Adjustable Upper Control Arm for '88 Front Suspension

[Series8217]

I'm almost done with my adjustable upper control arm for the '88 Fiero front suspension. This arm is a bolt-in replacement and fully adjustable for camber and caster. It also makes camber gain adjustable to a small degree because the factory adjustment method can be used to move the inboard axis, while the control arm length and offset can be adjusted with the threaded sleeves.

The new control arm consists of off-the-shelf parts, mostly from SPC (Specialty Products Co.) since they have good support (I got an e-mail response for some part dimensions after-hours the same day), and good availability (most parts in stock at Summit Racing). I intend to utilize the original '88 Fiero control arm. New cross-shafts are available from the Fiero Store for $70. I can't beat that with a custom heat-treated steel part.

The only custom parts are the reducer bushings to use the stock cross shaft, and the 1/4" steel ball joint plate.

Total cost per side is a little over $200 but you'll save $70 if you re-use your stock cross-shafts.

This is the current draft:

Note that the joint on the left side of the ball joint plate in the image will actually be a welded stud and there will be no hole there. The other 3 joints are bolted solid after adjustment.

I need to confirm caliper clearance (I want to make sure it clears the 12" WCF brake kit) and design the reducer bushings, but otherwise it's just about done.

The full parts list will be posted as soon as I build and test the first set.

Related Reading
Increasing steering axis inclination on '88 front suspension
Track Days in the DOHC Fiero

[The Dark Side of Will]

Awesomez

I want to build UCA's like that for The Mule, but I'd vastly prefer rod end pivots, though.

Why would you need a custom heat treated steel part for the center shaft? Just use a piece of 1" square bar, drill and tap a hole in from each end. Use (big!) shoulder bolts through the control arm pivots. Drill the mounting holes and you're done.

Have a link to the pieces you're using for pivots? Are those essentially steel on steel bushings that have to be greased?

[Series8217]

Why would you need a custom heat treated steel part for the center shaft? Just use a piece of 1" square bar, drill and tap a hole in from each end. Use (big!) shoulder bolts through the control arm pivots. Drill the mounting holes and you're done.

The 12 mm cross shaft mounting holes are on a 114 mm spacing and the inside edges of the bushings are 174 mm apart, so there is enough room for a little under 24 mm of thread length per side. However, all of the shoulder screws with an 0.625" or smaller shoulder (same as the bushing ID) have 1/2"-13 thread. I don't like the idea of using 1/2"-13 thread shoulder bolts in single shear for suspension loads.

Have a link to the pieces you're using for pivots? Are those essentially steel on steel bushings that have to be greased?

They are greasable delrin bushings inserted into metal housings. I just didn't model the bushing as a separate piece. Here's a link: http://www.summitracing.com/parts/sps-92025

I see no reason to use rod ends over these. The rod end design is more complicated. You need to use expensive (and weaker) high-misalignment rod ends, or you need to bend your threaded tubes so the rod ends are straighter in alignment. The reducer bushings to adapt to the stock cross shaft are also potentially more complicated due to the misalignment angle they have to accommodate.

[The Dark Side of Will]

The UHMW bushings I made for The Mule are worn out. Obviously to replace them I'd need to make more. I'm on a spherical bearing kick because I want quick/easy replacement with industry standard parts. When the delrin bushings wear out, will you still be able to get more?

Also, with fixed length through-bolt bushings like those, the length of the center sleeve has to be managed closely so that it can take enough clamp load to keep the bolted joint from failing, but NOT deform such that the bushing binds, while not being so loose that there is perceptible (significant?) end play.

I'd actually make the mount a little more complicated and make the cross-bolt through the rod ends vertical. That is, however, pending some BOTEC's to be sure that the angular misalignment capabilities of the rod-end can provide for the entire range of motion of the suspension.

[Series8217]

The UHMW bushings I made for The Mule are worn out. Obviously to replace them I'd need to make more. I'm on a spherical bearing kick because I want quick/easy replacement with industry standard parts. When the delrin bushings wear out, will you still be able to get more?

When they wear out, I'll make new ones that have a 12mm ID so they fit my stock cross shaft without any reducer bushing .

Also, with fixed length through-bolt bushings like those, the length of the center sleeve has to be managed closely so that it can take enough clamp load to keep the bolted joint from failing, but NOT deform such that the bushing binds, while not being so loose that there is perceptible (significant?) end play.

This is true. It has the same limitations as the factory-style bushings as far as control of fore/aft loads goes. However, it's far easier to make some reducer bushings with an accurate length than it is to design and build a cross-shaft.

