#ZedShed 2006 E85 Z4 M Roadster rear sub frame rebuild

[GazHyde]

This thread is to document a full rear subframe tear down and refresh on my 2006 Z4 M Roadster. Following an inspection service at my trusted independent BMW garage it was identified there was deterioration and play in some of the rear bushes. The diff is also has a whine most likely due to the mileage of 123k miles and has a leak on the input seal (fluid levels fine as I asked for it to be topped up, and it barely took any extra).

Plan:

• Drop the subframe and remove all bushes
• Send the differential to our tame local diff specialist for a tear down and refurbish. We'll leave him to determine what it requires but I'm thinking it will be our usual request to replace the bearings and crush sleeve, and possibly new clutch packs.
• Send the subframe, wishbones and anything else we can to be blasted and powder coated.
• Replace all 17 bushes that comprise the rear subframe and differential. Change hand brake cables, roll bar bushes and drop links.
• Refit everything

So, put the kettle on and put your feet up and enjoy the ride! There are some major differences between the Z3 and E85 Z4, there are also some subtle differences between the Z4M and non-M as well. We will be following this rebuild up with an identical process on Lee's 3.0si coupe so you should get to see all the differences.

First off then, lets consult the oracle realoem and show some diagrams of what we are looking at.

Subframe: Z4 E85 Z4 M3.2 Rear axle carrier

RealOEM.com - Online BMW Parts Catalog

BMW parts Z4 E85 Z4 M3.2 Rear axle carrier

www.realoem.com

Trailing arms and lower/upper wishbones: Z4 E85 Z4 M3.2 Rear axle support/wheel suspension

RealOEM.com - Online BMW Parts Catalog

BMW parts Z4 E85 Z4 M3.2 Rear axle support/wheel suspension

www.realoem.com

Differential: Z4 E85 Z4 M3.2 Differential-drive/output

RealOEM.com - Online BMW Parts Catalog

BMW parts Z4 E85 Z4 M3.2 Final drive, gasket set

www.realoem.com

Part numbers:
The rear subframe comprises 17 bushes, we've also ordered new roll bar bushes, drop links and handbrake cables.

I've compiled a list of part numbers, most of which have been ordered from BMW but some are OE equivalent due to the BMW price in comparison. Do not use this section as a direct shopping list if you're carrying it out. Part numbers change from time to time and some of these are not the ones listed on realoem, but alternatives which I've verified as compatible from other models (good old BMW shared platforms).

Realoem description	BMW PN	Amount	Actual description	Supplier
RUBBER MOUNTING front left	33312283573	1	Subframe bush	BMW
RUBBER MOUNTING front right	33312283574	1	Subframe bush	BMW
RUBBER MOUNTING rear	33312283419	2	Subframe bush	BMW
ARB bushes	31352229711	2	ARB Bush	BMW
Rubber mounting	33326770824	2	Wishbone bush	BMW
Rubber mounting	33321092247	2	Wishbone bush	BMW
Handbrake bowden cables	34416785397	2	Handbrake cables	BMW
Lemforder drop links	33552283743	2	Drop links	eBay
Meyle HD Rear trailing arm bushes	33326770817	2	Trailing arm	eBay
Meyle "ball joints"	33306852895	4	Ball Joints upper/lower	eBay
PowerFlex *	PFR5-4620 PFR5-4621	2 1	Diff front/back	eBay

* Note on the diff bushes. There are 2 rear on the diff cover and 1 at the front. BMW appear to only supply the rear diff bushes fitted to the diff cover, so you need to purchase a complete diff cover to change these part number has plenty of availability. Powerflex provide a kit for all 3 bushes which is what we opted for, I ordered Purple and received packages labelled with Purple PNs but they are Black. We're just going to run with them rather than mess around trying to change them in time.

Link to Powerflex Z4 M section.

Powerflex - Performance Polyurethane Bushes

www.powerflex.co.uk

Current build total in parts at this time: £560
Differential Oil: £63

 

[GazHyde]

Differential rebuild information:

The diff has had a complete strip down to replace the input seal which was leaking. Whilst he was in there he replaced all bearings, seals, crush sleeve and all torqued down to specification. An inspection was carried out on the clutch packs and did not require replacing.

Castrol TRANSMAX Limited Slip LL 75W-140 Fully Synthetic Hypoid Gear Oil

https://cdn.opieoils.co.uk/pdfs/castrol/Transmax-Limited-Slip-LL-75W-140.pdf

RED LINE Limited-Slip Differential Friction Modifier / Break-In Additive.

https://cdn.opieoils.co.uk/pdfs/redline/SynthGearOils.pdf

 

[GazHyde]

Subframe tear down:

Day One split over two posts due to around 40 pictures!

