Need A-arm help

Yamaha536 · 04-01-2014, 06:18 PM

Hey guys Ive been putting in some hours on this thing finally and now I cant figure out these **** front a-arms. Don't really know what I'm doing wrong here but the wheel is tilted in when the suspension is decompressed and when the suspension is fully compressed the wheel is tilted out. The hubs and spindles I'm using are off of a raptor 660. I messed around with different setups for a few hours and don't know if im over thinking things or what. Any help would be greatly appreciated!

slonomo · 04-01-2014, 06:42 PM

This is right up my alley.....

The problem is in your steering setup. To work properly, the dual a arm setup needs to have the tie rods located near the pivot point of the a arm. If not, you'll get severe bump steer. That's exactly what you describe, the wheel gets angled/steered when the suspension moves.

When I did my atv front end, I did a lot of studying of dual a arm suspensions, aka the dual wishbone suspension. The geometry needs to be spot on when building one of these, or you'll get handling that is worse than you had with a single a arm setup.

What I did to solve this: I used a rack and pinion unit that was the same width as the a arm mounting points. Mine was 14" from pivot point to pivot point. So I used a 14" rack unit designed for sand rails/dune buggies. Then, I used an EZGO TXT golf cart steering column to turn the rack. Then I ordered tie rods and heim ends with misalignment spacers to get it right.

In the pics below, notice how the heim joints for the tie rods match up with the pivot points of the a arms. Also, the tie rods need to be parallel with the a arms.

slonomo · 04-01-2014, 06:48 PM

You are also having a problem with the camber because the spindle mounting isn't quite right. It's hard to tell from the photos because they are sideways, but it looks like the bottom heim is way too far out. Also, your heims need to be mounted to the "ends" of the a arms, not underneath. This will throw the geometry off quite a bit.

What i would do is study the atv front suspensions and make yours look more like those. You might want to use actual atv parts, since they are already tried and true.

I noticed that your a arms mount at the same point/parallel from each other. On most atv's and sand buggies the a arms are not the same length and they mount up at different points. Look on my pics you'll see what I mean. The top a arm is typically shorter in overall length, and they mount up a little farther outward than the bottom ones to make up the difference.

Here's a few sand rail pics to illustrate....

Here's a good video that explains it some. You'll always have some camber change, but the idea is to limit it as much as possible.

â–ˆ Go Kart Building the A-arms #3 ( The Fullscreen Machine ) - YouTube

Yamaha536 · 04-01-2014, 07:02 PM

I like the rack and pinion setup but does it have any advantages over a gear box style that comes on it? I don't have the steering setup yet, just been trying to get the front suspension to function first. I've looked at pics of raptor 660s and my setup is close to those besides having the heim joints under the a-arm. I guess I never thought that would affect the geometry as long as the distance between the two stayed the same. My lower arm is longer in length just by adjustment. Thanks for the pics and info!

slonomo · 04-01-2014, 07:25 PM

The Raptor a arm pivot points are around 4" apart, or 2" from the center of the frame. Your's looks more like mine, mine's at about 14" apart, or 7" from center of the frame.

When you compare the mounting locations of the a arms and compare to the location of the tie rods on the stock golf cart pitman arm, they are way different, not even close. So what happens is, if you hook up your new tie rods to the existing pitman arm, severe bump steer will result. That's no good for the handling of the cart, it will want to steer all over the place, very sketchy.

The two solutions are this:
1. move your pivot points in to the same location as the pitman arm/tie rod locations, and reduce bump steer greatly, but deal with the small amount during turning OR
2. install a rack and pinon unit that will eliminate bumpsteer all together

You need to copy the geometry of the atv suspension as closely as possible. Otherwise, you will get negative results.

Yamaha536 · 04-04-2014, 07:13 PM

Thanks again for the info and pics! Definitely pointed me in the right direction. I should have time to work on it this weekend and at least get it a rolling chassis. Still have to order the rack and pinion and figure out what I'm going to do there

slonomo · 04-06-2014, 09:53 AM

It might work good enough if you relocated the heims to the very ends of the a arms instead of the bottoms.

Here's the rack I got. Works really well.

http://www.sandparts.com/servlet/the...-Pinion/Detail

You'll need a different steering column that uses u joints so you can make a shaft that connects to the rack and pinion.

This is what I used: ezgo txt 4 bolt steering column w/u joint shaft, 14" sand rail rack, custom made tie rods (the ones pictured are stock atv)

Yamaha536 · 04-07-2014, 10:04 PM

Parts are on order! Here's what I have done so far, almost a full roller.

slonomo · 04-09-2014, 06:27 PM

That looks a lot better! How does it cycle through the suspension movement? Did you try it out without the shocks and steering hooked up? If you did it right, you'll get zero/little camber movement through the suspension cycle. Once you get the steering hooked up, keep the shocks off so you can cycle it through over and over. Make adjustments with your tie rods and misalignment spacers to fine tune the "bump steer".

Looks good!

slonomo · 04-16-2014, 10:05 PM

Any update on this?

04-01-2014, 07:02 PM	#4
Yamaha536 Not Yet Wild Join Date: Nov 2010 Location: Wisconsin Posts: 21	Re: Need A-arm help I like the rack and pinion setup but does it have any advantages over a gear box style that comes on it? I don't have the steering setup yet, just been trying to get the front suspension to function first. I've looked at pics of raptor 660s and my setup is close to those besides having the heim joints under the a-arm. I guess I never thought that would affect the geometry as long as the distance between the two stayed the same. My lower arm is longer in length just by adjustment. Thanks for the pics and info!

04-01-2014, 07:25 PM	#5
slonomo Searching for The Way Join Date: Oct 2009 Location: Medina, Ohio (NEOHIO) Posts: 11,436	Re: Need A-arm help The Raptor a arm pivot points are around 4" apart, or 2" from the center of the frame. Your's looks more like mine, mine's at about 14" apart, or 7" from center of the frame. When you compare the mounting locations of the a arms and compare to the location of the tie rods on the stock golf cart pitman arm, they are way different, not even close. So what happens is, if you hook up your new tie rods to the existing pitman arm, severe bump steer will result. That's no good for the handling of the cart, it will want to steer all over the place, very sketchy. The two solutions are this: 1. move your pivot points in to the same location as the pitman arm/tie rod locations, and reduce bump steer greatly, but deal with the small amount during turning OR 2. install a rack and pinon unit that will eliminate bumpsteer all together You need to copy the geometry of the atv suspension as closely as possible. Otherwise, you will get negative results.

04-04-2014, 07:13 PM	#6
Yamaha536 Not Yet Wild Join Date: Nov 2010 Location: Wisconsin Posts: 21	Re: Need A-arm help Thanks again for the info and pics! Definitely pointed me in the right direction. I should have time to work on it this weekend and at least get it a rolling chassis. Still have to order the rack and pinion and figure out what I'm going to do there

04-09-2014, 06:27 PM	#9
slonomo Searching for The Way Join Date: Oct 2009 Location: Medina, Ohio (NEOHIO) Posts: 11,436	Re: Need A-arm help That looks a lot better! How does it cycle through the suspension movement? Did you try it out without the shocks and steering hooked up? If you did it right, you'll get zero/little camber movement through the suspension cycle. Once you get the steering hooked up, keep the shocks off so you can cycle it through over and over. Make adjustments with your tie rods and misalignment spacers to fine tune the "bump steer". Looks good!

04-16-2014, 10:05 PM	#10
slonomo Searching for The Way Join Date: Oct 2009 Location: Medina, Ohio (NEOHIO) Posts: 11,436	Re: Need A-arm help Any update on this?

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