Speedtoys

A rubber bushing has no friction. It has no moving parts. Entirely friction free.

But they are..as designed, very LARGE torsional springs. They could have been much smaller, without bonding, and without a procedure on when and how to attach them to operate neutrally. They could have been mounted with a pin, and allow rotation. But why're not.

And, they have no appreciable wear. Because no moving parts. I would be wary of calling any item made to flex "failed" after 30-40yrs. You should buy it a beer.

This is the trade off with parts that move and don't like friction, but create it just being there, they -have- to. Got room for grease? You got room to move in ways it won't like.

What bushing material is in the hottest street 911 today? Just wondering. Greg Brown might know.

The next Spider my daughter sees on the rack, I'll have her check that too. I'll have her poke around when the GT3 orders come in for pre delivery inspection. I'm kinda curious now.

Can they be "better", I guess, certainly. But with what trade offs and is any practical improvement of the vehicles use is warranted for those trades. That's up to the user. I won't call either decision wrong.

Any "upgrade" has the same considerations in any part in the car when deviating from oem.

I hope these work out better than the last 25yrs of poly upgrades to 928s.

DeWolf

All valid points. I must say though ( and it's lost in text as you can't see my face, nor hear my tone, but I mean it as if we were talking around a bbq ), I'm not bothered whether they last 25 years or not. Like I've said before, I'd gladly pull the front apart to re-grease just for the driving feel. This is the second car I've done the full poly bush deal on and both with the same results, amazing driving feel. The other was an E46 M3.

I guess it's the same as why use adjustable sway bar rods when the factory ones do their job. Why use mono ***** on your control arms when the factory rubber does it's job.

FredR

Scott,

I rather suspect your mechanic was being a little bit "flamboyant" with his vocabulary. In evaluating things like this I try to take a balanced perspective that includes looking at the issue as though I had designed it and given they are an item that never changed and have given excellent service for up to 40 years that is not shabby at all.

That is not to say that there is no scope for improvement and these bushes caught my eye some two years ago, mentioned them in a thread and then Greg contacted me to advise he was already in touch with Powerflex regarding them. We exchanged thoughts on them given that I was starting to plan for a possible refresh of my suspension system. Even so, as you have seen, this thread has already had some impact on my perception of the design. I have read the Powerflex fitting instructions and interestingly nowhere did it say it whether the bushes were a press fit or a sliding fit and as it turns out it is a combination of both. This is quite a radical departure from the original design concept which also has a metal insert between the inner and outer rubber layers.

I can see how the front bush works- that is encapsulated in an outer frame. The rear bush leaves me somewhat puzzled. As anyone who has "played around" with the lower arm will know, the rear bush is clamped and this distorts the outer bushing- presumably to ensure that the bush cannot move relative to the clamp. As we know, the arms are not "handed" so when the original items were fabricated they were done so with the front mount bonded at 90 degrees to the arm axis- the logic being that in the settled position the arms would be more or less in the horizontal plane. Thus why the rear bush clamps have to be tightened when the suspension has settled and why the arms have to be maintained on the given side for the rest of their service life. Now, if you look at the stock arms after removal, the rubber has taken a permanent deformed set. This leaves me wondering how this translates with the Powerflex bush design given that the outer bush is designed to move relative to the metal sleeve. Maybe the applied forces do not translate to the inner surface of the outer bush but I have difficulty seeing how that could be the case. Presumably one also has to maintain the higher torque values for the rear bolts [85 ft lbs].

That you have positive feedback is very encouraging and needless to say the big unknown is system life expectancy. Worst case scenario is they degrade and fail prematurely but they are not likely to do so suddenly and spectacularly. That Powerflex offers a lifetime guarantee is also a plus point assuming it is worth the paper it is written on. They seem like an outfit that knows what they are doing and that should also be encouraging.

Bottom line- when we depart from the stock system as with anything we are taking a degree of risk and there are no guarantees. For the cost involved it is an interesting alternative. I am assuming that my lower arm bushes are well past their best but I have no hard evidence that is the case. One of those things that in all probability one does not know how much degradation has taken place until one feels the benefit of fresh new components. That we now have an option over the stock bushes is a positive, if it can also generate a genuine improvement in ride quality even better.

slate blue

FredR

Greg,

The half moon shoulder [I presume] is there to restrain rotation- the interesting point is why they thought such was necessary. If you look at the photo of the stock bush I have attached you can see that the bush compression is not directly on the "half way line" so that tells us that the two halves are not equal as it were. Thus when the stock bush is compressed it pinches the rubber that duly distorts. One presumes that Powerflex would be aware of this and when such happens it is difficult to visualise how a bush could possibly rotate thus leaving me wondering about the half moon affair- put another way did Powerflex really understand how the stock system clamps up and deforms? Did they have a test mule?

