heim joints on wcm ultralite /xr7 and other 7s

[WestTexasS2K]

About 1.25 to the shock then .25 tappered spacer to trailing arm then another tapered spacer after trailing arm to washer then nut. I run the shock as close to the hub as possible so that the greatest load is close to the hub. The trailing arm load is less than the shock. Just check your shock clearance thru suspension travel on the half shafts.

[jimrankin]

The spacers on my car are 2 13/16" long and thin wall steel. As the face of the hub where the spacer mates to it are not machined flat for more than 1/8" a thicker spacer would not have an advantage. If the face of the hub mating surface were machined smooth for a wider mating surface a tapered spacer would work.

I think the longer spacer has something to do with keeping the lower control arm in a flat arc to reduce bump steer.

I have designed a brace that I'm going to fab up later this week after I get some stock to work with. Should be fairly light and since the bolt only seems to stress under "side load" only needs to address shear from one angle.

Once I actually get moving on this I'll post some assembly pictures.

[Jon W.]

As an engineer, this upright design looks scary. Is this a factory design?

 

The bolts fail in bending. The "rnr" post's photo arrangement with a shorter cantilever and larger OD spacer will have a larger bending capacity than the "rss" post's photo arrangement with a longer cantilever and smaller OD spacer. To gain the greatest benefit from the spacer, the portion of the upright in contact with the spacer should be faced square and the bolts torqued to max spec to maintain the spacer in contact during bending. This arrangement will essentially allow the spacer and bolt to act as a larger beam section.

[jimrankin]

The problem is the casting at the meeting with the spacer. It is rounded off so you do not get a good "base" for the spacer to mate with. Machining this off will allow only slightly more as the casting itself is narrow at this point. Your right about the design being a "lesser strength as you lengthen the fulcrum" so going shorted will be stronger but will put the lower control rod at more of an angle so you give up suspension geometry.

Will be a few days as I'm working on something else right now but have a pretty good fix in mind. Slightly heavier wall sleeve with a flat metal brace that spans the hub and spacer, captured under the "front" of the bolt at the forward part of the hub so it takes the leverage off the spacer at the back of the hub.

[jlumba81]

Upright is from the rear of subaru wrxs. It looks weird because its made to bolt to macpherson struts.

Edited September 15, 2013 by jlumba81
added link for the pic

[Jon W.]

Jim, Exactly what I was thinking. The bolt dia is limited by the size of the upright. Add an inner parallel stiffener beam to increase beam section modulus by at least 3 or 4 times. Capture on either side of bolt and incorporate/weld the normal spacer. All spacers should be full thickness (ID just clearing OD of bolt).

 

The McPher strut design definitely results in different loading forces. The design of this upright conversion was an expedient solution but doesn't appear well analyzed resulting in a weak link. Slicks greatly increase lateral and braking loads. I'd be inspecting those bolts on a regular basis, or preferably, reinforcing the design.

[rss]

About 1.25 to the shock then .25 tappered spacer to trailing arm then another tapered spacer after trailing arm to washer then nut. I run the shock as close to the hub as possible so that the greatest load is close to the hub. The trailing arm load is less than the shock. Just check your shock clearance thru suspension travel on the half shafts.

 

loren,

that makes sense. i wonder why my shock and trailing arm were mounted in the reverse order? when i changed out the heims i considered reassembling in the order you describe but ended up using the original configuration, only using real spacers rather than stacks of washers. my configuration is hub-1"spacer-heim-1/4"spacer-1/4"spacer-shock-1/4" spacer-washer-locknut. i figured there must be some reason for mounting the shock so far from the hub as it was done originally even though it seemed counterintuitive. i guess there must be some gain in suspension geometry at the expense of strength. i think i'll have a more robust spacer made like jim's or jerry's and move the shock closer to the hub. naturally i just got finished getting all the wheels aligned...

[rss]

here is my current configuration.

[jimrankin]

I purchased two extra bolts and made two extra spacers as a planned "change them every two years" type of item when I did the first repair. Since the first original bolt failed late last year I probably should have changed them both instead of just one as they had about four years of track time on them then.

Hopefully the brace will eliminate the design weakness and be a "one time" fix. Don't want to shorten up the overall bolt length as I think the extended length is a "good suspension geometry" improvement over some of the earlier shorter builds.

