Shock Adjuster Drift

[Jim Garry]

There's a problem with my Penske 8760 dampers and I'm posting to see if anyone has also experienced this.

The first important piece of information to know is that these shocks are about 25 years old. They were on a shelf for many years and I started using them for the 2022 season. Prior to use they were revalved with many new parts. This past winter they were revalved again.

Most of the innards are new but the adjusters on the shafts are not. The problem we’re experiencing is that the settings drift during operation of the car. And the drift is different for each shock, which shows that it isn’t temperature related. Some adjustments drift one or two clicks. Others drift 15 clicks and everything in between. The canister adjustments do not drift, btw.

I installed new wave springs, which as most know are situated under the adjusters because on some of the adjusters there wasn’t a good click to feel/hear. With new wave springs that situation improved. I later doubled up on the wave springs and got even more positive clicks.

Despite that the settings still drift.

Anyone have any thoughts on what might cause this?

Penske does sell updates to this style of adjuster but they are $360 per shock and before going that route I’d like to explore other possible fixes.

For the moment I use 1/16" OD pins that I place into the adjuster holes and tape in place. Clearly, that is a jury-rigged solution for the very short term.

[DaveW]

Are the canister pressures still what they should be? On some dampers a loss of pressure can make the click detents lose their grip and vibration, etc., could make the adjustments change.

[Jim Garry]

I lowered them to about 100 from the prescribed 125. I'll bump them back up Dave and check again after a few runs.

[DaveW]

I wouldn't think just going from 125 to 100 would cause that.

[roadracer]

Just a guess here, but if the pressure is good, say 100psi, it could be the dampers have not been bled properly. Getting all the air out of the system is critical for performance and may be the cause of your adjustment "clicks" getting weaker... and walking away from the original settings. A call to Penske might be the next step here.
Good luck with this!

[scorp997]

If the sweep adjuster physically move (adjust) during the runs on their own, it could be pressure related but I suspect something else. The tiny balls are spring loaded and can be lost (or springs) during disassembly or they are gummed up where they don’t protrude and ride in the detents.

do you happen to know if the shafts are the design for the double adjusters? I ask because standard shafts don’t have the detents cut in the top surface. I am modifying some longer standard shafts to work with the double adjusters.

[Jim Garry]

it could be the dampers have not been bled properly. Getting all the air out of the system is critical for performance and may be the cause of your adjustment "clicks" getting weaker... and walking away from the original settings. A call to Penske might be the next step here.

Penske isn't certain, didn't mention that, but I've arranged to send the shocks to them but not right away.

Do you know the procedure for bleeding the canisters?

[Jim Garry]

The tiny balls are spring loaded and can be lost (or springs) during disassembly or they are gummed up where they don’t protrude and ride in the detents.

do you happen to know if the shafts are the design for the double adjusters? I ask because standard shafts don’t have the detents cut in the top surface. I am modifying some longer standard shafts to work with the double adjusters.

Everything is clean so no gumming up of stuff.. I've never seen the balls. Perhaps they were lost a long time ago ...

As for the shafts, I was going to say they were designed as doubles but then realized I wouldn't know the answer to that question. But I'll take a look at one and see if there are detents. But with the new wave springs I can see and feel the clicks. It seems like I wouldn't hear them if there weren't any detents, or if the balls were missing ... yes?

[problemchild]

For the moment I use 1/16" OD pins that I place into the adjuster holes and tape in place. Clearly, that is a jury-rigged solution for the very short term.

I guess I like spending money less than others, but this sounds like a very clever solution that would be just fine for me. After saving thousands of dollars by recycling older shocks, why spend money now. You could perhaps clean it up by making a sheet-metal tab (fender shaped) with a hole for the pin that you tape. zip-tie, or hose clamp in place, but I would be proud of myself for the clever solution.

[Jim Garry]

I guess I like spending money less than others, but this sounds like a very clever solution that would be just fine for me. After saving thousands of dollars by recycling older shocks, why spend money now. You could perhaps clean it up by making a sheet-metal tab (fender shaped) with a hole for the pin that you tape. zip-tie, or hose clamp in place, but I would be proud of myself for the clever solution.

Wow, thank you for the compliment Greg. And the added idea.

[Rick Iverson]

…..You could perhaps clean it up by making a sheet-metal tab (fender shaped) with a hole for the pin that you tape. zip-tie, or hose clamp in place…..

Simply brilliant

[roadracer]

Holding the "click" adjustment in position won't fix the real problem. A damper expert will find the cause and it could be miss-matched parts or improper bleeding or improper assembly. Tie-wraps are not needed. Any air in the system (not bled out properly) will definitely change the performance and make those adjusters "weak" on the detents. Those Penske 8760 dampers are beautifully designed and even though 25 years old should perform perfectly if properly assembled. Some parts are subject to cracking and there have been updates but nothing too costly to replace, even for Penske.

[Jim Garry]

I emailed the Penske shock engineer I worked with and he is certain he bled the canisters correctly and put everything together. He has a stellar reputation. When I have a two week break in events I will ship the shocks to him to see if something is amiss. In the meantime I'll use the pin idea. Really not interested in spending $1400 to update the shock adjusters though. Hoping it's as you say, nothing too costly.

Thanks.

[Robert J. Alder]

I Really not interested in spending $1400 to update the shock adjusters though. .

How about the old reliable racer fix: "If doesn't move and should, WD-40. If it moves and shouldn't, Duct tape:"

Just a thought.

[Sorry, just couldn't resist.]

[DaveW]

I emailed the Penske shock engineer I worked with and he is certain he bled the canisters correctly and put everything together. He has a stellar reputation. When I have a two week break in events I will ship the shocks to him to see if something is amiss. In the meantime I'll use the pin idea. Really not interested in spending $1400 to update the shock adjusters though. Hoping it's as you say, nothing too costly.

Thanks.

If the Penske engineer is the man I am working with (Steve Horn in Reading, PA), he is, indeed, extremely skilled and competent. I would not suspect that he did anything wrong.

[problemchild]

If the Penske engineer is the man I am working with (Steve Horn in Reading, PA), he is, indeed, extremely skilled and competent. I would not suspect that he did anything wrong.

Absolutely! At the end of the day, all that matters is the performance of the shock, and if MaGyver is involved, who cares?

I owned a shock dyno for a few years and developed my own internals (with help from a legendary engineer) for Penske shocks. But perhaps the biggest advantage was that I could match up the shocks with identical curves without worrying about the settings matching. This is something you cannot do when you are doing it for a "customer" so you end up replacing all kinds of parts to try and get similar curves with the same settings (at least in pairs). You will never actually accomplish that, but you need to get it close enough that the customer does not freak out because you gave him a $2500 bill and the settings don't match. That the same performance could have been achieved for $500 with settings that don't match does not matter. Having matched settings, and selling a bunch of parts, is part of a shock rebuilders business model. I say this with no malice. If someone can earn a living by servicing shocks, I salute them.

I built 5 sets of identical shocks for my fleet. I probably had to buy adjuster parts for 2 of the 20 shocks, just to get in manageable range. I doubt that I had 2 that had identical settings, but that was fine with me.