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New rear subframe hardware vs. powder coating


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I am rebuilding the rear subframe on a '76 and have decided to have most of it powder coated.  I am questioning whether to replace all the bolts and related hardware with the IE hardware kit. A couple of hardware bits (e.g. the bolts in the diff hanger - which don't look like they are even in the IE kit) are pressed in with the knurled edges.  So I need the advice of the gurus on the forum, here are my questions.

 

1.  Should the hardware be replaced at all?  It is all original so has likely been stretched and used for 45 years, perhaps taken off a time or two and retorqued.  I'm inclined to replace it to ensure proper factory torque on reinstall.

2.  Assuming I go with new hardware, will the bits that press in (diff hanger bolts, lower shock mounts) still go in properly if powder coating has been applied?  And if they do go in, will the coating chip? 

 

Thanks in advance.


Doug

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I powder coated mine as well. You will need to mask off any of the contract points for those bits that require bushings(i.e. tailing arms mounting points, etc) A reliable shop should ID the stuff that requires attention anyway. You may find replacing the hardware as expensive as re-plating it depending on the going rate and environmental restrictions in your area. Small amounts of nuts and bolts can be costly to re-plate so thats a personal call, IMO.

 

I think the only area you may wish to use new are the hex head bolts for the CV drive shafts, but again some do some don't. Likely others will weigh in. 

 

....here's mine with the hardware cad plated.

 

IMG_0864.JPG

Edited by joysterm
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If the bolts aren't broken/rounded off/super rusty, then the only reason to replace them is if you want it to look pretty.

 

Locknuts should probably be replaced, but normal nuts should be fine for re-use.

 

https://www.belmetric.com/ has a good selection of yellow zinc plated metric hardware if you only want to replace what you need vs. buying a whole kit.

 

 

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Pretty much anything that isn't 'jacked up' you can order through BmW, some bits you can get through Belmetric.  I don't recall exactly which, but some are special (in terms of size and threaded section vs non-threaded).

 

Nice sub-frame shots above.  I will say though I believe you both have the orientation of the nut/bolt holding your differential(s) down reversed.  The head of the bolt should be on the bottom and the nut on the top.....

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+1 on replating, especially if of your hardware is original . Before sending the parts off to the plater, Buy yourself a cheap bench grinder with a wire wheel on one end . Clean each bolt under the wire wheel , including the threads. When they come back with the yellow zinc you’ll be happy you didn’t buy new.

The grinder comes in handy ... Add a rouge pad to one end and a buffing pad to the other and you can make the chrome on your car look like new. 

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Quote

 It is all original so has likely been stretched and used for 45 years,

 

Nope.  

 

Unless it's come loose, nothing in the rear end should have been deformed by installation or use.

Fasteners do not 'wear out'. 

 

If a fastener is 'powder coated' or even painted, the clamping surfaces must be cleaned back to

bare metal, or you run the real risk of the fastener coming loose, as the material in the clamping

interface squeezes out of the joint and reduces clamping force.  Undertorqued is far more dangerous

than overtorqued.  And the material in the interface, or on the threads, will modify the 

torque value.

 

Unless it's rusted, bent, or otherwise deformed, there is no good reason to replace any fastener

in 99% of the 2002.

 

If it's loaded to a significant percentage of its yield strength, there is a good reason NOT to 

replace it:

new fasteners come from anywhere and everywhere, and may or may not be as advertised.

BMW took care when they put the cars together, and did, indeed, make sure their fasteners were

up to spec.

 

there.

 

That's my take.

 

t

take it or leave it

and not very obsessed with bolts and nuts.

 

 

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^^^ yeah, what he said.

For those here who are interested, and may not have any formal background in the engineering aspects of mechanical fasteners, you might grab a copy of Caroll Smiths “Nuts, Bolts, Fasteners...” Clear and concise layman’s guide to the subject. You might find it a surprise to know what the real reason behind proper torque of a bolt is.... it’s not to keep it from loosening.