[jimrankin]

Hi Loren,

Where did you source the "U" shaped brackets the Heims bolt through? Instead of cutting off the old one and re-welding it to the new bolt I'd prefer just welding on a new one. See attached photo

Also, do you have the name of the fabricator/supplier for the aluminum threaded control arm tubes?

[rss]

the spacer on my long bolt is 2 7/16" long.

 

jim and jon,

that sounds like a clever means of reinforcing the bolt. jim, please post pics of your fix.

[MHKflyer52]

Shim stock can be purchased from McMaster-Carr here is the link

http://www.mcmaster.com/#shim-stock/=oiue3o

 

I also agree with Jon W. that the spacer must be square to the hubs mating surface to reduce the shear loading at the mating point of contact and the bore as closes to the diameter of the bolt that passes through it and torqued to the maximum torque for the bolt to help reduce the shear load by presenting a larger surface to carry the load.

 

Hope this helps.

[rss]

thanks martin.

[jimrankin]

The bolts are 5/8" and even with a 1/8" wall spacer flat and torqued it's a 7/8" platform at best (and about the max flat on the casting) with about 3 1/4" leverage to the centerline of the heim joint, still a pretty good mathematical advantage even with the thick spacer. I think that for most street driven 7's it has not been a problem. Lots of track time and wide high grip tires might be what it takes to stress the bolt back and fourth too many times. I was also getting all four wheels well in the air as the 5 bypass at TH in the backwards direction is prone to it at speed. Was a lot of fun but probably not all that smart ;-)!

[WestTexasS2K]

Bracket

 

http://www.speedwaymotors.com/Speedway-Weld-On-Upper-Mount-for-Bearing-End-Shocks,32397.html

 

threaded tubes

 

http://www.speedwaymotors.com/AFCO-Aluminum-Tube-12-Inch-Long-7-8-Inch-OD5-8-Inch,40963.html

 

You may have to search for your desire length.

[WestTexasS2K]

On my first Ultralite build I took a think 3/16 washer and a tapered steel spacer and tig welded the spacer to the large washer. With the machined aluminum plug slide into the back of the hub then tightened it down. This would spread the load thru the spacer and reducing flexing and remove some strain from the bolt.

 

This design has bothered me a bit from the start. I have literally thousand laps over over the years and never a failure with this set up even with slicks and with more power than most S2k owners run. I use every inch of track available including the curbs. Our One Lap trailer probably weighs about 1k lbs loaded with a tongue weight of 150lbs. We bounced up and down some of the worst roads in America and only suffered a slightly bent bolt about 1/4".

 

I think a bracket could be made to mount the shock to that would have a multiple mounting points. Single point failures can be eliminated with that design.

 

Im not an engineer so maybe you engineering guys can give some input on that thought.

[jimrankin]

Loren,

Thanks for the info, saves me some time.

I did an aluminum tapered spacer/brace for the shock bolt bend problem about 3 years ago and has been good since. It's the long bolt running fore and aft through the hub I have had fail twice. Think that's what we are addressing now and looks like either leave in the short spacer if you are running that, as it seems plenty strong enough, or work up a brace like I'm doing to leave the longer spacer and suspension geometry in place.

[WestTexasS2K]

Oh sorry I misunderstood. So the long 5/8 bolt running thru the upright broke? Did the bolt break or did the weld break? I hadn't seen or heard of that failure either. I could see the weld breaking off the end bracket if it didn't have enough penetration.

[jimrankin]

HI Loren,

The LH side bolt itself broke just at the point where it leaves the back of the hub. I previously had the RH side bolt break at exactly the same spot. The welded on bracket has not been a problem as there is almost no leverage and it's a very strong joint since it is welded 360degrees around the bolt head. I think that my bolt failures have something to do with the long spacers that are in place. The leverage produced is proving too much for the tensile strength of the bolt and it is failing right at the point it exits the hub casting.

My spacers are about 2 13/16" long and they seem to be longer than most, probably the cause for the failure. Will shorten them up about 1/4" and fabricate the brace I've designed and that should do the trick.

[WestTexasS2K]

Most of those spacers I have seen have a 1/4 wall aluminum spacer 2.5" long.