Montego Blue E86 is Long Gone - Z4MC Diff Rebuild

[lucasxdiniz]

I'm just back after a long break too. As usual, excellent work to be found in this thread.

Glad you're back! Looking forward to seeing your progress with that roof project you mentioned

[lucasxdiniz]

Since I will be road-tripping in Wales at the end of the month, I installed phone chargers for myself and the passenger. This time I ended up using a piggy back fuse and a 12V to 5V with super fast charging capability.

Pretty neat install as no cables are visible until I pull the USB-C from the steering surround to connect to my phone, which usually is on the RHS vent on a small magnet mount.

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[MrPT]

I'm just back after a long break too. As usual, excellent work to be found in this thread.

Glad you're back! Looking forward to seeing your progress with that roof project you mentioned

Ahh, I didn’t quite manage to get it started before another project took over!

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Moved into the house now, and the kids aren’t babies anymore, so hopefully will be able to make it out to a few more events.

[paddy wright]

Sorry to hear about Rusty- we lost one of our cats on New Year’s Day and it still makes me sad now. Great to see you back in a Z and looking forward to seeing you perfect this one.

[companycardriver]

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Hello. What paint did you use on the pump bracket? I removed my at the weekend and now not sure what to paint it with.
Thanks

[lucasxdiniz]

Moved into the house now, and the kids aren’t babies anymore, so hopefully will be able to make it out to a few more events.

That is some project! Look forward to seeing the garage when you're finished!

Sorry to hear about Rusty- we lost one of our cats on New Year’s Day and it still makes me sad now. Great to see you back in a Z and looking forward to seeing you perfect this one.

Thank you. I just hope it gets easier overtime.

Hello. What paint did you use on the pump bracket? I removed my at the weekend and now not sure what to paint it with.
Thanks

Hi! I used BMW Sunlight Silver from Halfords and matt lacquer. I'd recommend Hammerite of some sort so you know it's going to be long lasting. I did that as a quick tidy up before winter, intend on revisiting that at some point. But so far, it looks just as good as it did in that picture.

[companycardriver]

Hi! I used BMW Sunlight Silver from Halfords and matt lacquer. I'd recommend Hammerite of some sort so you know it's going to be long lasting. I did that as a quick tidy up before winter, intend on revisiting that at some point. But so far, it looks just as good as it did in that picture.

Thank you very much, I’ll pick up some tomorrow.

[lucasxdiniz]

Just realised I haven't really talked much about the Z4M since before my first road trip in it. Well, Wales with the Z4M was simply amazing, I am thoroughly in love with how this car performs and the noise! Oh, and the looks too <3

The car handled better than expected (given how stock the suspension is) and wasn't as uneconomic as I had expected. After the road trip, I couldn't help but have a couple of day trips to the Peaks for a bit of spirited driving enjoyment.





Random video for some noise - you can't see much [that's the point ;]

[lucasxdiniz]

Normally by now I would probably have already extensively modified this Z4. But any disposable money after buying a house vanishes at such a rate... it's depressing. I'm very much against SORNing cars (it's meant to be driven!), but I had decided to SORN it from October to April and use the money I would otherwise spend on tax and fuel towards some maintenance and mods. My initial plans were to rebuild the VANOS and buy an intake, but for my Birthday in November I treated myself to a day of driving my car in the Peaks with a couple of friends. It was a rainy day and there was a fair bit of oversteer moments and quite a bit of aggressive on and off throttle. On the way back I noticed that there was a more noticeable clunk from the diff if I lifted off the throttle quickly. After a lot of reading I thought maybe I had worn out the LSD clutches and was getting the well known 'M clunk'.

I put it on the lift at work to make sure the noise was from the diff and not the driveshaft or somewhere else resonating through the chassis, and to my relief, it was just the bush at the front of the differential. No problem there, only a £25 bush from BMW...



But then a combination of being an engineer, OCD, and some man maths caused some scope creep... If I need to drop the differential to replace said bush, I might as well refresh the diff properly and not just replace the pinion seal like most do - so £26 just became about £500 in LSD clutches, bearings and seals.

