SLC rear cross brace

[Murray Dowman]

I have purchased a part built SLC that has been sitting around for some time. I am just fitting up the rear cross brace.
It fits OK without lock nuts to rod ends, but is too wide once back nuts are fitted to rod ends.
Just checking to see if anyone else has had this issue ?

 

[Joel K]

Are you using thin Jam nuts? There shoukd be enough room for them.

 

[Howard Jones]

Be careful not to sit the car on its tires fully loaded with an engine and gearbox installed without the top cross brace in place. The geometry of the rear chassis without the cross brace will tend to transfer the loads in such a way that the top chassis rails where the shocks are mounted will be forced together transversely.

This can cause quite a lot of excessive moment-arm load on the bottom chassis welds, especially at the point where the vertical solid rear chassis rails are welded to the horizontal bottom chassis rails all the way to the rear. This will also tend to force the top rear cross brace mount points together somewhat.

That may be the cause of your seemingly too wide cross brace.

Support the rear of the car, without the tires and wheels on, it at the bottom near the junction of the forward solid down chassis element and the rear motor/ gearbox mounts with a jack stand at each side under the horizontal cassis tube's forward end. Now install the cross brace. All four rod ends should be wound nearly all the way in with rod end jam nuts installed, You may need to turn each rod end out a couple of turns but that would be it. Place washers, if needed, to shim up any space between the rod end thru-hole and the u-shaped top aluminum chassis element so as not the force pinch the vertical aluminum forks/tabs.

I bet it fits now.

What is a Moment?

 

[Murray Dowman]

Are you using thin Jam nuts? There shoukd be enough room for them.

Thanks for your reply Joel - ( have looked over your build - very nice ! ) I am new to SL-C's but been around kit cars and car construction for many years.
Car has been sitting around for some time without brace in place - hence my concern at getting brace in place as soon as.
Will check chassis rails for any deflection / distortion. Front brace connection point is fairly well supported / truncated - but rear connection is not.
Yes - using thin Back nuts.

 

[Murray Dowman]

Be careful not to sit the car on its tires fully loaded with an engine and gearbox installed without the top cross brace in place. The geometry of the rear chassis without the cross brace will tend to transfer the loads in such a way that the top chassis rails where the shocks are mounted will be forced together transversely.

This can cause quite a lot of excessive moment-arm load on the bottom chassis welds, especially at the point where the vertical solid rear chassis rails are welded to the horizontal bottom chassis rails all the way to the rear. This will also tend to force the top rear cross brace mount points together somewhat.

That may be the cause of your seemingly too wide cross brace.

Support the rear of the car, without the tires and wheels on, it at the bottom near the junction of the forward solid down chassis element and the rear motor/ gearbox mounts with a jack stand at each side under the horizontal cassis tube's forward end. Now install the cross brace. All four rod ends should be wound nearly all the way in with rod end jam nuts installed, You may need to turn each rod end out a couple of turns but that would be it. Place washers, if needed, to shim up any space between the rod end thru-hole and the u-shaped top aluminum chassis element so as not the force pinch the vertical aluminum forks/tabs.

I bet it fits now.

What is a Moment?

Thanks Howard - Points you outline indicate that you have a good understanding of the structural elements involved. I may well do some additional bracing in this area. Thanks again

 

[Murray Dowman]

I think I have found the issue after looking at some pics of other builds. I have some double rod end adjuster sleeves fitted. With sleeves and rod ends wound in as far as practicable - brace is still around 15mm too wide ( not just a wee bit !! ) - back to the tools!! Being the third owner and the car at a raw stage means a few challenges - all good !!

 

[Neil]

Three jam nuts?

 

[Murray Dowman]

Three jam nuts?

Neil, Two lock nuts. Adjuster with lock nut - and Rod end with lock nut.
This means that I can adjust or pre-load the brace with everything in place.

 

[Kyle]

Any idea what year it is? Looks like an older version of the upper arms.

I always wondered how many of these are sitting out there unfinished. I bought mine unfinished, never touched, originally a 2015.

 

[Murray Dowman]

Any idea what year it is? Looks like an older version of the upper arms.

I always wondered how many of these are sitting out there unfinished. I bought mine unfinished, never touched, originally a 2015.

Possibly 10 years old. Was imported to Australia and initially electric powered ( Varley Australia )

 

[Joel K]

Murray, for sure that is your issue. Glad it wasn’t the chassis deforming.

