Powder Coat vs Zinc Plate Torsion Bars

[frankc]

I will be dropping off another batch of parts to the powder coating shop soon, and thought about including the torsion bars (masking the splines, of course). However I was concerned that the 400 degree F heat cycle might alter the properties of the metal. Is this a valid concern?

Another option is to include them in my next batch of parts to be zinc plated.

Which is the better option?

[KFC911]

I would NOT do either on the torsion bars, and I've had a bunch of suspension stuff PC'd and cad plated. Coat the bars with grease, install, and fuggetaboutit...no good can come from what you are proposing imo.

[gamin]

Agree. Grease them.

[1QuickS]

Zinc plating WILL cause hydrogen embrittlement of the heat treated steel and they will break after time, probably a short time. I doubt the powder coating will cause any change in material properties (heat treating is performed at much higher temperatures than powder coating temps) but typically the torsion bars have a good finish on them already; be sure the finish is not damaged. Apply grease and install.

[Cory M]

New Elephant Racing torsion bars are zinc plated, and the Sway Away bars are powder coated.

[ClickClickBoom]

Originally Posted by Cory M

New Elephant Racing torsion bars are zinc plated, and the Sway Away bars are powder coated.

I think the Elephants are cadmium plated, at least my new ones look like it. The Powerbars I just listed in a WTB thread are powder coated....

[Cory M]

Originally Posted by ClickClickBoom

I think the Elephants are cadmium plated, at least my new ones look like it. The Powerbars I just listed in a WTB thread are powder coated....

It specifically says zinc plated on their website:

"Our Plated & Plugged Hollow torsion bars are the best available. The ends are plugged to prevent moisture entry that rots ordinary hollow bars from the inside out. The entire bar is zinc plated for superior protection. "

[ClickClickBoom]

Huh,
I guess that makes me a monkeys uncle, or caveman....

[KTL]

Cad plating is not all that common anymore due to enviro issues. Zinc is typically the plating of choice today, just like is the case on a lot of basic nuts & bolts.

I treated my t-bars to a coat of POR-15 Metal Ready (to make the paint adhere) which I believe etches it & applies a gold-ish color that is a zinc phosphate. Then put POR-15 paint on. I did it because the Sander Engineering t-bars I got were bare metal, compared to the factory Porsche t-bars that were painted with what looks like a hard epoxy paint. I figured some paint was in order vs. just grease since the bars are known to rust & break, even when painted!

I already had the paint on-hand for doing some suspension pieces so I figured why let it go to waste. Which is often what happens to my paints since I rarely use it all up.

[James Brown]

ok ok, they are a spring, nothing more. protective coating of something is in order but not something that will be worse than nothing. they do twist a little so a paint that remains flexible would work well followed with some grease slathered over them prior to install is all you need. They will be in the tubes for the next XXX years, out of sight

[KFC911]

Originally Posted by KTL

.... Then put POR-15 paint on. I did it because the Sander Engineering t-bars I got were bare metal, compared to the factory Porsche t-bars that were painted with what looks like a hard epoxy paint. I figured some paint was in order vs. just grease since the bars are known to rust & break, even when painted!

I already had the paint on-hand for doing some suspension pieces so I figured why let it go to waste. Which is often what happens to my paints since I rarely use it all up.

I was gonna POR the Sanders hollow t-bars I sourced from Steve Weiner many years ago, and he's the one who convinced me to just grease 'em and install....so that's the what I did. IMO, applying the grease is more important than paint, zinc, or cadmium...YMMV.

[Jim Sims]

Improperly done plating of high-strength steels without appropriate post-plating heat treatment can lead to hydrogen embrittlement and catastrophic failure of the part. Make sure the plater knows what they are doing.

[frankc]

Lots of good discussion here - thanks for the responses.

I knew that the ER bars were plated so I thought that would be a safe option. However, I have also read in the past about the hydrogen embrittlement associated with zinc plating that Paul mentioned, which is why I threw it out here for opinions. Are there alternate plating methods that mitigate the embrittlement issue? I have had springs zinc plated in the past and have had no issue with them breaking, not to mention the rows of zinc plated springs you see lining the shelves at your local hardware store, so there must be a safe way of doing this.

Regarding the comment that the bars will be "out of sight"; based on my experience I don't necessarily agree with this, at least not for the front bars. I agree that the rear bars are kept mostly protected from the elements as long as the rear bushings are in good shape. Indeed, when I removed the original rear bars from car after 30 years they were in very good condition.