Day One Part One quick link - Removing everything ready to drop the subframe through to subframe on the floor.

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

This thread is to document a full rear subframe tear down and refresh on my 2006 Z4 M Roadster. Following an inspection service at my trusted independent BMW garage it was identified there was deterioration and play in some of the rear bushes. The diff is also has a whine most likely due to...

zroadster.org

Day One Part Two quick link - Tearing down the subframe and inspecting the condition of the parts.

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

This thread is to document a full rear subframe tear down and refresh on my 2006 Z4 M Roadster. Following an inspection service at my trusted independent BMW garage it was identified there was deterioration and play in some of the rear bushes. The diff is also has a whine most likely due to...

zroadster.org

Day Two - Removing bushes, calipers and what's left to do.

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

This thread is to document a full rear subframe tear down and refresh on my 2006 Z4 M Roadster. Following an inspection service at my trusted independent BMW garage it was identified there was deterioration and play in some of the rear bushes. The diff is also has a whine most likely due to...

zroadster.org

Day Three - Painting calipers, brackets, half shafts and other bits. Getting to the bottom of the oil leak!

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

This thread is to document a full rear subframe tear down and refresh on my 2006 Z4 M Roadster. Following an inspection service at my trusted independent BMW garage it was identified there was deterioration and play in some of the rear bushes. The diff is also has a whine most likely due to...

zroadster.org

Day Four - All the bushes! Bit more painting, gearbox oil change and then all the subframe bushes and bearings.

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

Make sure that you reinstall the chain tensioner properly. I can't remember what you do, but it could be fill it with oil then press it twice. Check out the TIS. There is probably nothing wrong with it. It probably just needs a good clean and some clean oil. Here's me fitting a used chain...

zroadster.org

Day Five - Subframe reassembly!

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

Make sure that you reinstall the chain tensioner properly. I can't remember what you do, but it could be fill it with oil then press it twice. Check out the TIS. There is probably nothing wrong with it. It probably just needs a good clean and some clean oil. Here's me fitting a used chain...

zroadster.org

Day Six - Reassembling everything else!

#ZedShed - 2006 E85 Z4 M Roadster rear sub frame rebuild

Make sure that you reinstall the chain tensioner properly. I can't remember what you do, but it could be fill it with oil then press it twice. Check out the TIS. There is probably nothing wrong with it. It probably just needs a good clean and some clean oil. Here's me fitting a used chain...

zroadster.org

 

[GazHyde]

Reserved

 

[GazHyde]

Reserved

 

[Brian H]

Something I plan to do over this winter, I’ve renewed the diff oil already when the pinion seal had a small leak, bmw diff oil is super expensive!! Looking forward to your progress.

 

[GazHyde]

Something I plan to do over this winter, I’ve renewed the diff oil already when the pinion seal had a small leak, bmw diff oil is super expensive!! Looking forward to your progress.

I’ve yet to look at what oil and going to do some research first, not averse to BMW but just want to weigh up the options first. Will likely do the gearbox while I’m under there as well. Only place I’ve looked so far is Opie and they recommend this against my reg number. I’ll also source a bottle of friction modifier to keep on hand just in case it’s needed later on.

Motul Gear Competition 75w-140 Fully Synthetic Racing Transmission & Diff Oil

The UK's largest independent supplier of automotive oils, fluid and parts. We've products to suit any vehicle, from full blown Race / Track weapons, to Daily Drivers looking to save money. Plus FREE expert advice & recommendations - OPIE KNOW OILS

www.opieoils.co.uk

 

[Lee]

This will be our first full Z4 build, this will be one big learning curve so there will be lots of detail.

 

[GazHyde]

Post #2 of this thread will detail info on the diff rebuild, currently just has the oil and friction modifier I've ordered (from Opie with 10% forum discount).

 

[GazHyde]

Strip down has started! Day one part one of two scheduled for this week with myself, Lee and Trev all taking a couple of days of work to play.

First thing to roll her in and get her up on the axle stands.

Testing our new LED lamp, big improvement.

Removed the exhaust system, which is essentially Supersprint from the cats back. This includes the centre section and both back boxes.

Supersprint "race" exhausts.

Prop shaft removed, with clear view back towards the gearbox

...and here's the gearbox. Some discussion as to whether we drop it and check the usual things on it. Still to be decided, but seems sensible as we are almost there. Kodi the Shiba is hard at work carrying out safety inspections...

