When to replace rear shocks?

micky_ray · 05-09-2005, 12:12 PM

I have an 85 ROW Carrera with 38k miles, completely original. When I bought the car it had sat undriven for about 10 years and we had to raise the ride height in the back about 3/4" to get it back to euro height. The ride is rough, but not necessarily worse than I would expect from a 20 year old sports car.

What method do you use to determine if the shocks need to be replaced? I tried the "jump off the bumper and see if it bounces" method and they seem ok, but I experienced a lot of wheel hop at the last autocross that I haven't seen at other events.

Thanks,
Micky

livi · 05-09-2005, 12:39 PM

Second that question. The "bumptest" seems useless in these cars unless the shocks are really out. I´m starting to wonder about mine too but I´m not sure how the ridequality is supposed to feel like in a 85 Carrera.

laddsc · 05-09-2005, 02:28 PM

Third that question. Any pics of the car for a fellow 85 RoW?

t.brady · 05-09-2005, 04:31 PM

i replaced all 4 of my original '87 shocks last month. it made a huge difference. if they're bilsteins send them out to bilstein to be re-valved. it's approx. $65/ shock.

micky_ray · 05:20 AM

laddsc, here is a pic of "Otto" from a rainy DE last November. Please forgive the blue painters tape numbers :-)

I showed you mine, now let's see yours.

laddsc · 05-10-2005, 05:24 AM

Beautiful Car. Gotta love the red. Looks very clean and fun. I just joined the local PCA so I can start doing DE and autoX. Should be a lot of fun. Here is a pic of mine.

Jared at Pelican Parts · 05-10-2005, 07:17 AM

here's mine

JTL · JTL's Garage

The Bilsteins on my -84 targa seem ok; however, they are now about 20 years old. I assume many p-car owners are in the same situation. Can anyone comment on how the ride changed after replacement?

Tim, you mentioned revalving - shouldn't revalving be done to accommodate other suspension changes? To my understading suspension components should be matched. If you upgrade only one of the following: t-bars, shocks or sway-bars, what are you really doing?

What's a good place the purchase Bilsteins other than the way overpriced PP, Automotion, Tweeks etc.

Thanks, jt

micky_ray · 05-10-2005, 10:31 AM

I have the 20 year old Boge's on mine still. From what I understand they are gas charged, and the loss of the gas charge can affect the ride height, and thus explain why we had to adjust the spring plates all the way just to get things back to euro spec. Does that sound right or am I mis-informed? If I'm right, what effect, other than the height, would I experience from the loss of the gas charge in the shocks?

masraum · 05-10-2005, 10:37 AM

It's impossible to tell without removing the things, at least on end, and even then you can't really tell if they are bad. I replaced the shocks on my '88 at about 135K miles. They were original. The car handled well and passed the bounce test with ease, but when I pulled the old shocks they were the worst I had ever seen. They were original gas charged Boge units, but they had not only lost their gas charge, but 2 of the 4 would actually compress under their own weight.

laddsc · 05-10-2005, 10:59 AM

Masraum - If it handled well prior to the change, what did you notice most after the change? Was there a noticable difference in handling, cornering, etc.? My car handles very well in comparison to everything else I drive but I have to assume that the original Boge shocks are toast at this point.

smcdermaid · 05-10-2005, 11:41 AM

There is a self lubricating seal at the top of the shocks reserve tube that the piston rod passes through. (in our cars it is obscured by the outer dust shield). As the shock compresses and rebounds, typically 1700 cycles per mile under normal conditions, this seal wears out. Once worn it allows the nitrogen gas to escape. At 80,000 miles or 20 years it is very likely that this seal is shot. This leads to aeration and expansion of the internal fluid, causing the shock to lose most of it's effectiveness. While you may not have fluid leakage outside of the shock body yet, replacing or rebuilding your shocks will definitely provide a noticable improvement in suspension behavior. It may seem hard to imagine that your car could feel more connected now but the change is substantial. Masraum is right, most at that mileage and age will collapse under their own weight.

tommy911E · 05-10-2005, 01:25 PM

I would replace any shocks that are more than 15 years old, especially in a car you don't know the history of. Sitting for 10 years is just as bad as driving the car for 10 years, the shock seals can still dry out and begin to leak. The rears are more important than the fronts in a 911 and have a lot more weight on them.

masraum · 05-10-2005, 01:33 PM

Huge difference. The thing handled better than anything else I had driven, but handled much better after the new shocks were installed. I could tell a difference backing out of the driveway and tooling through the neighborhood. It felt better under acceleration and braking and quick transitions. Running over bumpy roads felt about the same though, so it didn't hurt the ride, just fixed the handling.

I highly recommend it.

micky_ray · 05-11-2005, 10:27 AM

Ok, so I think we have established that it would probably be a good idea to replace my shocks. So the next question is what additional hardware should I replace along with the shocks? I am going to use Bilstein HDs with my stock t-bars, and our host shows them as coming with the upper mounting hardware, but not the lower mounting hardware. What if any of the lower mounting hardware needs to be replaced when changing out the rear shocks?

Micky

masraum · 05-11-2005, 11:19 AM

If you are only changing shocks then you don't "need" anything else. You have everything that you need.

If you've got lots of money and time and you want to freshen the suspension then you may want to replace all of the suspension bushings.

qcwang · 05-11-2005, 12:53 PM

Quote:

Originally posted by livi
Second that question. The "bumptest" seems useless in these cars unless the shocks are really out. I´m starting to wonder about mine too but I´m not sure how the ridequality is supposed to feel like in a 85 Carrera.

The bumper test, I think is worthless just as you feel. If the shock is totally gone, then that's when the test will be positive. But if it were that bad, you would not have to ask.

Shocks were 21 yrs old when I replaced mine last year. Any bumps felt like someone was hitting the car with a hammer. With new shocks, I think the ride is a little firmer and bumps are firm thuds instead of jolts.

The old shocks were easily compressed by hand when I had them out. New ones of course much harder to compress.

azasadny · azasadny's Garage

I replaced my rear shocks and motor mounts last summer and it made a huge difference in the ride and shifting! I could compress the shocks by hand and one of the motor mounts was split and collapsed and the mounting bolt/bracket was bent, so that couldn't have been good! I did a partial engine drop and it was very easy. With a low cost, easy to do thing like replacing rear shocks that has the potential to improve your ride, why not?

carreradpt · carreradpt's Garage

I also have an 85 with the original Bistein sports. I called the kind folks at Bilstein in San Diego and asked them that same question. He asked me if they were leaking. I said no. He said they are fine. But if I wanted I could send them to them to freshen up or revalve but they didn't need it unless they were leaking. So I didn't.