Polyurethane Bushings?

[todd1561]

As is usually the case after one of Darren's tech meets, I get the motivation to get into some more projects on my car. One area I've always wanted to do a little more work in is the suspension. Presently, I have the Eibach springs installed and the KYB shock kit offered by Marty Maier of the Mid-State DMC club, not sure they're even sold anymore. Next I would like to incorporate some polyurethane bushings, I see John Hervey is offering a kit but reviews do not seem favorable - too soft apparently. The offerings across the pond seem to be well-liked, but the exchange rate makes them way too expensive. Does anybody know of a good source state-side to do the entire car? I already have Toby's kit on order to do the sway bar.

And yes, I realize this will create a considerably firmer ride, that's my goal!

Thanks,
Todd

[tgraham]

Check with DMC MW - I believe Dave stocks the poly bushes that Ed Uding sells. Also, it's worth mentioning that when ordering bits from Europe, check to see if the prices include VAT, which would dramatically lower the price when the part gets exported to the US. DMC EU's site includes VAT, for example, and Ed will just quote you a price without VAT.

Travis

[todd1561]

Hi Travis,

Thanks for the tip on VAT, if Dave can't supply them I'll contact Ed or Martin directly and get the skinny. Dave, if you're out there, do you have a set for sale and if so how much?

Todd

P.S. Travis, that looks like an insanely thorough restoration you're doing on your car from what I can tell from your site, excellent work!

[tgraham]

P.S. Travis, that looks like an insanely thorough restoration you're doing on your car from what I can tell from your site, excellent work!

Thanks! Though, I must admit I'm technically not *doing* very much to it at the moment :( Hopefully I'll be able to turn that around soon.

Travis

[refugeefromcalif]

One area I've always wanted to do a little more work in is the suspension. Presently, I have the Eibach springs installed

Thanks,
Todd

I'm thinking about going with the Eibach lowering springs myself. (Shocks I haven't made up my mind yet).

The problem that I've ran into is that I'll have to the car realigned. Nobody that does alignments around my area have the specs for a D.?
Where can they be found?

(Sorry to hijack your thread).

George

[DMCMW Dave]

Nobody that does alignments around my area have the specs for a D.?
Where can they be found?

George

In the manual.

[stevedmc]

I'm thinking about going with the Eibach lowering springs myself. (Shocks I haven't made up my mind yet).

The problem that I've ran into is that I'll have to the car realigned. Nobody that does alignments around my area have the specs for a D.?
Where can they be found?

(Sorry to hijack your thread).

George

Have you checked with your local Firestone shop? Delorean is in their alignment computer and I was able to purchase a lifetime alignment plan a while back for something like $180.

[Mark D]

DMCMW carries the full line of poly bushings from Europe. I ordered everything for the front a while back and I'm still working on putting my car back together. A few things to note about swapping to poly:

The LCA bushings are easy to do... the hardest part is pressing out the old bushings but that's pretty simple. To install the poly bushings you'll definitely need a press to squeeze the two halves of the new bushing into the arm tight so there is no gap in the middle and it can fit back in the frame correctly.

The UCA bushings are a pain in the butt. If you plan on doing these you'll need to get creative with spacers when pressing out the old bushings and replacing them with the poly versions. If you don't use spacers the "U" shaped channel of the upper arm will bend/squash together. I fabricated some steel spacer plates as you can see in the pics below. The washers are there so when the new bushing is pressed in then you can pull the washers out and remove the two big plates. Otherwise you'll just press the spacers in and won't be able to get them out.

http://dmctalk.org/attachment.php?attachmentid=14206&d=1350530536
http://dmctalk.org/attachment.php?attachmentid=14207&d=1350530552
http://dmctalk.org/attachment.php?attachmentid=14208&d=1350530566

I decided to stick with rubber bushings on the rear... I wasn't a fan of how the poly would rub on the frame, and from what I've read from other people who've installed poly in the rear it ends up being really stiff.

[todd1561]

Thanks mjdehlin,

Excellent info, glad to hear from someone who has had some first hand experience installing these bushings. Apparently these poly bushings are slightly different than ones I've done in the past. I'm used to not dealing with the outer metal sleeve, you can just simply hand-insert the poly into the suspension component and then slide the metal inner tube in. You'd only need a press on the removal side of things. I'm sure this is a more robust setup. Looks like some creative ingenuity on your behalf for the upper control arm, I'll keep that in mind if I actually go down this route. And thanks for the tip on DMCMW (and Travis!), oddly enough, when he replied to this thread he didn't mention one way or the other, I guess I'll call.

