On the topic of 3-link / Panhard rear suspension travel limiting

[LateApex]

I am curious how others have thought about travel limiting the rear solid axle on 3 link rear suspensions. I am sure this topic has come up before for both Coupe and roadster builds.

As a background, when for example the chassis is on jack stands, and the springs are correctly set for ride height, there is maybe an inch of slack in the rear coil-overs. Now I am not planning to get a lot of air over speeds bumps, but the idea of the rear suspension getting sloppy when it is fully extended, and the slap as everything comes back together when the rear touches down is a bit worrisome. I have seen a few photos of chains or other limiters in use on some builds. I am looking for the design rationale and any good examples.

Thx in advance!

[RoadRacer]

I have a few pretty severe high-speed bumps around here (on a empty fast freeway) that I regularly hit at 90-100, and get some air.. but I'm pretty sure it seems worse than it is. I have about the same as you - an inch of slack. I have uprated my springs an extra 100lbs and have double bumpstops and the car handles the "air" very well. Very stable (hence my speed). So I haven't tried to limit the travel which to me seemed it might be worse. Btw, I do have all my springs tie-wrapped to the top turret.

[LateApex]

Hi James. Thanks for the reply. What kind of "double bump stops" are you using and where are they placed?

[RoadRacer]

Hi James. Thanks for the reply. What kind of "double bump stops" are you using and where are they placed?

Yeah I bought these from summit (https://www.summitracing.com/parts/KON-7034540000) and just added them above the existing ones. hard to take a pic, but maybe this helps.

169013

[LateApex]

How do you get them around the shock shaft? Elbow grease over the top?

Dense R Us ...

Taking up the slack with extra bumpers does seem to address the "slap" part of my concern :-) And yes, tie wrap (x2) is needed to keep the hat in alignment ...

Thx!

[RoadRacer]

When the shock is out of the car it’s easy to disassemble (just a circlip IIRC) and slot on the shaft.

[edwardb]

The limiting straps you've seen on some builds (mostly dating back to donor rear suspensions) were mainly to keep the suspension from travelling further than the driveshaft was capable/designed for. Generally not an issue with upgraded suspensions using coilovers. But something to check.

I've done three Roadsters and now our Coupe, and all have the last inch or so where the spring is loose. Just like thousands of others. The instructions show putting tie wraps around the hat to keep it engaged with the spring. Other than that, I haven't done anything special and in 10+ years of driving have never experienced any issues or heard any strange sounds. Admittedly, mostly street driving and no Dukes of Hazzard flying jumps... I agree, though, it is a little disconcerting to hear it sometimes bang when dropping off a floor jack or lift as the springs re-seat. The most common way to take away the looseness, if you want to, is to add small helper springs to prevent the springs from loosening. Just one example: https://www.summitracing.com/parts/eib-helper225. I personally have no experience with this. But a buddy installed something similar in his Roadster. Seems like a straightforward approach if you really want to.

[GT_Rich]

169251169250

I don't have my kit yet but this is what I plan to use based on experience with other solid axles cars we race. These are Eibach tender springs. They come in different spring rates and collapsed heights. Pick something that is just barely collapsed at ride height. It will not only take up the extra room but it also adds load to the inside tire for the last bit of travel where a helper spring is doing almost nothing. If you have a Torsen diff, this is very helpful.

[cobrajj]

I moticed my driveshaft would bind and could not be rotated when at full droop. The driveshaft yolks were locked up, so I installed limit cables to stop the downward travel 1/2" less. That worked--no more bindup.

[GoDadGo]

169251169250

I don't have my kit yet but this is what I plan to use based on experience with other solid axles cars we race. These are Eibach tender springs. They come in different spring rates and collapsed heights. Pick something that is just barely collapsed at ride height. It will not only take up the extra room but it also adds load to the inside tire for the last bit of travel where a helper spring is doing almost nothing. If you have a Torsen diff, this is very helpful.

GT,

I'm running the Eibach Tenders on my car and they work great.
They are completely flat until the suspension unloads, which is what they are designed to do.

Steve

[LateApex]

Do you have any photos of the cables you installed cobrajj? Or could you describe your design?

[LateApex]

GT,

I'm running the Eibach Tenders on my car and they work great.
They are completely flat until the suspension unloads, which is what they are designed to do.

Steve

Steve, these look really interesting. And a simple solution to the "slap" I was in part concerned about (and $48 at Summit ...)

The post by cobrajj has me wondering whether under full "droop" I am exceeding U-joint specs. With such a short driveshaft, it's not hard to imagine how that could be an issue. Will check that shortly.

Thanx for the replies!!