Complete rear end refresh: paint, powdercoat, or other..?

[BTB]

Good evening E46 fans,

I am starting a new project to rebuild the entire rear end on my M3 with 205k miles. The car spent quite a bit of time in the midwest and seemed to be neglected by previous owners; the rear end is corroded AF. I just picked up a complete rear axle assembly (subframe, diff, axles, trailing/control arms, sway, brakes) from another car with 70k miles, and it's very clean other than some surface corrosion.

I don't have a complete shop, nor do I consider myself a proper mechanic, but I'd like to do as much of the work as I can such that I'll basically bring the refreshed rear end to a shop with the car and have them swap it in. My question is:

For those that have had their subframes and/or trailing arms refinished, did you paint or powdercoat (why?) and, in either case, how do I make sure I don't change ID dimensions for bushings and ball joints by coating parts? Also, what materials and methods do you recommend?

I'm debating how far I should go with the refresh, contemplating getting the diff rebuilt at diffsonline. I want to do solid subframe bushings and basically new oe everywhere else (RTABs tbd). Anywho, I would appreciate any insight from those who have tackled this already.

Thanks !!

[timmo]

Haven't powdercoated parts for my own car but have experience with other stuff such as welded tubular spaceframe and machined components. Powdercoating is going to be much more durable than paint. Usually as part of the powdercoating service the shop will sandblast your parts as surface prep and to clean off all contaminants. To maintain the size and surface finish of the bores for bushings & balljoints, you should not have those blasted or powdercoated and request that they are masked. Same thing with any screw threads, the shop will have small rubber plugs they put into any small holes so the powdercoating doesn't go into the threads.

[BTB]

Haven't powdercoated parts for my own car but have experience with other stuff such as welded tubular spaceframe and machined components. Powdercoating is going to be much more durable than paint. Usually as part of the powdercoating service the shop will sandblast your parts as surface prep and to clean off all contaminants. To maintain the size and surface finish of the bores for bushings & balljoints, you should not have those blasted or powdercoated and request that they are masked. Same thing with any screw threads, the shop will have small rubber plugs they put into any small holes so the powdercoating doesn't go into the threads.

Though I’ve heard some accounts that are anti powder coat/pro paint, this does seem to be the general consensus. I definitely want a durable finish as I plan to use the car a lot over the next decade (track, snow, gravel etc)

Would it be silly or impossible to have the parts coated with old bushings installed?

[timmo]

Though I’ve heard some accounts that are anti powder coat/pro paint, this does seem to be the general consensus. I definitely want a durable finish as I plan to use the car a lot over the next decade (track, snow, gravel etc)

Would it be silly or impossible to have the parts coated with old bushings installed?

Hmmm. I suppose you could, but with everything out now would be the time to change whatever needs changing. It's the classic "while I'm in there"

Another option that I've found pretty durable is POR15 paint. It's much tougher than conventional paint and you can DIY. It's expensive for being a paint but would still be cheaper than powdercoating I believe. With POR15 you'd want to properly prep it with metalready to ensure it won't rust though

[BTB]

Hmmm. I suppose you could, but with everything out now would be the time to change whatever needs changing. It's the classic "while I'm in there"

Another option that I've found pretty durable is POR15 paint. It's much tougher than conventional paint and you can DIY. It's expensive for being a paint but would still be cheaper than powdercoating I believe. With POR15 you'd want to properly prep it with metalready to ensure it won't rust though

I will definitely replace subframe bushings (likely solid) as well as the others, just wondering if leaving them in would work as 'masking' the internal bores. Then change them out.

I've heard of the POR15 too, I basically want to do whatever is best. Presumably the subframe needs to be sandblasted prior to paint as well..? Part of me just wants to throw in the rear end as is with new bushings, as it has minimal corrosion and should last another decade or more, just hard to say if getting it redone will be significantly more durable than it is now.

[timmo]

I will definitely replace subframe bushings (likely solid) as well as the others, just wondering if leaving them in would work as 'masking' the internal bores. Then change them out.

I've heard of the POR15 too, I basically want to do whatever is best. Presumably the subframe needs to be sandblasted prior to paint as well..? Part of me just wants to throw in the rear end as is with new bushings, as it has minimal corrosion and should last another decade or more, just hard to say if getting it redone will be significantly more durable than it is now.

Ah, I see what you mean. I suppose you could leave them in but I'd be worried about possible damage on the finish having to press those out. But then again, you need to press the new bushings in which is unavoidable... unless perhaps the parts can be safely powdercoated with the new bushings already installed? Just an idea, but maybe ask the powdercoater what would be preferred.

