As planned, I changed my differential, gearbox and power steering fluids yesterday, so here's a quick update of how it went.
First of all, I had to do a bit of shopping and purchase all the required fluids, but it wasn't all so straightforward.
The easiest part was the fluid for the differential, which should be 75W-90 (for open differentials), and I decided to go with Castrol Syntrax Long Life, because it's BMW approved, so can't go wrong with that. In my case, I needed 1.7L, so had to buy x2 1L bottles and had a bit left after we filled the diff.
Now the gearbox fluid was the tricky part. According to RealOEM, the gearbox fitted on my car is S5D310Z, meaning S = manual transmission, 5 is the number of gears, D = direct gear, 310 is the max input torque in Nm and Z means made by ZF.
To find out what's the correct oil that should be used in this gearbox, I decided to look it up in the ZF's list of lubricants in their catalogue here > https://aftermarket.zf.com/remotemedia/lol-lubricants/lol-en/lol-te-ml-11-en.pdf
It's listed as "S5-31" and there are 2 recommended oils for this gearbox: BMW's oil (part number 23007533513) and Castrol Syntrans B 75W.
Now it would be all well and good, if it wasn't for the red ATF label on the side of my gearbox and also the owner's manual recommending to use ATF for this gearbox. I was a bit confused by the fact that the gearbox manufacturer (ZF) and the vehicle manufacturer (BMW) were recommending different oils for the same gearbox?
After spending a few hours digging around BMW forums, it turns out that initially as per ZF's catalogue, BMW used thicker gear oil (75W-80 or MTF-LT-2) for these gearboxes, but over time a lot of customers complained about hard gear shifts, especially in colder climates, since gear oil needs time to warm up before it can provide smoother shifting.
As a result, BMW later switched to ATF, because it still provides required protection and lubrication for the gearbox, while the gear shifts are easy and smooth, regardless of whether the oil is hot or cold, because ATF oil is thinner compared to gear oil, so it works well in colder temperatures as well.
Long story short, you can use either what ZF says in their catalogue or ATF as per BMW's recommendation, because both will do the job fine. There was an interesting discussion on Bimmer Forums a few years back on this topic, which you can read here > https://www.bimmerforums.com/forum/showthread.php?958283-atf-or-mtf
Myself, I made the choice to go with what the gearbox manufacturer recommends to use, so I went with Castrol Syntrans B 75W, despite the ATF label on my box. In my case, I needed 1.25L, so again had to buy x2 1L bottles. To be honest, I hardly noticed any difference myself after changing to Castrol B 75W, but it's summer now, so the temperatures are quite high - it might be a bit different during winter.
And as for steering, you need to check what it says on your reservoir cap, so for me it was ATF. Essentially, you can go for any Dexron III ATF, but I wanted to find one, which was specifically equivalent to BMW's Dexron III, so the only one that listed BMW's actual part numbers was Fuchs TITAN ATF 5005, so I went with that. Various oil selector catalogues list that you need 1.2L for steering, so I bought x2 1L bottles, but strangely enough just one bottle was enough to fill the system - keep that in mind.
Be sure to buy 2 replacement washers for the diff plugs (07119963355), as your existing ones will most likely fall apart, like mine did, and also get 2 new washers for the power steering hose (32411093597), which you'll have to remove to drain the PAS fluid. I actually bought 4 washers, as I thought we'd have to remove the top smaller hose on the pump as well (it has smaller washers - 32411093596), but undoing the larger bottom hose was enough to drain all the fluid out.
Also bought a new BMW badge with the grommets for the bonnet, as mine was an aftermarket one with no edge to the letters.
I didn't want to waste my time going to BMW for the sake of a few washers and a bonnet badge, so I thought I would treat myself and upgrade my tatty gear knob to a proper "M" one. Now the thing is that regular E34's never had a 5 speed "M" gear knob, because the only "M" gear knobs were for the M5's, but those were illuminated and I wanted just a basic one.
Anyway, the non-illuminated 5 speed "M" gear knobs became a common thing starting from E46 and E39 models, although the very first time they were used on E36 318IS models. The correct part number that you need is: 25117503231. Some may say it's a bit pricy, but I got it for just over 50 quid from BMW.
It has some weight to it and it definitely feels heavier compared to my old one. Wouldn't say it makes a world of difference, but it's a nice touch and it's easy to fit. You simply pull the knob up when in neutral, but be careful not to hit the rear view mirror or anything else for that matter, as they fit quite snug, so can be a bit stubborn to come off. Line up the new knob and just press it down until it clicks into place.
Replacing the bonnet badge was also pretty straightforward, just use a plastic spreader to pop off the old badge, swap over the grommets and before putting the new badge on, apply a bit of grease on the 2 pins to help it fit smoothly. I've read that for the past 10 years, genuine BMW badges have always had black plastic backsides, but mine was chrome-silver, so either it was very old or just a eBay-special, although with a BMW part number on it. Pics below, old one out and the new badge fitted.
Changing the diff fluid was a bit tricky, because the access to the filler/drain plugs is a bit of a pain. We had to remove the small crossmember from the front of the diff, so we could get more access to the filler plug and move the diff slightly to the left to have enough space for the socket/ratchet to fit on the drain plug.
Make sure to change the washers on the plugs and possibly apply some PTFE tape to prevent leaks from the plugs in the future.
Moving to the gearbox, it was all straightforward with loads of space for access, so no issues here. Notice the red ATF label on the side of the gearbox, which matches the gearbox oil recommendation in the owner's handbook that came with the car. As I explained earlier above, you'll be fine with either what ZF says (Castrol Syntrans B 75W) or ATF Dexron III. The drain plug on the gearbox had some sealing tape on it, so we also applied PTFE tape around it before putting it back in. It's so unusual for me to see a dry gearbox, because I remember the box on my E30 325i was pissing oil from everywhere...
And finally the power steering oil. We undid the big banjo bolt on the bottom hose of the PAS pump and let the oil drain out. Then without running the engine, turned the steering wheel left/right a few times to make sure it all came out.
Put the bolt back in, filled up with new generic ATF to flush the system, run the engine turning the wheel left/right, then drained it all out again. Replaced the washers on the banjo bolt, filled up the system with Fuchs TITAN ATF 5005 and repeated the bleeding for the steering, making sure the oil level was correct. Like I said earlier, for some reason just 1L was enough with the level being at maximum.
After all the fluids were replaced, we checked underneath the car to make a list of parts that will be need for the clutch replacement, so apart from the obvious clutch kit, I will also be replacing the clutch fork + spring clip and pressure plate bolts, clutch slave cylinder + hose, the gear linkage with all the bushes, 4 gearbox mounts, propshaft guibo, centre propshaft bearing and the exhaust to gearbox bracket was a bit rusty, so going to change that as well. Will also renew the brake fluid for the clutch hydraulics.
That should be it for now. This will probably be the last major service work required on the car, because I can't really think of anything else that we haven't done, so it will finally all come together. I'll get all the shopping done, making sure to check part numbers, etc, then will update this thread before doing any work.
Any suggestions are more than welcome. Thanks for following.