Todd

[Mark D]

The other bushings you're thinking of are the what's used in the lower control arm and also in the LCA support brackets that Ed sells.

The note I made about them needing to be pressed in is because it's extremely difficult to push them in by hand and get them all the way into the lower control arm sleeve. Without a press of some type you'll end up with a gap in the middle between the two bushings and the whole assembly will be too wide to fit back into the frame. I had to use the press to get everything to seat fully into the lower arm so that it wasn't too wide.

IE:
http://dmctalk.org/attachment.php?attachmentid=14216&d=1350576493

http://dmctalk.org/attachment.php?attachmentid=14214&d=1350575807


The lower control arm supports brackets that Ed sells uses the same type of bushing as well, but those can be installed by hand.
http://dmctalk.org/attachment.php?attachmentid=14215&d=1350576260


The upper control arm bushings are the only ones that have an actual metal sleeve on the outside of the bushing since the upper arm itself has no sleeve.
http://dmctalk.org/attachment.php?attachmentid=14217&d=1350576493

If I had to do it all over again I would probably have left the upper control arms with the stock rubber bushings. I powder coated all my suspension components and anything rubber would have been destroyed when they baked the powder so that was the only reason I removed the old rubber bushings. If you simply want to replace with poly I don't know if the upper bushings are worth the trouble. The rubber is very firm to begin with and I don't see much advantage with the poly. NOS rubber upper bushings aren't available so if yours are dry rotted or worn and you don't want to replace the whole upper arm (comes with bushings already installed) then poly would be the cheaper alternative.

[todd1561]

Thanks once again for the the info, I really appreciate you taking the time to include the images and drawings! I hear what you're saying about the upper control arms, probably more hassle than it's worth. My plan was to take all the components to a sand blaster and then I'd POR-15 everything. Unless the blaster can't do it without destroying the bushings I may just skip the ones on the upper arm per your suggestion.

Thanks again,
Todd

[Mark D]

No problem with the info and pics :-)

The guy sand blasting your parts should have no trouble stripping the old paint off the UCA without damaging the rubber bushings.

POR-15 is good stuff... I used it on the frame rusted areas and a few other suspension parts that I couldn't get powder coated. I think the general concensus is that powder coating is still stronger and more chip resistant than POR15 though, so if there are parts that you've got sand blasted that could be powder coated instead of POR15 painted I'd recommend that route. The lower control arms and anti-roll bar seem to get hit with a lot of rocks and dirt as you're going down the road so I was especially interested in getting those parts powder coated. I also tore down my steering rack and did the center tube and the two outer arms.

Most places are willing to mask off any areas you don't want coated like the ball end of the steering arms, threaded holes, or the inner surface of the ball joint tapers on the steering knuckles.

If you haven't used POR15 before make sure to follow the instructions to the letter.

[vtdmc]

What is the popular opinion? Are polyurethane bushings better than the rubber bushings? Is it personal opinion?

[DMCMW Dave]

What is the popular opinion? Are polyurethane bushings better than the rubber bushings? Is it personal opinion?

Personal opinion and trade-offs.

OEM style - last a long time (other than sway bar ends), quiet, zero maintenance, engineered compromise between ride and handling.
Urethane - "Crisper" handling/steering feel cost of a harsher ride. Need to be greased peridically or they can be squeaky.

[ed uding]

Mark for the front pu busings we have special one,s.
With a cut out the top, you can install it simple.
The one on the photo are the rear one's.


Regards Ed
www.delorean.eu


The other bushings you're thinking of are the what's used in the lower control arm and also in the LCA support brackets that Ed sells.

The note I made about them needing to be pressed in is because it's extremely difficult to push them in by hand and get them all the way into the lower control arm sleeve. Without a press of some type you'll end up with a gap in the middle between the two bushings and the whole assembly will be too wide to fit back into the frame. I had to use the press to get everything to seat fully into the lower arm so that it wasn't too wide.

