Monday, September 19, 2016

Lotus Rear Inner Toe Links

The Lotus Elise and Exige have a few unique items that should be addressed by anyone pushing the limits of their car, especially on the track. One of these items is the often talked about rear toe link. Some of these cars are over 10 years old now but there are still those who do not know about this or may not know the full story. This blog will attempt to explain the issue as well as what we do about it.

The inner toe link is on the left side of this image.

The Problem:

OE inner toe link
The inner rear toe link on these cars is a ball joint similar to other cars with a key difference. Most ball joints are a tapered fit to eliminate any relative movement in the joint. Lotus could not use a tapered fit here because the balljoint pulls double duty as the pivot for the lower control arm. That means the balljoint shaft is more like a bolt. This bolt (especially on early cars) has a tendency to loosen slightly. This allows excessive movement and fretting between the balljoint and subframe. Once this happens, the balljoint gets a notch worn in it and the strength is severely reduced. Failure of the joint usually happens when the link is loaded (going around a corner), this is an exceptionally bad time for one of your rear tires to have a severe and rapid toe change. 

The Solution(s):

Lotus had a few solutions to this problem, the first was to increase the torque spec on the nut on this joint. This seems to be fine for those who have not driven on a loose joint and do not push their cars particularly hard. The other solution they came up with was replacing these ball joints with rod ends and putting a cross brace between the two to bolts to increase the rigidity of the joints and help stabilize the bolts. 

"Track Pack" toe link brace and ball joint

A visual representation of double shear (top)
vs single shear (bottom)
We enjoy the ability to come up with solutions to problems - especially since we don't have the same cost constraints that the Lotus engineers must manage.

We attack the problem in two ways. The first is to prevent the bolt from loosening up. We do this by using a Top Lock nut, this nut has threads that are not exactly round, they are a bit distorted so they really grip the bolt once tightened. We also use special lock washers called Nord-Locks, these fancy things actually tighten as they loosen up which makes it extremely difficult for the joint to loosen on its own. Watch the video below to show how these washers stack up against other methods of bolt retention.

The second thing we do is to put the joint in double shear, this makes the joint less likely to loosen as well because it eliminates the bending force that would tend to "rock" the bolt in its joint and cause it to loosen up. Creating a double shear joint also greatly increases the strength.

Nord Lock Demo 

We have 4 different kits that solve these toe link issues to meet a wide range of needs.  Our first rear toe link brace was introduced in 2006!

TLUkit- This kit is for cars with the factory "Track Pack" brace. It retains the factory brace but replaces the expensive factory rod ends with our own high quality units. The factory rod ends do not last very long. This video below shows the movement in one of these rod ends after 25K California street miles.

DSbrace - Our most popular and economical solution. This kit replaces the factory ball joint with a strong bolt and rod end. The whole system is put into double shear (hence the DS), by using two sheet metal brackets that bolt to existing holes in the frame. We ran this solution for a long time on several race cars with slicks and aero, this solution is plenty strong and up to the task of street or track use. 

RTDbrace - This brace uses the same rod ends as the above solutions and uses a brace similar to the factory track pack. The key difference with this setup is that our brace also attaches to where the transmission mounts. This creates a very strong joint and has the added benefit of stiffening up the subframe a bit. This setup is acceptable for both street and track use. We introduced this is in Aug 2006 and it has been the gold standard in the North American market.

RTD2brace - The ultimate solution. This kit includes everything in the RTDbrace with the addition of Nitron's S99 outboard rod ends. This replaces the outer toe link ball joint with a high strength rod end for reduced deflection and toe change under load. We recommend this as a track only solution. 

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