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Brunton Stalker XL #22 Build


toedrag

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I have a lot of pictures if you have a question I can look for you.

 

I don't have a scuttle and have to order some steering parts for the next step. Not sure what I will do next. Just figuring out and ordering all the parts can be time consuming.

 

My scuttle is on the side of the highway somewhere in Florida.... :(. It was not fastened to anything under the plastic wrap and when the plastic whipped away (didn't take long), that part was gone at my next rest stop.

 

Thx, I'll probably take you up on that. Sorry about your scuttle. So true on parts selection being time consuming...I spent the better part of my 4 month lead time researching parts, but I tend to over think things. It's still fun though.

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Tried fitting the hood and ran into some issues. Will revisit that later...

 

Moving on to suspension. It's nice to move from aluminum & fiberglass work to easy bolt-on stuff like control arms & shocks. The hardware kit is very nicely labeled in individual zip-lock bags, and it's been pretty darn easy to put the puzzle pieces together. That being said, I still ended up with some questions. I'm also leaving the wheel hubs off for now since they are press-fit & bolted in, so I figure I'll get the spindles powdercoated first and then install the wheel hubs - don't really feel like doing the press-fitting twice.

 

As far as my questions, I noticed that all of the bolts I've assembled thus far in the front suspension kit have the threaded portion loaded in shear. It's probably fine [as I tend to overthink things], given that there isn't anyone complaining of bolts breaking and control arms flopping about. But, I still have to do my 'due diligence' and make sure that these bolts are acceptable for the application. They are Grade 8 zinc plated from Fastenal, so that's good.

 

These are the Control Arm Bolts:

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27042&g2_serialNumber=4

 

These are the Control Arm to Spindle Bolts; it's hard to see, but the threaded portion starts just south of the cone washer, which is also about where the loading occurs (and also is the weakest point of the bolt as I understand it):

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27045&g2_serialNumber=3

 

Pretty shocks. A question has also come up about the bushings & washers that connect the rocker (the triangular piece between the push-rod & the shock) & the bracket on the frame:

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27049&g2_serialNumber=3

 

End of Day:

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27055&g2_serialNumber=3

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Toedrag, I envy your progress!

 

Those new uprights are so much sexier than the Miata uprights that came with my early model...

 

I have a similar over-thinking issue. Personally, I think you will be fine. I just do not think you will see enough shear load to worry about it. This is a light car, and those fasteners are already larger than typical OEM equivalents.

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Brit,

 

I don't think you're over thinking things by expressing concerns about bolts that have the threads loaded in shear, especially when it comes to suspension components. Having bolts with the proper grip length is a pet peeve of mine. When I built my car, I ordered all my mounting hardware (shocks, A-rms, steering rack mount . . . everything) from Aircraft Spruce because I could get every bolt with the correct grip length. There is a reason aircraft aren’t build using bolts with the threads loaded in shear. :ack: It’s a bit more money to go this route, but I think it’s good insurance against hardware failure. My two cents.

 

 

:cheers:

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I see your point X.

 

Cheap insurance, perhaps. Do you really think you could create the load via rubber (tire) contact patch?

 

I figure the extreme force would come via impact. In which case, the suspension tearing off would be welcome energy dissipation.

 

I am not engineer! I just play one on TV (and the interwebs).

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I see your point X . . . . I am not engineer! I just play one on TV (and the interwebs).

 

. . . . . . :jester:

 

I think more about stress fractures caused by long term driving on imperfect roads and having a bolt fail at an inoportune time . . . such as when you're at the track and running down the straight at 140 +. :ack: And Brit will be seeing a lot of MSR Cresson once the car is finished.

Edited by xcarguy
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Glad to hear of some like-minded ppl :cheers:

 

Let me say that I'm NOT a mechanical engineer, so the following is likely entirely wrong.