However there is a small gap where the front bars are open to the outside at the rear of the control arm, between the crossmember and rear bushing housing (red arrows in 1st photo). As you can see in the 2nd photo, moisture can certainly get in there and cause bad things to happen.

I assume the bars were greased entirely when installed by the factory. The rear bars were still covered in grease when I removed them. The front end of the front bars still had some grease on them and were in OK condition, but there was no grease left on the front bars towards the rear and you can see the result, which is why I was looking for a solution more robust than just grease.

I should note that there are foam seals that go around the ends of the front bars between the height adjustment cap and the crossmember (901-341-475-00, 3rd photo). Even though these seals usually deteriorate quickly, they appear to have done a decent job of keeping the spline ends of the bar free of corrosion. I had planned to install an additional one of these "donuts" on the other side of the crossmember to cover the gap shown in the 1st photo when re-installing my suspension, unless someone can tell me why this would be a bad idea.

Photo 1 showing gap exposing front torsion bar (redish color):


Photo 2:


Photo 3 showing seal 901-341-475-00:

[chris_seven]

ASTM F1941 has a hydrogen embrittlement (HE) relief requirement for fasteners made from steel heat treated to a hardness of HRC 40 or above. The exact time and temperature of the bake is not specified, but times between 2 and 24 hours at temperatures between 350 and 450°F are listed as suitable depending on type, size of fastener, geometry and other variables.

I believe that a torsion bar can be considered as analagous to a fastener for the sake of this discussion.

In extreme cases, normally involving components that have been acid pickled, HE can be an issue for steels with a hardness of between 30 and 35HRC and baking would again, be recommended.

I haven't measured the hardness of a 911 Torsion bar but I can believe it would easily exceed 40HRC

We always paint them in a PU paint that doesn't require any primer just a clean surface.

[Craig_D]

Originally Posted by Cory M

New Elephant Racing torsion bars are zinc plated, and the Sway Away bars are powder coated.

Funny thing is that my front torsion bars (Sway Away) were red powdercoated, and the rears are ER Zinc coated.

So...mix it up!

[Craig_D]

Here's a pic from the beginning of my ER build showing the fronts (Red PC) and the rears (Zinc).

[frankc]

Chris,
Thanks for that info - now that you mention it, I do recall reading about the baking process to relieve the HE issue. I'll call the plating shop I use and see what they say about it.

I would prefer to plate the bars because my bars are hollow (like Craig's) and plating will allow all surfaces to be covered. Where as with powder coating, the splines and the ID surfaces will not be protected.

Hmmm, powder coat after plating...? Forgive me, but I grew up in the NE and witnessed the devastation to unprotected steel caused by water and salt to vehicles subjected to those conditions (I always had a daily driver for such) - not that I have to deal with any of that now living in Central Texas.

[chrismorse]

Originally Posted by Jim Sims

Improperly done plating of high-strength steels without appropriate post-plating heat treatment can lead to hydrogen embrittlement and catastrophic failure of the part. Make sure the plater knows what they are doing.

Hi Jim,

I am about to embark on a zinc plating of various suspension and brake parts, using Caswell's inc plating set up.

I have read, (Carroll Smiths, Engineer to Win), i believe, that it is Chrome plating that engenders Hydrogen Embrittlement. I do not know if this might also include Zinc.

But Zinc is a very low power plating process and i believe that the chroming porcess uses 5-10 times the plating current.

Help me out here, because i am about to do spring plates and various brake parts, as well.

Thanks, chris

[Iciclehead]

I must admit the whole thing of hydrogen embrittlement leaves me baffled. Every time it comes up on this list, there is a pretty strongly held point of view by those who appear to know what they are talking about that you need to bake.

I have several times gone to my plater, who does a huge amount of plating for the oil industry including some pretty high pressure/high stress stuff and they keep on saying that it is not necessary for anything on a car and they actually never do it for anything in the oil industry...just for aircraft parts where they do it only because it is required by regulation.

I check with my son (an engineer who is in the oil industry) and he says my plater is right, they never specify baking for parts that are used.

So, I remain confused and so far have never insisted on baking....and over the last 15 years or so that my driver has been on the road, not one of my plated parts has failed (including stuff like spring plates, all sorts of bolts and fasteners in the suspension).

I guess it is just a risk I am taking...

Dennis

[frankc]

Dennis,

Thanks for sharing that. The plater I use does commercial work for some automotive parts companies, so it will be interesting to hear what they specify for their parts. I'll post back after I talk to him.