Adjustable Rear Drop Link Attachment
 

Why does it appear that all the adjustable rear drop link products available (ER, Tarett, etc.) attach to the trailing arm at the spring plate eccentric bolt instead of using the OEM point of attachment found on the 78+ arms?

Is it because there are two types of trailing arms out there that used different types of drop link attachments (up to 77 w/ball & socket, 78+ w/bolt), and going with the spring plate attachment allows a common drop link to work with both types of arms?

Or is there some inherent advantage to going with the spring plate attachment, which looks weaker to me due to the cantilever, but it must be ok as I've never heard anyone complaining about the links failing due to this design.

Can I simply attach the adjustable links to the OEM position on the trailing arm (not using the eccentric nut)? Btw, I plan to use an OEM (non-adjustable) sway bar - I just want to eliminate the pre-load when corner balancing.

Hi Frankc, I did the exact upgrade you're talking about and for the same reason. Only difference is that I went to thicker Carrera sway bars on my '78 SC. You'll see in these pics that I just used the stock mounts on the banana arms and have had zero problems. It was a nice upgrade with no down side or ill side effects. You can see in a few shots that the stock end link from the Carrera sways was very...un-round! :)

Cheers,

- Craig_D

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Craig_D,

Thank you - that's exactly what I was hoping I could do. I also went with larger Carrera bars (and later style trailing arms on my '77). Btw, are those the Tarett links?

Frank

Yes

And yes you can attach directly to the 78-89 trailing arms with threaded mounting boss, just as Craig shows.

Hi Frank, glad I could help. Yes those are Tarett links. Sounds like we have a similar set up. The new links did a great job removing slop from transitions and turn-in. It's a great upgrade.

Cheers,

- Craig_D

I've got that setup on my 85. I found that the heim joint was rubbing against the top knuckle, so I shimmed the bottom with some bronze phosphorous spacers form McMaster to get it to drop down vertical.
It looks like Craig has done the same, only he shimmed the top bolt.
Bill K

That is a good point Bill, and one I forgot to mention. I didn't like the clearance on the top, so I used some thick nickel coated washers on the top mount. I haven't had any issues with clearance since.

One other thing to do is to check the torque on all hardware after a few tank fill-ups. I had one side loosen up after a few hundred miles, so I retorqued them all and haven't had any problems for ~1000 miles of mountain use.

Cheers,

- Craig_D

If you wanna get fancy you can use rod end inserts that are designed to fit in the spherical bearing and space it away from the fixing point.

McMaster-Carr

I like that Kevin! I'm about to do a suspension refresh and will take a close look at those rod end inserts.

Thanks for the good tip (and link...no pun intended!)

- Craig_D

[I tried posting this once, but don't see it. Let me try again]

Perhaps it is because the suspension is unloaded in Craig's photo, but I don't see where the interference would be that requires spacers/inserts to be used. The new drop links are smaller in diameter where they attach than the OEM links, so I would think any interference issue would be improved with the new links. I'll look at where the links attach to the boss on the arms again tonight to see where the issue is.

YMMV
I shimmed mine because I've gone through a few drop links (on different cars) as a result of binding somewhere on the bar/linkage.
I like the drop link as verticle as possible.
+1 on checking torque every-so-often. I usually find that there is some take-up available when I do my pre-track run-down.
Bill K

Chuck, do you sell those style droplinks? I'd rather buy from you than someone else if possible.. I'm keeping stock sways on my hot rod, just upgraded the torsion bars slightly... and had the Bilsteins tweaked .. and put in RSR front spindles... :D

It's a little difficult to see but the top of the end link was very close to the mounting point on the trailing arm and I wanted to have a few extra mm of clearance for when the suspension moves through its range of motion.

I'll probably add these rod-end washer inserts: (Edit: this site doesn't direct to the actual product so click on the "Rod-End Inserts" and you'll see the "Washer Inserts": McMaster-Carr

Edit: I raised the car, and then put wooden supports under the wheels and lowered the car so that it was at stock height, but raised, so the suspension was actually loaded for this project. :) I've tried installing sway bar components on unloaded suspensions...tried.. ;)

Cheers,

- Craig_D

Sorry to kick such an old thread here...

I installed my Tarret drop links today, the sway bar seems too low and the links seem too extended. But this is where the holes lined up. Do I need to move it upward and move the links aftward, to raise the ground clearance? Any thoughts?

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Hard to tell from your picture but it looks like you have the threaded heim joint out all the way?

Thread the heim joint back in and push the end of the sway bar up to shorten it. You might need to loosen the center bushing clamp to get the bar to rotate.

"safety washers"
 

I got the same washers from Pegasus. They are often referred to as "safety washers" and are required on some formula cars to prevent the joint from coming apart if there is a spherical bearing failure. Additionally the cone shaped protrusion on the washer allows more misalignment without binding - which is crucial for the bearing to live.

I used these washers to correct a misaligned and weak bar installation on my other car. The manufacturer used some thin aluminum tubeing for spacers. They weren't the correct length for proper geometry and they crushed and bellmouthed with very modest torque on the mounting bolt. The front link geometry was particularly tbad but the photos didn't come out very well.

I bought the adjustable drop links from chuck and a 85+ 18mm bar to replace the 74 stock rear bar, as well as 85+ rear spring plates to allow for height/cornerweighting adjustments.

Looking forward to finally getting the front done so I can drive the car!!! I'll do the rear overhaul later :-)

chris
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Interesting. I got the joints tightened up and the bars sit much higher now. I did not use any fancy washers but maybe I should look into that.

Thanks for the help guys. Chrismorse, your clearance on your bars looks to be lower than mine were so I'm comfortable with where they ended up. You can see now that the helm joints are nearly tight - passenger side almost all the way; driver side a little longer due to preload adjustment.

Thanks!

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Reason why aftermarket sway bars use the control arm to mount the drop link.

IMHO, it's easier to manufacture straight sway bars then to introduce 90º bends on each end. The attachment point at the control arm is more direct.

In addition, aftermarket bars can use variable length arms to change the effective roll resistance. Can't do that with factory bars which are only available in a few sizes.

Sherwood

Actually, most of the rear aftermarket anti-roll bars I have seen want you to mount to the spring plates. That is true for Tarett and JWE (nee Smart Racing Products) anyway. The JWE folks say the geometry is better when using the spring plates too.

On my race car, I had to get special drop links from Tarett so I could use the trailing arm mounting method. Why did I use the trailing arm mount? Because my race car is quite low and the spring plate pivot point is raised quite a bit. The chassis longitudinal would get in the way and limit suspension travel. Not a good thing.

Actually I agree. I meant the attachment point toward the rearward end of the spring plate where it clamps to the control (trailing) arm. Right rear spring plate shown.

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Pelican also has a tech article with some good pictures about hardware order. I was a bit confused with the Tarrets because they have no instructions of any kind, i noticed the heim joint was at a pretty extreme angle without using the eccentric spacer provided when bolting to the trailing arm. My confusion was that spacer is used for installing on the spring plate, but also used for connecting to the trailing arm.

I plan to connect the sway bar to the spring plate when i overhaul the suspension in a few months.

Pelican Technical Article - Porsche 911 (1965-1989) - Standard and Adjustable Drop Link Replacement

Thanks Techno Duck. Below you can see what my shot stock drop links looked like. One had been struck on the road, I believe.

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Reviving an old thread...is there a drop link solution for 77 and older cars that have the old-school ball & socket connection for the rear sway bar? I purchased thicker after-market sway bars and the rear bar did not come with drop links. Thanks in advance for any advice.

Jim

+1 can the ball be modified to take bolt on drop links, could it be tapped to take a bolt? I don’t really want to change to later Ali arms especially as our 75 versions have just been refurbished

I studied this problem a bit. No one I know of has ever removed or modified those ball connections.

One company used to sell some adjustable drop links designed for this application: TRG. Their concept is shown in the pix below. Designed to use the factory plastic cups to snap around the balls.


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I do not think these are available any longer, but you get the idea. Easily replicated with some rod ends, jam nuts, alu, and drill and tap.

I decided to fab up something on my own. I bought some appropriate rod ends. And I bought some metal shaft collars (with set screws) from McMaster Carr. Their ID is virtually the same as the ID of the early-style fixed factory fixed drop links (into which the plastic cups are pressed). I drilled out and tapped the collars for a larger metric stud that matches the rod ends. I made the studs out of bolts (cut off their heads). Then I screwed the studs into the collars and had them welded in place.

So the result is a rod end that attaches to the bar, and an opposite end that uses the factory plastic bushing cups that snap over the trailing arm balls.

I have one of the excellent Tarett rear ARBs.

See picture below.

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I have not yet completely tested this arrangement-- just a few laps in September and October at Sears Point. I think it will work fine. Of course it is very important to make sure that whatever you fab up cannot behind in the range of travel you need. Binding = bad news.

Thanks Mike that looks great, do you think you could drill and tap the arm?

You are welcome.

I cannot any longer recall my exact process of inquiry regarding the modification of those balls, but it is likely I asked folks with vast street and race car experience, including those with IMSA and Porsche factory race team experience. I think those ball inserts are somehow glued in, and even if you cut them off, there is not enough remaining material there for a simple drill and tap. So I think you'd have to glue or weld in some material to drill and tap.

I should note that in my application, which is a very low race car, using the spring plates may not provide enough clearance, but I have not made confirmation. I decided to go for the arms first. I need to confirm my solution works and doesn't bind through the range of travel.

For the vast majority of applications out there, the spring plate attachment point makes sense. I am pretty sure that SRP/JWE (Watkins and Woods) did actual engineering work to support their design efforts-- check out their instruction books for more perspective. The way that their drop link set up is designed is very clever and well-sorted.

The Tarett rear ARB design (which I have installed recently) is sorted out with similar attention to detail.

The Tarett drop links are available separately and I have been told that they work very well. And they can be used with later-style factory bars. And of course you can create extra holes in these later-style bars for some adjustability (I just sold such a bar earlier this year).

One thing that folks need to ensure with the spring plate attachment point is that the fasteners are properly torqued and secured. It is well known that the fasteners for toe and camber can get loose under a variety of circumstances, and when that happens, the height drops, the rear goes to max negative and toe out. None of these things are likely good for handling.

+1
 

I was fortunate enough to start out with 20/18 Carrera bars on dad's car, so, I bought an 85 18 mm rear bar, chucks drop links and am also planning on drilling a few adjustment holes in the bar arms, for adjustability.
I have only cornerweighted one car, (77 308 Ferrari - see earlier pics of rear bar links), and decided to do what I could to facilitate getting dad's car "right".
I just purchases a set of used sway away adjustable spring plates to offer easier height adj.
If you drive in the wet, I recommend having the female rod end in the dominant position to avoid filling her up with water. Please, please do not misconstrue my ranting for sexist inclination. Perish the thought.
Juggling "safety washers" and regular washers is a good way to get the lateral link alignment near vertical.

Cheers,
Chris

My car is an 87 so these links are a direct fit for me, but we had to use a couple of washers on top and also did not need the eccentric spacers that were included.

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Good luck drilling new holes in the Carrera bars. I gave it my best shot on my milling machine and broke several tools. Gave up and got an Eibach 25mm hollow rear bar. I think I was customer #1 as they have since emailed me and told me the real hardware is now in stock. Killer bar for dirt cheap.
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