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Axle breathers - long



Just to follow up on Alan's message I was looking over one of the
listers 80s yesterday and we had a long chat about axle breathers.
His car had oil coming out from the steering knuckle seals and also
grease in the with the oil in the diff.
The factory breathers have a spring and small rubber seal in them.
As the axle warms out the air is expelled out of the breather, but
then when it cools the spring and seal stops the air from getting back
in and leaves a negative pressure in the axle.
If you have good seals that negative pressure can be in there for some
time - I have removed breathers from axles several days after the
vehicle has been parked and there is still a partial vacuum in there.
When the inner axle seal goes - as the axle heats up some of the diff
oil flows out into the knuckle diluting the grease around the CV and
then when the axle cools down the oil/grease mixture is sucked back
into the axle.
To be honest I have no idea of the real implications of this, but logic
dictates that you shouldn't really have grease in the diff or diff oil
in the CV so it is best to get the seals replaced as soon as possible.
TO avoid this cross contamination, it is well worth removing the spring
and rubber seal - you can find a write up on this at By doing this
if the inner axle seal does go, you only have to worry about the diff
oil in the CV.
One of the problems you can have with the factory breathers is that the
diff oil can be forced up the breather pipe and wet the breather top -
this attracts dirt and can result in the breather blocking. This isn't
helped by the fact that whilst the internal diameter of the breather
pipe is around 5mm, the actual hole in the joint where the breather
attaches to the axle is about 1mm - so the diff oil struggles to flow
back into the axle.
To try to combat this problem Toyota added a plastic plenum chamber to
the top of the breather so that the diff oil doesn't actually get up to
the breather, atlhough personally I prefer to also drill out the joint,
taking the inner diameter from around 1mm to about 5 or 6mm.
For extending the diff breathers I use 8mm/6mm internal solid plastic
pipe used for air brakes on lorries. This is immensly strong and you
can get some very neat small clip on T and Y pieces for joining the
breather pipes together.
I run the breather up from the rear axle up to the engine bay and then
remove the gearbox and transfer case breathers that come up and attach
to the auto box dip stick and join them with Y pieces to a 4th pipe up
from the front axle joining them all together and then running a single
pipe up on the firewall, across the engine bay and into the side of the
air box. If there isn't going to be a snorkel fitted I sometimes also
add an inline fuel filter just to keep the crap out.
When you remove the bearbox and transfer case breathers from the
gearbox dipstick, don't forget to get a small length of rubber fuel
line to act as a loop to 'short circuit' where the breathers connect to
the dip stick.
The key thing with the plastic pipe is to put it into a loop above the
axle so that there is plenty of flex - whilst these are plastic pipes
they are designed to flex - ideally to maintain the loop you may need
to usse a P clip riveted to the chassis to stop the pipe from twisting
- for the rest of the run you should be able to use cable ties.
Some people argue that the plumbing into the side of the airbox is
wrong because of the negative pressure caused by the engine, however
I don't actually believe the pressure is any worse than the pressure
exerted by the factory breathers. I'm sure I have actually read
somewhere that someone actuallyh tested the pressure and it was
One thing I hate seeing is the mess some 4x4 companies make when they
run breathers up from everywhere and then stick a hole in the wing, run
the pipes up the side of a snorkel and then shove the pipes into the
back of the snorkel head - it looks messy and makes it a lot harder to
rotate the snorkel head whe going through deep water, heavy rain or
Finally, when thinking about breathers also consider extending the
breather on the fuel tank - on the 80s this runs back from the tank
into an inline filter and then a rubber pipe runs into the chassis rail
running across the rear axle. This rear chassis rail soon fills up
with dust and mud blocking the breather so a common trick is to extend
the breather pipe up into the 'D' pillar up to near where the cabin
vents are.
Julian Voelcker
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift