Thread: Disco 3/4 Automatic Transmission FAQ - 6 Speed

Couldn’t agree more. I bought my old D3 done 140,000k with a shuddering box. I kept dropping fluid and topping it up every 30,000km with everything from genuine lr fluid to fuchs to Shell atf, all had different dye colours, sulphurs contents etc. Sold it with 350,000k on it with a perfectly shifting box - better than when I got it.. applying the same methodology to my D4 (I’m using Fuchs), same positive result. My humble suggestions (and excuse the detail but someone might value it):

1. Put a steel pan and filter on it once.

2. When topping up, do it with the engine running. Ie - Make sure disco is level, Drain atf out trans sump hole, put plug back in, pump atf in side hole, keep putting in til it drips out side hole, leave the side plug off, get in, put foot on brake, turn it on, push through reverse and a 1st /2nd/3rd manually without moving, put in Park, handbrake on, get back under it, put more atf in side hole until it drips out while it’s idling, tighten up side plug. People sometimes don’t put the last 800ml in. When I forgot to it flared and carried on like a female dog until I did.

3. Use an iid tool or something to reset the trans ecu settings once every 90,000k to tell it to not compensate for old fluid anymore. IID tool handbook advises this is done post fluid change but not too regularly. Independent lr shop might do this for you.

4. Drive it 1000k before you pass judgement. While I always notice a difference straight away. It’ll often take a while for the ecu to recalibrate itself (regardless if it was reset or not) and for the fresh fluid to have its full effect.

Makes me wonder how many time a disco trans has been “rebuilt” when all they did was chuck a pan on it, top it up properly, reset its ecu and drive it for a bit.

Sorry for the rant but i suggest thinking about it this way - would BMW, Jaguar, Ford, Aston Martin, Hyundai, Rolls Royce, Mercedes, Maserati, Kia, Bentley, VW, Audi and Landrover all be using or have used a variation of this box if it was a fragile, high maintenance POS? finicky, perhaps. Tough as nails if you treat it properly, IMO, my oath my friends ..

PS, draining the ATF fluid and a top up can be done with minimal tools, i think a 10mm socket and 2 allen keys, size dependant on the sump you have on, a cheap plastic oil pan and a tom thumb pump and a funnel (O and a towel that's fallen out of favour with SWMBO). Its a 4 stubby job if you drink quickly and can be done on a concrete slab with the suspension set at off road height.

STM TOM THUMB UTILITY PUMP

I use Fuchs 4134, it's supposedly the correct one for D4 and is used by heavier Mercedes applications, have found absolutely no reason to disagree. Burson's sell it.

This is just what I do but it works. Anyone wanting to take my 165k D4 SDV6 for test drive around the block to validate my theory is welcome within reason.

Thanks for the posts, I have been carefully reading. So my rebuild is booked in for next Tuesday. And even though it's cheaper than normal at 4.5k, thats still a lot of money. So why not try this first. Can I get your options first... my tranny guy reckoned pretty well everything about the box is stuffed. It takes 6 seconds to engage revered. It's constantly searching for gear. I get an error code to do with shift malfunction. Is it worth trying the oil and filter change and leave for a month? Thanks.

Following on from above, there is also a slight grinding noise (sounds like actuator to me) between gears. I'm happy to give the fluid change a go just wanted to check of its a complete waste.

Ok so I decided to drop the fluid today. Replaced about 4L so far, will drive for 100kms and do it again. I also cleared the adaptive data in the transmission module. It's now driving awfully, as expected. 3 transmission codes now appearing relating to shift between gears and gear ratios. I'm guessing u should give it a few hundred kms to see if it improves?

Originally Posted by casta66

Ok so I decided to drop the fluid today. Replaced about 4L so far, will drive for 100kms and do it again. I also cleared the adaptive data in the transmission module. It's now driving awfully, as expected. 3 transmission codes now appearing relating to shift between gears and gear ratios. I'm guessing u should give it a few hundred kms to see if it improves?

Make sure you fill it as described above with the engine running as well else you won’t have put back enough fluid

Originally Posted by casta66

Ok so I decided to drop the fluid today. Replaced about 4L so far, will drive for 100kms and do it again. I also cleared the adaptive data in the transmission module. It's now driving awfully, as expected. 3 transmission codes now appearing relating to shift between gears and gear ratios. I'm guessing u should give it a few hundred kms to see if it improves?

I’ve personally never dealt with a transmission that’s taken that long to find reverse or shown codes but I’d have done the same thing you’ve done. If the new fluid is going to save it I think it’ll take at least 1000km before you’ll start to feel improvement though.. was the fluid you dropped out as black as the ace of spades? If not it probably means someone’s tired the fluid trick with no results....

This is a 4hp22e correct? D2 is shown in signature line...🤔

Jc