Lowered suspension makes the rear literally bounce around? (Page 3/3)
fierosound MAY 16, 02:21 PM
oops

[This message has been edited by fierosound (edited 05-16-2020).]

fierosound MAY 16, 02:23 PM
oops
cvxjet MAY 16, 03:01 PM
Dang-nabbed double posts- I always kill Pennocks window and then re-enter after doing a post (Hitting back button causes double posts)

Couple of things, some of which has been stated....I was driving Redwood road, chasing some MCs, and hit a big dip which caused my car to bottom out- once started it kept hopping until I stopped- there was no damage to the sturts, just bottomed out and started hopping. I then started working on increasing the amount of travel before hitting the bump-stops; Eliminated the normal Fiero bump stop and cut down the top of the strut to allow some entry into the bump-stop housing at the top...Now I have approx' 2.75-3" of upward travel before it hits the smaller rubber bump-stop up inside the top bracket

Next up, had a problem driving home across bridge; If I hit the gas, it would pull to one side, if I let off or hit the brakes it would pull the other way...Inspecting everything, I noticed that one of my GR-2s was wet- oil! Leaking....I had had Arraut convert them to coil-overs and possibly at that point he cracked one while removing the spring seat. If you have this weird problem, check your struts; I pulled mine off and that left one could be pushed down but would not return up- loss of gas pressure and some of the fluid. What I am saying here is, make sure your struts are working and properly filled/pressurized. Take them off and push 'em down, then watch- within a few seconds they should extend back up.

Third, while driving home after the Redwood road fiasco, I noticed the car was driving very strange- the camber had changed from all of that hopping......So check your alignment.
Threedog MAY 16, 04:54 PM

quote
Originally posted by fieroguru:

Bouncy ride when lowered is caused by 4 things.

Physically riding on bump stops... this happens all the time where people do not verify suspension travel range of motion for desired stance. When you ride on the bump stops, you have virtually zero suspension travel, no shock/strut dampening control, and the car bounces based on the tire sidewall stiffness.

Riding on the end of motion of the shock and strut. I see this all the time... If you remove the springs and bump stops from a Fiero suspension and raise the wheel as high as possible, the shock and strut will bottom out before the tire is within an inch of the fender/top of wheel well. So if you target a 2" fender gap, you have 1" of shock/strut travel and you will bottom them out. If you target 1" or less fender gap, you will be riding on the shock/strut bottomed out. Depending on how much travel you have, this could be a slamming sensation where you have some travel and then hit the limit, or just constant bouncy like riding on the bump stops (because you are). This is why most flip the rear strut hat (on 88s and fastbacks) and alter the front shock mounting point with spacers (88s) or relocating holes to maximize the available travel. This is more of an issue in the rear if you didn't install new bump stops with your new strut

Worn shocks/struts - zero dampening. This will have large amounts of body movement and will oscillate at a much slower rate will will take a long time to settle down after a bump (6+ oscillations)

Springs to stiff for shocks/struts to properly dampen. This is normally found after a bump where it takes several 3-5 oscillations to settle down. Stock front and rear spring rates are about 145 (88) to 195 (84-87) and 145 (88) and slightly higher for the 84-87. Going with 350+ lb springs will be an issue with dampening control. 300 lb/in normally isn't too bad with the KYBs, but I recommend a lot of 250 lb/in rear coilovers.

OP isn't the first one to complain about the ride with the eibachs as several sets of the coilovers I have sold were to replace poor riding eibachs. I haven't ever had the eibachs to measure spring rate, but I suspect they are 350+ spring rate

I have also ran across one brand new KYB strut that had about 2-3" of free movement w/o any dampening effort. So event new parts can be bad... that is why it is good to check prior to install.




This is exactly what happens. It is oscillating. Thank you so much!

My first attempt is going to be to cut the bump stops. I did not install new ones that were correct. It would also explain why they car seems not to move a lot when I push down when it is parked. My fear is that if I cut the bump stops a little, it will seem fine for a while but if i hit a big enough bump I may lose control, is that a possibility?

If cutting the bump stops doesnt work, I may go with a new setup in the back completely.

Patrick MAY 16, 05:25 PM

quote
Originally posted by Threedog:

I bought new struts when I installed my lowering springs in the rear. They are the stock struts with springs that are 3/4in lower, so not much.




quote
Originally posted by Threedog:

My first attempt is going to be to cut the bump stops. I did not install new ones that were correct.



I didn't cut the rear bump stops in either of my Fieros, one with a duke and one with the 2.8 V6. Both with 5-spds. Neither car has ever bottomed out the rear suspension. Both cars are lowered at least an inch in the back. (I also flipped the rear strut hats on both cars.)

There may be something wrong with the inherent design/function of the Eibach springs, or with these particular KYB struts (faulty?)... but I find it awfully difficult to believe that just a 3/4-in drop alone could be causing all these issues.

However...

I don't know what tranny the OP's Fiero has, but it does have a 3800sc. Perhaps it's a lot heavier and therefore has issues with these springs and struts that a "stock" Fiero wouldn't experience.

[This message has been edited by Patrick (edited 05-16-2020).]

fierosound MAY 16, 07:16 PM

quote
Originally posted by Threedog:

This is exactly what happens. It is oscillating. Thank you so much!

My first attempt is going to be to cut the bump stops. I did not install new ones that were correct. It would also explain why they car seems not to move a lot when I push down when it is parked. My fear is that if I cut the bump stops a little, it will seem fine for a while but if i hit a big enough bump I may lose control, is that a possibility?

If cutting the bump stops doesnt work, I may go with a new setup in the back completely.



Are you sitting on the bumps stops? I suppose it is possible and should be investigated.
Wheels off with weight of the car supported on stands under the control arms to see what's going on.
theogre MAY 17, 06:52 PM

quote
Originally posted by cvxjet:
Next up, had a problem driving home across bridge; If I hit the gas, it would pull to one side, if I let off or hit the brakes it would pull the other way...Inspecting everything, I noticed that one of my GR-2s was wet- oil! Leaking....I had had Arraut convert them to coil-overs and possibly at that point he cracked one while removing the spring seat. If you have this weird problem, check your struts; I pulled mine off and that left one could be pushed down but would not return up- loss of gas pressure and some of the fluid. What I am saying here is, make sure your struts are working and properly filled/pressurized. Take them off and push 'em down, then watch- within a few seconds they should extend back up.

That's often cause by iffy cradle mounts and off-center loading of the "dog-bone."
That can twist the cradle thus "steer" the rear axle when you hit the gas etc.
Contrary to popular myth even solid mounts for 84-87 and 88 can have this problem if cradle hardware is loose etc.

------------------
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