Suspension Bushings

[Rob-O]

I'll bet this stumps some folks. Some background first though...

Awhile (a long, long while) back I pulled my trailing arms to weld on the boxed trailing arm kit. While doing so, I figured I'd pull the shaft that runs through the trailing arm. This way I could replace those rubber bushings with some of those cool racing (i.e. rock solid) Weltmeister bushings. So I pull the shafts and notice that there is a decent amount of rust on them. Not on the part of the shaft that would reside inside the trailing arm, just on the part that was covered with the rubber bushing. So smart me, I grind those down a tad, weld 'em up, and have them machined down to the diameter of the rest of the rod. Now I have a nice smooth rod, from one end to the other for the new bushings to ride on.

My questions are these: First, does anyone know exactly what the diameter of that rod is supposed to be? Like I said, I just assumed it was the same thickness from one stud to the other. But when I try to hand fit the new bushings, it's purdy tight. I'm afraid that if I press them in, they'll give me the reknowned squeak that we're all so fond of hearing about concerning these bushings. Second, if you know the diameter of the shaft, how about the diameter of the housing? I've heard that part of the reason that those polygraphite bushings squeak is because of irregularities in the dimensions of the trailing arm. Lastly, if we can't get those dimensions, how much interference do you think would be needed to get these things to fit right? In other words, I could measure the bushing I.D., and then just machine the shaft that will ride in the bushing .00xxx bigger. Same thing with the trailing arm itself. I could measure the bushing O.D., and then make sure the trailing arm housing is .00xxx smaller so there is a certain amount of interference in the fit.

I figure as solid as these bushings are, they should be snug but not really have to be pressed in.

Rob-O

[DSPTurtle]

When I did my weltmeister bushing replacement on the front I had to take a lot of liberty with the bench grinder on the bushing. They really needed to be turned down to fit properly (hand pressed in and still rotatable with solid hand force). I would say you might have to "hone out" the bushing. Bushings are cheap to replace if you go to far in the "honing" process. I don't think I would mess with the shaft or the control arm. IMHO I would "make" the bushing fit into its new home.
Good Luck!!!

[Joe Ricard]

I would also make provisions for grease retention. Depending on your access to machine services cut a few grooves on the inside to keep some grease in there. maybe .010 deep by 1/16 wide not all the way to the edges.

[DDS]

Done that. Grease zerks front and rear.

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=3286

Got the grease zerks at the FLAPS. Easy job.

Did the welding thing on the rusty rear pivot axle things as you did, didn't worry too much about the sizing as the originals were in rubber anyway and things turned freely in the end.

the bushings I bought turned by hand no problem, front and rear without modification once I made sure I was using true (meaning perfectly round) carriers on the A-arms.

[maf 914]

I would like to ask those of you who have used Weltmeidter or similar bushings how rough the ride quality is for normal driving. I noticed that Weltmeister offers two resiliencies, Street and Race. Is there a significant difference in these. Are there bushings that are better than others or are they all about the same?

Thanks,
Mike

[DSPTurtle]

I've only done the front so far and I think the ride got smoother but they may be cause the rubber was totally worn out and probably not provided much support if any.

[philinjax]

I have been wondering, why are we all installing or considering the use of aftermarket poly bushings. Porsche has not installed any in factory cars, that I know of. Is it possible that the factory figured that there is some value in the stock rubber bushings. Is there some deficiency in the cushioning effect of the stock bushings as opposed to free moving poly bushings? Is there any demonstrated handling improvement in poly bushings vs stock?
I have not been convinced that there is. To me, it's like many of us who box trailing arms, worthless.
What do you guys think?
Phil

[Rob-O]

I disagree.

I'm not using these bushings because I think I can outhandle the car next to me with them. It's merely a necessary evil of repairing the suspension arm. Inserting these bushings is easier and cheaper than buying a new trailing arm. The rubber bushings aren't available seperately, you have to buy the whole control arm. Even if you could buy the rubber bushing, you'd have a heck of a time getting it into the trailing arm. Heck, they're a bear to get out!

As for handling, I am thoroughly convinced that they have benefits. Anytime you can keep your suspension componentry in the relationship it was in when you measured your camber, caster, toe in and everything was tightened down, you're doing good. You're right, Porsche doesn't use them on their production cars, but that's for reasons such as the noise they make and the harsh ride they provide. But do you honestly believe that they're not on their race vehicles? Most serious racers will use something even more solid than the polygraphite bushing that we're using. Maybe a heim joint variation or even a metal to metal connection. So if Porsche uses polygraphite bushings in their racing applications (or something even more extreme), where they must believe the suspension geometry relationship is critical, then I would think you would have to agree with them that they must have some benefit. I don't think the argument that they have no benefit flies.