I'd actually make the mount a little more complicated and make the cross-bolt through the rod ends vertical. That is, however, pending some BOTEC's to be sure that the angular misalignment capabilities of the rod-end can provide for the entire range of motion of the suspension.

Not a bad idea from an engineering standpoint. I thought about doing that too, since it would also be easier to accommodate double-shear mounting for the rod ends at the inboard pivot point... but it greatly complicates the construction of the control arm, and the whole point of this exercise (for me) is to adapt readily available off-the-shelf components so that I can easily service the car through race car supply shops. Nobody stocks Fiero parts anywhere near the racetrack.

The title of this thread should really be "practical/minimal effort fully adjustable upper control arm". Adequate off-the-shelf beats more-than-adequate custom in this case.

[The Dark Side of Will]

When they wear out, I'll make new ones that have a 12mm ID so they fit my stock cross shaft without any reducer bushing .

I used 3/4" drill rod for my center bushings, and the holes in the UHMW wallowed out. 12mm is going to have an even higher contact pressure and greater tendency to wallow out. Delrin may be tougher than UHMW in this respect, though.

This is true. It has the same limitations as the factory-style bushings as far as control of fore/aft loads goes. However, it's far easier to make some reducer bushings with an accurate length than it is to design and build a cross-shaft.

How big are the holes in the delrin? Can you use a thin sleeve and 16mm bolt?
I don't think it would be hard to make the center block... just may take a little consideration. For example, you could offset the control arm pivot bolts inboard or outboard from the mounting bolts in order to put them into the block deeper. This could also allow you to flip the mounting block around to have a "digital" camber change and/or greater ability to adjust the length of the control arm.

Not a bad idea from an engineering standpoint. I thought about doing that too, since it would also be easier to accommodate double-shear mounting for the rod ends at the inboard pivot point... but it greatly complicates the construction of the control arm, and the whole point of this exercise (for me) is to adapt readily available off-the-shelf components so that I can easily service the car through race car supply shops. Nobody stocks Fiero parts anywhere near the racetrack.

The title of this thread should really be "practical/minimal effort fully adjustable upper control arm". Adequate off-the-shelf beats more-than-adequate custom in this case.

Other than the body mount, the only difference in OTS components for the rod end design vs. the delrin design is the use of rod ends vice delrin bushings. While the body mount would be moderately intricate for the early crossmember, I think a version for the '88 crossmember could be made from 1.5" square tubing fairly easily.

[Series8217]

I tried to measure the taper on a Rodney Dickman upper ball joint and it's pretty close to 10 degrees. Even a small error in measurement will change the angle by quite a bit, so I'm going to assume it's 10.

This means the standard Moog K5208 ball joint should fit... which means a custom ball joint plate is not necessary. SPC 92006 should work.

Other than the body mount, the only difference in OTS components for the rod end design vs. the delrin design is the use of rod ends vice delrin bushings.

... if the parts can tolerate the amount of misalignment you'll get by using straight adjuster sleeves.

[The Dark Side of Will]

I tried to measure the taper on a Rodney Dickman upper ball joint and it's pretty close to 10 degrees. Even a small error in measurement will change the angle by quite a bit, so I'm going to assume it's 10.

This means the standard Moog K5208 ball joint should fit... which means a custom ball joint plate is not necessary. SPC 92006 should work.

Sweeet. I haven't been down to my dad's place yet to get you the taper dimensions... Cool that you were able to get them otherwise.

[Series8217]

I should mention a few things about NASA Time Trial rules since it does influence the implementation of the control arms.

NASA Time Trial rules assess an additional +2 points for altered ball joints (E.16). Using the stock ball joint makes the adjustable delrin-bushed control arms a +4 point mod (E.9) instead of +6 total (if the K5208 is used then both E.9 and E.16 are assessed). That is is enough savings to make the stock ball joint worth using since there is no advantage to the Moog balljoint except not having to fabricate the plate.

The minimal-points mod for camber and caster adjustment might be useful for someone else out there if the free mod (slotting the stock adjustment holes) doesn't provide enough room for adjustment, and they don't otherwise have points assessed for similar rear suspension mods:

If you don't already have spherical bearings in the rear lateral links, a front control arm with rod ends at the inboard pivots would be assessed an additional 3 points for "metallic and/or spherical-design replacement suspension bushings" (E.22). Moving the inner pickup points (which would happen with one of Will's rod end mounting bar designs) is assessed +6 points for relocation of front suspension mounting points (E.13). This is separate from the +6 for rear mounting points using fieroguru's lateral link brackets.

Based on my reading of E.9 and E.22, using lateral links that only have rod ends at the outer pivots is included in the +4 for E.9 and is NOT assessed +2 for E.22. Once the inboard side is involved, E.22 is assessed.

