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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 04-23-2013, 08:32 AM   #1
Drkhse
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a quick suspension question.

okay so here's the deal, I'm looking to drop the front of my XI a little bit but my wife will not let me spend any money on it right now lol. so what I was thinking was to cut the perch and weld it further on down the strut. essentially these would be the same as drop perches, or even coilovers minus the sleeves. as long as there's tire clearance I couldn't see how this be a big issue. the car isn't even a daily driver its just a toy so longevity wouldn't really be a big factor. it would just have to get through a couple of months of occasional use. and as far knowledge into welding goes I'm a journeymen high pressure welder so I'm not terribly concerned about the welds holding. just wondering if this was completely unheard of or not. at least its not cutting stock springs which would never happen on my car. I just don't see how this would change anything other than the length of Life of the strut, which I'd be happy to see go anyway then there would be a broken part so I could buy coilovers lol.
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Old 04-23-2013, 08:47 AM   #2
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the spring rate should be uneffected however the travel would be decreased. I don't see how that would be a problem to and from the grocery store. I'm just awfully sick of that horrible wheel gap on the front and want this thing fixed immediately lol.
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Old 04-23-2013, 08:54 AM   #3
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No.

Just no.
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Old 04-23-2013, 08:58 AM   #4
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Will the heat from welding damage the internals of the strut? or as you die grind off the bracket and you go too deep ?
Just thinking............
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Old 04-23-2013, 09:10 AM   #5
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On a continuous bead yeah it would also if it was welded with a mig welder. I was going to use low heat tig much narrower heat affected zone. With continuous pulse. 1/4" at a tine with significant cooling time. Done like that it woukd save the internals fron heat damage. I've done it before and on trailers etc and its been fine if done this way. Just never on a bmw. And its my understanding that the perches will just pop off. No grinding required.
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Old 04-23-2013, 10:37 AM   #6
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Just wondering why you would say just no? Failed attempt? Engineering degree? Something?
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Old 04-23-2013, 10:43 AM   #7
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Just wondering why you would say just no? Failed attempt? Engineering degree? Something?
Engineering degree, common sense, and a good eye for safety. Those spring perches essentially carry the weight of the entire car. Are you sure you want to fvck with them? I sure wouldn't.

Either convince your wife to give you your balls back and/or just wait until you have the money to do this right. It's a wheel gap, not a rusted through hood.
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Old 04-23-2013, 11:04 AM   #8
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Wheel gaps hurt my heart, except on trucks :-)

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Old 04-23-2013, 11:25 AM   #9
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Wheel gaps hurt my heart, except on trucks :-)

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Rewelding a perch to save money on reducing your wheel gap will make your heart hurt more...especially when your rewelded perch fails and your car spins out into a ditch where you get impaled with a road sign.

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Old 04-23-2013, 11:28 AM   #10
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Then with an engineering degree you would know that an ER70S-2 tig rod will have a minimum as welded dynamic load yeild strength of 70, 000lbs/in. Off hand I'd say the actual tube is around 2" which means approximately 4" of weld. So 70, 0004=280, 000lbs of force reqired to break the weld outright. Which is far greater than the yeild of the actual perch in question. The weld strength is not in question, and I'd trust my welds a lot more than the ones from the factory, as like I said I am a certified red seal high pressure welder and the welding would be completed with a miller dynasty div For an e34 this has been done over and over. Would you're response be different if these where coil sleeves on a vastly heavier 5series? How this differs from that I don't know. Everything I know about technique and metallurgy give me the common sense and safety aspect covered. I guess it my lack of a toilet paper engineering degree then...
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Old 04-23-2013, 11:28 AM   #11
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Rewelding a perch to save money on reducing your wheel gap will make your heart hurt more...especially when your rewelded perch fails and your car spins out into a ditch where you get impaled with a road sign.

Yeah I agree, this isn't a civic to be doing things like that...I've been there and its stupid

Better to be patient and buy a good suspension.

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Old 04-23-2013, 11:36 AM   #12
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Again, the weld wouldn't be what i was worried about. I could equally worry about a meteorite, or alien abduction. By the numbers and my experience i really see no reason why this wouldn't work. All ive heard is thar the weld would fail. I know otherwise. Id like to hear a actual reason instead of speculation. And if it were a honda you'd just cut the coils and call it a day
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Old 04-23-2013, 01:11 PM   #13
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Then with an engineering degree you would know that an ER70S-2 tig rod will have a minimum as welded dynamic load yeild strength of 70, 000lbs/in. Off hand I'd say the actual tube is around 2" which means approximately 4" of weld. So 70, 0004=280, 000lbs of force reqired to break the weld outright. Which is far greater than the yeild of the actual perch in question. The weld strength is not in question, and I'd trust my welds a lot more than the ones from the factory, as like I said I am a certified red seal high pressure welder and the welding would be completed with a miller dynasty div For an e34 this has been done over and over. Would you're response be different if these where coil sleeves on a vastly heavier 5series? How this differs from that I don't know. Everything I know about technique and metallurgy give me the common sense and safety aspect covered. I guess it my lack of a toilet paper engineering degree then...
With my toilet paper engineering degree I will give you the following:

- Your TIG rod has a yield strength of 70ksi, which is pounds per square inch, not just inch. Even if you use a 1/8th inch rod (guessing overkill, I'm not a welder) that gives you a welded surface area of 1.62in^2. Doing some simple math, that gives you a welded "strength" of 113.4ksi in an ideal condition.