The argument that we don't necessarily need them on our 914's may hold water for certain users, but who knows what all the folks who have replied to this post are using their cars for. Me, like I said, will be replacing them so that I can reuse the trailing arm after I made what I would call some significant repairs. Others may have giant 6 cylinders in their cars and be using them out on the autocross track. And in their instance they may feel there are benefits.

My belief is that it is infinitely more justifiable than putting say, a "Type R" sticker on the side of your car. I look at it this way, what you use your car for may not warrant using these bushings, but if you can live with the ride, hey, your car should handle better for the trade. The "Type R" sticker however adds nothing to the already underpowered Civics of the world, in speed or cornering ability.

As for the stock rubber bushings, they do lose their resiliency over time. I personally think 25 years or so is a lot to be asking of a little piece of rubber that is taking some pretty nasty flexural forces directed towards it while helping to suspend some 2000 lbs. of machinery.

just my $2.00,

Rob-O

[DDS]

Rob mentions two good reasons, performance and availability. Also, WRT Porsche's design intent - remember that the 914 was intended as a mass market vehicle like the Miata, not the enthusiast's machine we by definition consider it to be. Also, plastics have come an awful long way since the early 70's. I bet there weren't many options for non-hygroscopic, machineable, chemical resistant, strong, cheap materials then.
WRT what was suppied vs what's best, wider tires weren't stock on the car, but are not questioned as a benefit.
My rubber bushings were shot.
I wonder what the factory GTs used for bushings?

[philinjax]

I suspect that poly bushings do provide some benefit for autox
and racing applications. Don't know if there is any demonstrated proof of it, however.
I believe I have bought more than a dozen teeners, mostly parts cars, in the past 15 years yet, I have never seen trailing arm bushings that were defective. Weather checked on the outside perhaps but they remain bonded internally to the arm and the shaft. Trailing arms are really a dime a dozen, not much of a market for them.
I notice that new Porsches, at least through 95, use rubber bushings in suspension and sway bars. Don't know what they install on racing cars but, the 914 GT used rubber.
Seems to me that if most driving is on the street, it would be unnecessary effort and expense to install poly bushings. Just my thought.
Phil

[Dave at Pelican Parts]

Unless a car lives on a trailer, most driving is street driving. Just driving to and from events puts more miles on the car than autoXing or (unless you live next to the track) track days.

Ask Charlie Davis on the Rennlist about bushings. His wore out. In fact, they wore so badly that the metal of the front A-arms started to wear in that spot. He had to do some welding before the bushing replacement.

Rubber can easily wear in a spot where friction occurs. Bushings allow movement--so there's friction. Rubber also eventually deteriorates. Does a particular car need new bushings? Dunno--that's an issue with that particular car.

The bushings make a real difference in how a car handles. It transforms a car that's nice and fun to drive into one that is damn near telepathic. You do not have to wait that split-second for the car to react to your inputs, as soon as you start turning the wheel the car reacts. It's a very interesting feeling. In fact, that plus a few other modifications got my buddy's 73 911 to handle about as good as a good 914--I was very impressed by the car.

Harder bushings keep the suspension geometry more correct, and the pieces better located. They also make the car react quicker to driver input, by taking up some of the "slop" in the suspension. The downside is that they transmit a whole lot more noise and harshness to the cabin. Those downsides are not acceptable for most normal everyday drivers, so Porsche did and still does use softer bushings.

An individual has to decide if the small gains in absolute cornering (and the larger gains in transient response characteristics) are worth the extra harshness. It's up to personal tastes, and just how muchh pounding your kidneys can stand.

Softer bushing replacements are usually still harder than the stock rubber ones, but may be an option for those who have cars with worn bushings. Again, the feel and responsiveness and low cost have to be weighed against the comfort factor and high cost of the stock parts.

Used trailing arms would make me nervous--particularly used passenger-side ones.

