KBS Mk7 rear suspension

Chris Kirkham · Joined: 11 Sep 2010 Posts: 14

My Mk7 has a QRE 4-link rear end. Can someone tell me if the triangular telescoping link in the photo below is necessary? I haven't seen it on other similar cars, Jeff Blumenthal questioned it, and as far as I can tell, the only thing that it can do is prevent the axle carrier from rotating. Is this an artifact from the original rear end design?

To clarify the design of this piece, the front of this link has a rod end threaded into a tube, and that tube slides (rather sloppily) inside the lower tube of the triangular link. That rod end is currently free to slide on the bolt that spans the rather wide attachment point at the front. The two pieces that make up the triangle attach to brackets on the top and bottom of the axle carrier.

Bill Schmidt · Posted: Sun Mar 20, 2011 9:54 pm Post subject:

That is what I like to refer to as a "modified 4 link" arm. Ed Kramer taught me about this piece about 5 years ago. The link is lighter than the regular 4link and it has 1 less rod end (savings$$$$) per side of the car. The slop at either end of the link needs to be gotten rid of. Use tubing as spacers for this setup. The tubing will contact the inner race of the rod end, but still allow it to rotate, like it is designed to. I have no knowledge about the telescoping part of this design. Hope this helps.
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Chris Kirkham · Joined: 11 Sep 2010 Posts: 14

I should also point out that this link exists only on the right side of the car.

Tim Friest · Joined: 10 May 2009 Posts: 20

It depends on the axel housing you have.

On the original KBS Mk 7's, it kept the axel housing from rotating because the 4-link was not attached to the housing.

If you have a modified Q 4-link, you might not need it (the Invaders don't use it), if one (or both) sides of the 4-link hook to the axel housing instead of a bearing carrier, you don't need the extra torque arm thingy.

Dave Phaneuf · Posted: Mon Mar 21, 2011 6:27 am Post subject:

Based on the picture you need it. Ask Jeff what would happen without
it when the brakes were applied.
Dave

Jeff Colegrove · Posted: Mon Mar 21, 2011 7:48 am Post subject:

That looks like it might be a pain in the butt to take belts on and off. Wouldn't it be simpler just to undo the jam nuts on a normal 4 link and twist the trailing links shorter/longer? And is it really saving that much weight?

Cory McLeod · Joined: 19 Mar 2007 Posts: 340

This is a trailing arm and is essential to the suspension. To those more familiar with the Invaders and KBSs than me - doesn't it look like someone changed the 4-link to a 3-link? Why would someone do this?
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mark vollbrecht · Joined: 07 Apr 2007 Posts: 126

No it was used to hold the axles tube from twisting as the four link as stated before. It was not connected to the the axle tube itself. the four link was connected to the bearing carriers independently for you that do not remember the fives had two Aluminum bearing carriers and no axles tube. then Q welded in a tube on them. Then the Sevens came with a axle tube like the photo. That is a kbs tube I believe. The sevens and fives also came with a two piece cross over shaft. that the belt side gear moved with the trailing arms or the swing arm on the fives. the fives originally only had a swing arm on the right rear. Q could better explain this because he was the one that modified the KBS and when Kerns could not get parts to customers Q started to just make the invaders with his mods on the cars. also that tube is not in the way of changing the belt or the gear. The gear is next to the two trailing arm that are off of the car in the picture. the gear would be just inside of the two trailing arms. the bearing mount for the cross over shaft is also off of the car on this picture. which would give you a better idea how it is setup.

Jeff Blumenthal · Posted: Mon Mar 21, 2011 10:24 am Post subject:

Just for clarity...this car has the 'typical' QRE 4-link setup with a panhard rod that is welded to the axle housing at one end, and the frame at the other end.. IMHO, the triangular/sliding trailing arm is not necessary.

With the standard 4-link and panhard rod, why would this additional trailing arm be needed?
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Chris Kirkham · Joined: 11 Sep 2010 Posts: 14

Perhaps I should post some photos from before I started tearing it apart. I'll do that later. The four links attach to the bearing carriers (that is outward of the rear sprocket on the right). As I was taking it apart it occurred to me that that this "torque arm" is the only thing that prevents the axle carrier from rotating, but Jeff thought it was odd at first glance.

So my question is this... is this a QRE four link? Does a normal QRE four link normally attach to the axle carrier or is there some other mechanism that prevents the axle carrier from rotating?

Does anyone have photos or diagrams that show what a standard four link setup looks like?

Jeff Colegrove · Posted: Mon Mar 21, 2011 11:10 am Post subject:

Cory McLeod · Joined: 19 Mar 2007 Posts: 340

Steven Thompson · Joined: 19 Mar 2007 Posts: 32

Not sure about this but there is really no reason you need this if the other end is standard Mk7/Invader 4 link. The other side (assuming it has an upper and lower link and also has the brake caliper mounted to the axle tube) will carry the torsional loads of the brake in the axle housing preventing it from rotating. Post a pic of the other side when you get a chance.

As far as why it is on there I can only think of 2 reasons. The first is to somehow support the other side of the gear and prevent flex on a smaller diameter axle (waste of time). The second is that you've potentially created a torsion bar using the rear axle tube as the twisting element if the other side of that tube is connected to the 4 link. Since the 3 link is mounted on only one pivot it constrains the axle tube to rotate as the same angle as the arm itself (in other words if the 3 link displaces upwards at a 5 degree angle the axle tube must rotate with it as they are constrained to be at 90 degrees per the mount design). Assuming the other side is mounted on 2 links of a 4 link this should create a twist in the tube from side to side and therefore add roll stiffness. See if you can put the rear suspension at a roll angle without torquing the tube. If you can't they've put this in as a swaybar. It's also pretty much illegal if it does.

If the other side of the 4 link is not connected to the same center tube and the brake caliper is then it is to react the brake loads.

Steve

Jeff Blumenthal · Posted: Mon Mar 21, 2011 5:35 pm Post subject: Re: 4 Link - Mk7

Chris Kirkham · Joined: 11 Sep 2010 Posts: 14

Here's a photo of the left side, fully assembled.

And, here's a photo of the left side, intact enough that it can be understood. The links are disconnected from the carrier, but are still present, and some of the parts from the axle (hub, spacers, rotor, etc.) have been removed.

So I now clearly understand that this "torque arm", or whatever we want to call it, is required to prevent the axle tube from rotating because the bearing carriers are indeed separate from the axle tube on each side. Both bearing carriers are aluminum.

Steven's analysis is correct given his assumptions, but he must have missed that the front end of this link has a telescoping end. This telescoping end prevents the link from having any influence on the path of travel of the rear end. All it is capable of doing is preventing rotation. In other words, it does not force the axle to move in an arc defined by the length of the torque arm, because the torque arm's length is variable.

Thanks for helping me talk this through. I was fairly certain that I understood it, but without a greater knowledge of other configurations and cars to look at, I wanted to make sure that I wasn't off base.