C4 suspension LCA mounting method change?

69427

69427

The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
I've had my (lighter replacement) aluminum LCA crossmember 90% finished for quite some time, but I'm not comfortable with the regular method of attaching the lower control arms (clamping/bending the crossmember tabs/flanges to prevent the steel bushing from rotating around the attachment bolts). I'm considering trying to fabricate a shaft piece that looks like what the C3 LCAs use, that then bolts to the front crossmember (or modify a C3 shaft, as the dimensions are somewhat in the same ballpark). This would allow me to just bolt the LCA shafts to the crossmember, with no tabs or bending stress involved. (I could also shim the shaft mounts outward if I wanted to change the camber or trackwidth.)

Just kicking around ideas at the moment. Please feel free to comment about this.
 
Had to refresh my memory of the C4 rear suspension. I think this is the stock LCA setup right?

008.jpg
 
BBShark said:
Had to refresh my memory of the C4 rear suspension. I think this is the stock LCA setup right?
...................
Click to expand...

Yeah, that's a C4 rear suspension, but I'm working on the front suspension LCA (A-arms). I'm trying to come up with an alternate method of bolting in the lower control arms without having to squish any parts of the aluminum crossmember I welded up.
 
I don't know where I came up with rear suspension:huh2:

Now I get it. Could you shim/spacer the bolts so they don't bend the aluminum tabs? The C3 part is a chunk.

s-l640.jpg
 
95c3533dc377a0de73e39800fba22c82.jpg
There is a lot of stuff in that image - but I'm looking at the lower wishbone. Note how it mounts to the C3 front cross-member (K-bar/A-bar- I forget). That cross-member attaches (bolted) to 2 tabs on the C3 member.
Could something like that be in the works? It's the heavy - dog bones that bolt up.
Seems simple enough with your welding skill to fab that piece up. (No challenge intended.)
You could use heim/rod ends on either the outboard and/or inboard ends to give heaps of adjustment.

Cheers - Jim
 
vette427sbc said:
phantomjock said:
..... It's the heavy - dog bones that bolt up......

Cheers - Jim
Click to expand...

A cross shaft is going to be more than a few OZ’s... I vote some poly bushings to limit the squish. Can I assume you don’t want the tabs to squish for metal fatigue reasons?
Click to expand...

Correct. The C5-C7 LCA tabs on the cradle are part of the crossmember casting. Any tabs I put in my crossmember would have to be welded in (most likely). I'm a double E, not an ME, and I occasionally run into scenarios that are out of my comfort zone.

I can't disagree that the cross shaft would be an inefficient use of additional weight.
 
BBShark said:
I don't know where I came up with rear suspension:huh2:

Now I get it. Could you shim/spacer the bolts so they don't bend the aluminum tabs? The C3 part is a chunk.

s-l640.jpg
Click to expand...

I've entertained that. The issue, as I understand it, is that the inner bushing steel tube needs to be compressed lengthwise to lock it to the tabs, so that the tube doesn't rotate relative to the through bolt during suspension travel. I keep envisioning these shim spacers in the same light/function as the rear axle preload shims on each side of the differential carrier side bearings. Perhaps if I collect a pile of assorted thickness 1/2" washers, I could use one thickness when welding the tabs in solidly, and then use (ie: pound in) a couple slightly thicker washers between the tabs and the bushing tubes. I think I'll measure a bunch of washers tomorrow to see if I can find a range of thicknesses.

I suspect you're correct that the C3 cross shaft is a chunk of weight.
 
Been a while so I won't run any numbers - but what about 2 separate sections with a web between? Think "I-Beam". Less weight - all those spars in aircraft etc are basically similar "displaced" members.

Cheers - Jim
Rather than add a post - I'll edit...
This looks like an interesting approach:
092fe5c215d5b448c168461854954a3a.jpg
and:
Chassis_Assembly2.jpg
Replicate for the LCA - You wouldn't need a full dogbone - just some bearing points. Remember that the LCA takes at least 60% of the load and the UCA 40 or less!
For more images:
http://www.quarkdog.com/El_Camino/Pages/Sub_Pages/Front-Suspension.html
 
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phantomjock said:
Been a while so I won't run any numbers - but what about 2 separate sections with a web between? Think "I-Beam". Less weight - all those spars in aircraft etc are basically similar "displaced" members.

