makes it to the breather. The lines go near the top of the breather and you want enough capacity so that those lines aren't exposed to fluid. This is why you may need to empty the breather from time to time. A check valve would prevent oil from flowing back, but it would also prevent air from being drawn into the system when things cooled.

In addition, my engine has a supercharger and a Daily dry sump so I'm not sure which way air is flowing -- perhaps both ways?

 

[Jac Mac]

On Jack Ondracks TVR ( Dry Sump SBF) we were emptying the catch tanks after each race, I built a system where the engine continually emptied the catch tank while running andfrom thereon we only had to manually drain the catch tank after last race of the day and that was minimal.