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Wednesday, November 26, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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Saturday, July 16, 2011

Control Arms Research

I spent a good amount of time in the past two weeks researching my front suspension options. The first item on the agenda was control arms. My original plan was to install 1995 M3 control arms. My latest research confirmed that the arms are correct for my application and that I should use centered bushings with these arms.

The main difference between the stock and M arms is that the outer ball joint is rubber encapsulated, in that there is a thin ring of rubber between the outer metal ring that is pressed into the arm and the ball joint itself. BMW did this to eliminate noise and vibration, but the unfortunate and predictable side effect is a reduction in steering feel and an increased risk of failure, particularly on the track.

I also confirmed that the stock ball joint is replaceable while the M equivalent is not, but that's not a limiting factor since most people acknowledge that when it's time to replace the outer ball joint it's just cheaper to install a new arm.

While on the same topic, I discovered that most control arms from the various flavors of the E30 and E36 have the same geometry. The notable exception is the 96-99 M3 arm, which adds caster. The 95 M3 achieved the same thing with offset control arm bushings to push the kingpin a bit farther forward in the wheel well and enhances the effect with offset strut supports that push the top of the strut backward. Since I have no need for increased caster on this car I plan to install the centered bushings from the 96-99 M3. This will allow me to preserve the stock non-M geometry and gain the strength and feel of the M3 ball joints.

My research additionally confirmed something I'd known instinctually for some time: that the solid control arm bushings should only be used with the solid ball joints of the M arms. Mixing and matching will result in increased wear and premature failure of the weaker parts.

Camber Plates Research

As you may recall, my original justification for camber plates on this car was to dial out the eccentricity of my shock towers in both caster and camber. A close second goal was to be able to run anywhere from 1.5 to 2.0 degrees of negative camber to dial out some understeer. Back then, my preliminary research revealed that Vorshlag was at the top of the heap so I naturally assumed I'd buy them and went about my business.

Since the use of camber plates affects other parts choices and because I always try to spend my money wisely, I decided to look more deeply into my camber plate options before I pulled the trigger. I will not admit exactly how much time I spent researching this topic last weekend, but let's just say I needed a shave afterward. I found lots of conflicting information being reported by both users and vendors, some of it understandable given the myriad options including strut and spring types, track and street applications, and new vs. second hand parts. Frankly, I found it difficult to decipher who was telling the truth based on real world experience and who was trying to sell me something, but I'll try to relay what I learned.

First, some nomenclature. As shown in the adjacent picture (Source: Vorshlag), you can see the camber/caster plate at the top (Arrow 1). Below that is the upper spring perch (Arrow 2), in this case Vorshlag's proprietary equivalent of the stock OE perch, and below that is the strut (Arrow 3). You may note the beefy double-row ball bearing that is provided with the perch (Arrow 4). Note: The spring is missing this picture.

The stock strut mounts are designed with a bearing surrounded by a large rubber isolation bushing which helps reduce coupling of noise and vibration from the road surface transmitted by the strut to the shock tower. You can clearly see the bushing by popping the hood and looking at the top of the shock towers. The bearing type utilized in the mount differs based on the suspension type. The standard suspension mount uses a simple plain bearing, while both the sport package non-M and M3 mounts utilize a ball bearing. When you realize that the entire strut -- and therefore the strut rod -- turns as the wheel is turned, the need for a bearing in this location, as well as the merits of a ball bearing relative to a plain bearing become clear.

(Image: Closeup of Vorshlag camber plate stack)Unfortunately, with the exception of one vendor's offering, all the camber plate designs eliminate the isolation bushing in favor of a spherical bearing of some sort to reduce flexing of the struts that can change alignment in unfavorable ways during aggressive turning or braking. No matter what way you slice it, no matter how much the vendors try to sugar-coat this issue, the reality is the use of camber plates will result in increased NVH (for the noobs, this refers to any undesired characteristic in the areas of Noise, Vibration, or Handling). The overwhelming majority of people pointed out that the Vorshlag plates are the quietest in this respect, but the more honest folk admitted that NVH can be an issue with ANY plate. It's just that the vast majority of people who use these places use them on the track and simply either don't hear the noise through the helmet or accept it in return for the increased performance camber plates afford them.

Some other honest people also admitted that spherical-bearing designs are susceptible to damage from potholes. If the strut ever bottoms out, it loads the spherical bearing in a way it was not designed to accept. Depending on the severity and frequency of the strikes, the bearing can loosen up or break entirely, leaving the owner to deal with clicks and/or clunks until they get the time to pull the struts and install new plates (or new parts assuming the vendor sells them separately...not all do). I couldn't underestimate the potential impact (no pun) of this problem on both my vehicle and wallet. The fact that I'm concerned about this and that I'm no cheapskate when it comes to this car should tell you something.

Most people seemed to recommend three vendors: Vorshlag, Ground Control, and TC Kline. There were a few other vendors mentioned, but let's just say they weren't mentioned in a positive light. Just so I don't have to listen to those manufacturers (or their legal representation) whine they'll remain nameless. Here's a summary of the pros and cons of the most popular brands:

Vorshlag

Pros:

Cons

Ground Control

Pros

Cons

TC Kline

Pros

Cons

Conclusion

Sadly, all the research did was to confirm that camber plates are designed primarily for track applications and really have no business being on a street car, at least as the vast majority of the plates are currently designed and finished. The lack of isolation between the strut and the strut tower begs for damage to the plate, the strut tower, or both. I understand that race parts are designed for a particular mission and isolation isn't one of them, but it seems to me there is a market for a camber plate meeting all of my requirements. GC comes the closest to my ideal with their street plates, but they made some design decisions I don't like on those units.

The end result is that I'll be skipping the camber plate installation and installing new OE strut supports. If I ever decide to "retire" this car to the track and transition to coilovers of some kind, I can always install a set of plates at that time. For now, I don't need a caster adjustment and the stock camber (-1.0 degrees) is, as they say, good enough for government work. And it's probably just as well, as I'm sure I'll find somewhere else to spend that $500.

Front End Overhaul - First Parts Arrived

I placed an order with Turner Motorsport for their E36 front subframe reinforcement kit and, because they were $50 cheaper ($100 total savings), a set of their SKF OEM front hub assemblies, wheel nuts and protection caps. Total for that order was $300. While inspecting the bearings I became concerned about the fact that the ABS trigger ring looked nothing like any other E36 or E46 trigger ring I'd ever seen. I double-checked the part number on the box and confirmed with Turner that I do indeed have the correct parts. Since I'm a "measure twice and cut once" kind of guy, I'll double-check that with my technician before installing them.

I also made what has become a ritual appearance at my dealer and ordered the 1995 M3 control arms, 96-99 bushings, and related hardware because there are no OEM equivalents available. When the parts came in late in the week and I went to pay for the invoice I found a woman complaining to the cashier about paying $12 for a bulb. I asked the woman if she wanted to trade invoices and looked at the cashier and smiled. When the woman heard the cashier rattle off my $460 obligation, the woman smiled and said "uh, no". All I could say was "I wish my average invoice here was $12". That seemed to diffuse the situation. Some people don't know how lucky they are.

Next on the list is the X-Brace with associated nutserts and installation tool, brake hoses, sway bar links, engine mounts, strut tower reinforcements, strut assemblies, and everything necessary to overhaul the steering column. Without the camber plates, and assuming the brake pistons aren't pitted (which would necessitate new or overhauled calipers because the pistons aren't separately available), I'm estimating $2500 in parts for the project.

Mileage: 209900, Parts: $760, Parts Saved: $200