Draining the Auto box

[Freebird]

Hi All

I have a 1996 X300 3.2 and tried to change the gearbox oil last weekend.

Following the manual, I could only get about 2-3 litres out of the pan. How do you get the rest out of the torque converter?

Cheers

Glen.

[PeterDavisX300]

To do mine, (rightly or wrongly) (Advised by a retired auto transmission specialist, he must have been good because he's rolling in money and retired at 55!) I disconnected the feed-pipe at the front of the sump whilst the engine was warm and running. Of course I was on a ramp at my work in the M/V department (local college) and had big collection trays underneath (and my students to clean the mess up that the trays missed ) There was a lot of mess! This seemed to get quite a lot of the oil out. I did it as a routine rather than the gearbox oil needing change, the old oil was still nice and pink, and there was very little sludge on the magnets in the sump. The gearbox doesn't really behave any different since the change about 15 thousand miles ago.

[ptjs1]

Glen,

As you have found, on these ZF boxes, you can only pull about 2.5 litres (out of a total of approx 9 litres!) by draining the sump. So you really have two options:

- You can drain and refresh a number of times which then keeps diluting the residual dirty fluid until you've reached an acceptable degree of cleanliness

- You can pump the old fluid out by disconnecting the return pipe from the transmission oil cooler to the box and replenish at the same time as the old fluid is being pumped out. The new fluid is then effectively moving through the system and helping to push the old fluid rather than doing a complete new/old dilution.


On my XJS, I'm actually in the middle of a hybrid approach that I'm taking. I realised that I had 10+ litres of Dexron II in my garage, which is the fluid that was originally specified. However, I wanted to end up with the box filled with Dexron III, but thought I could use the Dexron II as part of the process.

So, I've now done 4 flushes with the Dexron II. I remove the old fluid using a compressor-driven oil extractor which draws between 2.45 & 2.60 litres. I then replaced exactly the same amount of fresh Dexron II, drove for 10 miles then repeated. After 4 refills, I've used 10.28 litres of clean fluid and calculate that I still have just over 26% of the original fluid diluted amongst the fresh fluid.

So, I could keep up this process although it would take me 11 refills to get below 3% dirty fluid remaining. However, I've now used most of my spare Dexron II fluid, so I've bought 10 litres of Dexron III and I'll move to the next stage next week. I will drain the fluid, drop the sump, replace the filter and gasket, replace the sump, then the interesting bit. I will refill the box with the amount that has been drained, disconnect the oil return pipe to the box, get a friend to start the car and whilst the fluid is then pumped out from the return pipe into a container, I will get another friend(!) to start replenishing the fluid through the dispstick tube. I'm not sure if I need to cycle the box at the same time or if it can be done in neutral. Anyway, when about 10 litres has been pumped out of the return pipe whilst being replenished. I'll shut it all down, reconnect the pipe, and then do a proper hot check of the fluid level.

The alternative approach is just to change the filter and do another 4 fluid refills of Dexron III as per the original manner, but I quite like the idea of the above in terms of getting the most dirty fluid out and trying to get the maximum amount of Dexron III in the system to replace the Dexron II.

Whatever you choose,it does make you realise that if you just do a drain, filter change and refill, which I guess is what many owners and even garages would do, you'll have about 72% dirty fluid still in your system!

Hope that helps

Paul

[Freebird]

Thanks for the tips guys, what a palaver!

The oil that came out was nice and pink and there was very little residue in the pan or on the magnets, so I am happy leaving 72% old oil in at least until the weather improves.

Cheers

Glen.