Somebody should come up with a new mixed drink and call it a Young’s Modulus 

Edited by Mike A
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On 2/24/2021 at 1:49 AM, PaulTWinterton said:

I replated all my hardware except studs of course.  Yellow zinc. subframesml.jpg

@PaulTWinterton amazing shot- my question is- when repainting the underbody of your car, did you have any sound deadening layer like rubber paint etc? or just straight colour over primer? 

I ask because I'm unsure how best to treat the undersurface of mine- I love the colour but wonder whether something tougher, blacker and more insulating both of sound and heat is better?

 

also, to bring back to OT- when you send a lot of hardware off to be plated how do you sort it out when it comes back? just from photos and notes? must be a slow job? or can they somehow keep it all organised for you as they plate?

 

 

thanks!

 

 

george

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On 2/23/2021 at 4:17 PM, Mike A said:

+1 on replating, especially if of your hardware is original . Before sending the parts off to the plater, Buy yourself a cheap bench grinder with a wire wheel on one end . Clean each bolt under the wire wheel , including the threads. When they come back with the yellow zinc you’ll be happy you didn’t buy new.

The grinder comes in handy ... Add a rouge pad to one end and a buffing pad to the other and you can make the chrome on your car look like new. 


Here’s another viewpoint, Mike:

 

The two re-platers I used in Atlanta said that to best replicate the parts’ original sheen when re-plating, don’t media blast or mechanically clean the parts to be plated: it produces a duller finish. Simply remove any paint or overspray on the parts. The acid bath that precedes re-plating takes care of most filth. Yes, I agree: parts caked in grease and dirt are not something I wish to hand to anyone! Chemical cleaners such as Simple Green are fine, and that’s what I use to wipe off the lion’s share of filth. I usually chase the threads on nuts, bolts, and screws before and after re-plating. This might be considered mechanical cleaning, but I really don’t care about the sheen on threads. Sorry! 😊

 

I don’t have control tests to verify what these platers said, but the results impressed me time and again, so I’m not switching “recipes”! And, yes, I had to remove the Inka overspray from the headlight buckets below before my plater would accept them! The brown areas underlying the Inka are not paint, so I left them un-touched. And, indeed, those rusty-metal areas became bright and shiny when re-plated.

 

Best regards,

 

Steve


 

 

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0D19DEAB-65B8-4A41-A16A-303C4E5E0687.jpeg

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5 hours ago, ozgeorge said:

 

... also, to bring back to OT- when you send a lot of hardware off to be plated how do you sort it out when it comes back? just from photos and notes? must be a slow job? or can they somehow keep it all organised for you as they plate?...

 


George,

 

A lot of guys drop off a whole car’s worth of nuts, bolts, screws, and brackets for re-plating at once. I’m not that efficient, plus I like to put these fasteners back from whence they came. I would find a car’s-worth of re-plating simply overwhelming. So I do batches of re-plating, each representing a number of “project areas”, e.g., “fuel injection”, “emissions controls”, “rear subframe”, etc. If you mix a lot of very different “projects”, e.g., front subframe and lights, it’s easier to distinguish the parts. Plus, I take lots of photos of the fasteners coming off each project.

 

Below, for instance, are the items coming off an injection pump, before the pump itself goes off for rebuilding. Some of these components, the aluminum gear and the triangular bracket, will not go to re-plating: aluminum doesn’t lend itself to re-plating and the bracket will be powdercoated. But I lay out the hardware and use the photos to identity the parts after re-plating, powdercoating, or other restoration. These injection pump parts are currently in a much larger batch with brake booster fasteners, airbox fasteners, etc. But the batch isn’t yet large enough to get “my money’s worth”, so I’ll keep building it with these sub-projects. It’s tedious, but fun, I suppose! 😉

 

Regards,

 

Steve

 

A2BBC1C1-F949-4486-9C46-7BB3013ED314.jpeg

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