 

Ran a few quick calculations for the 3/8" A-arm bolts in the 1/8" thick brackets:

Major Diameter = 0.375"

Minor Diameter = 0.2983"

Grade 8 Tensile Strength = 150k psi

Grade 8 Shear Strength = Fastenal doesn't provide shear strength numbers, so using the industry std of 60% of Tensile Strength: 150k psi * 60% = 90k psi

 

Assuming that the cross sectional area of the bolt/bracket that will be loaded will be no more than 1/2 the bolt circumference, I calculate the cross sectional area as follows: ((pi * D) / 2 )*bracket thickness

 

 

For Full Shank = (pi * 0.375)/2 * 0.125 = 0.073 sq in ---> * 90k psi = 6.57k pounds of force

For Threads = (pi * 0.2983)/2 * 0.125 = 0.058 sq in ---> * 90k psi = 5.22k pounds of force

 

I'm kind of surprised that it's only 1300 lbs difference between the two; I thought it would be more.

 

Moving on...since we're talking about a double-shear application for the A-arm brackets, and since there are two brackets per A-arm, I think that means the total force can be:

2*6.57k + 2*5.22k = 23.58k total pounds exerted on only ONE A-Arm to shear the bolts (using the industry std 60% of Tensile strength rule)

 

Maybe we can double the 23k number since we 2 A-arms, so maybe 43k pounds, only on 1 wheel.

 

I guess that makes me feel a little bit better about the A-arms, because I have a hard time seeing how one wheel or A-Arm could approach that kind of a load unless it was a collision.

 

In contrast, the 5/8" thick A-Arm to Spindle bolts are a single shear application. Doing the calculations in a similar way, I come up with:

Major Diameter = 0.6250"

Minor Diameter = 0.5828"

Grade 8 Tensile Strength = 150k psi

Grade 8 Shear Strength = Fastenal doesn't provide shear strength numbers, so using the industry std of 60% of Tensile Strength: 150k psi * 60% = 90k psi

 

Calculating the cross sectional is different b/c the Heim joint is 3/4", but the Rod End is 7/8". I suppose I'll use the 3/4" b/c it's smaller.

 

For Full Shank = 0.7363 sq in * 90k psi = 66k pounds

For Threads = 0.686 sq in * 90k psi = 61k pounds

 

Again, I feel a little better b/c I'm happy that the single shear 5/8 bolt can seemingly handle the load + margin of both A-arms. And, like the A-arms, I have a hard time seeing how those forces could be reached unless it was a collision.

 

--

 

I suppose the last question would be will the threads slowly saw away at the brackets and/or Rod ends making them loosen up over time? Not sure...maybe? How long would that take to notice? Who knows...

 

Stuff to noodle over...

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Brit,

 

You nailed it with your last sentence. The threaded portion of the bolt, when coming in contact (under load) with the eye of the support bracket is more than likely going to cause irregular wear over time, especially if you drive the car aggressively (my thought). Where the bolt thread and bracket eye meet, there is essentially no 'grip' to speak of. You could very well end up with an elongated eye and a worn bolt, both of which could, at the very least, cause slop in that area of the suspension. This would, in turn, effect alignment, handling, etc. Using bolts with the correct grip length is a relatively cheap, quick fix for warding off potential problems down the road.

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I am an old air plane builder, so I noticed the thread loading problem also....... I bought all new grade 8s that had the right shank length and of course removed the excess thread to save weight. When I disassembled a Vett on another project, I noticed all suspension parts were fastened properly also so it is a practice that has found its way into autos also.

Gale

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Brit,

 

You nailed it with your last sentence. The threaded portion of the bolt, when coming in contact (under load) with the eye of the support bracket is more than likely going to cause irregular wear over time, especially if you drive the car aggressively (my thought). Where the bolt thread and bracket eye meet, there is essentially no 'grip' to speak of. You could very well end up with an elongated eye and a worn bolt, both of which could, at the very least, cause slop in that area of the suspension. This would, in turn, effect alignment, handling, etc. Using bolts with the correct grip length is a relatively cheap, quick fix for warding off potential problems down the road.

 

Well put.

 

I am an old air plane builder, so I noticed the thread loading problem also....... I bought all new grade 8s that had the right shank length and of course removed the excess thread to save weight. When I disassembled a Vett on another project, I noticed all suspension parts were fastened properly also so it is a practice that has found its way into autos also.

Gale

 

Who did you buy your new Grade 8's from? McMaster's Zinc-plated Grade 8 choices are a little limited b/c they seem to always thread the last 1" to 1 5/16", which means I'd need a 3 1/4" or 3 1/2" bolt and use more washers plus cutting off the extra threads. Not a huge deal, but if I can avoid it, I'd like to. Fastenal & Grainger don't seem to list the grip length or thread length anywhere that I can find, but maybe I'm just not seeing it.

 

The AN bolts from the aircraft suppliers are an option, but I'd also have to buy new nuts due to the thread pitch differences. The shear strength of AN bolts is listed in the AN spec, and in the 3/8 size, it's higher than what I calculated for Grade 8 @ 3/8" diameter, but the shear strength for AN in the 5/8" diameter is much lower than what I calculated for Grade 8, which makes me wonder if I've miscalculated for the Grade 8's. The AN spec lists the 5/8 diameter as 23k pounds vs my calculated Grade 8 of 60k-ish pounds. But, even at 23k pounds, it's still tough to reach that force on the spindle.

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If I recall correctly, SAE grade 8 is a bit stronger than AN bolt material. Plus, if you look up the MIL-SPEC for those bolts, it uses the ultimate tensile, not yield strength. When I get back to my desk at work tomorrow, I'll post a spreadsheet I made showing strength of various AN and NAS bolts in various materials. If I forget, just holler at me in ALL CAPS to remember. :)

 

Also, the calculations I've seen so far are good, but real-world design practice needs to include margin for corrosion, and allowance for things like hitting curbs while steering. Steering loads are unequal and the 'share the load' assumption is no longer valid.

Dan

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Hmmm... Now I wish I had these aircraft bolt sources when I built my chassis. I did actually purchase new lengths of bolts in many areas, but it was due to my OCD on too much exposed threads. I did not consider the threads cutting into the mounting brackets over time... And I primarily settled for what Mcmaster had (at least it was better than the local hardware store selection). I think you guys have changed my stance on this issue. Perhaps a winter project will be switching out to ideal length bolts.

 

Toedrag, you are kind of early in your build to worry about this yet, but how do you intend to vent your CTS diff? I cannot find a source online for the vent itself, but while searching I found a lot of threads on the matter, it seems the simple press in unit (that does not come w the new diff for some reason) tends to leak. I assume it will be much worse at high speed. The dealer fix seems to be adding a length of hose to the factory diff vent, which is what I was thinking. I hate having to go to the stealership for an overpriced vent, but I cannot find another source.

 

Anyway, that is my noodle issue of the day.

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I have a great local supplier in Joplin that I can go in with a shank length list and measure each one to get what I want. There were still a couple that I had to add a grade 8 washer to the nylock side to get a nut on properly.

Gale

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Hmmm... Now I wish I had these aircraft bolt sources when I built my chassis. . . . . I think you guys have changed my stance on this issue. Perhaps a winter project will be switching out to ideal length bolts.

 

. . . . . how do you intend to vent your CTS diff? I cannot find a source online for the vent itself, but while searching I found a lot of threads on the matter, it seems the simple press in unit (that does not come w the new diff for some reason) tends to leak. I assume it will be much worse at high speed. The dealer fix seems to be adding a length of hose to the factory diff vent, which is what I was thinking. I hate having to go to the stealership for an overpriced vent, but I cannot find another source.

 

Anyway, that is my noodle issue of the day.

 

That's an easy winter project; won't take that long and you'll buy peace of mind.

 

While it's a different animal (S-10), theory is the same. When I found my rear carrier, the vent tube was broken and I wanted something a bit more substantial (and something I could easily/cheaply replace if needed). Here's what I did to the old S-10 rear. If you decide to go this route, make sure you use a tapered pipe thread tap . . . . and it has never leaked since:

 

 

http://www471.pair.com/stalkerv/gallery2/main.php?g2_itemId=27057

Edited by xcarguy
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I had planned on tapping in a brass fitting, but, ended up installing the rear before I did. Now it isn't so easy to get to and a real pain to remove. So, I am hoping the OEM one will press in easily enough, then run a tube off it (like the CTS-V guys do).

