Bolt-on A arm modification

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TZepeSH
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Bolt-on A arm modification

Post by TZepeSH » Wed Feb 12, 2020 1:57 am

Look what I saw yesterday! A kit that would transform the stock suspension to A arm, bolt on. http://www.german-performance-parts.be/ was mentioned, and MBT.
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vwrx_las_vegas
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Re: Bolt-on A arm modification

Post by vwrx_las_vegas » Fri May 15, 2020 8:52 pm

there's plenty of options now for the a arm conversions for the bug!

https://imohr.com.br/en/

https://www.facebook.com/santiagoadaptacoes/

here's some from brazil! but they still are pretty pricey. hopefully they will drop prices soon!

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Jadewombat
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Re: Bolt-on A arm modification

Post by Jadewombat » Sat May 16, 2020 8:52 am

The Imohr setups are very interesting, however, looking at their designs I'm wondering a few things.

Is this an extension on the tie rod end? Those look like washers stacked up, not sure how sturdy that is.

Image

ALL production cars have either some positive angle on the angle of the a-arm or very close to neutral. Here on their bus a-arm setup it's very negative, not sure why:

Image

Ol'fogasaurus
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Re: Bolt-on A arm modification

Post by Ol'fogasaurus » Sat May 16, 2020 9:51 am

In engineering there is a considered limit of 3 washers used for shimming w/o going to a spacer. While the stack looks perfect the stack of washer can move and limit the amount of in-line transmitted full contact between the top and bottom pieces (I would have to draw a diagram and that is a pain in the poo-poo!)

https://www.phoenixspecialty.com/resour ... e-industry

A best description would be that the inner hole in a quality washer is (usually) not a tight fit due to the need to deal with the radius of the head to shank/threads. If you look at the bolt head from the side you can see a radius between the bolt head and the working flanges so they can be easily used to turn the bolt when tightening things up (the same use for a washer) so the gripping part of the bolt head is defined by a round limit you can see from the underside of the and the outside part of the head's inner radius.

If the washers are stacked, and stay perfect the load from the head and/or nut travel straight down the stack of washers but if there is any off-set then the loads get to be less due to the miss-alignment. The taller the stack the potential for less complete load distribution. One a long stack of washer this can be devastating hence after the need for three washers you go to a solid spacer to eliminate this problem.

Washers have so many uses and designs it is amazing but they can be misused also.

I hope this is not too confusing.

Lee
Last edited by Ol'fogasaurus on Sat May 16, 2020 11:48 am, edited 1 time in total.

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Jadewombat
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Re: Bolt-on A arm modification

Post by Jadewombat » Sat May 16, 2020 11:43 am

The other thing the more I look at it with the bus a-arm setup they have is their design is heavily dependent upon the bus "frame" to take up the loads, which it was never designed for. The stock front bus beam is designed for up and down loads because that's the motion of the trailing arms, up and down and are essentially localized in the stock bus beam.

Those a-arms are taking a side-to-side load and there's one section of box steel tubing, which means the bus chassis is taking up rest of the load which again it was never designed for with only two c-channels running through the vehicle.

Image

Ol'fogasaurus
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Re: Bolt-on A arm modification

Post by Ol'fogasaurus » Sat May 16, 2020 12:23 pm

Like the bug, the bus was designed for what it was designed for... which is not what a lot of us are using them for. :roll: :lol:

Have you noticed lately on the TV build car shows that the unibody cars are now getting the underside of the assy cut away for a ladder style of frame. With the different styles of puffed engines that are getting up into the 4 digit level and the swerving around like on the tracks (and autocrosses) the unibodies are not able to handle what the "go-have-fun" people are using them for.

Saw a '67 Nova yesterday on TV that was getting a detuned double turbo'd Chev V8 in it that was detuned from something like 4000 (? I think that is what they said anyway) HP to a tested, at the rear wheels, 2200 HP.

Lee

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Jadewombat
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Re: Bolt-on A arm modification

Post by Jadewombat » Mon May 18, 2020 7:29 pm

After more digging, it's the roll center that's affected. Unless I hear otherwise, I'm going to guess that imohr just essentially copied someone else's a-arm design without doing their homework since they're running a negative roll center.

It's really sad and weird seeing a LOT of "a-arm" suspensions on the market nowadays (just do a search on pinterest, instagram, etc.) that haven't done the trial and error of caster, ackerman angle, scrub radius, again roll center, bump steer, etc.

