Vito.A

Helpful info on changing C4 Bilstein shocks.
There have been some previous threads on this, but I found a few differences and tried to put it all together. This particular car was a 1985, but 84-87 should be identical and 88-94 very similar. I shopped around, but purchased my set of four Bilstein shocks from Mid America for $279.99.
Removing and replacing the rear shocks took less than an hour, but the fronts took a little longer. These are gas charged shocks so they should go on and off with the suspension in the extended travel position. It is probably easier to do this job with a floor jack and jack stands than it would be on a lift. The reason is the shock travel is slightly shorter than the suspension travel and you have to raise the suspension and shock mount slightly with a floor jack to remove the shocks.
I did the rear first because it is easier and gets you “half way” done quickly. Raise the car about 6 inches so that both rear tires are off the ground. Make sure you use good jack stands as you will be raising and lowering the suspension and wrestling with bolts and you do not want the car falling on you. If you are really into pain, the shocks can be removed without removing the tire/wheel, but it really is much easier to just remove the tire/wheel so that the shock mounts are easier to access.
Spray both the top and the bottom shock mount bolt threads with liquid wrench first so it can soak in. If you car has a lot of corrosion, I would do this the night before. Remove the 18MM nut from the bottom shock mount stud. To remove the shock from the stud, you will have to jack the suspension up slightly to take the stress off the shock (the shock is limiting the end of suspension travel). The shock bottom mount stud inserts into the shock at an odd angle, so when the shock is about half way off, you may have to readjust the suspension height again with the floor jack so that it will slide off easily the rest of the way. The top shock mount bolt requires an 18MM wrench on the one side and an 18mm socket on the opposite side. I had difficulty getting an 18mm socket to fit on the nut as it interferes with the chassis, so it really helps to have an 18mm wrench. Then you just slide the upper mount bolt out and remove your old shock and slide the bolt back into your new shock. When sliding the new shock onto the bottom stud mount you will again have to adjust the suspension height with the floor jack to get it in without hammering it. You can now torque both top and bottom nuts and install the wheel.
The front is slightly more difficult. Again, get the car about 6” into the air and remove both front tires/wheels. Immediately put some liquid wrench on the upper shock shaft threads. Use your floor jack to jack up the lower “A” arm about ˝ inch. Like the rear, this takes the suspension limiting stress off the shock. Loosen the two small bolts that hold the lower end of the shock to the lower “A” arm, but do not remove them completely until the top is removed first. The top of the shock is mounted with a single self locking nut. The OEM Bilsteins use a mechanical crimped self locking nut and it is a pain. The problem is the shock shaft turns with the nut. So, you must hold the shock shaft from turning. There are two flats on the sides of the very top of the shock shaft. You can fit a 6mm wrench on these flats, but because of the small size, you do not have much holding power. Also, once you finally get the self locking nut almost off, the nut pushes your 6mm wrench off and you can no longer hold the shock shaft from turning. You may have to use a vise grip on an exposed portion the shaft for the last few turns. This is the most difficult portion of this entire job and takes some time and patience. One of the new ratcheting box end wrenches or special shock sockets makes this job easier, but you will need a set of them as the new Bilsteins use a different size nut than the OEM Bilsteins. Now you can remove the two lower shock mount bolts. Lower the floor jack and slide the entire shock and the rubber bushings out of the top mount. Install the new shock into the top mount along with the new rubber bushings and start the top retaining nut. Make sure you install the bushings and washers just as they came on the new shock. I also recommend starting the two lower bolts so the shock is held into place while you wrestle with the top. You will notice the new Bilsteins use a much nicer Nylock nut. Another difference is the new Bilsteins do not have the flats on the top of the shock shaft, but a better design Allen hex broached into the end of the shaft. This is great, except the Corvette chassis does not have an access hole to get the Allen wrench through. You will have to drill a small hole into the wheel well from the top. This is an easy hole to drill as it is in fiberglass. Just take some time lining it up, or you will have Swiss cheese holes all over. I suggest drilling the initial hole very small and trying your alignment, then if it is good, drilling it to about 5/16 dia. You may have to remove the A/C hose retainer strap on the passenger side and a wiring harness retainer on the driver side to gain access to the top mount area where you need to drill the hole. Now you can insert the Allen wrench through the hole and hold the shock shaft while you tighten the Nylock retaining nut. If you do use a ratcheting wrench, be careful you do not trap it as you tighten the upper mount. There may not be enough clearance to remove your wrench. Once the top is tight, tighten the two lower mount bolts. Another hint is to use anti-seize on all the threaded surfaces as they go on much nicer, but more importantly they come off much easier if you ever have to remove them again. Next install your wheel and tire and torque everything and you are done.

