How to bleed (if needed) new hydropneumatic shocks..?
 

I just put in a new set of shocks and springs on my 85 300TD wagon (w123).

Im assuming the shocks are self bleeding? Theres no outlet on the new shocks (or old ones) to bleed the hydraulic fluid. (kind of like bleeding brake callipes...) So is there another method?

Is it obvious when the shocks are full of fluid?

Thanks...

AFAIK the whole system is self bleeding. Better check the FSM tho, air might blow out a seal or something.

The system is self bleeding (the air will eventually get pushed out with the flow through the collector tank), but it requires driving. I don't think it will bleed sitting still (mine did not, anyway).

In my case it required about 15 minutes worth of driving and finding some moderate bumps seemed to help.

The FSM talks about putting something like 200lbs in the trunk to drop the rear end down and force the SLS to pump up which should draw in fresh fluid and make it self bleed. Have a buddy or two sit in the trunk while its running and monitor the fluid level.

So I finally put the car on the road today, (I had to wait for a replacement brake caliper), and the suspension did go up but not as much as I would expect yet.

Ive driven about 20 min in two trips, going over moderate, small and some larger bumps. The small bumps, (potholes) are the worst it seems. Im getting a real knock when it hits a pothole now. as if metal is hitting metal in the rear somewhere.

However the suspensions has gone up some. There was a broken spring and a broken shock on the drivers side with the old set, so this should make a noticeable difference...

Any Valve adjustments to think about? Or any valve issues that may not allow the shocks to rise more? Both accumulators were replaced less than two years ago...

Does the hydraulic pump work continuously or only when theres a demand for pressure?

Thanks

Self bleeding takes a long time and I am not sure it ever gets the job done. I have eventually gotten to this. I fill the struts with fluid using a syringe. Then, with the rear suspension drooped, the valve is open to the return line, so I use my large syringe to back flush the lines, and accumulators collecting the fluid from the line to the strut until fresh fluid appears. Doing both sides, I reconnect the lines not worrying about the small amounts of air getting in.

When the car is back on the ground the struts will have displaced their fluid and air back to the lines. At this point the rear will be sagged all the way down and valve will be open to the supply line and the pump. I remove the high pressure line from the pump and back the fluid, again through the return line at the reservoir using the syringe.

It may be helpful to remember how this works. The sway bar rotates under load and opens the valve releasing fluid to the struts until the level returns and the valve is closed. Just like a toilet filling valve, except this one works backwards as well. So when the load is removed the rears rises the roll bar opens valve in reverse releasing fluid from the struts until the rear returns to level and valve is once again closed.

I like to remove the linkage from the valve so I can most completely bleed the system. This way with the engine running I can lower the lever arm and fully lower the rear, then raise until the rear rises to it's maximum height. Just a few cycles should fully bleed and everything and restore that amazing ride quality from such a simple system

Thanks Charlie, By "drooped" suspension, you mean lifting the body and letting the suspension hang down?

As someone lese actually put the shock in, is the opening to the shocks/struts easily accessible if the car is simply raised up?

So If I got your procedure right, "droop" the suspension, (extending the cylinders to their maximum) fill them up with fluid manually while the lines are disconnected.

Quote{so I use my large syringe to back flush the lines, and accumulators collecting the fluid from the line to the strut until fresh fluid appears. }

"Backfushing" meaning pushing fluid into the lines toward the reservoir? and until fresh fluid appears where?

Sorry, as I havent studied the system as much as other parts of hte car, im still trying to grasp where everythign is and how it works.

Your call if you want to do that, I have no opinion one way or the other, however it sounds from what you described as though the car is not far off normal ride height.

If you could post a pic that would be helpful to confirm.

In any case, ride height is adjustable through the length of the control rod on the leveling valve at the rear of the car. There is a guide to the system somewhere either here or on BW that someone wrote that talks about how to do it, I cannot remember offhand if you expand or shorten the rod to raise ride height. The adjustment is intended for a situation like this, not to compensate for a system fault (though many shops actually use it that way, to placate customers).

Also you asked if the pump works all the time, answer is yes it is simple mechanical arrangement, it is working as long as the motor is running.

I didn't want to jump in and answer immediately as I only know what I know from my own TD, there are others who know much more but I think right now the forum is in a bit of a summer dead zone for responses.