Rear adjustable lateral links are assessed +4 points for "replace, modify, or remove control arms" (E.9). This means the delrin-bushed adjustable control arm is a "free" mod if you already have the lateral links, since E.9 has already been included. The rod-end bushed adjustable control arm is likewise included if you already have adjustable rod-end lateral links, since E.22 was already assessed. Otherwise it's +2 points to have the rod ends in the UCA, and you might as well put them in the lateral links.

[Series8217]

I tried to measure the taper on a Rodney Dickman upper ball joint and it's pretty close to 10 degrees. Even a small error in measurement will change the angle by quite a bit, so I'm going to assume it's 10.

This means the standard Moog K5208 ball joint should fit... which means a custom ball joint plate is not necessary. SPC 92006 should work.

I received the K5208's and tried to fit one in the '88 Fiero knuckle. Unfortunately, the balljoint stud is too large. It fits in the lower balljoint hole but not the upper. It may be possible to drill out the upper balljoint hole to accept the larger stud, but then the taper won't be engaged far enough to keep the grease boot compressed and the ball joint will be effectively longer. I also don't know how much the knuckle would be weakened by drilling it out to fit the K5208 stud.

[The Dark Side of Will]

There are tapered reamers on the market

[Series8217]

There are tapered reamers on the market

I know. The angle is fine, the stud is the wrong size. The stud is physically larger. There isn't a lot of extra meat around the existing taper hole or stud region.

[Series8217]

Done with the first design.. going to prototype it this weekend if my ball joint plate material comes in.

[Series8217]

I have all of the parts and materials now, so I'll hopefully have a pair of these built by the weekend.

[The Dark Side of Will]

Cool. I'm thinking that it will be pretty easy to do the same with the early style front suspension. I may have to have a little fun getting around the spring, but it shouldn't be too hard. I think I can use the lower plate from my anti-dive kit as the basis for a structure that holds vertical pivots for the rod ends.

[The Dark Side of Will]

In thinking about this a little more, I'm not sure I could make a purely triangular control arm that would clear the upper spring seat.

However, I could use a u-bend to make one that would. http://www.chassisshop.com has "threaded tube adapters" like these:

http://secure.chassisshop.com/partdetail/C73-890-2/



made for 1" tubing with ~.058 wall thickness and 5/8-18 rod ends.

With a single U-bend, two threaded adapters and a couple of VERY simple flanges/tabs, I could make UCA's for the '84-'87 suspension. They wouldn't be as infinitely adjustable as the ones for '88's, but would be extremely adjustable.

Columbia River has the 1" U-bends I need:

http://www.mandrel-bends.com/catalog/1- ... d-496.html

I need to stretch a tape across my spare crossmember... but this could be surprisingly easy.

[fieroguru]

Here are some that a friend made for the 84-87. Simple ball joint bracket and some threaded tube with a slight bend. Not as light as what Will is suggesting, but still quite simple to make.

[Series8217]

In thinking about this a little more, I'm not sure I could make a purely triangular control arm that would clear the upper spring seat.

However, I could use a u-bend to make one that would. http://www.chassisshop.com has "threaded tube adapters" like these:

http://secure.chassisshop.com/partdetail/C73-890-2/

made for 1" tubing with ~.058 wall thickness and 5/8-18 rod ends.

With a single U-bend, two threaded adapters and a couple of VERY simple flanges/tabs, I could make UCA's for the '84-'87 suspension. They wouldn't be as infinitely adjustable as the ones for '88's, but would be extremely adjustable.

Columbia River has the 1" U-bends I need:

http://www.mandrel-bends.com/catalog/1- ... d-496.html

I need to stretch a tape across my spare crossmember... but this could be surprisingly easy.

I was looking at those inserts as well when I saw that I would need to use bent tubing to accommodate rod ends at a reasonable misalignment angle for the inner pivots. However, I didn't realize that pre-made u-bends were available in the appropriate wall thickness. Nice find!

[Series8217]

I cut out the ball joint plates on the CNC mill tonight.



Getting close...

[Series8217]

I finished the control arms over the weekend and installed them on the car last night. I had no problem dialing in 3 degrees of camber and 10 degrees of caster. No clearance issues that I can see so far, except the upper caliper slide bolt when using 12" C4 rotor brackets from WCF. There appears to be less interference than with the stock arm though.

With 10 degrees of caster the steering arm has moved up quite a bit. Not good for bump steer. I may reduce the caster some, or look into some bumpsteer correction. Unfortunately its not easy to relocate the steering rack, so I'll need to find a good solution at the steering arm end. I'd prefer to continue running stock settle sealed ball joints instead of rod ends.

Pics and parts list to follow.. I gotta get some sleep!