Here's on difference of note, the handbrake mechanism is removable from the car. 6 nuts and it drops down through the car once you remove the gaiter in the centre console. This then gives access to the self adjusting mechanism, irrespective of us changing the handbrake cables this time it still needs to come off as the cables route through the subframe.

The handbrake mechanism on the floor, you can clearly see how the cables route through the subframe to the hubs. You can also see that a lot of the sensor cables also route through the trailing arms to give them some additional protection, whereas all Z3 cables are general surface mounted.

Prop shaft much beefier than the Z3/Z3Ms.

Differential coupling different to Z3's and is much more similar to the half shafts.

Random bits from underneath, mostly reinforcement and a part of the rear diffuser. A little bit of diff oil going a long way covering the rear reinforcement plate/undertray. Part of the reason for dropping the subframe.

Rear discs are past it, thought I might get away with them for a while but they are now added to the list. You can just about make out that they are floating discs like the fronts if you look closely enough.

Rear calipers, brake hoses (being replaced with braided) and discs now removed. Not seen such decent backing plates, so they will be blasted and powder coated and straight back on again.

and then after more items disconnected we dropped the subframe. Essentially at this point we disconnect rear trailing arm and the 4 subframe nuts while the trolley jack supports the diff roughly balancing the subframe in the middle. Slowly letting the jack down while manipulating the frame so if comes down to the floor.

A better look at the subframe on the floor, now it's ready to be torn down to the individual parts. Took us just over 3 hours to get to this point.

End of Day one Part One

 

[GazHyde]

Day One Part Two (or continuation of the above post).

Now we can go through the condition of the subframe and bushes which is why we are here in the first place. There are some horrors in here, but it pretty much looks like everything at the back is original from factory.

Rear trailing arm bushes are one of the most common issues on the Z4, and cause the rear end to feel loose. These are completely failed as you can see in the close ups, these are being changed for Meyle HD.

The four main subframe bushes can be seen as the 4 circles in the picture below, these are weakened and have some lateral movement. These are being replaced with BMW OEM bushes.

The limited slip diff. We'll wire brush the diff before dropping it off to the local specialist for a full tear down, bearing and seal replacement. Will need him to advise if we need new clutch packs and order if needed so he can rebuild it. This will not only stop the input seal leak but make sure she's good for another 123k miles!

The bolt hole directly under the embossed numbers is to bolt it to the front bush (soon to be Powerflex Black)

Twin eared diff plate with massive cooling fins. The two bushes in the top corners are being replaced with Powerflex Black.

Another subtle change, BMW logo on the diff serial number sticker.

A close up of the crusty "patina"...

Half shafts will get a wire brushing and thick coat of Hammerite to tidy them up. Nothing to worry about here, just not appealing as they are.

Some random pics, these are the rear upper wishbones.

Rear drop links have failed. Replacing with Lemforder (OE quality supplier).

Starting to tear down the rear hubs.

This is how the hub bearing removal magic happens!

A bare trailing arm ready for powder coating.

So ends Day one. Back again tomorrow to complete the removal of all 17 bushes!

 

[Brian H]

Great work, 3 hrs is excellent to drop all of that, I would defo replace the handbrake cables whilst your at it.

i know you guys get great discount on parts but I found these guys reasonable when looking for discs.

BMW z series car parts

Car parts for BMW z series cars

www.c3bmw.co.uk

 

[Palmetto]

Looking good. We are just doing this with my wifes E36. We bought a bolt kit from Autobolts and also had a load of parts zinc plated. Everything is bolted back up but not yet torqued to spec. It's so satisfying when you bolt a shiny subframe back up.

 

[GazHyde]

Day Two.

Less photos from today mainly down to the repetition of removing 17 bushes/ball joints and that being pretty repetitive. However, here are the ones from today. Once the bushes are removed they go in to the pile for grit blasting and powder coating.

We the subframe to sort. This has 4 main subframe bushes and the front differential support bush. All of these are pushed out on our 10 ton press, none of them sit in place too comfortably to push but with 3 apes surround the press we get by.

Front diff bush tucked away, once removed we found the rubber core was very soft and clearly past it's best.

As the subframe is bulky we move the press outside for more room (Oldguysrule for scale). This press has paid for itself a hundred times over!

Application of plenty of heat to the subframe bushes, generally wait until the rubber starts bubbling and popping and then over to the press. They usually don't take much to push out then!