IE:
http://dmctalk.org/attachment.php?attachmentid=14216&d=1350576493

http://dmctalk.org/attachment.php?attachmentid=14214&d=1350575807


The lower control arm supports brackets that Ed sells uses the same type of bushing as well, but those can be installed by hand.
http://dmctalk.org/attachment.php?attachmentid=14215&d=1350576260


The upper control arm bushings are the only ones that have an actual metal sleeve on the outside of the bushing since the upper arm itself has no sleeve.
http://dmctalk.org/attachment.php?attachmentid=14217&d=1350576493

If I had to do it all over again I would probably have left the upper control arms with the stock rubber bushings. I powder coated all my suspension components and anything rubber would have been destroyed when they baked the powder so that was the only reason I removed the old rubber bushings. If you simply want to replace with poly I don't know if the upper bushings are worth the trouble. The rubber is very firm to begin with and I don't see much advantage with the poly. NOS rubber upper bushings aren't available so if yours are dry rotted or worn and you don't want to replace the whole upper arm (comes with bushings already installed) then poly would be the cheaper alternative.

[Mark D]

Yeah sorry that picture I referenced is a little confusing. The ones I ordered for the lower control arms have the notch like you are talking about. To get them pushed all the way in though I still needed a press. It could have been because I loaded them up with quite a bit of silicone grease to prevent squeaks. The grease had to be displaced before both halves of the bushing would seat completely.

17691

[ed uding]

Yeah sorry that picture I referenced is a little confusing. The ones I ordered for the lower control arms have the notch like you are talking about. To get them pushed all the way in though I still needed a press. It could have been because I loaded them up with quite a bit of silicone grease to prevent squeaks. The grease had to be displaced before both halves of the bushing would seat completely.

17691

http://dmctalk.org/images/smilies/thumbup.gif:thumbup:

[dmc6960]

Interesting. I had similar issues with the poly bushings I got from the UK. In my case, I was easily able to get both bushing halfs fully inserted, but due to the size of the sleeve in the LCA they still technically stuck out to far even with the forward end slit as pictured. They physically needed to seat further into the LCA. The only way I was able to accomplish this, was to actually cut all around the outer lip, thinning out the bottom of it extremely carefully. This allowed the bushings to seat deep enough to fit into the frame. A few months later I noticed a drawback of this method as one half of the bushing has now been completely pulled inside both of the LCAs. The outer lip had been compromised too much to support the twisting force of the LCA. This behavior has been observed on other poly bushings, though none from DMCMW/DMCEU that I've noticed yet though. I need to take apart my front suspension again this spring for frame rust mitigation and other issues; and I'm contemplating going back to OEM style rubber for the LCAs, or Ed's poly bushings from DMCEU/DMCMW. I have not decided which yet.

[jmettee]

I need to take apart my front suspension again this spring for frame rust mitigation and other issues; and I'm contemplating going back to OEM style rubber for the LCAs, or Ed's poly bushings from DMCEU/DMCMW. I have not decided which yet.

I JUST finished this task this weekend - front end refurb & rust mitigation. I boxed the LCAs & went with poly bushings only on the sway-bar. I decided against poly on the control arms due to hearing some end up having issues after some driving & also worrying about dumping a lot pf force back into the "fragile" frame by using the firmer poly bushings. I replaced all bushings with OEM rubber. I probably didn't have to replace any of the pivot bushings on either the UCA or LCA because they still looked pretty good, but the sway-bar bushings were definitely shot (as Dave mentioned above). The rubber was all mis-shaped & at least 1 had the rubber pulled off the steel collar.

[Chris 16409]

Back when I did my bushings, Houston had not come out with the reproduction suspension bushings yet. It turned out to be about the same price to buy the SuperFlex poly bushings from Martin as buying NOS bushings from DMC. Back then, each bushing was like $50. Now the reproductions are ridiculously affordable. If I were to do it now, I would probably go with the standard rubber bushings, except for the trailing arm ones.

[JMLaux]

Instead of creating ANOTHER new post about polyurethane bushings, I might as well just add to this thread:

Is there any information out there on the shore hardness of the various poly bushings the vendors supply? I've done a lot of research on poly bushing in general and it seems like most auto clubs/forms tend to geek out over the technical specs of aftermarket bushings but the only info I have been able to find on the DMC forums is they are stiffer than stock rubber.

[Morpheus]

Lots of great info in this thread! I am about to embark on a full poly upgrade for my front suspension and this will come in very handy. One question though:

Is it ok to use my stock LCAs (blasted and powder coated) with new lower ball joints, poly bushings, and Ed's brackets? I know the originals had their weaknesses, but with the improved strength of the LCA brackets they should last a lot longer, no?

[Patrick C]

Lots of great info in this thread! I am about to embark on a full poly upgrade for my front suspension and this will come in very handy. One question though:

Is it ok to use my stock LCAs (blasted and powder coated) with new lower ball joints, poly bushings, and Ed's brackets? I know the originals had their weaknesses, but with the improved strength of the LCA brackets they should last a lot longer, no?