Cheers - Jim
Rather than add a post - I'll edit...
This looks like an interesting approach:
092fe5c215d5b448c168461854954a3a.jpg
and:
..............
Replicate for the LCA - You wouldn't need a full dogbone - just some bearing points. Remember that the LCA takes at least 60% of the load and the UCA 40 or less!
.....................
Click to expand...

Yeah, I have been wanting to copy the UCA attachment method above for the LCAs, but I have never seen it done on any cars. Corvettes don't do it so that they can use the LCA eccentrics to adjust the camber. I adjust camber via the UCAs, so I'm not constrained there. The thought/possibility that I'm neglecting a key issue that makes this (UCA) mount design unwise for use in the LCAs was why I was entertaining the dogbone (C3 design) mount for my setup. This worry may be valid, or nonsense. I don't know which.

I don't have a C5-C7 UCA to look at here (all my stuff is C3 and C4). Is the UCA rubber portion of the bushing "glued/cemented/splined" to the anchor pin so that there's no relative rotation between the materials? From any pictures I've seen, there's not an obvious steel tube (that needs compressing) between the rubber and the anchor pin like on my C4 control arm bushings.
 
I'm thinking that the forces acting on the A-arm are greatest under braking (which produces a rotational force) that tries to push the rear mount towards the center of the car and the front mount away. If you were to bolt simple plates onto the outside of the arm mounts, you could sim those plates through the bolted connection and shear forces axial to the plates would be countered by the bolts.

In between the A-arm pivots would be U bent bracket that would be bolted (or welded) but would not be a welded "tab" with a stress concentration at the bend.

This is all fabricated stuff with bolted connections which may be easier to make and with some adjustability.

4602d9a5541298.jpg
 
BBShark said:
I'm thinking that the forces acting on the A-arm are greatest under braking (which produces a rotational force) that tries to push the rear mount towards the center of the car and the front mount away. If you were to bolt simple plates onto the outside of the arm mounts, you could sim those plates through the bolted connection and shear forces axial to the plates would be countered by the bolts.

In between the A-arm pivots would be U bent bracket that would be bolted (or welded) but would not be a welded "tab" with a stress concentration at the bend.

This is all fabricated stuff with bolted connections which may be easier to make and with some adjustability.

4602d9a5541298.jpg
Click to expand...

Yeah, I like that. I could probably do that with only minor modifications to the present configuration of the crossmember. :thumbs:
 
BBShark said:
I'm thinking that the forces acting on the A-arm are greatest under braking (which produces a rotational force) that tries to push the rear mount towards the center of the car and the front mount away. If you were to bolt simple plates onto the outside of the arm mounts, you could sim those plates through the bolted connection and shear forces axial to the plates would be countered by the bolts.

In between the A-arm pivots would be U bent bracket that would be bolted (or welded) but would not be a welded "tab" with a stress concentration at the bend.

This is all fabricated stuff with bolted connections which may be easier to make and with some adjustability.

4602d9a5541298.jpg
Click to expand...

Well, I'm getting my winter project list written up, and getting the front aluminum crossmember finished is high on the list. (It's 8# lighter than the current steel crossmember.) I've kicked around several ideas, and none have seemed as feasible (and user friendly if I have to modify the mounts for suspension geometry changes) as what you have in your drawing. I'm going to go with your suggestion. Thanks, Larry. :thumbs:
 
I'm sure you'll consider (perhaps) remounting the steering rack in the design?

Just asking as I'm getting ready (as always) to once again relocate mine - back to rear steer as there is so much more room with the engine aft.

Would like to see your plans once you have something sketched out if you'd be willing to share.


added: Just found this nice looking modular approach. Could get all the key points at once - stiffness, placement of LCA/UCA, steering rack shock options...

273cbccbaf7ca58191e86859c9b0fd66.jpg
Cheers - Jim
 
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69427 said:
BBShark said:
I'm thinking that the forces acting on the A-arm are greatest under braking (which produces a rotational force) that tries to push the rear mount towards the center of the car and the front mount away. If you were to bolt simple plates onto the outside of the arm mounts, you could sim those plates through the bolted connection and shear forces axial to the plates would be countered by the bolts.

In between the A-arm pivots would be U bent bracket that would be bolted (or welded) but would not be a welded "tab" with a stress concentration at the bend.

