Z3 Rear diff oil change - how easy

WorldClassAccident · #1 28th February 2015, 17:10

Having sound proofed the boot a bit I could hear a new noise. A bit hard to describe but if I coasted to a halt there was a slight scraping sound as it slowed and then there was a slight clunk and it seemed to free wheel a bit more freely.

I decided it was the rear diff as that seemed the easiest bit to check. I thought I would change the oil so here goes what I did.

Stick it on a ramp. The slope of the ramp almost exactly compensates for the slope of the drive

Slight left to right slope but acceptable

Rear diff with top fill hole and bottom drain hole easy to see on the back plate

14mm hex keys. Make sure you can loosen the top one BEFORE you loosen the bottom one. You don't want to drain the diff and find out you can't refill it!

Oils should not look like this

Leave to drain for 15 minutes.

Put the drain plug in and tighten.

Pour in 1.5 litres of 75W140* Oil for LSD and fit the top plug.

Drive around and listen how quiet it is.

*If your car doesn't have a LSD** you can use 75W90 apparently

**Jack up the centre rear of the car. Rotate a wheel on one side. If the wheel on the other side rotates the same way you have an LSD. If it rotates the other way then you don't.

Tribute Automotive · #2 28th February 2015, 18:46

Nick you have had your car far to long if you are doing this sort of maintenance!

I'm not sure I understand the term "sound proofing". To me it's the excess weight that manufacturers add to cars to slow them down. Pull it all out and fill your wheelie bin up, you will find your car goes faster..... well it will sound like it's faster anyway.

landmannnn · #3 28th February 2015, 19:39

Nice to see a WCA story with a happy ending.

Mister Towed · #4 28th February 2015, 19:47

Quote:

Originally Posted by landmannnn

Nice to see a WCA story with a happy ending.

Still plenty of time for scald/slip/swallow action with the used diff oil...

redratbike · #5 28th February 2015, 20:59

Quote:

Originally Posted by Mister Towed

Still plenty of time for scald/slip/swallow action with the used diff oil...

H. Ha ha let's not tempt fate

y cymro · #6 2nd March 2015, 12:49

Quote:

Originally Posted by WorldClassAccident

Having sound proofed the boot a bit I could hear a new noise. A bit hard to describe but if I coasted to a halt there was a slight scraping sound as it slowed and then there was a slight clunk and it seemed to free wheel a bit more freely.

I decided it was the rear diff as that seemed the easiest bit to check. I thought I would change the oil so here goes what I did.

Stick it on a ramp. The slope of the ramp almost exactly compensates for the slope of the drive

Oils should not look like this

Pour in 1.5 litres of 75W140* Oil for LSD and fit the top plug.

Drive around and listen how quiet it is.

*If your car doesn't have a LSD** you can use 75W90 apparently

**Jack up the centre rear of the car. Rotate a wheel on one side. If the wheel on the other side rotates the same way you have an LSD. If it rotates the other way then you don't.

Hard to tell from a small photo but your oil looks as if it contains a lot of metal particles. Have you disposed of it yet? Otherwise pass a magnet through the oil and see how much it picks up.

Also, all 2.8 Z3s have a LSD as standard. It's a Torsen diff which means you can't test it by turning one wheel. You could either remove the diff end casing and take a look (I have a photo of mine if you want a reference photo), or spin the wheels from a standing start and count the rubber lines on the road. Two is good.

Torsen diffs don't require LSD oil.

It seems to be a common problem with 2.8 Z3 to have some diff noise above about 40mph when travelling on flat ground at a very light throttle setting. Many diffs were changed under warranty but users reported similar problems afterwards.

WorldClassAccident · #7 2nd March 2015, 13:23

Thanks for the correction regarding the LSD - I was just quoting what I read on the web :-(

I hope the choice of 75w140 LSD oil won't be an issue

y cymro · #8 2nd March 2015, 16:56

Hi Nick
Wasn't meant as a correction, just adding to your useful advice

I think oil recommendation is a 75/90, but as you say, a heavier oil will quieten gear noise.
Steve

WorldClassAccident · #9 2nd March 2015, 17:55

Thanks.

I am planning to change the transmission fluid next. I have a new filter, gasket and bolts on order.

y cymro · #10 2nd March 2015, 20:01

Quote:

Originally Posted by WorldClassAccident

Thanks.

I am planning to change the transmission fluid next. I have a new filter, gasket and bolts on order.

I recommend Opie oils that has always provided good service in my experience.

The manual gearbox also requires an ATF (Nick's is an auto) and Opie recommends Redline D4 which it says is well proven at sorting out shifting issues that BMW boxes can suffer with. Other recommendations are Amsoil ATF and Fuchs 5000/5005. As a cheaper option Opie suggests going for Castrol Transmax Dex III, Fuchs ATF 4000, Millers ATF DM or motul Dexron III.

http://www.opieoils.co.uk/c-1432-atf...ion-fluid.aspx

Opie recommends a 75w-90 for the diff

http://www.opieoils.co.uk/c-673-75w-...ion-fluid.aspx

It states that Fuchs Syn 5, Millers CRX, Redline 75w-90 GL5, Motul Gear 300 and Gulf Competition are ideal for the diff and that Fuchs Sintopoid, Castrol Syntrax Longlife, Millers TRX, Motul Motylgear, Mobil SHC and Amsoil FGR are also good choices.

For what it's worth I've just filled my gearbox and diff with Redline oils.

scimjim · #11 2nd March 2015, 23:34

WCA, was the oil hot when you drained it? I think I'd be doing a second change on that diff!

Scottie22 · #12 3rd March 2015, 07:24

If I remember correctly, in the old days car sharks would fill a noisy diff with thick oil and sawdust, which by all accounts worked briefly...........
Would not recommend that for you though WCA!

WorldClassAccident · #13 3rd March 2015, 07:44

The oil was warm rather than hot. Flowed freely though and I left it to drain a while.

Are you suggesting a second change just because of the state of the original oil? Just to make sure it is properly flushed clean? Should I just rag it around for a month so the new oil picks up the old crud and then change it?

Already contacted Opie oils regarding transmission oil. Was going to go with Fuchs. Partly because the was a review somewhere saying some guys were moving away from using Redline for some reason but mainly because I smile when I say "Give me some Fuchs" to the lady on the phone*.

*say it out loud, as it is spelt.

IanA · #14 6th April 2015, 19:34

Thanks for the easy to follow instructions. Took me about 20 mins tonight to do the job. The oil that came out was in much better condition than yours but I changed it anyway for some EP90.
I'd splashed out on a drain key kit which included the requisite 14mm hex key whose base fitted into a 19mm socket.

WorldClassAccident · #15 6th April 2015, 21:41

Now try the transmission. Easy but needs the car raised and a better oil syringe than mine

mobilerobbie · #16 7th April 2015, 06:20

Looking at your car, how did you. Anage to get the barchetta doorlock in the door?
I bought a set for my 250 build but found out that one end of the handle is bent a bit so not a straight fit....

WorldClassAccident · #17 7th April 2015, 06:58

I asked Chris nicely and he made the handles fit