Box Panther Converging 4 Link: What I did.

[Alice87]

Hey yall, I pieced together some upper & lower rear control arms for my ‘87 Wagon and posted about them over on the 2024 thread a few months back. I've put just over 500 miles on them, including driving through some pretty hectic rain storms these last few weeks. I got some interest from other members and was asked to start a thread on them… so here you go:









The parts I used:

For uppers:
X2 Allstar Performance Heavy Duty 3/4in Suspension Tube (7in length) part # ALL57448
X2 Allstar Clevis End Right Hand Threaded Part # ALL99320
X2 Chromemolly PTFE Lined 3/4-16 in. Left hand Threaded Rod Ends
X2 Allstar Performance High-Misalignment Rod End Bushings/Spacers part # ALL99321

For Lowers:
X2 Allstar Performance Heavy Duty 3/4in Suspension Tube (17in length) part # ALL57468
X2 Chromemolly PTFE Lined 3/4-16 in. Right hand Threaded Rod Ends
X2 Chromemolly PTFE Lined 3/4-16 in. Left hand Threaded Rod Ends
X4 Allstar Performance High-Misalignment Rod End Bushings/Spacers part # ALL99321

I used 1/2" hardware from my G-Body days which work well with the spacers (it's either grade 8.8 or 10.9 high strength nuts/bolts/washers).

I went for the strongest I could get within reason. DOM steel .160 thick tubes with plenty of thread engagement. 3/4” Chromoly PTFE/Telfon lined spherical rod ends (QA1 style). Ive used these heims before on a IROC-Z I sold a while ago… I put over 22K miles on them without noises or looseness developing here in North Texas. I personally wouldn't use standard heims as they were loud and vibrated in my experience on a 4th gen F-Body project.

In regards to the Box Panthers Converging 4 Link: I was having way too much axle movement both straight line and in corners. I have 250lb springs & bilsteins; however the rear would occasionally dance about. The main culprit was the old rubber bushings…

This is not my first rodeo with a converging 4 link rear suspension, as my ‘88 Monte had a very similar rear suspension as the Box Panthers. As a matter of fact the control arm dimensions are very similar. Technically the box panthers are prone to *less* bind as the arms are longer than G-Body’s (Box Panther: 20.5” Lowers & 12” Upper VS G-Body’s 19” Lowers VS 11” Upper). When I put heims/tublers in the Monte, it made a major difference in both straight line & cornering for the better. It felt much more smooth and predictable.

Anyway, I'm used to just buying pre fabricated control arms with heims ready to bolt on and go, preassembled with correct spacers and all. However there is not much aftermarket for the Box Panthers unfortunately. Weird considering the Boxes drive real nice and are cool looking IMO.

My original plan to fix my rear axle dancing around was to use Poly bushings on one end and rubber on the other pressed into the original panther arms. However no vender sells the correct replacement rubber bushings anymore unfortunately. So I started digging to see if G-Body bushings and arms would work on Box Panthers: they do not. The diameter of the bushings are different. The lengths are also different as mentioned above. However the width of the arms are almost identical.

The more I looked at my old UMI arms from my 3rd gen F-Body the more I realized how easy it would be to assemble them my self. And there you have it, i’ll keep yall updated on how many miles I put on them and how the heims perform... based off my previous experience I think they will last a while. I personally torqued everything down real good and used blue loctite on the jam-nuts just to be safe.

So far on the wagon it’s been the same experience as with my old Monte. It hooks up and handles much better.

-Kyle

[Alice87]

In regards to using heims on both ends of the lower control arms.

In theory the triangulated upper arms should not allow side to side movement.

I personally have experienced less side to side movement of my axle in the wagon with these tubular/heim uppers. With the original uppers and lowers the inside sidewall of my 295/50 tires would rub on the inside body just above the frame on hard turns.
I applied some gym chalk on the areas where the tire rubs and have driven the wagon thru some twisty back roads and can confirm they no long rub. So side to side movement on my wagon was reduced with the heims & tubulars. More Info on that in a post below, I measured how much movement there is side to side.

In regards to Heims/Rod Ends on the street: Ive had quite a bit of experience with them. I personally will never run standard heims again. They make too much buzz like vibrations and eventually start to clunk as tolerances loosen up.

On the other hand, the stronger chrome moly PTFE/Teflon lined heims have worked out very well for me. I put about 22K miles on a set of these heims on my old ‘89 iroc without any issues. Compare that to the standard heims i had on my ‘88 monte… those standard heims had to be lubricated constantly to shut them up (i ended up replacing them with roto joints).

If you dont want heims you have a few other options:

Threaded rubber cylindrical bushing
Threaded poly cylindrical bushing
Roto joints/johnny joints/delspheres:

Roto joints are similar to a heim but they have bushing cups surrounding the heims ball to keep out metal on metal contacts.

You can also run a combo of bushings. For example on my uppers I have heims on the frame side and a rubber bushing on the axle side.

Note for the axle housing bushing: there is no bearing that I'm aware of that has the correct dimension's to work in a box panthers axle. Mustangs use a much smaller OD mounting bushing from factory and as a result the aftermarket only sells small OD bearings. You can use ES part #3345 for axle bushing if you cant find rubber. Just be aware of poly bind, with a heim on the frame I assume you would be ok but I cant confirm that… last thing you want to do is crack your frame mounts or egg out the mount holes dues to polys inability to flex! Use a lot of synthetic grease on the sides where it mounts to the upper arms…. May even try not tightening the bolts down quite as much (within reason, obviously you dont want the nuts backing off!).

[Alice87]

Note: this post and the ones above are all a bit of an info dump. I have been writing down observations for the last few months... I'm only just now posting it all.