--DD

[philinjax]

DD,
Your points are partially taken. Although I don't doubt that poly bushings do feel differently to the driver and perhaps are much more rugged, I do doubt subjective evaluations necessarily translate to faster times at the track. It sort of reminds me of the fraudulent engine tuner who once told me that he can polish the ceramic on the plugs and loosen the throttle return spring, makes those dummy customers think and feel as if they have a hot car. Did the guy, who replaced his warn A-arm bushings with
poly, actually document faster track times?
I submit that when a suspension system is properly set up, the selection of tires (part of the suspension) and tire pressures will have a hell-of-a-lot more to do with track speed than any mico-tinkering with poly vs stock bushings.
Trailing arms, new or used, are one of the most solid components on a 914. The pick up points for the arms are the baddies.
I worked all day, today, on my wife's teener, corrosion control, fixing floor pans, the drudgery, but hey, I love the little buggers.
Phil

[Dave at Pelican Parts]

Well, Charlie said that the fact that the whole chassis didn't lurch when the front A-arms moved certainly helped.

And in my own subjective opinion, the "tautness" and "with-you" feeling that the 911 I drove had really did help. I'm not sure that the absolute cornering capacities were increased by enough to tell, but I am quite sure that the more positive feel that the car had over stock contributed to being able to get more out of the car. Perhaps I should say that the limits may not have changed much, but seemed to be easier to keep the car at its limit. And the reactions were quicker, without having to keep your movements ahead of where you were. It may be that a better driver, one who could "drive ahead of" the car better than I, would not see as much improvement.

I'm thinking that the difference would have been less on the big track, because you do not have to react as quickly in general as at an autoX. Plus you have more time to plan ahead for your attack on the next corner/set of corners. But I feel it had a significant impact on the autoX times.

I do not have a good A/B on the 911 I drove, however, as my friend already bought the car set up that way.

--DD

[karlp]

All this talk of rotten bushings certainly has me feeling I should replace mine tonight!!
Where are they located exactly, and what to look for concerning condition?

[philinjax]

Karlp,

Don't worry about bushings, pay attention to your tires and brakes. That's what counts.

Phil

[Rob-O]

Well now Phil, you said you hate the subjectiveness, but you are subjective in your last post. You said that the bushings on your car were weather beaten on the outside, but were intact and connected to the a-arms (or trailing arms). But how do you know, really? If you haven't taken them off, they may be wasted in there. And even if they look good, how do you know if the resiliency of the substrate is within design parameters? Ironically, determining the condition of substrates after artificial weathering testing is what I do for a living. I can tell you that while I haven't done any testing on teener bushings, that I never base material failure solely on visual examination.

Here's the thing, you live in Florida, so this may not apply to you (or DD out in CA. for that matter). But the trailing arms that came off my teener were from my very first 914 that lived it's life (along with me) primarily in Michigan (and Pennslyvania before that IIRC). The bushings did in fact look pretty decent, with the exception of the weatherbeaten look that you mentioned. However, on the rear trailing arms, I noticed that the shaft was a little corroded where it met the bushing. I decided to take a closer look. Prying the bushing around a little showed me that there was a decent amount of corrosion that had eaten away the end of the shaft. I think you'll have to agree this wasn't a design intention and that the missing metal on the shaft due to corrosion would cause some slop in the suspension system. However small that may be. So I decided to correct what I could. I pulled the shaft and re-welded it, problem solved. Now, I would rather have the rubber bushings, but in the process of taking the shaft from the trailing arm, they were destroyed. I'm forced to replace them with the polygraphites. I could have gone out and searched around for a new trailing arm (well, new for me), but it would have been used and subject to the same problem that I had experienced.

Now I'm in Texas and I just got me another teener (a roller to put my original 914-6 equipment in). I have the set of polygraphite trailing arms, and the set that came on the rolling chassis I just bought. From the appearance of the car I just bought, I will probably use the trailing arms that are already on the vehicle. But if I have any doubt, those polygraphited trailing arms are a goin' on. I'm too old for the kidney dance, but I guess I'll have to live with it. At least the roads here in Texas are a lot smoother than those in Michigan. Some of the winter potholes up there would swallow a teener.

I do agree that wheel and tires and other things make a whole lot more sense in making gains in handling prowess, but if you had identical (theoretically impossible I know) cars and one had the polygraphite bushings and the other didn't, I think the one with would provide a quicker "feel" to the inputs from the driver.

Just my $1.25 (I'm short on cash today)

Rob-O

[philinjax]

I'm from Michigan too, but I didn't buy my teeners up there. Road salt in the winter, you know.
Now that I'm in Florida (been here since I retired from the Navy, back in 70), I maintain a stack of trailing arms in the unlikely event that I may have to change a set due to warn bushings or corroded shafts. So far, so good.
Phil