Recently put new KYBs front and back. Car seems to bottom out on the back end easily going over speed bumps.

Is that normal or are my springs done? Ride height is fine.

 

Original springs on a 30 year old car? Yep, they’re shot.

 

What setting do you have the AGX's on?

 

Well my ride height is good. I would have expected sagging if the springs were shot.

They are not the Gas Adjusts, just the standard Excel-G.

 

Sorry, for some reason I was thinking you had AGX's. Have you tried stiffer shocks?

 

Rear springs are CHEEEEEEEEEEP and very EEEEEEEEZY to replace.

This is one of those relatively rare times when this applies:

"When in doubt, swap em out"

Say that about 10 times as fast as you can and let the effect sink in.

It takes longer to jack the car up than the whole rest of the job. (assuming the hardware isn't rusted solid... soak the lower shock nuts w PB Blaster for a week or 2 before trying)

Replace with either Moog CC635 (stock variable rate) or 5665 (same height but constant rate). My preference is the CC635 but either one will ASTOUND you.

 

What is the equivalent spring for the fronts if you use the CC635 springs?

 

The spring will settle over time, meaning the compressed height will change, but the spring rate does not change over time. If your ride height is fine then the spring is as good as ever. If spring movement is not being controlled then you need better shocks.

 

^^TRUE^^

 

Thanks all. Yep. That's what I thought. If the ride height is good, then the springs are good.

However, this car is a mystery to me (bought it in Feb) I would not be that surprised if the wrong springs are in there.

I may just change them out anyway (got to do the front control arm bushings and ball joints)

Should the car bottom out that easy?

Would the wrong lower rate springs make it bottom out easy but not bouncy? Perhaps the V6 springs are same ride height but lower weight.

 

Better shocks Tootie. The Excel model is just above the stock twin tube shock. I used the KYB Gas-Adjust which is a mono tube shock, non adjustable. Also I got new trailing arms instead of just replacing the bushings. That also helped tighten the whole thing up.

 

I'll look into tighter shocks. It does feel a bit bouncy come to think of it.

 

Lower spring rates will result in more suspension travel. So yes, a lighter spring might be controlled (not bounce) by a rather wimpy shock but still allow a lot of travel (bottom out).

Generally, the higher the spring rate the more damping rate you need to control the spring too.

 

Back in the days of abject poverty, I may have driven my 3.1L Firebird with shocks so bad it bottomed out everyday on the same bump about a block from my apt. Eventually I tossed a set of the most miserably cheap POS Gay Bree L gas shocks on there from Vato Zone. Bottoming out against the rear bump stops went away at that point.

I can't imagine KYBs being worse than Gabriels. I'd probably get under the car and wiggle things around to make sure it's not something stupid like a bad exhaust hanger or swaybar endlink allowing parts to clank together. The worst springs and shocks in the world (short of being completely failed) should keep the rear out of the bump stops.

 

On my old thirdgen, I had the same problem. Swapped the rear springs out for moog replacements and new kyb shocks. Still had the same problem and the car sat higher than it was suppose to.

Current car, same kyb rear shocks but I've never noticed it bottoming out. I also haven't drove it much.

 

Change em out.

Did I mention, they're CHEEEEEEP and EEEEEEEEZY to change? In fact, they'll literally FALL OUT ON THEIR OWN while you are swapping the shocks. Might as well pick up good ones off the ground to put back in, instead of old wore-out shot ones.

You'll be glad you did.

My preference is the CC635. I have those and 5664 fronts on my car.

 

I've had bad luck with KYB shocks in the past with the exact some complaint.

I switched to some used Bilsteins from a 4th gen and it solved my problems.

 

Ok, thanks all. Years ago I used to be able to trust the entire range of KYB but I guess their low end has gone the way of Gabriel and Monroe, just crap.

 

I'm guessing it's your springs. I replaced the entire suspension (everything) in the past 6months, went (cheapily) with KYB struts/shocks and don't have any bottoming out problems what so ever. Yes they are crap shocks/struts but not that bad.

Or you got used items in box.


whats your ride height to top of wheel well arc (all 4 corners)

 

Basically springs hold the car up and shocks control bounce.
The KYB "Gas-A-Just" is a self adjusting "Monotube' Shock that is not only a stiffer shock but a better design than the Excel-G or older G-2 twintube's.
Believe it or not a lot of KYB products ware made in Japan and of excellent quality. Great reviews. I think there made in Mexico now.

I use the 5665 MOOG springs in the rear to give me the ride height I want and the "Gas-A-Just" shocks in the rear and have no trouble with bounce.

Take a look at some of these videos starting with this one =
https://www.kyb.com/kyb-tv/the-diffe...n-tube-shocks/

If you change springs use a little tape to hold the "Isolaters" to the top of the spring when installing it. Keeps it from moving around on you and makes it easier to keep them in there place.
When you are not sure about a project it pays to watch a video or two on YouTube about it.

 

Ops didnt realize that he was talking about the G-2, thanks for catching that