This is all fabricated stuff with bolted connections which may be easier to make and with some adjustability.
Click to expand...

Well, I'm getting my winter project list written up, and getting the front aluminum crossmember finished is high on the list. (It's 8# lighter than the current steel crossmember.) I've kicked around several ideas, and none have seemed as feasible (and user friendly if I have to modify the mounts for suspension geometry changes) as what you have in your drawing. I'm going to go with your suggestion. Thanks, Larry. :thumbs:
Click to expand...

Glad I could help. I wish I could plan out my projects. I have be re-doing a lot of stuff lately :suicide:
 
phantomjock said:
I'm sure you'll consider (perhaps) remounting the steering rack in the design?

Just asking as I'm getting ready (as always) to once again relocate mine - back to rear steer as there is so much more room with the engine aft.

Would like to see your plans once you have something sketched out if you'd be willing to share.


..............................
Cheers - Jim
Click to expand...

I don't know if I have any pictures (I'll look), but I'm just reusing/transferring the rack mounting bracket from the current steel crossmember to the aluminum crossmember (whenever I get the darn thing completed). Most every suspension and steering mounts on my car are bolt-on pieces, which allow me to remove and modify/replace these pieces when I want to tweak the suspension (or correct a mistake). The rack bolts to an aluminum bracket (27 oz), and this bracket then bolts to the LCA crossmember. This bolt-on option came in handy a few years ago when I wanted to move the rack placement to change the Ackermann level.
 
BBShark said:
69427 said:
BBShark said:
I'm thinking that the forces acting on the A-arm are greatest under braking (which produces a rotational force) that tries to push the rear mount towards the center of the car and the front mount away. If you were to bolt simple plates onto the outside of the arm mounts, you could sim those plates through the bolted connection and shear forces axial to the plates would be countered by the bolts.

In between the A-arm pivots would be U bent bracket that would be bolted (or welded) but would not be a welded "tab" with a stress concentration at the bend.

This is all fabricated stuff with bolted connections which may be easier to make and with some adjustability.
Click to expand...

Well, I'm getting my winter project list written up, and getting the front aluminum crossmember finished is high on the list. (It's 8# lighter than the current steel crossmember.) I've kicked around several ideas, and none have seemed as feasible (and user friendly if I have to modify the mounts for suspension geometry changes) as what you have in your drawing. I'm going to go with your suggestion. Thanks, Larry. :thumbs:
Click to expand...

Glad I could help. I wish I could plan out my projects. I have be re-doing a lot of stuff lately :suicide:
Click to expand...

I can relate to the bolded above. BTDT. It used to bother me, but several years ago there was a Corvette guy (NorvalWilhelm/Strider) that used to do a bunch of fabrication stuff, and I was always envious as I had to too often redo my stuff to get it to look decent. I complimented him about that, and he was honest enough to say that he frequently redoes his stuff until he's happy with both the operation and appearance of it. I thought, wow, even some of the experienced guys aren't always happy with the results of their first design, and end up reworking things. I've gotten better at my welding and fabricating over the years, but I still redo my stuff on occasion, and I cope better with it than I used to.
 
Shortening/welding camber struts?

BBShark said:
Had to refresh my memory of the C4 rear suspension. I think this is the stock LCA setup right?

008.jpg
Click to expand...

Borrowing your picture, and hijacking my own thread here. I've been pondering shortening the strut rods to reduce the camber gain. My main concern at the moment is if it's an unwise move to modify an aluminum suspension component, and just go with steel tubing and Heim joints. I might entertain installing a Heim setup to dial in the handling, but that one non-engineer molecule in my brain likes the stock look of the aluminum struts. FWIW, I cut and narrowed the outer batwing area on my setup to fit inside the C3 frame with no problems seen, or any sleep lost, but active suspension components cause me a little more discomfort.

So, any comments/advice on the safety aspects of rewelding and gusseting the stock aluminum struts? Or should I just hope that the tube/Heim setup is lighter, and let the weight issue trump the appearance issue?

Thanks for any and all input.
 
The rack bolts to an aluminum bracket (27 oz), and this bracket then bolts to the LCA crossmember. This bolt-on option came in handy a few years ago when I wanted to move the rack placement to change the Ackermann level.
Click to expand...

As you have time, that would be a great layout/picture to see/copy.

Thanks - and Happy New Year! :trumpet:

Cheers - Jim
 
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