If you previously had worn bushings, the car may sit slightly higher.
Hope this helps some of you.

Calderone

what's so special about this shocks ?
I Have Bilstein shocks on mine

dclafleur

Thank you for the write up, I'll save it for the hopefully not to distant future.

Vito.A

Calderone,
Yes, most Corvettes came with Bilstein shocks and most of our C4s have been around for a while and need them replaced.

mdlfcrss

i actually just ordered a set from ajusa.com... $305 complete. The shocks on my 91 don't have a lot of miles on them but they are 16 years old and it's getting a little squirrelly around corners. I'm thinking of changing names for my baby...I'll call her Hoover from now on

TUNED87vette

Do Corvettes need to be realigned after replacing the shocks? I'm used to strut cars where you pull the whole darn thing out.

I'll definately save this to eliminate problems with new shock install.

enventr

I noticed that the car sits higher (new shocks installed) and then after some good use it will get slightly lower

mdlfcrss

There are no alignment adjustments on the shocks, but if you haven't had one done in a while, it might not be a bad idea.

rickit

my 94 has 64000 miles on it,when do you need to replace them?i have noticed the rear right seems a little twisty at times

Terrible Juan

The general recommended change interval for shocks is 60,000 miles.

Given the age of your car, you would benefit from a fresh set.

Vito.A

My 85 had 80,000 miles and the shocks are now 22 years old, so I thought it was time. Also, all the other gas charged parts like the hood and rear hatch struts had lost there charge, so it made sense that the shocks were due also.
With the new shocks on smooth road their is no difference. But, when you go over railroad tracks or rough road it is much smoother now.
My next task is to lower it slightly. With the new wheels/tires and now the shocks, it looks like it sits to high,

CentralCoaster

Thanks for the tip. Bilstein also rebuilds the shocks, not sure what the price difference is. I'll try since they're local to me.

Also, never, ever use vice grips on the shock shaft. I know you may have to hold it from turning for to get the nut all the way off, but put a thick folded rag over it to keep the jaws from chewing up the shaft... unless you're throwing the shocks away.

Atok

I just replaced my Bilsteins today, 50k miles and it made a big difference. My old shocks had a place for a wrench at the top so you can hold the shaft. The new shocks have an allen key hole in the end of the shaft. No need to use vice grips in my opinion.

I found it more economical to just buy a new set from Mid-America rather than have mine rebuilt. I think it might be different for FX3 shocks (mine are base).

kize

Just additional info on this write up. FSM details specific instructions for installing and or replacing shocks. You must tighten upper rear shock mounts at normal curb height. Otherwise it will change your ride height, left or right side height as well. Installing shocks on a vette jacked up is NOT the proper way. TO the non- believers---- read your book.

OldCorvetteFan

When I changed my Bilsteins a few months ago, I had also read that section of the FSM. So, before I jacked up the car, I measured the distance between the wheelwell lip and the center of the wheel. Then, when I got around to the rear shock installation, I put my jack under the suspension and jacked the suspension up to the previously measured distance. I then installed the shocks & tightened everything up.

When the installation was complete, I didn't have any issues with significant changes in ride height.

Steven

CentralCoaster

Just because the book says to do it one way doesn't mean it's the only way. All this effects is how much torque you need on the nut, since this preloads the upper shock bushings.

So if you torque it while on jackstands, then let it down, they won't be as tight as they should be. Since the weight of the car will unload the upper half of the bushing.

kize

I don't believe I stated It (the FSM) was the only way to do the job. One sentence from your reply, you state the bolt torque effects the preload- the next sentence you state they won't be as tight as they should be. I would like to hear more of your BS.

CentralCoaster

Ok then, why are you arguing with what I said? It sounds like you're taking it personal. Are you the author of the FSM or just overly-sensitive to smiley icons?

Atok

I changed mine this weekend. No change in ride height. I did not jack the car to change them, I just wiggled under the spare tire/mufflers and changed the rears.

rocco16

Really? I can't imagine how it could do that..............................






Larry
code5coupe

__________
not easily impressed....