How flexible do you think a stock, trailing arm is Options

[Brando]

I'm wondering what the deflection is with stock bushings (IMG:http://www.914world.com/bbs2/html/emoticons/popcorn[1].gif) Definitely good info in this and I can't wait to see how a reinforced trailing arm compares.

[Dead Air]

This is a cool thread. I'm just thinking out loud and sorry about the rough graphics.

The "focus" of the stress would move out board and not be a static force?
Uhhm...
The twisting force would change relitive to the trailing arm as the approach changed. Not just the Ft. lbs.
Do I make any sense?

[SpecialK]

QUOTE (r_towle @ Dec 19 2005, 09:08 PM)

so, is carbon fiber an option here.. Can it be effectively bonded to steel... Rich

I've got Boeing's best composite engineers (three of them actually) working on this very question. I posed the question to Jim, a senior engineer at Boeing (and a motor-head at heart), about which would be the most structurally sound way to stiffen my 914's inner longs with the 900' roll of uni-CF I got recently.....lay-up and bag the material directly to the longs, or make molds (or use a parting agent between the longs and composite) and bond the composite long stiffeners to the longs using a high-strength structural adhesive. He loves this kind of shit (anything car related) and said he was going to get with a couple of other guys on the subject and "crunch some numbers" (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) . Personally, I think the HSSA method would be stronger than laminating directly to the steel, but either method would virtually eliminate corrosion from forming between the long (or swing-arm in this case) and stiffener. I may just make a couple of test billets while I'm off for Xmas break utilizing both methods, and abuse them until something cries "Uncle"..... (IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif)

[Katmanken]

Kevin,

I think the reason that people don't glue to steel is corrosion. A rust bubble can place a lot of stress on a glue joint and would probably enlarge until it caused delamination- right when you don't want it.
(IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif)

I have done a lotta aircraft structural type work with structural epoxy and rivets but aluminum doesn't form rust bubbles as readily as steel. The rivets are used both as reinforcement and as a means of squeezing the glue as thin as possible (max strength). Glue joint strength is primarily dependent on adhesive strength and glue area.

Ken

[jhadler]

Hey Chris,

Any new data on the trailing arm flex experiment?

-Josh2

[ChrisFoley]

Hey Chris,

Any new data on the trailing arm flex experiment?

-Josh2

Yes, just a small amount of new info.
I was measuring the flex with the digital level mounted on my lever arm. After further examination it appears that there is measurable flex in the mounting end of the lever, so I moved the level to the brake mounting ears on the trailing arm. This change subtracts 0.3 degrees from the previous measurements.
Also my latest reinforcement, as described in the last picture, did not reduce the flex any more than a single bulkhead in the middle of the trailing arm. My next test will be two bulkheads, parallel to each other, several inches apart.

[brant]

Chris,

did the measurement changes (the .3 degrees) subtract from both the before and after?

so .7 before
and .5 after


brant

[J P Stein]

How's about filling the arm with some hi-density foam.
The problem would cleaning the inside of the arm well enuff to have the stuff adhere.....plus selection the right foam. I don't know what is available.

Molten aluminum poured in would be gud too.......then start drilling holes. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[goose2]

QUOTE

How's about filling the arm with some hi-density foam.

Not as crazy as it sounds....we once filled all the cavities in a bugeye racecar with foam and got a noticible increase in chassis stiffness. We abandoned the idea later though...when we had to do some welding on it (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) Another possible filler would be a lightweight epoxy mix with lots of micro-baloons.

[J P Stein]

QUOTE (goose2 @ Dec 29 2005, 09:52 AM)

Not as crazy as it sounds....we once filled all the cavities in a bugeye racecar with foam and got a noticible increase in chassis stiffness.

I may be crazy, but I ain't stupid. (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

If a guy could come up with sumthing to pour in and not add more than 4-5 lbs of weight you'd be in fat city.
Epoxy: maybe half full & rotate along the long axis till dry.
Maybe add an inch of wall thickness.

Thinking outside the box (NPI)
What else do I have to do while sanding off orange peel? (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

[Brett W]

There are several companies that sell a foam injection kit for cars. Sport and Compact did a project Miata with one of the kits. I know all of the new Ford SUVs have a two part foam injected into the hollow areas on the chassis. There is a substaintial difference in the harmonic resonance levels as well as chassis stiffness.

Many of our chassis are fairly clean on the inside of the longs and other areas. You could do this and probably pick up some serious reductions in NHV. The problems are when you go and put this in rusty areas it will not bond, nor will it stop the rust. Also if you do this to a chassis it will cause problems if you try and weld over it. Poof, your car burns to the ground.

Otherwise it would be a good upgrade. You could acid dip the arms and then inject them with foam. Won't five substantial improvements in just the arms but it will help out a little.

