1990 ZR-1 Suspension - Restoration or Upgrade to 93+?

[Erik]

As the old girl is 30 years old, and though low mileage and well kept, I'm guessing there are lots of rubber parts in the suspension that ain't what they once were.Plus, time moves on, and even in the run of the ZR-1, there were improvements made. So, my question is, do I just restore it to what she was in 1990, or go mostly stock, and upgrade to the 1993+ FX3 setup. Hib Halverson has written a fair bit about the changes, and John Heinricy sure seemed to think they were a good thing. I understand the Bilstein controller needs to be updated too, but it isn't a big thing. Springs change also.

So my thoughts are first:
New stock FX3 Bilsteins or 1993 FX3?

And here's where it gets harder:
New bushings.

From what I understand, the stock bushings are no longer available. As I'm planning to keep my ZR-1 as a grand tourer, and the roads in this part of the world are not exactly smooth, I'd prefer not to add any impact harshness.

So what's the best option I have for bushings?

What are my goals? Great steering feel and response, a comfortable controlled ride with minimal impact harshness, and great stability.

Finally, I know there are some rear suspension kits available. Is there anything I want to look into there?

And yes, I'd prefer to keep it stockish, and not go to coilovers.

[secondchance]

To start, 90 to 91 from what I understand has stiffer springs (compared to 92 to 95) and softer shocks (again, relative to later Zs). Later FX3 shocks will bolt right in but may require later controllers. I believe actuators are the same. I think SRC controller may interconnect with BCM and have no clue if later controller will play nice with 90 to 91 BCM. If you go this route, may consider changing springs also. I would recomend trimming off pucks at the end of front spring to reduce higher ride height Of later cars. This probably was done to keep front air dam from scraping due to softer spring.

As for the bushings, you might consider Super Pro bushings which are softer compared to urethane bushings.

https://www.zr1.net/forum/showthread.php?t=31253

https://www.corvetteactioncenter.com/tech/c4/susp_chart.html

[Erik]

To start, 90 to 91 from what I understand has stiffer springs (compared to 92 to 95) and softer shocks (again, relative to later Zs). Later FX3 shocks will bolt right in but may require later controllers. I believe actuators are the same. I think SRC controller may interconnect with BCM and have no clue if later controller will play nice with 90 to 91 BCM. If you go this route, may consider changing springs also. I would recomend trimming off pucks at the end of front spring to reduce higher ride height Of later cars. This probably was done to keep front air dam from scraping due to softer spring.

As for the bushings, you might consider Super Pro bushings which are softer compared to urethane bushings.

https://www.zr1.net/forum/showthread.php?t=31253

https://www.corvetteactioncenter.com/tech/c4/susp_chart.html

My understanding is that the 93+ Struts got different, and better valving, so they could soften the springs and have the better struts look after it.

Thanks for the heads up on the Super Pro bushings. I'll take a look.

[Erik]

Maybe @hib halverson has some thoughts on this.

[Erik]

Oops. And after rereading a bit, the title should read "... or upgrade to 92+".

[Vette73]

Yeah urethane sucks....I mean yeah if you have roads where its as smooth as your hardwood floors in your house go for it..

I lowered my 91 in the back and totally love the look but replaced with urethane....Not happy with the ride on uneven roadways..

Going to put my stock bushings back in..Their in decent shape...

[CamP]

What do you mean by low mileage?

My '90 has 33k miles and all the rubber bushings are original and still in great shape. Still rides like a new car.

Surface cracks in the rubber doesn't necessarily mean the bushings are bad. In a low mileage car, those cracks are often superficial and the rubber underneath is still good.

[Erik]

What do you mean by low mileage?

My '90 has 33k miles and all the rubber bushings are original and still in great shape. Still rides like a new car.

Surface cracks in the rubber doesn't necessarily mean the bushings are bad. In a low mileage car, those cracks are often superficial and the rubber underneath is still good.

But rubber does age. I remember reading ages ago that rubber bushings had a service life of about 15 years. Yes, this would be effected by sunlight, air, heat cycles, etc. So our pampered babies could be expected to exceed that to some degree. But any rubber part, once it's hit it's 30th birthday, is not gonna be what it was when new.

[Erik]

Yeah urethane sucks....I mean yeah if you have roads where its as smooth as your hardwood floors in your house go for it..

I lowered my 91 in the back and totally love the look but replaced with urethane....Not happy with the ride on uneven roadways..

Going to put my stock bushings back in..Their in decent shape...

Yeah, not a lot of suspension compliance in other areas to make up for that impact harshness.

[CamP]

But rubber does age. I remember reading ages ago that rubber bushings had a service life of about 15 years. Yes, this would be effected by sunlight, air, heat cycles, etc. So our pampered babies could be expected to exceed that to some degree. But any rubber part, once it's hit it's 30th birthday, is not gonna be what it was when new.