On the other hand, if they did know about this would they have considered putting a shim in there to reduce or eliminate the deformation? That they put that shoulder there suggests to me this was their solution to stop rotation and thus begs the question whether they even understood how the stock system pinches the bush.

Bottom line if the system as marketed requires a modification then "something not quite right" or so I would think?

Edit : still cannot get the photo to upload

DeWolf

I think that's the point Fred. It was designed in the 70's. I'm not sure, but I'd suggest it's the only Porsche that uses a bush in that manner. The Panamera, being probably the closest living relative to the 928 doesn't use that system. I'd really like for some one to drive my car compared to an original set up that is fairly new.

DeWolf

Easy way to find out Fred. Send them an email. I would think they are completely aware of how it works. When I inquired about the rear bushes and the Weissach joint they were well aware of the duty the joint performed and designed the poly one around those parameters. I think I posted their response here on a thread.
The other thing I've read is about the rubber bonded to the control arm. Mine certainly were not bonded. I used a bearing race puller to remove them. The fact you can purchase new ones begs the question, how do you re-bond them?

Found the email

Hi Scott,
The image I sent you was a concept rendering to show our intention, not an exact illustration of how the end design of the Powerflex Rocker Bar and Bush will be. We are mindful of the Weissach set-up and the requirement for some movement to ensure we retain some of the passive rear steer and the positive effects of this system. The concept of our bush/bar is actually not that different to the original in terms of its functionality, apart from it uses polyurethane rather than rubber. The CNC machined bar will have an outer polyurethane ‘sock’ very similar to the original in its design and then we will be using a polyurethane bush at the end of the bar. The OE rubber bush is actually very stiff as standard so it’s not something that we’re looking to go drastically harder with. Our goal is to offer slightly less compliance, but with enough movement to ensure we are still seeing wheel toe-in as the Weissach axle was originally designed to do. I hope this helps explain it better.

Kind Regards
James Bourn ~ Sales Director

Bedfordman

I have used POWERFLEX poly bushes on other cars (Saab) and never had a problem. They seem to last for ever.

On the 928 (S4 , MY 1991) I went for 'SuperPro' - they come from Australia - to replace worn out bushings on the front upper control arms.m . They are superb, so far.
These Australians seem to know a thing or 2.
The only problem being getting the old ones out. Had to drill through the rubber bushes to provide gap for hack saw blade to carefully cut through the metal inserts in the arms so that the inserts could be prised out. Corrosion preventing them being pressed out.

FredR

Scott,

As I can tell the Cayenne and the Panamera front suspension systems are virtually identical to the 928 conceptually speaking. The bushing is a bit different in that the Cayenne and Panamera systems use off the shelf press in bushes made by the likes of Lemforder but they work in just the same way with the rubber in torsion.

Ironically it seems they were both a step backwards as the Cayenne's bushes only last about 60k miles and Porsche were so concerned about it that for my Cayenne Turbo S they modified at least one of the lower arm bushes to a more robust item. Mine were inspected recently and apparently they are on their last legs and thus I am thinking Powerflex for that application. For the Panamera there are endless reports of clunking- non of these issues on the 928 suspenders.

Seems you are something of a guinea pig! So far you are the first owner I have heard about running these things

FredR

Scott,

I also concur with your observation regarding bonding - or the lack of it! I cut the open bush off one of my spare arms with the dremel and pulled the closed one with a press- no sign of any bonding material anywhere.

Your note from Powerflex presumably was referring the upcoming development for the Weissach bush. It would be interesting to know if anyone has a method for determining whether the stock items are shot [or not].

FredR

You should have been able to push the old bushes out with the rubber being destroyed in the process unless your press was a bit on the weeny side.

Both Scott and myself have the Super-Pro bushes on the upper arm and so far so good. The Powerflex bushes we are talking about are made in good old blighty as I am aware [that or discretely outsourced to our friends in China?].

hacker-pschorr

Has anyone talked to Powerflex about the rear control arm?

For anyone who's upgraded the front, what did you do in the back?

BC

I actually think the rear control arms produce alot of wiggle that I can feel, even after I replace bushings, but maybe the wiggle is there so the rubber on the tires can find some tractions mid corner on accel.

FredR

As I understand from the boys down under Powerflex are about to launch bush kits for the rear including the Weissach thingy next February

hacker-pschorr

Ohhh.....exciting. I'm tearing the *** end off my 79 this winter and figure that would be a great time to update everything.