- The ideal yield strength of a normal average steel, since I have no idea what the shock case is actually made out of is ~75ksi so your weld is still, in theory stronger but your factor of safety is now much less than before. Your shocks have now been on your car for just about 10 years and the material has deteriorated over time due to salt, corrosion, wear, heat, etc so I'd say your "ideal condition" is no longer valid but your weld is still in theory stronger.

- Adding to the fact that your material has degraded over the past 10 years, you want to weld to it and heat treat and brittle that heat affected zone...ok now we are getting to the point where problems can occur.

- Remember that a shock absorber also has stuff inside of it and it isn't just a hollow tube. Heating an area that hot to get a good through and through weld can melt a lot of things inside that case even if it's for a short period of time. The interior of a shock unit is largely made of plastic o-rings and valves, those materials do not handle that kind of temperature and I'm sure many of them are located right where you want to weld. This doesn't even mention the oil inside of them.

- The strut is designed with the spring perch sitting on the top of the piston housing for a reason and the system is designed to transmit that load from that point through the column to the knuckle at the bottom of the strut. Changing that loading point to a side load will not be the same and you can cause severe damage to the strut housing in doing so and that in itself can cause catastrophic failure.

You can do whatever you want but I'm going to stand my ground in saying this is a dumb idea. Kudos for being an expert welder, that takes a lot of skill and effort to get and you have my mad respect for being able to do it...but you are changing the design of a critical component without the proper research and that is where problems can occur.

Again, this is your car and your life that we are talking about. If you think you can do it, then go for it but it's on you.

FWIW, cutting springs is also a dumb idea.

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Old 04-23-2013, 02:12 PM   #14
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Alright, fair enough. The side load aspect is a good point that was previously not considered. My major problem with previous posts were the lack of specificity. I was not concerned with the weld tensile strength for a moment. As you even stated it is stronger than required. (After this many years I can weld a cats a** to a plate glass window) and as far as internals go with the right technique it is possible to weld without melting internals. but that being said I think I might try something else and make a set of drop perches using the top of the struts as bracing. and I must say my hat is off to you for being the first engineer I've met in a long time that could find his a** with both hands lol.
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Old 04-23-2013, 02:16 PM   #15
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but in theory wouldn't the sideload aspect be exactly the same just by shortening up the strut? as legitimate Coilovers just have a shorter strut assembly
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Old 04-23-2013, 02:52 PM   #16
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but that being said I think I might try something else and make a set of drop perches using the top of the struts as bracing.
This was the first thing that went through my head and as I was reading the thread, it was the suggestion that I was going to make... but you beat me to it!

To me this is the ideal approach if you insist on this modification as it is a modification that is not permanent, maintains the loading of the strut in the intended design location, and with your welding skills, should be a piece of cake! The strut lower perches could then be transplanted to new struts when you decide to replace them, unless you get lowering springs at the same time.

Two other possible concerns come to mind:

1.) Alignment? You've likely thrown it off by only lowering the front and would need to shell out some more cash to correct this. If this mod might be done to save some money, factor this in too!

2.) I know that in the rear, if you throw lowering springs in (AKA increasing the gap between the ends of the spring and the upper & lower perches), when the suspension is fully unloaded, you can have the springs fall out. This is one of the reasons why it's not recommended to just put lowering springs in without putting in a shorter shock as well. Now I know the spring is contained around the strut as an assembly, and that you have to compress the spring to take it all apart, but I what I don't know is by how much the length of the spring is compressed. If less than an inch compression is needed to get the top nut on, and you then drop the lower perch by an inch, you're essentially going to have a similar problem as the case I noted above for the rear... the difference is that the spring "can't fall out." But it can spin and not stay seated where it is supposed to in the perches themselves. What also can happen is for the entire weight of the front of the car to not be supported by the perch and spring in the event that the entire front suspension drops.... then all that weight comes slamming down on the top of the spring. I don't think it would take much to seriously deform the strut towers, especially considering just driving the car hard with a stock setup can cause troubles.

Granted, this is all under the assumption that at full front suspension travel there would be a gap introduced between the spring (AKA no pre-load) and the strut tower by the amount that you choose to lower the perches.