Way too much hardware bolted on your K-brace. Anyway, if you ever need any pics of something let me know. My chassis is just about fully assembled and without the body mounted so real easy for me to snap some pics for you,

 

[Murray Dowman]

Murray, for sure that is your issue. Glad it wasn’t the chassis deforming.

Way too much hardware bolted on your K-brace. Anyway, if you ever need any pics of something let me know. My chassis is just about fully assembled and without the body mounted so real easy for me to snap some pics for you,

Thanks heaps Joel - have checked chassis, and alignment looks fine ( Thank Goodness )

 

[Ken Roberts]

Murray….is this your car? This was the all electric Varley SLC from Australia.

 

[Murray Dowman]

Murray….is this your car? This was the all electric Varley SLC from Australia.

View attachment 123952View attachment 123953View attachment 123954

Yes......Now running LSA with Graziano..........All these years on, I think the electric option - developed further, would have been a viable solution.
There is so much clutter around the LSA engine !..........looking at the Varly pics I see there are no double adjusters on the brace. They must have been added at some stage later - problem solved.

 

[Howard Jones]

Murray, As far as additional bracing goes, I really don't think the x brace needs any fundamental changes to increase its strength. When the rear of the car is all together it's very strong. There are a few tabs here and there that should be welded on both sides if they are not but other than that I think it's all good.

If you want to do something useful you might consider adding two additional triangular sections opposite the ones in the upper inside rear corners of the chassis section that forms the square around the driveshafts at the lower forward inside corners. And I believe the bell crank that dives the shocks needs to be put in double shear with a little brace from the center bell crank through-bolt to the rear upright "ear" of the solid vertical square chassis element using the bolt that holds the forward cross brace on. This is an old edition that appears on several different builds.

How about posting pictures of the adjusters when you take them out? I am going to make similar pieces to make the A-arms adjustable so the camber can be changed without taking the rod end off the through-bolt.

Once you have assembled the car and are happy with the four rod ends on the x-brace settings you will never change them again anyway. I have considered replacing them with simple solid tabs but I have never done it.

 

[Murray Dowman]

Howard, Spot on........Everything is fairly well truncated apart from those square sections you mentioned.
Will definitely be doing something there - ( My engineer commented as well ) and bellcrank pivots in double shear sounds the go.
Would appreciate any links that might show what others may have done.
Double adjusters on A arms saves so much time when doing wheel alignment !!
I have scratch built a couple of single seater cars - triangulation and loaded points in double shear is mandatory !
Really appreciate your input Howard. Pic of one of my single seaters.

 

[Ken Roberts]

Here you go……..https://www.gt40s.com/threads/bellcrank-reinforcement-plate-ideas.52607/

 

[Murray Dowman]

Here you go……..https://www.gt40s.com/threads/bellcrank-reinforcement-plate-ideas.52607/

Thanks Ken, Being a new Boy - I apologize if I am going over old ground

 

[Scott]

The thread that Ken listed above shows lots of ways to fabricate an arm that puts the bellcrank in double shear. Whichever approach you take, I suggest replacing the top misalignment spacer with one that's welded to the arm. One less part to misplace and/or shift. My approach is shown below. Everything is made from 4130 and the 3D printed cap keeps dust and water from getting into the bearing.

A few SL-Cs have had a weld on one of 2x2s crack after years of racing abuse. The ones that I'm aware of occurred in the same area - the upper bellcrank tube that connects to the front billet upright. To address any potential issue, I welded a gusset. Not necessary for a street car with some track use, but that's how I roll. A lot of heat is required to do this, so you need to strip the entire engine bay and fabricate a temporary cross brace between the billet uprights to keep things from warping.

The best way to stiffen the rear tube chassis is to add the largest possible triangles to cross brace the corners. Both sets of billet uprights create a trapezoid (i.e., billet uprights, cross brace and billet piece under the transaxle) and the engine and transaxle make it difficult to cross brace the corners. The stock configuration has an indexable link that connects the bottom of the rear billet uprights to the rear suspension cross brace. However, the links are in generic location that provides room for pretty much any transaxle and exhaust. Not a bad generic approach, but it results in a shallow angle which isn't ideal. When running your exhaust, you should consider how you might move the tab on the cross brace to relocate the link and/or add additional links to maximize the triangulation of the corners.

My transaxle has a billet bulkhead plate which allowed me to utilize it as a stressed member and cross brace the corners. Once the links are snugged up the rear becomes really solid. I took the same approach up front a tied the front billet uprights to the billet bellhousing.
'

 

[Howard Jones]

here's mine