How we remove most bushes...
This is the upper left wishbone bush, it's cast aluminium so we are being gentle to not put too much heat in to it. Just enough so when pressed in the vice it slides out nicely. This actually removes the core and most of the rubber leaving the thin out bush to be removed by slotting with a hacksaw and punching out. You'll see this better on the diff bush in a minute.

Close up of the front diff bush before we use our puller setup to remove it.

With the core of the bush removed then a cut is made through the bush outer sleeve, then a punch and hammer to peel it inwards to the point it collapses and comes out. You can see the bush starting to peel inwards just at the far end of the slot if you look closely.

Disc calipers.
We've remove front and rear as it would be rude to not have them all grit blasted before we paint them later. All in pretty good condition and the pistons are the cleanest I've seen in a while. Added seal kits to the shopping list and then need to decide on what colour to paint them, although I'm likely just going to stick with black.

First load delivered at the powder coaters. Usually when the word gets around we are dropping parts off we end up with people dropping off random parts to include, so we have some old Yamaha bike parts included this time. Got another old bike tank & parts along with the subframe and the Zeds calipers to be dropped off tomorrow morning.

That's essentially the end of phase one, we've nothing else to strip down as you'll see in the next photos. We have however added a few extra jobs to the list,

• Braided clutch line as an upgrade and to also ditch the clutch delay valve.
• Removing the gear box, we think that the output seal may have a leak. We're 30 minutes away from the gearbox coming off so it's kind of daft not to while we are there. Will can also check the condition of the clutch plate and flywheel which is no bad thing.

Some random photos of the underside with everything removed, this is to show we have some prep/remediation work before everything goes back in again.

Underside of the boot floor, we'll be spending a fair bit of time under here cleaning up the diff oil, wire wheeling the subframe mounts, rust proofing and Waxoyl sealing the exposed areas. You can see the diff oil as the shiny areas on the petrol tank.

Rear subframe pins are pretty similar style to the Z3 ones, the floor here needs to be cleaned up and sealed again to stop the rust going further.

So that's it until Saturday when the boss is away, but myself, Trev and Paul will likely spend the day cleaning up and rust proofing anything and everything underneath!

 

[GazHyde]

We've had a delivery of parts back from the powder coaters and it's like Christmas! Here's a couple of sneaky pics

Subframe:

Trailing arm

On any Z3 we've blasted and powder coated you'd never retain this kind of detail - although nothing is stamped on those. These are 15 years old, so not much newer than the Z3's and the quality is almost perfect.

Gratuitous ///M logo close up

 

[MarkPlant]

Very jealous

 

[Bazza]

oh powdered polished parts love them

 

[GazHyde]

Day three... send more cake, we got all the painting to do...

A little light on crew today, mainly myself and @Oldguysrule holding the fort. Thanks go to @mwpe Mike for rolling up his sleeves and grabbing a paint brush as well .

Today was mainly about painting brackets, brakes and sundries with Hammerite and also looking in to an oil leak up front. @Rally was down as well who helped identify the likely cause of the oil leak (and also tell me part numbers).

Most of the parts, everything will be black except for the upper wishbones that get a coat of silver which is closest to their normal aluminium colour.

Trev is also going to work his magic on these.

The drying rack

///Mmmmmmmmmm

Upper wishbones (ignore the run on the left one please).

Various smaller brackets

Front subrame bracket also in silver, caliper and rear trailing arm bush bracket.

Didn't get pics of the oil leak, but it appears to be the timing chain tensioner which is common on the S54 engine.

Another part to add to the list, but this is a simple unscrew/screw back in again and it's not horrendous to access either. Part 5 on this diagram referred to as "chain tensioner" pn 11317838675

 

[GazHyde]

Forgot this pic, soooo many parts. Got more delivered this week including an OEM set of rear discs, EBC Yellowstuff pads, HEL braided brake lines, Bigg Red caliper rebuild kits, Febi gearbox oil. More parts arriving this week, also forgot to order new bleed nipples for the calipers.

 

[GazHyde]

Just collected the diff from the transmission specialist we use. It had a leak on the input seal so it was fully stripped down, primarily because you have to take everything out to get to the front seal. The had all new bearings and seals all round, new crush sleeve and everything torqued down to spec. He inspected the clutch packs and they didn't need changing (thinks they may have been done previously). Just needs filling with the Castrol Syntrax and a dose of RED LINE Limited-Slip Differential Friction Modifier/Break-In Additive.

The case and rear plate will get a good wire brushing and the case will then get a coat of black Hammerite before she goes back in again.

Only parts I'm waiting for now are a single nut and bolt and some plastic clips that hold the sensors to the trailing arms. Ready for reassembly!