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Alright, fair enough. The side load aspect is a good point that was previously not considered.
Anyways... just throwing my 2 cents in. Not that I am saying this should be done or should not be done (it's your car, do as you please), but that a fair amount of thought should go into this from a safety standpoint. Sam made a valid point for safety's sake by quickly pointing out something that you overlooked. We're not here to shoot everyone down just because we can, but hopefully be able to chime in with things that one of us didn't think of. Whatever comes of this, I'm sure the decision will be made with safety taken into consideration as well as the thoughts of more than one engineer. ( I'm one too! )

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and I must say my hat is off to you for being the first engineer I've met in a long time that could find his a** with both hands lol.
Props for being able to take some constructive criticism, and not turning this into another freaking flame war on the forum. Too many people get butt-hurt because someone they don't know on the internet offended them...


....also, it's nice to talk with fellow enthusiasts that have a degree in engineering and can back up their information / decision making process with facts and principles, understand how a lot of this stuff works and interacts, AND can think outside the box!
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Old 04-23-2013, 02:56 PM   #17
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but in theory wouldn't the sideload aspect be exactly the same just by shortening up the strut? as legitimate Coilovers just have a shorter strut assembly
I don't think so... if I am not mistaken, the sideload that Sam is talking about is from the fact that instead of just having the strut be solely in compression from the top to bottom, by mounting the perch to the exterior of the tube, you now have a moment that is wanting to cave in the tube below the mounting point and pull out the tube above.

The strut tubes were (I am assuming) designed to support the load in compression, without thinking about forces pushing radially inward on the tube. Besides, you've got a lot of components inside the tube with tight tolerances that are sliding around... any appreciable amount of force squeezing the tube could potentially cause problems.

Coilovers don't have this issue... as they were designed to handle the load on the exterior of the tube, instead of just straight axial compression.
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Old 04-23-2013, 03:19 PM   #18
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Good point, I was thinking more geometrically as to the side load comment and less structurally. So in theory if it were designed to take the weight at the top of the strut as it was originally designed that would alleviate the sideload thus making the assembly more structurally sound? Perhaps sam could chime in on that as well. As I now believe his degree is on real paper lol. Sorry for the shot btw. My line of work is full of questionable engineers.
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Old 04-23-2013, 04:26 PM   #19
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as far as internals go with the right technique it is possible to weld without melting internals. but that being said I think I might try something else and make a set of drop perches using the top of the struts as bracing. and I must say my hat is off to you for being the first engineer I've met in a long time that could find his a** with both hands lol.
1.) With the internals, some of the melting temperatures can be as low as 300F. With the thickness of that tube, can you get the metal to melt while keeping the insides lower than that?

2.) They make drop perches to do this exact thing already. They run about $35...I think.

3.) Not sure if that was a jab or not but I'm going to take it as a complement.

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but in theory wouldn't the sideload aspect be exactly the same just by shortening up the strut? as legitimate Coilovers just have a shorter strut assembly
Coilovers have a threaded sleeve over the cylinder housing that is used as a variable perch. The sleeve is designed to deal with the loads generated and the cylinder itself is a different part.

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Props for being able to take some constructive criticism, and not turning this into another freaking flame war on the forum. Too many people get butt-hurt because someone they don't know on the internet offended them...
+10000000000


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....also, it's nice to talk with fellow enthusiasts that have a degree in engineering and can back up their information / decision making process with facts and principles, understand how a lot of this stuff works and interacts, AND can think outside the box!
I like these discussions too. If you ever want to shoot the sh!t let me know, my real specialty is in fluid mechanics/aerodynamics and composite materials but I dabble in many other things too. Any questions on those things, feel free to hit me up. That goes for everyone reading this.

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Good point, I was thinking more geometrically as to the side load comment and less structurally. So in theory if it were designed to take the weight at the top of the strut as it was originally designed that would alleviate the sideload thus making the assembly more structurally sound? Perhaps sam could chime in on that as well. As I now believe his degree is on real paper lol. Sorry for the shot btw. My line of work is full of questionable engineers.
Yup, that should work just fine and as I said they already make a product for just that. It's basically a piece of sheet metal formed into the right shape.

The only thing I'll caution you on is that doing this will effectively take away the amount of suspension travel you drop the car. Meaning dropping 1in will take away 1in of suspension travel. That can either be ok or a huge mistake depending on your driving habits and road conditions.

And thanks for the complements. The world is full of arrogant d-bag engineers who got 4.0's in college but can't do any real practical work. The ones who are arrogant d-bags and know their stuff are the ones to really be afraid of.

Worse still are the arm chair engineers.
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Old 04-23-2013, 05:59 PM   #20
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disregard wife acquire mods.
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