The stock LCAs will still be weak, and now you are adding new stresses to them with stiffer bushings and braces. Many LCAs fail near the ball joint area, which the LCA braces will do nothing for. I strongly suggest updating them before you have a failure.

EDIT: Example photo attached.

[Mark D]

Lots of great info in this thread! I am about to embark on a full poly upgrade for my front suspension and this will come in very handy. One question though:

Is it ok to use my stock LCAs (blasted and powder coated) with new lower ball joints, poly bushings, and Ed's brackets? I know the originals had their weaknesses, but with the improved strength of the LCA brackets they should last a lot longer, no?

This is exactly what I did on my car and so far I've had no issues. I payed really close attention to the condition of the lower control arms as I was stripping and blasting them. Once they were in the raw I didn't see any evidence of severe pitting from rust or cracking so I powder coated them and installed new DMC Club UK ball joints. If you see any obvious signs of damage or if the corrosion has started causing the sheet metal to get pitted out you may want to replace them instead.

I also stripped and blasted the LCA support brackets. There was a lot of slag on the welds that was causing the paint to chip and peel off before I even had a chance to install them. Blasted them smooth and rounded off the hard edges slightly so that the powder coating would have a more rounded surface to adhere to. Sharp corners and edges tend to cause powder to thin out so if you radius anything sharp it will help with adhesion in the long run.

I think the new LCA braces that Ed is offering are stainless so you may not even need to worry about paint on those unless you are planning on painting the stainless black.

[MikeWard]

Lots of great info in this thread! I am about to embark on a full poly upgrade for my front suspension and this will come in very handy. One question though:

Is it ok to use my stock LCAs (blasted and powder coated) with new lower ball joints, poly bushings, and Ed's brackets? I know the originals had their weaknesses, but with the improved strength of the LCA brackets they should last a lot longer, no?

This is exactly what I did on my car and so far I've had no issues. I payed really close attention to the condition of the lower control arms as I was stripping and blasting them. Once they were in the raw I didn't see any evidence of severe pitting from rust or cracking so I powder coated them and installed new DMC Club UK ball joints. If you see any obvious signs of damage or if the corrosion has started causing the sheet metal to get pitted out you may want to replace them instead.

If you are going to go to the trouble of stripping the LCAs then it is a good idea / ideal time to weld in some strengthening plates before getting them powder coated, and rebuilding them with new balljoints and bushes.

47791

[Morpheus]

If you are going to go to the trouble of stripping the LCAs then it is a good idea / ideal time to weld in some strengthening plates before getting them powder coated, and rebuilding them with new balljoints and bushes.

47791

Does boxing in the OEM LCAs really help? I keep hearing that the weak spot is where the ball joint is pressed in. The LCA brackets help to provide strength and reduce the flexing of the rest of the arm, right?

[Morpheus]

This is exactly what I did on my car and so far I've had no issues. I payed really close attention to the condition of the lower control arms as I was stripping and blasting them. Once they were in the raw I didn't see any evidence of severe pitting from rust or cracking so I powder coated them and installed new DMC Club UK ball joints. If you see any obvious signs of damage or if the corrosion has started causing the sheet metal to get pitted out you may want to replace them instead.

I also stripped and blasted the LCA support brackets. There was a lot of slag on the welds that was causing the paint to chip and peel off before I even had a chance to install them. Blasted them smooth and rounded off the hard edges slightly so that the powder coating would have a more rounded surface to adhere to. Sharp corners and edges tend to cause powder to thin out so if you radius anything sharp it will help with adhesion in the long run.

I think the new LCA braces that Ed is offering are stainless so you may not even need to worry about paint on those unless you are planning on painting the stainless black.

Thanks for the reply, I intend to examine the arms after they are blasted to see if they are up to snuff. Mine only have 11K miles on them, so I'm hoping for the best.

[Mark D]

Does boxing in the OEM LCAs really help? I keep hearing that the weak spot is where the ball joint is pressed in. The LCA brackets help to provide strength and reduce the flexing of the rest of the arm, right?


I went back and forth when I was trying to decide if I should to box the LCA's or not... I ultimately I decided not to, but I may have been just being overly cautious.

