I'm getting ready to upgrade my Z51 shocks to some bilstiens and was trying to determine if the existing Z51 shocks with 45k miles are even worth trying to sell to someone. They feel like they work great still.

 

Good question, I'm interested in an answer as well.

 

Replaced mine at 181,000 miles. Both the front & rear driver side shocks died at about the same time. Probably due to Michigan's wonderful pot holes. Purchased GM direct replacement shocks from a GM dealer. Had to go to 4 dealers and got prices from $263 per set /4 to almost 1,000 for a set/4. Those prices didn't include installation charges. Purchased the $263 set and installed them myself in a couple of hours. Easiest installation of shocks I ever did - and that includes everything from '52 Hudsons to '95 Impalas. However, I wouldn't spend time & energy to install used shocks - too chancy!!!

 

Hi everyone,

I too would very much like to read the answer to this question.

I can start with some of my observations.

1) Typically an automotive shock test calls for removing the shock from the car and then pushing/ collapsing it to see if it is hard to collapse and whether the rebound come up slowly.

I always see old shocks pass this test.....BUT....heat is not taken into account.
Once the old, broken down oil in the shock heats up, that is when I believe we all feel shock degradation.

2) On hobby fast motorcycles, one can feel when a shock goes bad. It is very noticable. Many of these shocks are rebuildable with oil changes and fresh charges of nitrogen. 5000 miles is an average point when these shocks go bad for a rider who pushes the envelope (a little bit ya know :blueangel: ).

3) Cars are heavier, hit more bumbs, carry more weight, yet the shocks, in my opinion, are usally smaller oil capacity than motorcycle shocks.

On my C5 with 30,000 miles (base shocks) I feel the fronts need refreshing.
It is relatively expensive to experiment, and I have never seen any discussion answering whether a C5 needs more front rebound or more rear compression damping to balance the chassis for road racing.
On my C4 (base Bilsteins) I changed the shocks at 50,000 and there was not a great improvement, but some improvement.

Very much I look forward to following this thread.

Kenny

 

ttt, anyone?

 

If the question is "how long will they last", then the answer is probably the life of the car. You should probably be more interested in "how long will they perform as designed", and that's impossible to predict because everybody drives different. Shocks slowly degrade over time - seals wear out, oil viscosity changes, bearings wear. Most of the time you can't tell when a shock is losing its original capability, but it will be obvious when replaced with a new one.

Your 45k Z51 shocks will not perform like a new one. But unless they've blown a seal and lost all fluid, they will still function. Good enough for the next guy? Dunno.

 

The answer may surprise you........
A very good tech article was written on shock absorbers a few years back. The article was in a 4x4 magazine but it also applied to automotive shocks. It said that most shocks are toast after as little as 20k miles. What may feel like a good shock when you pull it to check it out may feel completely different when it gets hot. And trust me.....shocks get hot. A worn shock may feel completely normal when cool but once it heats up the cylinder expands possibly allowing the seal which separates the inner chambers to leak internally. I have found this to be true on my truck. Usually by the 20k mark I always have at least 1 shock that is shot.....and these are on lifetime waranteed shocks. On a car with suspension as sensitive as a Vette, I wouldn't be surprised if shocks were history between 10-20k miles.

 

is the bilstein shock the best way to go for a Z51,or is there something better out there?
i've lowered mine 1", will the bilsteins have the same height as the stock Z51 shocks?

oo,nbm,vert,mn6,Z51,hud,ah

 

Re: Motorcycle shocks: Motorcycle shocks are more important to the motorcycle rider than auto shocks are to the auto driver for several reasons.

First, the weight of the wheels and tires on a motorcycle are a bigger percentage of the entire package (cycle+rider) than are the wheels and tires on an auto. An uncontrolled wheel on a cycle is deadly rather than just inconvienent!

Second, the front fork shocks are also the suspension elements (more like struts) than plain shocks. This being the case, cycle shocks must deal with holding up the bike with its rake and trail parameters, deceleration loads (braking) as well as bumps and dips. Cycle riders generally change the fork oil at 5,000 to 12,000 mile intervals. Different shock oil formulation can be used to tune the damping (soft...hard) and different valving can change the bump..rebound ratios.

Third, cycles accelerate faster, decelerate just as fast, and combined with the first point, mean a larger percentage of the vehicular cost can be (should be) allocated to the shocks than would be prudent in an auto. The differnece in cost between the low range 900 CC Ducati ($7500) and the uprange Ducati 900 SS ($9500) was bodywork ($600) tires ($200) and suspension ($1000)--same motor, wheels.... The low end shocks were unadjustable, overdamped, and generally disagreeable. The higher spec equiptment were dual adjustable, could be perfectly damped, and adjusted for any tire combination and rider preference.

Rear shocks on cycles (race rep-like) are more conventional in nature and last on the order of 20,000 and can be rebuilt. Often just recharging the nitrogen performs wonders, but changing the oil is very benefitial.

 

Hi all,

Looks like the best data is from the 4x4 magazine.

Life vs. performance is the question.

So, are we concluding 10 to 20K mileage before performance degradation?

If so....how do we approach warrenty replacement?

(Can someone try an experiement to drill a hole into an OEM shock body, drain out the old oil, install a fitment, and install new oil w/ a shot of nitogen? I do not have the tools...but I have a shock..San Francisco North Bay area..is this possible?)

Kenny

 

thanks for the reply's. I think just to be safe, I'll just throw away my old Z51 shocks.

evil-1, I'll let you know in a couple of weeks. I may do the install next weekend but I plan on putting my T1 bars on at the same time and I'm waiting on them to come back from the powder coater.

 

I found That I had a bad left rear shock at 10k miles. Replaced with bilstein sports. :D

 

For offroading (4x4 kinda stuff), I had to replace the shocks on my old Ford Bronco every 25-30K, but that was serious offroading. My old Isuzu Rodeo went 110K without replacements, but it did not see a whole lot of offroading.

I had an 84 Camaro, and it went nearly 120K before the shocks couldn't take the Louisiana roads. The replacements lasted another 60K, but then car died one rainy day. :cry

What I'm saying is that it all depends on the road conditions and how you drive. For most C5 owners, the shocks will be probably outlast the rest of the car.

If the roads are bad, and you drive like a monkey on crack, probably every 30K.

:cheers: