The suspension mystery continues, and I don't know where to go from here. (Page 1/6)
Threedog AUG 01, 05:09 PM
Car: 3800SC 87 Fiero

Issue: The car bounces back and forth like there are no shocks on acceleration above 20 mph.

Basically, I will be accelerating and everything will be fine and dandy until I hit a bump or jerk the steering wheel back and forth quickly. Then the back of the car gets WAY out of line. It bounces back and forth so much that if I don't let off the accelerator I would lose control of the car. If I let off the accelerator, the car straightens itself back out after a bump or two. If I brake, the issue stops immediately (the harder I brake, the faster the bouncing stops).


This started when I went to lower the car. I had it on lowering springs, I took it to the alignment shop, drove it home and had this issue. I also replaced literally every part of the suspension.

What I replaced:
- Struts in back twice, shocks in front twice, didn't fix it. I currently have coilovers on the rear, but going back to stock in the rear did NOT fix the issue.
- Springs: I have tried lowering springs, stock springs, did not fix the isssue
- The bushings in the rear are old poly ones, the front are new poly ones
- All ball joints are brand new and from Rodney Dickman
- Rear tie rod ends are brand new
- I replaced all bolts(A-Arm, Cradle, and Strut tower bolts) with metric 10.9 and grade 8 bolts of the exact same size and length. I have tried going back to the stock bolts everywhere, didn't fix the issue.


Does anyone have any idea what could be causing this?
IMSA GT AUG 01, 05:23 PM
I know this may be a stupid question but are you sure the upper frame rails haven't rusted through? It seems like you covered all the bases with the suspension so I would look at the frame just for the hell of it.
Here is a pic from someone in Canada who had issues. You need to remove the wheel well liner to see this part of the car. If this is the issue, unfortunately the car is finished.

You can see that when this occurs, the only thing holding the entire rear of the car together is the front cradle mounts.

[This message has been edited by IMSA GT (edited 08-01-2020).]

Threedog AUG 01, 05:36 PM

quote
Originally posted by IMSA GT:

I know this may be a stupid question but are you sure the upper frame rails haven't rusted through? It seems like you covered all the bases with the suspension so I would look at the frame just for the hell of it.
Here is a pic from someone in Canada who had issues. You need to remove the wheel well liner to see this part of the car. If this is the issue, unfortunately the car is finished.





So, they have certainly not rusted through, there is next to ZERO rust on the vehicle (it is from New Mexico and the body has like 50k miles).


The only way I could see those nut housings being loose is if they got over torqued and broke the welds, but I was able to get them as tight as ever when I checked just now.
Rickady88GT AUG 01, 05:44 PM
When you say "bounce" is this up and down or does the car sway back and forth?
Threedog AUG 01, 05:46 PM

quote
Originally posted by Rickady88GT:

When you say "bounce" is this up and down or does the car sway back and forth?



Honestly, its both. Or the up and down is so severe I can't tell. If I continue to accelerate and let it get worse and worse the front suspension bottoms out.

It is definitely not a "sway". I currently can't do more than 30 miles an hour because it is so bad.
Threedog AUG 01, 05:48 PM
I did shorten the front bump stops by about an inch. Could that have caused it? I have stronger springs in the front now, and I feel like because it only happens under acceleration the issue has to be in the back.


Edit: Nevermind, the issue existed before and after I shortened them.

[This message has been edited by Threedog (edited 08-01-2020).]

qwikgta AUG 01, 07:47 PM
Not sure if you covered the rust issue or not but I guy in the local club had an issue like this and it was b/c his cradle was loose b/c of rust issues. All new parts and it could not hold an alignment. Front cradle was the issue. Car felt loose all the time. Even put in a new front cradle thinking it was bent or something but it was the space frame that was shot. He parted the car b/c it had a lot of great stuff on it and thru the frame away.

Rob
Threedog AUG 01, 09:11 PM

quote
Originally posted by qwikgta:

Not sure if you covered the rust issue or not but I guy in the local club had an issue like this and it was b/c his cradle was loose b/c of rust issues. All new parts and it could not hold an alignment. Front cradle was the issue. Car felt loose all the time. Even put in a new front cradle thinking it was bent or something but it was the space frame that was shot. He parted the car b/c it had a lot of great stuff on it and thru the frame away.

Rob



Yeah, everything is good in terms of rust, not a spot on it.

I did have the front cradle removed and powdercoated..but I have checked. All bolts are right, it was put together correctly.
I am going to change the front inner and outer tie rod ends as well, to see if that fixes the issue. Maybe it is more back and forth than up and down?
cmechmann AUG 01, 10:41 PM
You state this is a 3800 swap? And you have lowered it?
This may may be an off the wall check, but check to make sure none of your cv joints are binding. Pay close attention to the inners. You could have took out one of the inner cup bearings when taking apart the suspension. Or one could be pushing in too far into the tripot. This will give a loping feel. And sometimes very violent.
Recently replaced the center section on the right side. I had forgotten what I had used before and installed one that was about 1 inch too long. Every time the car loaded down the rear(over bump, acceleration, etc.) would have a violent vibration.
Will AUG 02, 03:29 PM
Did you have the car aligned after you installed the lowering springs?
Check the torque on the big bolts that join the strut to the suspension upright. I've known alignment technicians not to torque those fully, which results in big handling problems when they slip