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Hello all, Im installing the SPC adjustable control arms(SPC p/n: 94360) on my 78 and have a question about the ball joints. So the arms are compatible with the stock ball joints. My question is do the ball joints drop down thru the top of control arm(like stock)?
Original Arm:
New arms with ball joint dropping thru from the top:
OR
Going underneath and bolting from underside:
And lastly, whichever way they mount, will the bolts come from the top down or vice versa(nuts on top of control arms)?
This may not make a difference either way but Id hate to get to re-assembling everything and run into a problem because of doing it the wrong way. Thanks for any help you can provide!
I am also installing these SPC upper control arms and mounted the ball joint under the arm. The problem i see with the top mount is loss of travel on the drop of the control arm hitting the frame. I have the viking semi coil overs and double adjustable shocks. I would assume the length of your shock will determine how far the upper arm will drop before hitting the frame. Still replacing some power steering parts and reused my lower control arms with new bushings. http://www.suspension.com/spc/spc-94360
Last edited by White 68; Jan 31, 2021 at 12:47 PM.
I am also installing these SPC upper control arms and mounted the ball joint under the arm. The problem i see with the top mount is loss of travel on the drop of the control arm hitting the frame. I have the viking semi coil overs and double adjustable shocks. I would assume the length of your shock will determine how far the upper arm will drop before hitting the frame. Still replacing some power steering parts and reused my lower control arms with new bushings. http://www.suspension.com/spc/spc-94360
Hmm...so yours is opposite of bikespace’s. I wonder if the 1/4” is enough to make a difference(whether on top or on bottom). I know a lot of guys have installed these but you would think this question would have came up before...especially considering it mentions nothing about it in the instructions. I assumed that it would drop down and rest on top of the arm(like factory). But when you assume or at least when I do, its always the opposite. Trying to save a future headache before it started...
https://www.suspension.com/prodimage...60-large-1.jpg
I looked at the pictures I found online
They also sell and recommend an extended length ball joint stud due to frame contact if shocks are not short enough to stop the travel.
Last edited by White 68; Jan 31, 2021 at 01:10 PM.
Lack of a bump stop is troubling with these arms, although I have yet to go airborne.
When I bought my set, a tall ball joint was an option. I haven't checked but if that is still the case, I recommend it highly. It will get you some extra clearance if nothing else.
https://www.suspension.com/prodimage...60-large-1.jpg
I looked at the pictures I found online
They also sell and recommend an extended length ball joint stud due to frame contact if shocks are not short enough to stop the travel.
So I checked SPC’s website and I did see the .5” extended ball joints but not for our Corvettes. Saw them for several others(A bodies, G bodies & F bodies).
Mounting the ball joint under the control arm will raise the outer end of the control arm.
The thickness of the control arm mounting plate + the ball joint mounting plate.
Not necessarily a bad idea.
Howe makes 3 hole mount ball joints with extended stud lengths in 0.1" increments up to 0.9".
Mounting the ball joint under the control arm will raise the outer end of the control arm.
The thickness of the control arm mounting plate + the ball joint mounting plate. Not necessarily a bad idea.
Really? Those three mounting bolts are now constantly in tension. I wouldn't do it.
How are they in loaded in tension?
They are dynamically loaded in shear.
The upper arm just locates the top of the spindle and sees a small portion of the wheels load.
Really? Those three mounting bolts are now constantly in tension. I wouldn't do it.
Originally Posted by MCMLXIX
How are they in loaded in tension?
They are dynamically loaded in shear.
The upper arm just locates the top of the spindle and sees a small portion of the wheels load.
Not constantly in tension. Only when you get airborne, and the suspension expands to the fullest extent, only to be stopped by that upper A-arm. Or when the car is on jackstands. If the shocks stop the travel, no problem.
Still, there's a reason that GM mounted them from the top AND held them in place with three big rivets. So that's what I did, but with bolts.
Last edited by Bikespace; Jan 31, 2021 at 07:00 PM.
How are they in loaded in tension?
They are dynamically loaded in shear.
The upper arm just locates the top of the spindle and sees a small portion of the wheels load.
Statically the weight of the front of the car is just sitting on the lower arm so that's a no load condition.
But I have to compress the spring to get it in there so it wants to pull things apart when I remove the compression. And if I jack the car up the spring tries to pull things apart. The upper arm always ends up resting on the frame and the spring still has a ways to go to be unloaded.
In motion, every time I hit a bump the coil spring compresses then expands pushing or pulling on the upper arm, so obviously there are forces being transferred to the ball joint..
But .... now that I think some more about it, maybe either way there is tension on the bolts. Still doesn't feel right to put it below the arm but maybe that is just me. (and thank you Bikespace)
So Im guessing the best idea would be to install like the factory does from top through the control arms but look into aftermarket ball joints that are longer? MCMLXIX mentioned Howe joints. How much longer should I anticipate? I do not plan on goin dune jumping, however Id like to know that its what it needs to be. I dont wanna have go back in once fully assembled because its an issue...
Last edited by austinseanchris; Jan 31, 2021 at 08:16 PM.
GM used rivets because they are cheaper and faster to install than bolts, and are self locking.
Replacement ball joints use bolts because a riveting job takes skill, the right tools and proper procedure.
Almost anybody can screw a nut on a bolt.
Both are way more than adequate for the use in question.
The stock a arm is stamped sheet metal and the 3 fasteners are much stronger than the arm.
The clamp load of the bolts is more than the weight of the whole car.
The tensile strength is more than 5 times.
Except for the resistance of a stock rubber bushing the upper a arm just rotates up and down.
The long stock spring will pull down on the upper ball joint when the wheel is in the air and the a arm has hit the bump stop.
The aftermarket springs I have installed were loose in the pockets at full droop and easily installed without a spring compessor.
An aftermarket a arm that eliminates the soft bump stop and allows the a arm to crash directly into the frame is not optimal.
You are more likely to bend or break the adjusters on the arm than pull the ball joint off.
Short of a catastrophic crash the most tension load those bolts will see is when they are initially torqued up.
Good discussion on the aftermarket control arms ! When I get the viking shocks in I will see if the upper hits the frame or not. They also sell spacers and suggest no more then 3 spacers. The picture shows the 4 hole model with the ball joint on the bottom. Anyone mount a bump stop on the frame before ?
Last edited by White 68; Jan 31, 2021 at 11:24 PM.
Well for me, Ive got new springs from Vansteel with the advanced street suspension kit. Theyre about half the height of the stock springs. The new rear suspension definitely lowered the car some and assume it’ll do the same in the front. Hopefully those arms wont cause any issues...
Looking at my picture of the original design upper arm resting on the frame, It looks like these would impact the frame even sooner. Savitski assured me that the shock would prevent that and that it would never happen dynamically. Statically that's not true.
It does say "best clearance" in the blurb, but why?
There really is no easy way to add a bump stop, and there are no impact marks in my powder coated frame.
SPC Adjustable Control Arms Ball Joint Question
