DIY: Filling Rear Diff , Trans Fluid using Air Compressor

[cn90]

Hi guys,

Whenever you fill the Rear Diff or Trans, it is always awkward under the car with spilled fluid etc.

Some of the solutions are:

1. Squeeze bottle ---> slow and incomplete emptying.

2. Fill by suction gun ($10 at Harbor Freight) ---> messy.

3. Fill by gravity. The only problem is you need 4-5 ft of tubing, but it is a minor issue.
Please see photo of my tip below...

4. Fill using compressed air. I just tried this today and the best thing is: it costs you less than $1 for the tubing if you already own an air compressor!

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* Fill by gravity: Please see 1st photo.



* So, I have some time today, if you already have an air compressor, these are what you need:

1. An empty bottle, I like the "Simply Lemonade" bc the bottle is sturdy, the cap is solid plastic, and it is FREE (I already drank all the lemonade lol...).
Of course you wash the bottle and cap and let it sit overnight in your kitchen so it dries properly. Absolutely do not allow any trace of water in the
bottle. Any doubt, use small amount of gasoline to clean the bottle and hose and let it evaporate first...

2. Clear hose is cheap at local hardware store, about 30-40 cents/foot.
One hose is short and enters the cap for only 1": this is for compressed air.
The other hose needs to go to the bottom of the bottle: in the illustration, this hose is not long enough in the photo bc this is all I have in my garage
for the test. You will need about 2-3 feet so it can go into the rear diff.

3. I have a 60 mL syringe lying around.
- With syringe: water shoots out about 10 inches.
- With compressed air at 5-7 psi, water shoots out at 5-6 feet!
So, turn your air compressor on for only 5 sec. stop and measure the pressure, if it is < 10 psi, it is OK. I honestly do NOT know the pressure at which
the bottle starts to bulge: can someone test and test the rest the burst pressure?

Of course 75W90 fluid is thicker than water, so it will take more time to pump 75W90 into the rear diff. I have not tried the 75W90 fluid yet. So far it
is only testing with water.

Good Luck and hope you guys find this useful...

[crystalworks]

Nice pictures. This is how I fill all my driveline fluids.

[cn90]

Originally Posted by crystalworks

Nice pictures. This is how I fill all my driveline fluids.

Just curious what your bottle setup looks like?
Do you use air compressor?

[cn90]

I was inspired by this video: this person used air compressor to push ATF out of his bottle to fill the transmission.
He did not mention how many psi in the video:

https://www.youtube.com/watch?v=a3M9itMA0DM


Then I wonder if I should test when a typical bottle would explode. Glad I did NOT!
Came across this video that says a 2L Coke bottle (which is similar in term of plastic material to the Lemonade bottle)
exploded at 150 psi.

So, at 5-10 psi, I think it is safe for our use of pushing oil out of the Lemonade bottle lol...



https://www.youtube.com/watch?v=PXeZIISDiNw



https://www.youtube.com/watch?v=r3RP0trKgI0

[Purplefade]

I just did it with the top of a Pentosin bottle, but in order to get it to work (reliably) you have to pour a little bit out of the container as you open them and before you put the modified cap on or the short tube can be submerged. It isn't to bad though, you just pour the little bit off in to an old empty container until it's full enough to pump on


Yea, you can't fill a vessel full and get it done in one push per say, but it's easy to change a cap and you have to open each container individually anyway.


Can also do it for gear oil, etc, etc, just modify and save "that" particular cap.

[crystalworks]

Originally Posted by cn90

Just curious what your bottle setup looks like?
Do you use air compressor?

Yes, air compressor. I use different length tubes for different fills. This bottle is still going after being pressurized at least 15 times over a couple of years. Used it for diffs, Xfer cases, and at least 4 trans services. The trans services are a little annoying as pointed out you have to refill the bottle (4-8 times) for a transmission service.



Purplefade, what's wrong with submerging the short tube on the inside? I'll have to check it but I'm pretty sure mine is long enough to get submerged and the setup still works?

[cn90]

For ATF, I use gravity fill.
This is the DIY ATF for 2004 X3 that I wrote a while back:

https://xoutpost.com/bmw-sav-forums/...g-gravity.html



The clear tubing ends up in the engine compartment, very very easy method by gravity:

[cn90]

A nice thing about the Lemonade bottle is: it is clear plastic, so you can see exactly how much fluid is being pumped out.

The green cap is very sturdy.

If something goes wrong, you can always buy another Lemonade bottle.
When life gives you lemon, make lemonade lol...

[Purplefade]

Originally Posted by crystalworks

.

Purplefade, what's wrong with submerging the short tube on the inside? I'll have to check it but I'm pretty sure mine is long enough to get submerged and the setup still works?

It applies pressure under the surface of the fluid you’re pumping and is more prone to introducing bubbles. I find that having the “pressure tube” above the fluid doesn’t do that.

EDIT: though that really only has any impact on break fluid, most others the bubbles don’t matter, was just a habit that I got in to

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