Just design it in 3D, cut the parts and weld 'em nowadays. Should work WAAAYYY better than the stock VW setup. Yeah right. :lol:

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Ol'fogasaurus
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Re: Bolt-on A arm modification

Post by Ol'fogasaurus » Mon May 18, 2020 9:03 pm

Jadewombat wrote:
Mon May 18, 2020 7:29 pm
Just design it in 3D, cut the parts and weld 'em nowadays. Should work WAAAYYY better than the stock VW setup. Yeah right. :lol:
Very true! There is a lot more to design than just using CAM for designing parts. CAD (assuming they are using computer aided design with Boolean logic) when done right (in this case meaning a complete design) has a lot more in it than just parts. It is the way us'n old engineers and tech designers did things; you had to prove the whole design worked not just design the individual parts.

Lee

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theKbStockpiler
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Re: Bolt-on A arm modification

Post by theKbStockpiler » Tue May 19, 2020 11:06 pm

"Is this an extension on the tie rod end? Those look like washers stacked up, not sure how sturdy that is."


The nut for the tie rod has a ways to go before it is tight as well. :D
Super beetle with attitude

Ol'fogasaurus
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Re: Bolt-on A arm modification

Post by Ol'fogasaurus » Tue May 19, 2020 11:27 pm

It is a picture I can't copy to clean up and post here but at the first look I did not notice the coupler type of join in-between the spacers and the nut. Without knowing about the fastener for sure: loads of any kind should not be applied against the threaded part of a connection as threads are weaker (rolled or cut) don't handle sheer/side loads well. If that is a long shank (the unthreaded part of the connection) then the washers being used for spacers, while not the best way to go, should be usable.

Lee

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GS guy
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Re: Bolt-on A arm modification

Post by GS guy » Wed May 20, 2020 8:07 am

Trying to fix a bump-steer problem, but something about that tie rod end doesn't add up? Looks like a standard TR end on the upper part (where the ball portion is located), but the tapered shank looks way too long for a normal TR end. With the spacer & washers, the tapered portion of the shank would be inside them and threaded portion would wind up inside the spindle? Looks like a non-standard TR end, or some other trickery going on!
Race cars do similar with a rod end as the TR end, using spacers and longer through bolt and is generally accepted practice. That doesn't work with tapered fittings. There are adapters with a tapered end to fit the spindle, with integral straight partially threaded shank to allow fitting a rod end as the TR end. Maybe they've drilled out the spindle for straight through-bolted connection? Not a TR end I've seen before (without a tapered spindle connection).
Jeff

Ol'fogasaurus
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Re: Bolt-on A arm modification

Post by Ol'fogasaurus » Wed May 20, 2020 8:29 am

I wonder if the tie-rod is being spaced up to clear the upper A-arm on full compression. That looks like it is potentially putting the fastener under some "Whoof!" loads.

The ball-joints look proper but then that is hard to tell also with everything in tight clamped order.

Interesting!

Lee

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GS guy
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Re: Bolt-on A arm modification

Post by GS guy » Wed May 20, 2020 9:23 am

Most of the Mohr pics show a fabricated spindle, so it could likely be set-up with a non-tapered TR mounting point. Not sure abut the pic shown in jadewombats post above?
Couple of things looking at Mohr's pics: The nearly parallel A-arms gives a super low ground-level roll center (same as the VW trailing arms), which can change to above and below ground level depending on bump and roll conditions, as well as move side to side significantly. This means the car will want to roll more in corners and may give unexpected "feel" during extreme maneuvers as the RC moves about. I don't see any provisions for an anti-roll bar, needed to counteract the high roll tendency. The a-arms (upper arm length and angle) also look to provide very little camber gain, which to me would be the primary reason to swap suspensions. Last, the Beetle version steering rack position and apparent inner tie rod end locations relative to the inner A-arm pivots looks like there would be a major bump-steer problem? Always hard to tell how this actually measures out or performs from just pics (armchair quarterbacking at is best!), but I'd definitely want to check those areas out carefully before spending that kind of $$$!
Jeff

maurice
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Re: Bolt-on A arm modification

Post by maurice » Thu May 28, 2020 1:53 am

I just got my imohr front suspension today. It uses either their spindles, or stock vw ones. Not sure if the steering rack helps with bump steer or not, it’s mounted pretty high and back if that helps assess.

Imohr also just came out with a sway bar for it... which I didn’t happen to order. I may try to modify my sway bar for a stock suspension setup onto that one and see how it lines up. I’m thinking I might need it but who knows

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GS guy
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Re: Bolt-on A arm modification

Post by GS guy » Thu May 28, 2020 6:15 am

Maurice - since this thread has drifted from the OP's Super Beetle based modification, you should start a dedicated build thread detailing your A-Arm conversion! I'm sure many here would be interested in what you learn about the Imohr suspension and seeing how it looks in the flesh - pics man pics!
Jeff

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