[ChrisFoley]

Chris,

did the measurement changes (the .3 degrees) subtract from both the before and after?

so .7 before
and .5 after


brant

That's about right, except I am using 1.1 for the original stock measurement and I get 0.8 with the level attached to the brake caliper mount (ie. vertical).

Today I added a second bulkhead to the most recently modified trailing arm. There was no further improvement - still a deflection of 0.5 deg.

I think I'll try adding some Chrome-Moly sheet in selected areas next. (IMG:style_emoticons/default/idea.gif)

[ChrisFoley]

QUOTE (J P Stein @ Dec 29 2005, 04:32 PM)

If a guy could come up with sumthing to pour in and not add more than 4-5 lbs of weight you'd be in fat city.

4-5 lbs???
JP, I'm barely willing to add one pound. (IMG:http://www.914world.com/bbs2/html/emoticons/cool_shades.gif)

[J P Stein]

QUOTE (Racer Chris @ Dec 29 2005, 05:34 PM)

QUOTE (J P Stein @ Dec 29 2005, 04:32 PM) If a guy could come up with sumthing to pour in and not add more than 4-5 lbs of weight you'd be in fat city. 4-5 lbs??? JP, I'm barely willing to add one pound. (IMG:http://www.914world.com/bbs2/html/emoticons/cool_shades.gif)

I hear ya, I ground down my trailing arms castings, cuf off the ears for the backing plates and all them little support ears to get 2-3 lbs off them.....even painted them yellow (YPAF, ya know (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) ). But I'd put some back on to stiffen em'.....but not them fishing lures "they" sell for the job.

[ChrisFoley]

I had time for one more trial before 2005 ran out. (IMG:style_emoticons/default/smile.gif)
This was a continuation of the modifications to the first trailing arm I upgraded. This one already had the bulkhead added to the center of the box section and a fancy gusset between the box and the pivot shaft tube.
My observations indicated that the pivot shaft tube was flexing significantly, after the box section was stiffened, and the gusset didn't stop that. I decided to add a reinforcing layer over the exposed front side of the pivot shaft tube, as shown in the picture. The overlay is .065wall mild steel, a half section of 2 1/2" od tube about 7" long.
The original trailing arm flexes about 0.8 deg. under stress.
With the bulkhead added the flex drops to about 0.5 deg.
The gusset didn't stiffen the trailing arm noticeably - at least not in torsion.
The tubular overlay resulted in a reduction of the twisting to 0.4 degrees.
The trailing arm "feels" stiffer when I put my weight on the lever and is 50% stiffer than stock by the numbers. (IMG:style_emoticons/default/smile.gif)
I will probably use these three reinforcements (that weigh less than 16oz.) on my race car's trailing arms, but there is one more area where I want to focus my attention.
The part of the trailing arm that is pocketed to make clearance for the brake caliper bothers me. I want to fill that in so the pocket no longer exists. I think there is still room for a front caliper after filling in that area.

[TravisNeff]

Looks great as usual Chris, good job!

[slivel]

This is where my arm cracked multiple times. After boxing the arm it is the weakest point it seems. The fix was to press in a piece of mild steel tubing (same size as my roll cage, I think). The arm was drilled in multiple spots and then welded to fix the pressed in tube to the arm. This seems to be a good fix - I do stress my suspension severely andso far no cracks. The additional advantage is that the weight that you add is mostly sprung weight and not unsprung as it would be if it were far out on the moment arm of the suspension. I am sure that this also minimizes flex in this area.

[Al Meredith]

Chris great stuff! thanks. My $.02 . Have you thought about using a lazer pointer witha magnetic base on the part you are monitering. Then put a piece of sheetrock on the ceiling to put the bean on. This way you would see deflection in two axis at the same time. Comments? Al

[brant]

So Chris,

now that you about have it nailed down.. one thought still sticks in my head.

how much negative camber can you easily dial in?
would it be basically limit-less?
I don't know that I need any more, but it makes me think......

here is what I think: "too bad I have monoballs at this point, its just not worth new wheel bearings and re-doing the monoballs."

two more questions sir.
since you have the arm with the old style kit handy.
how much does that one weigh, and how much total does your lovely new one weigh?

do they both have similar bearings and pivot shafts (weight wise)

and finally,
I lost track a tiny bit.
with the 2nd style of measurement, what is your measurement for an old style reinforced arm. Is it also at .5 deflection now? (I know at one point it was .8, but I'm not clear if it was remeasured when you switch measurement modes)

brant

[URY914]

QUOTE (Al Meredith @ Dec 31 2005, 07:03 PM)

Chris great stuff! thanks. My $.02 . Have you thought about using a lazer pointer witha magnetic base on the part you are monitering. Then put a piece of sheetrock on the ceiling to put the bean on. This way you would see deflection in two axis at the same time. Comments? Al

Good idea, Al. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

Paul