 

However, for the guys with their CTS diffs still off the car, I think your route may be ideal, X.

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I had planned on tapping in a brass fitting, but, ended up installing the rear before I did. Now it isn't so easy to get to and a real pain to remove. So, I am hoping the OEM one will press in easily enough, then run a tube off it (like the CTS-V guys do).

 

subtle,

 

I wouldn't pull the diff either. Since it seems to be the consensus among the CTS-V owners that the vent leaks, this might even be a better solution, especially for guys with news diffs that have no vent. Install the vent as you were saying and add a tube. But, before adding the tube, seal the area where the vent housing contacts the diff casing with this stuff:

 

http://www.skygeek.com/flamemaster-cs3204b1-2pt-fuel-tank-sealant-pt.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=flamemaster-cs3204b1-2pt-fuel-tank-sealant-pt&utm_campaign=froogle&gclid=CLWJxYj5rMACFehj7AodnlIATQ

 

I’ve used this on gas tanks, pipe threads, valve cover baffles, etc. and have never had it fail. If you seal the vent housing and add a tube, you should be leak free for life.

 

 

Okay . . . . :jester: . . . . . back to Brit's build. :cheers:

Edited by xcarguy
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I'm glad you guys brought up the diff venting thing...had no clue about that.

 

Tried some Rear Suspension test fitting today and ran into more questions. It appears the Toe Rod mounting location on the spindle isn't forward enough because its current position allows the toe rod to make contact with the lower control arm, and in fact, there is so much interference that the toe rod can't be moved where it needs to be on its bolt (you can see the giant gap near the frame). The inboard toe rod heim joint is just loosely sitting on a bolt, btw. In the build video, the toe rod mounting location on that spindle looks to be about 1/2" further forward than mine, which would put it in the correct location.

 

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27085&g2_serialNumber=2

 

For comparison, here are two screenshots from the Build Video. The Toe Rod mounting point is clearly further forward than mine, and the toe rod is essentially parallel to the lower control arm. But, maybe this is a red-herring. These days, I immediately think these issues are somehow user error, so I'm starting with that assumption. Then again, I'm 90% confident my rear A-arms are oriented properly, which doesn't leave much explanation for why there is contact between the toe rod & A-arm, when there should be a noticeable gap:

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27087&g2_serialNumber=2

 

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27089&g2_serialNumber=2

 

 

On the Rocker, the 1/2" holes where the pushrod mounts appear to be drilled a tiny bit too small b/c the 1/2" bolt wont' fit, but a 12mm bolt will. Looks like I'll need to buy a 1/2" drill bit to widen the hole...Plus, the opening/gap of the rocker is about 1/16" too narrow for the shock's spacers, so I suppose I'll need to grind the spacers down a bit. I tried the BFH approach and there is a noticeable flare created once the spacers are where they need to be, and that doesn't seem like a good idea...

 

Then I realized I had mistakenly used the Rear spindles on the Front (somehow on both sides of the front), and after swapping them, sadly, it didn't solve my toe-rod problem. In any case, the 4-hole wheel hub mounting pattern on the LEFT is for the FRONT spindles, and the 3-hole wheel hub mounting pattern on the RIGHT is for the REAR spindles.

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27074&g2_serialNumber=3

 

All in all, a semi-frustrating day.

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Does it clear if you move the tie rod to the top instead of the bottom?

 

Oooooh, good thought. I bet that's it. That would explain why I never found the 3.5" bolt advertised in the build video; the other control arm bolts are 2.5", and the extra 1" from the 3.5" bolt was supposed to be for the toe rod to mount. I think I noticed some extra 2.5" bolts, which is probably what they are for. Will give it a go after kiddos are in bed tonight, and it's gonna be an early bedtime for 'em. :cheers:

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