Here's a couple of pics of the car being prepped for the winter work:




Here's a couple of videos of the intial work showing the diff being dropped and the worn-out bush:




I'm still in the process of waiting parts to arrive and deciding just how deep to go. So far I have already ordered:

• Racing Diffs clutch set with pre-load shim
• Koyo Bearings and OEM seals and washers
• Rear drop-links
• ARB and gearbox bushes
• Exhaust gaskets
• Full OE shifter rebuild kit

I have already decided to do a light refurb, so will be removing all the surface corrosion of the subframe, then treating and painting everything. I'm also getting quotes for zinc plating and powder coating for a lot of the hardware I removed to get the diff out. I need custom tools to do the diff job and while I wait for those, I am cleaning things up with a combination of parts washer, sand blasting and water bead blasting:









Yesterday I managed to press new OE bushes into the diff housing. Long winded process of having to turn a tool to align the bushes properly and heating the cover up. Managed to get it in without making it crack, so that's some money saving right there, right!? £50 vs £180 (for a new diff cover with bushes).




Some of you may be wondering if anything is going to be modified in this process... I think the answer to that is possibly. Does anyone want to buy a kidney?

[Mr Tidy]

Some mission creep there, but it's preventative work so probably not a bad idea.

As for modifications I think you're standing at the top of a slippery slope!

[1536Z4]

wondering if anything is going to be modified in this process.

You already have a history for modding so I would bet on Yes

[lucasxdiniz]

A whole lot more preparation since last weekend. And loads more to come...

At the weekend I started cleaning the dirt from the subframe in preparation to treat the surface rust. Cleaning the baked on diff oil was much harder than I had assumed - it had to be scrapped off and only then I was able to clean the remaining residue with engine degreaser and brake cleaner.

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I had a custom tool machined to press the front differential mount bush out of the sub-frame. Look at how knackered it was:

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Unfortunately I screw up the installation and will need to order a new bush. Lesson learnt, just because the old bush was pressed out very easily, doesn't mean I don't need to freeze this bush to -18°C and to use a bit of heat to expand the bore on the subframe.

More masking and sand-blasting:

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All bolts catalogued and sorted to help me make a decision on zinc plating or replacing the fixings. Some of these cannot easily be replaced as you can't get the right sizes/specs if not from BMW, but at £15/bolt and needing about 12 of them would make this decision easy towards zinc plating. However, I don't know if I trust zinc platers to do the right heat treatment to avoid hydrogen embrittlement of the 10.9 bolts. May just suck it up and buy new fasteners (not from BMW) for what I can, and run rusty axle bolts.

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There's a list of the bolts here. The grades were read from the bolts taken from the car. Given the clear indication of zinc flake, I know they are OE. But some of the bolts that are 8.8 marked are listed as 10.9 on RealOEM, so not sure what's going on there.

https://1drv.ms/x/s!AoAAw4ET48j5hJJAspo ... w?e=IXwR1n

[lucasxdiniz]

Since I removed the gearbox mount brackets, it would be rude to not clean it up properly:



I also treated all surface rust with Iron Phosphate and painted it with POR15.





As usual I failed to take pictures of the process, but I spent a whole weekend running a wire wheel attachment over the subframe to get all the surface rust I could off and then treating it with iron phosphate + zinc solution. I also decided to remove the rear camber arms so I could paint into the subframe, however, the eccentric bolt could not be removed from the bushing, so I ended up using a 8lb mini sledge hammer to get it free, which knackered the bushes (as expected). So bushes, arms and tools on order... yay.

I only took pictures of the subframe when the paint was wet, so it looks awful. When I'm back under the car I will take photos with everything nicely cured.






I've bought new fasters for pretty much everything I removed so far - not from BMW mind. BZP is no where as good as a coating as the Zinc flake on the OE bolts, but BZP is definitely better than the surface rust on most of the bolts already. I'm not replacing the torx bolts (£150+), so I chose to treat and paint their heads just so it's less of an eye sore. The shank and threads are absolutely fine, and so is the serration.

[D.Bryce]

I know the feeling of this.

Had a rattling exhaust clip, which then led me to a potential leaky diff seal, which led to a 4.1fd, which led to full polybush subframe and arms it’s a slippery slope.

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[lucasxdiniz]

I know the feeling of this.

I definitely approve! Wish I had the space to do the sub-frame properly! One day...

I could not resist the ultimate scope creep: