How to fix "clunk" in rear-axle on high articulation

[skidd]

Suspension Details:
Sold rear axle with 3-link.
Koni Red coilover shocks. Mounted with body of shock "up". (not my car, but this is the orientation https://www.ffcars.com/forums/attachments/factory-five-roadsters/29484d1327867446-installing-rear-ffr-koni-coilovers-need-pics-100_7417.jpg)

Cliff Notes:
I get a substantial "clunk" in the rear-suspension as it returns from a very high articulation. It's the shock sleeve and spring.

Long Story (hope I can articulate what is happening):
On my drive home from work (yes, I commute in my Cobra), there is a low speed 90deg right turn from the road into a back alley. The road is flat and level, but the entrance to the alley has a pretty aggressive ramp up. As a result, while turning in, the front right and back left corners carry the weight of the car. The right-rear of my car momentarily comes off the ground, and the suspension goes full droop on that side. As I straighten up and the right tire goes back under the cars weight, there is a very loud "clunk" sound. I emulated the scenario in my garage with jack-stands and a couple of floor jacks. What I found happened was that under full droop and with the shock at full extension, the spring was completely unloaded and had plenty of slop. Gravity pulled down the spring from the aluminum adjuster sleeve by a good amount. As the cars weight put load back on the spring, it for a moment gets caught on the tiny lower lip of the adjustment ring, before finally just skipping off that edge and "clunking" down seated to the correct location in the ring.

So.. the question.. what is the "correct" fix for this?
Axle Limiting Straps (seems the best option)?
Grease on the sleeve so it follows the spring (seems iffy)?
Invert the shocks (don't know what that would do)?
???

[GoDadGo]

I'm running Eibach Helper Springs with a Coupling Spacer out back.

https://www.summitracing.com/parts/eib-helper250

https://www.summitracing.com/parts/eib-spacer250/overview/

You can even create a progressive spring set up by using shorter main springs with their Tender Springs if you want to go down that path.

Also, I doubt if I'll ever be driving my car that hard to know if they are working.

[skidd]

Nice! Hadn't even thought of anything like that. That seems much cleaner than trying to add straps.
Are those the exact parts you used? 2.5" ID springs?
I know what I'm installing this weekend.

[GoDadGo]

Nice! Hadn't even thought of anything like that. That seems much cleaner than trying to add straps.
Are those the exact parts you used? 2.5" ID springs?
I know what I'm installing this weekend.

Yes, I believe they are but I'll need to get under the car to look.
One thing to know, my coil overs are at the lowest adjustment point so I I can't go any lower.
Check out my ride height, see videos attached below, to see if I am sitting higher than you want to be before ordering.

https://youtu.be/CaRlqMmKIzk

https://youtu.be/uLmHEoWTEHg

Good Luck!

[CraigS]

Another option, depending what rate springs you have and how you like the current ride, is to go to softer rate springs. Think like this. Say your current springs are 350 and you replace them w/ 250s. If you count turns as you move the adjuster to swap the springs and put the adjuster back to exactly where it is now, since the springs are softer, the car would sag to a lower ride height. So then you would need to move the adjuster to raise the car. That would remove some of the spring free play and 'might' keep the spring from falling off the adjuster lip.

[Itchief]

I have to agree with Craig, I have a steep driveway and mine would make a loud popping sound almost every time I backed out into the street

Once I changed out the 350lb 8 inch rear springs for 250lb 9 inch springs with about 2 turns of preload I no longer have the popping sound when I back out of the driveway

Good luck

Rick

[NAZ]

As mentioned above, your spring rate is way too stiff -- there is seldom a reason to have a spring totally unload before the travel is topped out. However, there are advantages to using softer springs with more pre-load, not the least of which is improved weight transfer and diminishing the tendency to upset the chassis over rough surfaces. The goal is to keep the tire in contact with the ground. Too stiff a spring usually defeats that goal.

[edwardb]

Not going to defend it one way or the other. But every single Factory Five I've built the coilover springs were loose with the suspension at full hang once the ride height was set. That's one of the reason they show using a tie wrap on the shock hat. To keep the coilover springs engaged. Sounds like your noise is coming from the other end. I notice that sometimes too when I jack the car up and then when set down sometimes makes a loud noise as the spring re-seats. I've never encountered that in actual use though. Can't say that I've ever been close to completely unloading the suspension, e.g. to full hang, or lifted a tire while actually driving. Changing the springs is one solution. The helper spring suggestion is a good solution that would leave the existing spring rate unchanged. A friend in our local club did that with his and said it cured the problem.

[CraigS]

Another partial solution is to taper the end of the collar so there is less of a 'ledge' for the spring to catch on. Another option would be to find something to make a sleeve of that could placed on the threads just below the collar to eliminate the ledge. It would need to be the same OD as the part of the collar that centers the spring. Find an appropriate diameter tire tube that you could cut into 2 inch lengths and put 2 or 3 of these lengths over the threads to build up the diameter. A stack of o-rings could also do the job.

[skidd]

More good ideas. Thanks guys. I don't have enough seat time to really know if my spring rates are too high or not. But I'm liking the idea of the softer longer spring.

[GoDadGo]

I'm running Eibach Helper Springs with a Coupling Spacer out back.

https://www.summitracing.com/parts/eib-helper250

https://www.summitracing.com/parts/eib-spacer250/overview/

You can even create a progressive spring set up by using shorter main springs with their Tender Springs if you want to go down that path.

Also, I doubt if I'll ever be driving my car that hard to know if they are working.

I got under the car last night and these are the exact parts that I'm running.
Also, please know that my main springs are tie wrapped per the manual.
The helper springs just takes up the gap as they are designed to do.
They are totally flat when the car is sitting on the ground.
I may go to a 50 Pound Tender once I really drive it.
No Clunk, No Gap, No Problem!

[NAZ]

There is a lot to suspension design and I recommend you do some research into it before just throwing parts at your car. There is a wealth of information out there from reliable sources. The front and rear suspensions are a system and changes on one end affect the other. Choose the wrong spring rates and you could end up with a poor handling car or one that porpoises down the highway like a tuna boat. I use a couple suspension modeling programs to set-up mine.

From the photos I've seen I suspect my rear coil-overs have a motion ratio not too different than the roadster. I run 150 lb/in coils in the rear and they support 1416 lbs at race weight. The front coils are 250 lb/in and both ends work in harmony. The coils do not leave a gap when the shock is topped out as they are pre-loaded. My tires stay planted and I have never come close to bottoming out, even on the rough roads out here in the country.

Here's what wire ties are for: put one on each rear shock shaft and it will indicate the max travel your shock makes under actual driving conditions. I use o-rings but that requires pulling the rod end off the shock. A wire tie can be used without disassembling the shock and will tell you how much your rear suspension is compressing. I suspect you will not be close to bottoming and probably be surprised that your suspension is not moving as much as you may think.