Dropping rear subframe - What things should I replace?

[Smudgemanuk]

Hi all,

Over the next two weekends my father and I plan to drop the rear subframe on my Z3. The main reason for this is to replace the front to rear hard brake pipes, which will then finally allow the cracking rubber rear subframe brake line to be replaced. All of this before a Nurburgring trip on the 7th August.

My question is what bits will I definitely need to replace (because they break when they come off etc) or definitely should replace (rear subframe bushes) (bear in mind I dont have loads of time) etc

These are my lists:

1. Definitely replace:
Rear subframe bushes
Diff bush
ARB bushes (drop links are already done)
Rubber brake pipes (the reason for this whole job)
Front to rear hardline (the fitting on subframe brake pipe is so corroded it is clear it will not come apart cleanly)
Exhaust hangers
The hex bolts shown below

2. Would be great to do if time/ money permits:
Sandblast, treat and underseal rust
Powdercoat stuff
Trailing arm bushes

3. Would be great to do but not feasibly possible this time around:
Rear CV boots

Suggestions for stuff in any of these lists would be fantastic. I have numbered them for easy reference.

Furthermore, what brand bushes should I go for (from experience) :
Diff bush
Rear subframe bushes
Trailing arm bushes

I do not want the car's ride to be any more harsh or put any more stress on the spot welds in the boot floor.

Thank you,

Chris

 

[Mazza]

Replacements for these 4 bolts ( 2 each side ) which hold the left and right beam plates

These Hex drive bolts can be a nightmare to remove. I bought an Erbauer kit from Screwfix as the hexagons almost non existant.
Replace with M8 x25 Hex head Bolts As the originals now obsolete.

 

[Smudgemanuk]

These Hex drive bolts can be a nightmare to remove.

They look like it!

Thank you very much, I shall order some now

 

[Devon Z]

Thought I should see what mine looked like while I was underneath the other day, They popped out with a long Allen key so greased them up and put them back in

I also smear high temp grease around the exhaust down pipe flange nuts on every oil change.

 

[Stevo7682]

If its just the brake pipes that is the main concern all the rear metal brakes pipes and flexi hoses can all be replaced with the rear suspension in place i have done this work on 3 different zeds now without removing any suspension components.

Re the diff bush if you do not want to split the rear cover off of the diff then the only thing you can fit is a poly bush the oe rubber bush needs pressing in off of vehicle.

If you do drop the rear then definitely trailing arm and subframe bushes as both of these difficult to do in place.

If your thinking about cv boots and therefore having to remove drive shaft then i would consider backplate and bearings while disassembled

New bolts where possible.
I helped @Scooblitz do Stevie's refurbishment on rear think if remember right was over £100 just in nuts and bolts and that was not replacing the 2 big bolts the subframe sits on as these were around £80 each
At the end of the day what you replace depends on how far you want to go what i would say is subframe bushes are an absolute must and over the years now i have been under a good number of zeds now from clean low milers to less clean high milers but all the same if the subframe bushes haven't been replaced they are done.
Easiest way to tell is if the rear beam is sitting on the plates below it ( the one with the allen bolts into inner sill) and there is not around a fingers wide gap bushes are done.
Stephen.

 

[Smudgemanuk]

If its just the brake pipes that is the main concern all the rear metal brakes pipes and flexi hoses can all be replaced with the rear suspension in place i have done this work on 3 different zeds now without removing any suspension components.

Fantastic! Thank you.

 

[Scooblitz]

They look like it!

Thank you very much, I shall order some now

I bought a set of 4 from Accu.co.uk which is a marine bolt specialist that carry a huge variety of bolts. They also offer the correct tensile bolts, thread pitch and measurement to replace these.

The bolt you have pictured do look a little crispy. Mine were also pretty crispy. @Stevo7682 used an induction heater to target these bolts and without this tool, it would have been very difficult. Snapping one of these would be painful. Penetrating fluid, heat, slowly slowly, patience.


In regards to a full refurb, I would suggest taking a step back and having a think about trying to get as much done as possible. It is a bit of 1 time job and certainly not an easy one. There are so many items to consider, replace and refurb that it deserves a bit of time spent. If you are looking at replacing cv boots, this would probably be the time to do it as well.
I spent perhaps 12 months buying bits incrementally so that I had a mass of parts. I bought second hand trailing arms, subframe, anti roll bars, chassis plates and had them stripped and powdercoated so everything was fresh and clean. I then sold on the items that were taken off the car. To aid the sale I also got those powdercoated for the next person to do the same.

Brands to look for are Meyle, Lemforder and Febi. They will cover subframe, trailing arm and drop links. For the diff, powerflex for ease or BMW direct for the more compliant original bush. The OEM part requires a bit more work as the casing needs split to install iirc.

Antiroll bar bushes: Depending on the year and engine of your car, it can be tricky to find a matching set for the front and back. I ended up using a poly kit from Super Pro.

Stevie

 

[Peter1450]

You’re a better man than me taking on that amount of work in the timescale.
Did my wife’s a couple of years ago unfortunately if you don’t have access to a ramp or lift it’s hard work .
If you’re lucky the trailing arms will be ok, ours weren’t and needed repairing/ welding, getting under a 20+year old Z is opening a can of worms!
Good luck and enjoy your trip.

 

[Smudgemanuk]

Fortunately thanks to Stephen's input I am not going to drop the subframe for this particular job (replacing the hardlines and flexi brake pipes) and allow much more time in the future. It is a great point that when working on these cars you never know what your are going to uncover when you undertake a job like this.

Thank you everybody for your input. I am sure it will come in very handy in future.

 

[Andyboy]

Trailing arm bushes - don't bother. They can look split and nasty on the edges but they're solid rubber and perfect where it counts. They're a b*****d to get out and given rubber quality these days, will be cracked again in a couple of years.

Replace the fuel tank straps!

The diff bush can be replaced with an OE one but it's risky. Do not try to press or hammer the old one out. Cut it from the inside with the hacksaw blade going into the actual diff cover not on the outer ring. Heat up the cover in the oven and have the new bush in the freezer. You have one shot and pressing the new one in. I'd poly bush it.

Those four allen bolts for the plates either side can be a nightmare. Good luck!

 

[Althulas]

I would agree and advise the same just replace/refurbish the lot while you’re there. You will most likely find the grease a bit tired on the drive shaft bushings so a great opportunity to clean up and re grease the bearings and Carriers. Your just down the road from me, so your welcome to borrow my dolly and motor cycle lift for lifting/ manoeuvring the rear beam/diff assembly.