The reasons were:

-I didn't want to strengthen the arm unevenly and relocate stress to the areas where the boxing plates didn't have good coverage. I was concerned about getting more stress near where the ball joint is pressed in, which is where the arms typically like to fail. The plates that MikeWard posted look pretty nice though and look like they go all the way up the end of the flange to get pretty good coverage. It's still somewhat of an unknown as to how much the boxing actually helps. And there is no one standard design for the bottom plates that people use so in my mind it was sort of an untested solution.

-I was also concerned about being able to fully paint inside the arm once it was boxed to prevent future corrosion issues.

-I'm not an expert welder myself so I'd have to trust someone else to not to screw up welding on parts that were no longer available at the time. I was thinking about the possibility of getting excessive heat into the arm and residual stress issues/ distortion of the parts.

I finally just decided that I'd leave the stock arms alone and that adding the bolt on side reinforcements would reduce the forces on the arms and that would be enough for me. If I were doing it today and had the money I'd probably buy a set DPI's stainless arms or DMCMW's aluminum arms. When I did my car neither of those options were available yet.

I'd be interested to know if anyone has ever failed a boxed in control arm, or if anyone has ever failed a stock arm while using Ed's reinforcement plates. I haven't heard of any failures of either setup.

[MikeWard]

Does boxing in the OEM LCAs really help? I keep hearing that the weak spot is where the ball joint is pressed in. The LCA brackets help to provide strength and reduce the flexing of the rest of the arm, right?
With how much flex those arms are under in use, the boxing can only help in my opinion.

Re the area where the ball joint is pressed in, it's good practice to add a ball joint reinforcing collar.

These LCAs had the boxing, PJ Grady ball joint reinforcing collars, new ball joints and bushes, and Eds support brackets. Belt and braces.
47792

That's about the best you can do before you step up to upgraded LCAs such as DMCMWs ally arms, or DPI Stainless arms. Although those are significantly more expensive than refurbing your own arms as above. Depends on how much budget you have to play with (I'm running DMCMWs ally arms on my car)

[MikeWard]

The plates that MikeWard posted look pretty nice though and look like they go all the way up the end of the flange to get pretty good coverage. It's still somewhat of an unknown as to how much the boxing actually helps. And there is no one standard design for the bottom plates that people use so in my mind it was sort of an untested solution.
That design has been finessed a little more since those arms were refurbished. The new plate design is now a single piece rather than two separate pieces.
47793

[David T]

While a full plate may be the strongest option, a few stiff pieces across the bottom can achieve the same effect with less weight and allow you to see inside and not trap dirt and water. Anyone attempting to modify or weld a critical part of the suspension must know what he is doing or you can damage the part in such a way as to cause it to fail. Better to leave it alone if you don't know what you are doing. The biggest cause of damage to the lower control arm is tow operators hooking their recovery hooks to them and pulling on them to move or secure the car. Next comes hitting things in the road followed by improper procedures removing and installing ball joints and/or wrong ball joints. I haven't seen one rot to the point of collapse, the frame gets there way before the LCA but I suppose it can happen.

[MikeWard]

The UK show 'For The Love of Cars' which was shown a couple of years ago, used a full plate with several holes in it for added drainage. So that is an alternative single piece strengthening plate if someone felt that added drainage was required.
47830
Given that the LCA is open at each end, plus the hole in the middle there should be more than enough drainage for any water which may get in there. Weight wise it would be a very insignificant saving using two piece vs one piece.

Agreed though, given that it is a critical part, any work like this needs to be undertaken by someone who knows what they are doing.

[Morpheus]

I'm putting my front suspension back together and I had a few questions for the group:

Is there a particular orientation these lower ball joints should be installed? I can't see that there are any alignment marks on them. They are from DMC Europe, which i presume are DOCUK units.
48625

Should I use silicone spray lube when pressing in my poly LCA bushings? The poly ends went in fairly easy by hand, but the inner sleeve seems to be a bit oversized. Should I insert the sleeve before putting in the bushing?
48626

I have the lower ball joint reinforcement collars as well. They are flat on one side and have a beveled edge on the other. Which way should these be installed on the LCA?
48627

Appreciate the help, guys.

[MikeWard]

They are from DMC Europe, which i presume are DCUK units.

Ed has had his own ball joints made, they are not the UK lower ball joints.

[ed uding]

There is no direction for the ball joint it work in any direction, it is not a cheap after market product.
Silicone is ok to install the bushing.
I dont know your source of the collar ring, but we don,t use/sale it.