I use to buy into that time thing until I replaced perfectly good rubber bushings. Lot of effort and money for nothing.

Now I focus only on mileage wear. If it's old but low mileage, I leave it alone.

[Erik]

I use to buy into that time thing until I replaced perfectly good rubber bushings. Lot of effort and money for nothing.

Now I focus only on mileage wear. If it's old but low mileage, I leave it alone.

That's good, but we have that whole science problem. As in, rubber does age. Yes, there are things that can slow the aging, or mitigate some of the damage caused by it. But rubber parts will age and deteriorate. They just will. And a 30 year old part, installed in a car, will not be the same as it was when new.

[CamP]

Just don't be suprised when you do the work and discover no discernable difference in ride quality. If the car had a lot of miles I'd say go for it, but if it's a low mileage car you're probably just making work.

New rubber isn't necessaribly better rubber. The quality of new rubber products has gone down hill. The 50 year old trailing arm bushings in my 71 vette are still good. I also have a 45 year old schwinn unicycle with the original tire and inner tube that still holds air. I have other equipment that the rubber is junk in only a few years.

[viper107]

^^^^^^^^^^^^^^^^^^^^^^^^^^ what he said

[Erik]

Just don't be suprised when you do the work and discover no discernable difference in ride quality. If the car had a lot of miles I'd say go for it, but if it's a low mileage car you're probably just making work.

New rubber isn't necessaribly better rubber. The quality of new rubber products has gone down hill. The 50 year old trailing arm bushings in my 71 vette are still good. I also have a 45 year old schwinn unicycle with the original tire and inner tube that still holds air. I have other equipment that the rubber is junk in only a few years.

That is the challenge. Knowing the quality of the modern components. Well stored, NOS parts are probably the best option, but not easy to find.

And I'll guarantee you, a 50 year old rubber part is not what it was when it left the factory.

[Vette73]

Yeah, not a lot of suspension compliance in other areas to make up for that impact harshness.

Yeah not crazy about our suspension in our cars......I remember someone saying " The car rides like a Cadillac on the softest setting...... " Yeah until you hit uneven pavement.".

[ram_g]

I have no doubt that rubber deteriorates with time. But in a sample size of (2), *all* rubber and plastic components (suspension, hoses, vacuum lines, weatherstrip, misc. interior parts, etc.) in my 1991 ZR-1 with 13K miles are in way better shape than in my 2-year younger 1993 Mustang LX 5.0 with 73K miles. So while the Mustang may have received lower spec components from the get go, IMHO use conditions (mileage, storage, etc.) have as much or more to do with the condition of aging rubber components than age alone.

Currently I have no plans to change the suspension parts on my Z.

[Black Red '90]

So my thoughts are first:
New stock FX3 Bilsteins or 1993 FX3?

And here's where it gets harder:
New bushings.

From what I understand, the stock bushings are no longer available. As I'm planning to keep my ZR-1 as a grand tourer, and the roads in this part of the world are not exactly smooth, I'd prefer not to add any impact harshness.

I just had to replace my front FX3 bushings. The passenger upper half was torn bad (not sure how it happened). The other side looked & felt like new. Poly was the only thing I could find. I've noticed zero difference in ride quality. They do look a little odd as they are much smaller in diameter than OE.

[32valvesftw]

As stated by several folks, you may not notice the difference...but you will have piece of mind. That said maybe drive it for awhile and see what you think. Mine is a 91 and is not very soft except on touring setting, even then it is not what I would call squishy, on sport it can be a bit harsh on bad roads. However my suspension has a lot of aftermarket parts in it, that someone else put in. I did recently replace the shocks and found that the bilstein originals were slightly different than the bilstein replacements. The difference is where the top bushings sit, on one set the tops were concave and on the other (newer) they were convex.

[Erik]

As stated by several folks, you may not notice the difference...but you will have piece of mind. That said maybe drive it for awhile and see what you think. Mine is a 91 and is not very soft except on touring setting, even then it is not what I would call squishy, on sport it can be a bit harsh on bad roads. However my suspension has a lot of aftermarket parts in it, that someone else put in. I did recently replace the shocks and found that the bilstein originals were slightly different than the bilstein replacements. The difference is where the top bushings sit, on one set the tops were concave and on the other (newer) they were convex.

I'm planning some top speed type stuff for next year, so I do want the suspension to be 100%.

Hmmm. How did it effect the installation of the Bilsteins? Anything I should prepare for?

We do always have the option of going with the 1992+ springs. Would definitely give us a better ride, and I still think the 90-91 Bilsteins could certainly control them well.

[32valvesftw]

Steve at Crossed Flags did the install, I think he ended up swapping the top hats. so it fit like it was meant to.

[Erik]

Steve at Crossed Flags did the install, I think he ended up swapping the top hats. so it fit like it was meant to.

Always good to have guys like that on hand.