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How to change the ATF fluid in a Mazda Bongo 2.5 diesel auto box

The Automatic gearbox on my Mazda Bongo doesn’t have a drain plug, so I sucked out the ATF fluid using a Pela 6 litre pump with the extractor tube inserted into the dipstick tube under the driver’s seat. It’s a slow job, but with a bit of patience and periodic re-pumping as the vacuum needs replenishing as oil comes out, just about all the oil can be extracted. It was black and nasty looking and there was about 5 litres of it.

It seemed like a good idea to clean out the sump while the box was empty of fluid. It’s quite a stretch to reach the sump-retaining bolts but can be done by lying on the ground with a ring spanner (10mm) at arms length. There are 18 small bolts. I approached the sump from both sides of the vehicle in turn.

I completely removed all but the 4 corner bolts as I didn’t want the sump to drop and possibly bend its mating surface. It’s quite a long way to the ground and so I positioned something (a plastic washing up bowl) near to the sump so that, when free,  it could be lowered just a short distance.

I also used strong spring clips to hold it in place while I removed the final 4 bolts. This made it easier to control the release without straining the sump edges. It’s worth noting that I didn’t have to do anything to break the seal. The sump separated under its own weight. You can see how dirty it was (right) - remains of the black fluid and the circular magnet full of steel swarf. (This sits in place at the FRONT end of the sump.)

The underside of the box with the sump removed is shown on the left. There’s a mesh filter, held in place with 4x 10mm bolts, that I removed and cleaned with petrol. (The box view is minus this filter, which fits in the hole bottom left of the photo.)

I cleaned up the inside of the sump with old newspaper and also carefully cleaned up the mating surface. I smeared a very fine coating of sealant and clamped the sump back in place with the spring clips prior to inserting the 18 bolts. The procedure was the reverse of the removal. 4 corner bolts first and then the other bolts loosely. Don’t screw any bolts tight until they’ve all been engaged and screwed in slightly so that you know they can all be located. Then I started tightening bolts at the centre of each side first, working towards the sump corners last.. The spring clips can be re-positioned as the bolts are tightened, and the clips removed when the sump is securely in place.

Then the gearbox was re-filled with Dexron Type III ATF oil. I used semi-synthetic. Because there’s no filler cap, all the new fluid had to go in down the dipstick tube as well. I used about a metre of narrow gauge garden hose pushed into a ‘silicone sealant’ tube nozzle at one end and taped to a funnel at the other.The nozzle was a good push fit into the dipstick tube and I found that if I propped the driver’s seat up with some wooden blocks, the funnel could be screwed to one of these to keep it in place! It took about 5 litres to re-fill, pouring in 500ml lots at a time - run the engine till warm, move in and out of gear a few times, and measure the level with the engine running and the gears in Park.

Top and bottom of this filter are shown on the left after cleaning, along with the muck flushed out of the filter into the bowl, and the cleaned magnet.