Regards Ed
www.delorean.eu

QUOTE=Morpheus;212379]I'm putting my front suspension back together and I had a few questions for the group:

Is there a particular orientation these lower ball joints should be installed? I can't see that there are any alignment marks on them. They are from DMC Europe, which i presume are DOCUK units.
48625

Should I use silicone spray lube when pressing in my poly LCA bushings? The poly ends went in fairly easy by hand, but the inner sleeve seems to be a bit oversized. Should I insert the sleeve before putting in the bushing?
48626

I have the lower ball joint reinforcement collars as well. They are flat on one side and have a beveled edge on the other. Which way should these be installed on the LCA?
48627

Appreciate the help, guys.[/QUOTE]

[DCUK Martin]

Someone on the old forum FEA modeled the system and proved the lower arms do not benefit from being "boxed", something that is pretty obvious with a bit of basic structural analysis. All the "boxing" does is increase bending strength in the XZ plane* - ie carrying the car's weight, and I don't think you'll find any instances of a failure there. It also improves torsional rigidity which is perhaps a bad thing as the arm is put under torsion as the suspension moves up and down thanks to the roll bar. Boxing can also create lovely moisture traps.

Most are damaged by improper use as tie-downs or a failure of the roll bar bushes to prevent excess rearward swing when under heavy braking.

Get Toby's bush kit and other than corrosion protection, leave the lower arms alone is my advice.

(X is left/right, Y is front/back, Z is up/down)

[Morpheus]

Someone on the old forum FEA modeled the system and proved the lower arms do not benefit from being "boxed", something that is pretty obvious with a bit of basic structural analysis. All the "boxing" does is increase bending strength in the XZ plane* - ie carrying the car's weight, and I don't think you'll find any instances of a failure there. It also improves torsional rigidity which is perhaps a bad thing as the arm is put under torsion as the suspension moves up and down thanks to the roll bar. Boxing can also create lovely moisture traps.

Most are damaged by improper use as tie-downs or a failure of the roll bar bushes to prevent excess rearward swing when under heavy braking.

Get Toby's bush kit and other than corrosion protection, leave the lower arms alone is my advice.

(X is left/right, Y is front/back, Z is up/down)

Thats all I did... had the arms blasted and powder coated and re-assembled with Toby's and Ed's poly bushings. Also added Ed's stainless LCA braces for added support.

[Drive Stainless]

All the "boxing" does is increase bending strength in the XZ plane* - ie carrying the car's weight, and I don't think you'll find any instances of a failure there.
(X is left/right, Y is front/back, Z is up/down)

I find it very difficult to believe that boxing does not increase bending strength in all three planes.

For example, if I place the LCA on its side in a 50-ton press and apply force, the LCA will bend in a "U-shape" until the ball joint is almost touching the bushing. If I had boxed the arm and applied the same procedure, it would require more force since the added sheet metal will deform. As we know, metal does not deform without resistance, which makes it suitable as a material for construction generally.

If it were true that boxing did not increase strength in the Y plane, then you should be able to perform the aforementioned pressing procedure without incurring any damage to the added sheet metal; you cannot.

I would agree with you only if you could show that the arm could be bent in the Y plane without causing damage to the added sheet metal.

[DCUK Martin]

I find it very difficult to believe that boxing does not increase bending strength in all three planes.



Indeed. Can you explain how the arm is loaded along its length in anything other than bending (carrying the car's weight), and along its own axis in compression and tension?

All the failures I've seen relate to the arm being dragged rearward too far. Boxing will, if anything, make breakage more likely in this scenario.

To clarify: Yes, boxing does make the arm stronger but not in any way that's of use on the car. The original design is good, but assumed the continued health of the roll bar bushes and the sympathy of people tying the car down.

[David T]

Indeed. Can you explain how the arm is loaded along its length in anything other than bending (carrying the car's weight), and along its own axis in compression and tension?

All the failures I've seen relate to the arm being dragged rearward too far. Boxing will, if anything, make breakage more likely in this scenario.

To clarify: Yes, boxing does make the arm stronger but not in any way that's of use on the car. The original design is good, but assumed the continued health of the roll bar bushes and the sympathy of people tying the car down.

"Boxing" the LCA's will add a lot of rigidity in all planes. It will also add "Unsprung Weight". The LCA's were intentionally designed for maximum strength where they needed it and not as much were it wasn't needed. Lotus was, and is, all about "adding lightness" and in this case not adding weight were it isn't necessary. IMHO it can't hurt to box them but you do have to take precautions so you don't trap water and dirt. The LCA's won't be strong of they rot! BTW the LCA's are also twisting under braking loads and boxing them would certainly help with that.