For POR15 you don't really have to sandblast it, just get rid of existing corrosion, then the proper metalready procedure (keeping it wet for 20 mins I believe) and cleaning and letting it dry properly would be fine.

Honestly, if the new parts are from the south and are pretty decent, you'd be okay seeing as you're also in the south (in a place with no salt). But of course, shiny new powdercoated parts would be quite nice!

You should see my subframe haha, I no longer winter my car since all the rust on the body itself was repaired. But my subframe is absolutely disgusting:

[BTB]

Ah, I see what you mean. I suppose you could leave them in but I'd be worried about possible damage on the finish having to press those out. But then again, you need to press the new bushings in which is unavoidable... unless perhaps the parts can be safely powdercoated with the new bushings already installed? Just an idea, but maybe ask the powdercoater what would be preferred.

For POR15 you don't really have to sandblast it, just get rid of existing corrosion, then the proper metalready procedure (keeping it wet for 20 mins I believe) and cleaning and letting it dry properly would be fine.

Honestly, if the new parts are from the south and are pretty decent, you'd be okay seeing as you're also in the south (in a place with no salt). But of course, shiny new powdercoated parts would be quite nice!

You should see my subframe haha, I no longer winter my car since all the rust on the body itself was repaired. But my subframe is absolutely disgusting:

Hah... I feel your pain! See subframe image while getting diff bushings done along with rod bearings in 2019... also attached is the new assembly I picked up.

POR15 sounds like a good option for me, as I feel slightly odd about stripping down a rather clean subframe that should last 10+ years if I just leave it alone. Adding some coats of supposed rust prevention (maybe a dash of red paint..) seems smart enough. I would probably do the same do the trailing arms as there is some surface corrosion on them as well. Aluminum upper arms don't seem worthwhile to do.

[Jersey_M3]

Hey BTB, I have gone down this rabbit hole. Check out my Insta Jersey_M3 . I took some decent photos of sandblasting my entire rear end during my subframe reinforcement. I did a lot of research and decided on going with steel it spray paint. I sandblasted first, wiped all the parts down, and then sprayed on the paint. The final results came out great. Holding up well too, even in the rust belt with daily driving. Best part about the product is that if I find an issue, or rust crops up, I can just sand it down to bare metal and hit it again with more spray paint. It blends excellent. Cant do this with powder coating or paint.... as far as I know. If powder coating cracks or chips, gotta redo it.... again as far as I know. There was no interference upon install as well, bushings went right in once I figured out the right way to press them in. I went solid bushings on the subframe, RTAB bushings are Syncro Design Works, and all other bushings got replaced with OE, highly recommend this combo. I did all of this myself in my garage so if you have questions, shoot me a PM.

[Geroz1]

that's beautiful! Might as well just do all the underbody

[BMWahba]

I powdercoated all the subframe parts that I could when I was doing my rear vincebar install. I also painted the underside of the chassis since at that point everything was looking factory fresh. I wouldn’t do it any other way now looking back at the finished product!





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[cbean]

BMWahba that looks SEXY AF!

[TexaZ3]

I powdercoated all the subframe parts that I could when I was doing my rear vincebar install. I also painted the underside of the chassis since at that point everything was looking factory fresh. I wouldn’t do it any other way now looking back at the finished product!





Sent from my iPhone using Tapatalk

Dang...man.

[BTB]

Holy heck, awesome stuff guys. For the moment I'm thinking POR15 on subframe and trailing arms, not too worried about the aluminum uppers. I'm mostly concerned with durability/function, though the fancy colors are cool too. Thanks for the input

What did you guys do to your diff? Rebuild stock unit, 2- or 3- clutch, or keep your original?? I'm a bit torn, I'm not cut out for these high dollar decisions lol. Partly have mind to throw in the 70k mile used diff and just run it, I basically just want something I can beat on on a variety of surfaces

[BTB]

Bumpity bump bump. Curious what people have done for their diff refresh? Mostly just fresh oil/bushings on stock diff?

[oceansize]

Bumpity bump bump. Curious what people have done for their diff refresh? Mostly just fresh oil/bushings on stock diff?

All new ball joints, sway bar bushings, rear diff cover with bushings, oem front diff bushing, Ground control ARCAs with ball bearing, OEM inner bushings on upper control arm, and 3.91 diff from diffs online plus parking brake rebuild.