I don't see how air can remain in a system like that forever, given that it isn't closed, it vents out at the return line into the SLS reservoir.

Azitizz, yes to all. Except I push fluid through the return line at the reservoir. You will need plenty of rags and catch cans. If the car has been run and the system is pressurized you can release the pressure by cracking open the banjo fitting at the top of the strut, easy to get to, very messy. Or connect a small hose to pressure relief bleed screw on the valves it self, hard to get to but preferable.

I have found that since the valve is mostly closed and the fluid returns directly from the valve to the reservoir it can take some time, like months, for the air to fully self bleed.

If you're really concerned that the system isn't bled correctly, just release the swaybar link and manually work the valve lever all the way up and down. Just be very careful, as you'll be raising and lowering the car to full height and full drop as you do this, and the action is very fast. A few times will guarantee that the struts are properly charged. Best done on a lift or ramps, and allow plenty of safety clearance as the car moves up and down.

The pump operates continuously. When the valve is in the mid-laden position, the flow is routed back around to the reservoir.

When I flush these systems, I suction oil out of the reservoir while running the motor. Work the suspension as described to drop the car to it's lowest postion, suction anything that comes back to the reservoir. Then refill the reservoir and work the suspension through it's travel as described. Suction out as before. Finally fill, work the suspension up and down and check the level. Shouldn't need to be done all that often, unless you have leaky struts.

Finally, as long as the struts don't have major leaks, they have nothing whatsoever to do with ride quality. That's controlled by the spheres, which either work or not. If they've lost some or all of the nitrogen charge, no amount of bleeding can restore them.

Thanks Mxfrank, This seems like a good option. I was wondering how finicky the valve is. Ive never done any adjustments or anything to it, At one point i thought I could se a little oil leaking from somewhere on that valve but neve pinpointed it.

Ill try and post pictures of how raised the car is, but I do feel an improvement with the height.

Or more theres been a lound clunking when I go over certain small but sharp bumps like potholes or something quick, and its somethign that sounds on either side depending on where the bump was. I Imagine the suspension bottoming out (however I konw this cant be so considering the height of the rear when I look at it stopped). Its a clunk that sounts like something is loose on either strut and it clunks when a bump is hit, quite loud and it was never there before even with the old suspension.

Ive noticed it has become less and less with the more driving I do, but it hasnt gone away completely.

I was expecting some improvement with the rear end swaying once the new suspensions was installed and working but I dont feel any difference.

Someone mentioned the rear sub-frame bushings.. is there an easy way to tell if they are finished or not? would this really cause lots of sway-like feeling?

Clunking and sway with good rear height suggests a rear sway bar bushing or drop link. Could be sub-frame bushings, but they're the largest and lightest loaded of the lot...usually one of the other bushings goes first. A bad sway bar bushing would also affect ride height, since the valve is articulated off the sway bar.

So Ive found the clunking problem. It was that the fellow who installed the new shocks left out the rubber spacer that goes between the shock and the body of the car.

We took it apart and put it back together today, and as the loose strut was clunking around the hydraulic hose became loose and leaked, so ride height was lower than it should be...

Luckily nothing was damaged.

Now, I did what you suggested Mxfrank, for bleeding the air through the SLS valve. It seemed the simplest as the car was up on a large lift in a shop and we disconnected it from the sway bar and manipulated the arm. (see picture) this arm was very loose before the engine was running and I could turn it 180 degrees without anything stopping it. Is this normal?.

Once the engine was running, it still was loose, but firmer when it got to it normal operating location and you can hear the hydraulic fluid working through the system somewhere, but nothing happened with the struts. They didnt budge. We wiggled the lever around lots and experimented where there was some kind of resistance, and you can hear some whining kind of sound slightly, but again no movement.

The car was supported on a lift with the suspension and rear wheels and arms hanging. Will the hydraulics actually lift the suspension up (compress the struts), or is it just the weight of the car that will send the struts to its minimal height?

I thought fir sure something was wrong as the struts weren't compressing, but perhaps they wont on their own. Its just the weight of the car?

Can't do it on a 4 pt lift. The car has to be resting on the wheels.

what about the valve lever, does that sound normal?