Boxed Trailing Arms

I did a search on boxed trailing arms and I still have questions. Everyone that answered the previous threads seems to think it just adds unsprung weight and is unnecessary. I went to the track today, I pulled into the pits during my runs because the car felt weird. While checking underneath I saw that I have a crack down the inside of the passenger trailing arm, it continues underneath and at the very bottom where it looks like the two sides meet it is opened up about 1/8" wide by 3". I'm thinking that boxing them might not be such a bad idea. I'm still learning to drive the car at speed but I'm starting to post some decent times. My car has a 2.7 twin plug that is putting out about 240 h.p. I'm running Hoosiers. I don't want to just buy a new trailing arm and next year be sorry I didn't box it now while it's apart. So what do you think? Should I box them or not?

[J P Stein]

I dunno.
I admit to being ambivalent about the boxed arms.

I thing you need to analyze the crack to see if boxing the arms would have kept it from happening. Did the crack propragate from the welds? I *think* the boxing is done to keep them from twisting. I know the factory welds are sh** at the split .....humm, poetry....sorry. Anyhew, if the box pieces don't overlap the begining of the crack...act as a doubler plate, they prolly wouldn't have helped.

You get to look at it, what do YOU think?
A pic would be good.....when you have a chance. I'd really like to see it.

I don't have a digital camera ( waiting till they come down to $1) but I'll try to borrow my friends and post a pic. Pushing on my tire from the top I could flex it in and out. At first I thought it was a bad wheel bearing.

[campbellcj]

From what I understand (recently learnicated on this), if you weld in the boxing kit properly, by taking the time to spot-weld every one of the little holes after you do the main seams, then you will end up with a very solid structure.

BUT...then you have a rock solid arm, which just means that if you exert a huge amount of force on it, such as bouncing off a curb or whatever, you're just that much more likely to bend or break something else on the car. Such as the 'ears', CV's, or whatever else feels like busting loose to relieve the stress.

I'm still not convinced on this mod either, but since my car had the kit already, we took the time to clean up the welds and rebush the arms, and will use them. If I didn't have the kit already, not sure I would spend time and money on it.

I got under the car to take some pics and It's really worse than I thought. Besides the large crack in the trailing arm the third picture is a crack at the top of the ear on the chassis where the trailing arm mounts. The crack returns forward a couple of inches and looks like it will be tough to weld. Where do I get a replacement trailing arm. Is that a Porsche only part? (Please say no.)

Now I'll try the pics:

[campbellcj]

I noticed a good sized pile of arms in the back room at Ottos (Venice).

If he doesn't have a good one for you, try Rich Bontempi at HPH up north.

[Dave at Pelican Parts]

You should be able to get one from your favorite Porsche parts place. I would suggest giving the Sales guys at Pelican a chance: 888/280-7799.

--DD

[campbellcj]

Originally posted by Dave at Pelican Parts
You should be able to get one from your favorite Porsche parts place. I would suggest giving the Sales guys at Pelican a chance: 888/280-7799.

--DD

I thought PP didn't deal with used stuff anymore...or are the arms still available new at a less-than-stratospheric price?

[Dave at Pelican Parts]

Used? He already has a used one...

Anyway, if he wants new then he might try our Sales guys. Otherwise, there are a number of people/places that have used ones.

Gary Emory, Tom Woodford, Br@d, Glenn of Don and Glenn's Swap Meet fame, Camp Counsellor Craig, etc.

--DD

Pelican guys say they don't have anything in stock. Porsche says they are no longer available, stratospheric pricing was not enough incentive. So it appears used is the only option. Hopefully I won't find one quite as used as mine.

[Racer Chris]

The trailing arms are pretty sturdy, and don't flex as much as the ads for the boxed kit would have you believe. With the big engine you run it might be worthwhile though, especially if you have other upgrades and run on very wide tires. Buying a pair of used arms and boxing them before installation seems like it might be a good idea. I wouldn't expect them to crack just because they weren't new. The photos look like there was a previous repair that failed maybe? I've never seen anything like that. The chassis crack is much more common. It's a good idea to reinforce the chassis/suspension mounting area.

[Dave at Pelican Parts]

Heck, it's a really good idea to check the suspension pickup areas (and all the critical areas of the car for that matter) !!! I know of several cars that have not had all of the factory spot-welds welded. Jon Lowe, PCA's national 914 tech guy, found only about 1/3 to 1/4 of the spot-welds in the suspension console of his club racer were actually welded. It appears to have been this way from the factory!!

--DD

[J P Stein]

I agree with RChris....looks like someone was in there with a torch & welder (and not too good with the latter). Top pic.

The arm pic shows a failed weld around the tube for the caliper access ....not to mention the tube itself.....WAG.....the hole for the tube is where it started.

I've got a couple spare arms (doesn't everyone?) put away for a rainy day. If you really get to hurtin', lemmeno.

Thanks for the offer JP, I think I found a used one for a reasonable price. I'm still considering boxing the arms, I run 245/45-16 rear Hoosiers. I'm going to install 180# springs and adjustable perches while the suspension is apart. My mechanic is an expert welder and reinforced the ears on his 911 after they ripped off. If he can reinforce mine and I box the trailing arms I might be good to go for a while. He can't start on it for 10 days so I have time to decide.

[Dave at Pelican Parts]

Anderson said that it helped when they ran Walt Maas' 914-6 race car in IMSA. They did find that the trailing arms flexed, and boxing them evidently did help that problem. He did not relate the testing procedure, nor what if anything else was 'fixed' at the same time...

--DD

[Ron Meier]

If you found one - good

If not - Glenn Sager ( a914luvr@earthlink.net ) (and I - ronmeier@rccauto.com ) have several.

Location - Riverside, CA

Thanks for the offer Ron, I picked one up from Glen yesterday in breezy Sandberdo.