Trailing Arm/Drop Links
 

Hi All,99 Boxster Base. Need to replace my trailing arms (rear) and all drop links. EPS or TRW thats the question. Any preference? V

TRW arms were cheap on Amazon a few years ago...Drop links are cheap anyway so might as well go OEM.

eps design is suspect.

TRW all the way

TRW except the Lower control arms as you can't find those anymore.

Out of curiosity, and for those who don't know (me!) what is suspect about the EPS design?

the type of bushing they use in that area does not articulate in the same sway as the stock plastic ball. There is also evidence of one of these EPS arms breaking in the 996 forum on rennlist.

What type of bushing is it that they use?

I am genuinely curious about the EPS suspension bits because I was looking to refresh my suspension system and did reach out to a handful of 996 guys on Rennlist, and most seemed happy with their decision. Another option I was looking at was Elephant Racing, and then the thread where one owner tracked their 996 (or was it 997?) where the control arm or something broke, but it seemed to be a one-off more than the norm than anything else. I chose not to go with Elephant Racing and EPS simply because they weren't readily available to us in Canada, and time was of the essence for me (car was already on the shop hoist, so time was a-ticking.)

Understand that I try to keep an open mind about what products to buy for my car, and try to make an informed decision on my purchases, and that the community has a reference point on how to make their decisions. I am in no way trying to support or villainize any vendors our there.

I think I read on Rennlist it was an EPS arm that broke.....Anyway....I went w/ TRW for the track arms and drop links. The ride is less clunkier not a big difference but better. I guess a Boxster ride is pretty hard. V

I personally would not go with EPS trailing arm links. Originals were designed with ball bushings, which can sit vertically and allow up and down movement. actually, they allow movement in all directions. EPS puts in a bushing style that's designed for lower control arms, where the movement is along their longitudinal axis. I.e. the bushing lays horizontally and the movement is up and down. The way EPS uses them, the bushings lay vertically while the movement is up and down. The bushings don't move that way, so it causes excessive force on the trailing arm and maybe the mounting point. EPS actually shows a video touting their 'solution', but if you look carefully, the trailing arm is actually flexing and the jaws of the vise are moving side to side, while there's little movement in the bushing itself. It's evident that those bushings cannot allow for that kind of movement and the parts are over-stressed.

https://www.youtube.com/watch?v=GoQ7LR6AuaQ

This could be why rennlist has posts of them breaking.

I bought the EPS front arms recently to give them a try. So far I like the feel although there is not much of a noticeable difference on the road. I was able to easily change them my self in less than an hour using a shop lift keeping the wheels under load. Honestly, I don’t think they will break easy, but if they do, it is what it is.

pretty serious safety issue if they break. You sound kind of blaise about a broken arm, but if that occurs at highway speeds, you could be in real trouble.

The arm does not bend or is not under tension at ride height. In fact they were replaced while the wheels were under load like I stated. If they were to break it would be at a fairly low speed over deep pot holes. The other guy that broke the arm in rennlist was pulling up to his home when his broke (maybe pot holes in his area?). If you disagree with my idea let me know.

I am not familiar with the Rennlist description of a failure/s . Does anyone know how many documented failures are out there ? Just curious how many failures vs. number sold . Is it 1 out of 100 ? 5 out of 1000 ? 98 out of 100 ? I bought a rear set of EPS a few years ago and haven't gotten around to installing them yet . Every component on a vehicle fails at some point that's why we replace parts . But a catastrophic failure is a different issue . Any feedback on actual numbers ?

I didn’t do a deep search but the amazon review and the rennlist post I saw were the same guy that bought the EPS front arms. Didn’t see any other person having the same issue with either arms.

so, the oem trailing arms are on a ball at the inner connection point - as a result the outer end of the arm can move up and down as well as in and out.

the eps trailing arms are on a bushing such that they can move in and out but not up and down.

the inner trailing arm connection point is tied to the body of the car and is fixed, however the outer point is tied to the control arm. the control arm moves up and down as the damper compresses and rebounds and, as a result, the outer end of the trailing arm needs to be able to move up and down. note that the role of the trailing arm is not to resist the up/down motion of the control arm, but rather to keep it from moving forward/backward (caster).

the eps trailing arm bushing doesn't allow this motion, but the suspension still has to compress; as a result the deflection occurs in the arm itself.

making it all worse is the design of the arm itself. if you look at it, it looks like a little 'I' beam. I beams are designed to be strong in one direction; how the eps arms get loaded is the perpendicular direction - where they have no strength (on the front, anyways).

Thank you for explaining it better than I did! :cheers:

I bought a set of MTC links off ebay and I'm happy with them. Price for pair was roughly the same as 1 TRW. But I haven't seen them on ebay anymore.

I wouldn't expect anyone to do a deep dive I was just curious about a " rough " number . If we assume it is one it is possible that one could have been a defective casting . Or it could have been because it was an EPS bushing . Or maybe it was damaged along the way . Too many variables and not a large enough sample size to be conclusive .

If you are driving at high speed and hit a pot hole, curb or other obstruction in the road, it could easily snap at speed. If you engage in spirited driving the car does not stay perfectly level, this swaying of the body and consequent uneven loading of the suspension left to right could also snap such a design.

I wouldn't put one on my car, FWIW.

Steve

I agree with your point. However, given my age and driving ability, while engaging in such spirited driving, the chances of me getting associated with a car accident is greater that the arm breaking. :p

Edit: I’m not trying to say that the arms will not break. But, I’m more than willing to “field test” them and provide a feedback if they break.