Front Suspension Project.

[Richardnew]

This is the year of front suspension. I knew things were not good but it turns out it was really worse than I thought. Isn't that always the case though?



We knew the bushing weren't great. This is what we found when we took things apart.



The bushing allowed the torsion bar to bang against the mount. I've circled the worn area. I caught this in time. There's no damage to the torsion bar that a little emory cloth won't take care of. Another year and it might have become a bigger issue.

Next time you're under the car check the condition of the rubber in your mounts.

Richard Newton

[Jim Breazeale]

I would replace the torsion bars, while you are at it. Yours don't look good at all! It's not just the area that contacted the inside of the A arm, either.

Regards

Jim

[Richardnew]

A couple of old experienced 911 folks and I had that very discussion this morning. No one really felt the need to replace them. We are going to clean them up and grease them before they go back. We're also checking all the splines.

The pitting in the photos looks much worse than it actually is. Actually there is no pitting - just about 2-inches of surface rust.

We even discussed powder coating but we aren't sure about the temperatures that the powder coater uses. Most of them use a fairly high temperature which is bad for the steel.

Richard Newton

[Jim Breazeale]

A couple of old experienced 911 folks and I had that very discussion this morning. No one really felt the need to replace them. We are going to clean them up and grease them before they go back. We're also checking all the splines.

The pitting in the photos looks much worse than it actually is. Actually there is no pitting - just about 2-inches of surface rust.

We even discussed powder coating but we aren't sure about the temperatures that the powder coater uses. Most of them use a fairly high temperature which is bad for the steel.

Richard Newton

So is "surface rust" . That is why they are painted.

Regards

Jim
This ain't my first rodeo, either

[chris_seven]

Richard,

The real issue is that the corrosion pits are much more likely to be worse that they look and not the other way round. The fact is that the pits are likely to be full of an oxide debris that has been polished a little by the rubbing action which will camouflage the extent of the damage.

The slight step that is present will also act as a stress raiser and will not help.

Trying to remove this damage with emery cloths is not always the best idea depending on the grade of cloth being used and the manner in which it is applied,

Fatigue of steels is generally described in terms of an Endurance Limit which is the stress at which a steel should never fail and can be determined from a number of different test regimes and data is readily available for a wide range of materials.

The influence of surface finish on a typical steels Endurance Limit is significant and often defined by a simple factor usually referred to as k which generally correlates well to Ra.

Emery cloth finishes do not have a very good reputation in providing a well defined control of surface roughness and can introduce significant surface defects that can be problematic and when used with relatively notch sensitive material may not produce the desired result.

Using a lathe and a fine cloth would be the best approach but it may take a significant time to remove all the pitting and the step.

The problem with corrosion pits is that although there is good qualitative evidence that they do have a significant and measurable impact on fatigue crack initiation and hence fatigue life the quantitative data available is less secure.

The morphology of corrosion pits seems to be as important as their depth and there are several research programmes trying to quantify and model their effect but it is really tricky to draw any firm conclusions.

As best fatigue crack initiation should be considered as unpredictable (stoichastic), the condition of an individual bar in terms of surface damage and the subsequent road/load loading spectrum that will be applied to a specific vehicle all being very significant in terms of failure probability.

Recent papers published in Acta Metallurgica and the international Journal of Fatigue suggest that at least 90% of all engineering failures are due to metal fatigue in one of its various forms.

To consider a notch sensitive material such as a spring steel used with a significantly less than idea surface topology fitted to a high performance car with an undefined road/load duty cycle fit for purpose seems a bit of a stretch and I would agree with Jim Beazeale that are certainly well past their best.

Commercial Powder coating temperatures are typically 200 to 250degC which shouldn't be an issue for a torsion bar.

I would expect that this type of spring would have been tempered at around 500degC so they shouldn't be affected.

Small Music wire springs would be tempered at lower temperatures as the wire is strain age hardened during this process.

If you heat to 275 degC this type of spring can become brittle and lose a substantial amount of its ductility (temper brittle).

Most heat treated steels are, of course, tempered and the temperature/duration depends on the material chemistry.

The only common products used in an 'as quenched' condition are metal files.

Good luck with the torsion bars

[Richardnew]

You guys are making me think. Now my hair hurts.

I may replace these as I have a variety of torsion bars around the garage (don't ask). Most of them are of a larger diameter but I think I can find one in this size. That may be the best solution.

Richard Newton

[RSTarga]

Jim should have a bunch of those 19mm bars.

[Jim Breazeale]

Jim should have a bunch of those 19mm bars.

David

Thank you for mentioning me. The last thing I want to do or need to do is recommend a replacement part and then say "oh, by the way, I just happen to have that". There are good, solid, scientific reasons for replacing torsion bars with "surface rust". Thank you, Chris, for that. Yes, I do have a bunch of them. We rarely get calls for them, except from the mid-west where rust is an issue. Snapping off a torsion bar in your A frames or, worse yet, in your rear torsion bar tube is not a fun thing to have to deal with. A pair of good used torsion bars from a certain junk yard in California are neither, rare nor expensive. Pay me now or pay me later....................

Regards

Jim

[michaelaiellosr]

I think I have 6 or 8 of them with no defects. Pay the freight and two of them are yours. Mike

[Richardnew]

This project is still going on. It's a normal Porsche project. It's going to cost twice as much as I originally thought and it will take about 4 times as long to finish.

I probably got carried away with the powered coating but I do like it. This is hardly an original car so I'm really not concerned about powder coating. The car will look better and these parts are below the surface. The only problem is I might start cleaning my control arms. Now that is really a sick thing.







The bushing selection has been a freaking circus. First Stoddard sent me the wrong bushings. Then we (the shop and myself) decided we didn't like the Automotion bushings.

That left us with Elephant and Rebel. I hate using grease. You can never keep all the dirt out. Dirt and grease is like the old valve grinding compound we used to use.

Several people here seem to prefer the Rebel product over Elephant so I just ordered almost $400 worth of parts. I wonder how that translates into frequent flyer miles?

Richard Newton