I confirmed the side to side Lateral movement with the rear end in the air/body on jack stands and with my floor jack putting pressure via differential pumpkin. By slowly rolling my floor jack side to side, i recorded a max of 1/2" of lateral movement. In theory the 4 link should prevent side to side movement. In comparison with the factory arms: the original uppers allowed nearly an 1.5" of lateral movement side to side! The inside of my 295/50 tire sidewalls would just barely rub on hard cornering with the original arms. Like I said earlier, my axle was dancing around a lot. Now they dont even come close to rubbing, so these tubular uppers have definitely helped keep the axle centered.

Ideally I would use a heim or roto joint in the upper differential housing mounts to completely eliminate side to side lateral movement & prevent bind. However the Box Panther bushing mounts are oversized in comparison to the much smaller ones being sold for mustangs/other ford 8.8’s…

So that leaves me with the cylindrical bushing dilemma: Either run urethane in the diff mount and have better straight line tracking but have bind (even well lubed and not torqued down urethane tends to bind).
Or run rubber in the diff and have a bit more lateral flex side to side but overall reduce bind.

I may just press in some NOS rubbers for now and see how they compare to the original shot rubber. There will certainly be side to side flex. However i think it will still be an improvement. The tubular uppers with heims on the frame end have already proven to reduce lateral movement.
I'm thinking with new rubber on the diff in combo with the tubulars/heims, the new rubber will limit side to side lateral movement a bit more. It wont completely prevent it, but it should help. If I don't like how that turns out I will use urethane in the diff. I just don't like the idea of going through all the hassle of burning out rubber within a foot of the gas tank… just to find out the urethane gives me a bunch of binding issues.

Some more observations: After driving a fair bit (especially in slow speed parking lot maneuvers), I noticed that the lower arms will rotate. From what research I've done: As long as both ends are still in the same plane, that is normal. They will still be able to articulate, As long as the uppers arms are keeping the axle centered, the rear end cant laterally walk side to side or bind. Interestingly, I have heard no clunking or any feedback with the lower arms fully rocked one way or the other. They tend to straighten back out when driven in a straight line.

-Kyle

[Alice87]

One other thing, I'm using a chassis mounted sway bar from the Aero-up years. I mounted it just like a 3rd & 4th gen F-body Camaro/Trans Am. Originally I used OE F-body axle mounts I had laying around in the shop with some spacers, but just recently switched over to BMR weld on mounts (part # SMK006) that give me more space as to not come in contact with shock absorbers with axle at full droop (frame on jack stands with axle suspended in the air). I'm using OE F-body end links and drilled into the box frame to attach them.









-Kyle

[friskyfrankie]

Cool! Are you going to repair that hole right near the muffler?

[Alice87]

Cool! Are you going to repair that hole right near the muffler?

Which pic you referring to?

[sly]

I think this hole is the one he's referring to. But if you zoom in on that, it's just a large weld blob on the exhaust hanger casting a shadow. So it's not a hole.

[Brown_Muscle]

Wow! This is well documented and written. The rear end movement in boxes have always bothered me, it's the weak link in handling once all other bolt ins have been upgraded, not to mention just plain disconcerting when making sudden turns or turning at high speed and hitting a bump. My biggest concern would be binding...but it appears you've solved that issue with the different combination of heim joints and the rubber bushings.

I was actually considering putting a parallel 4 link with a panhard bar to help eliminate the lateral movement...

It seems like you were able to do this for a pretty reasonable cost overall, which is impressive. How is the ride quality now? NVH? (noise vibration harshness?) I certainly noticed with poly bushing alone in stock police arms the bumps are far more noticeable

[Alice87]

Phil, It’s a good idea, a parallel 4 link with a pan hard rod or wattslink is probably the best all around way to center a solid axle car without getting too far into uncharted territory... its a much better suspension than the triangulated 4 link IMO. Good news is the box’s converging 4 link has relatively good over all geometry when lowered: the uppers are parallel with the ground and the lowers are appropriately lower on the axle side in relation to the chassis side. As long as you use heavier spring rates the arms should stay in a good position through travel.

The uppers made a big difference in the firmness and overall harshness of sound. The lowers did not make too much of a difference (keep in mind this is in comparison to the original arms with old bushings).

It rides firmer than factory for sure, and road noise is increased a little bit. The main thing is interior parts vibrating. I went through my whole wagon with 3M foam tape and silenced all the various plastic on plastic noises… I suspect that if you did not attempt to silence a rattle trap interior, the ride would be given the illusion of being much harsher.

With the AC on and radio turned off I cant tell a difference in noise. With AC off, I can tell there is a little more road noise… but nothing extreme. Definitely not enough to affect a conversation. In comparison, I have to speak very loudly in the Jeep with passengers. It has off road tires and is far and away much louder and harsher of a ride.

-Kyle

[friskyfrankie]

Which pic you referring to?

The next to last photo just above my original post.

[Alice87]

Oh, Its like Sly said. My dual exhaust has some cheap welds lol.

[massacre]

Great thread, thanks for posting!

[gadget73]

The bushings through the upper ear of the axle is not the same as on a Mustang? hm, I'd have expected all 8.8 rears to use the same bushings up there.

and yes the lateral location on these is crap and it just gets more-crap with bad bushings.

[friskyfrankie]

Oh, Its like Sly said. My dual exhaust has some cheap welds lol.

Looks much more like a hole but then it is a photo so seeing it in person should determine it. It is coming right off the muffler near where the exhaust pipe connects to it.

[87gtVIC]

The bushings through the upper ear of the axle is not the same as on a Mustang? hm, I'd have expected all 8.8 rears to use the same bushings up there.

and yes the lateral location on these is crap and it just gets more-crap with bad bushings.

that’s correct. Not the same. I ran into that issue when I was trying to install some spherical upper axle bushings marketed for mustangs.