SLS noise question - PeachParts Mercedes-Benz Forum

kerry · #1 07-24-2008, 08:44 AM

I replaced my accumulators about a month ago. What a difference. Car rides great, but most significantly, it doesn't drop down overnight. I had thought that the overnight drooping was caused by a bad control valve but apparently not. It was bad accumulators.
But here's my question: I've noticed that when a load is removed from the car, with the engine off, I can hear a hiss as the control valve releases pressure to bring the rear end down to the correct height. I first noticed it when I removed my 200lb raft from the back compartment. But I can hear if even if a couple of passengers get out of the car. Is this normal? I can't recall ever hearing it before I replaced the accumulators.

Chad300tdt · #2 07-24-2008, 08:52 AM

My guess would be that you still have a little air in the system or a hydraulic line is touching the body somewhere.

kerry · #3 07-24-2008, 08:56 AM

Noise seems to be emanating from the control valve itself as the fluid bleeds through it.

Chad300tdt · #4 07-24-2008, 09:05 AM

When I discovered I had a leak in my SLS lines, whenever the valve would operate and fluid would flow through it, there would be a noise that sounded like a water faucet. I figured that the sound was air bubbles whistling though the valves. The air in that case was introduced by the leaks in the lines. I'd imagine if you had some air in your actuators after replacing your accumulators, it would have the same affect.

Since there is no leak and no air in the system, there is no more sound.

Chad300tdt · #5 07-24-2008, 09:12 AM

Now that I'm thinking about it more, there is a light noise like what you're describing. I don't really notice it though since it is faint and I live near a major road that masks quieter sounds pretty well.

Yours is either really loud or you live in a very quiet neighborhood.

jt20 · #6 07-24-2008, 09:17 AM

So the the SLS is NOT supposed to make noise when raising and lowering?

mine makes the same noise near the valve when lowering.

If you remove weight from the rear, the springs rebound, the rear raises, and the control valve compensates by releasing fluid.---This was my supposition to the recurring sound. If you bled your system using the bleeder on the valve in the rear, there shouldn't be air in the system (unless there are leaks). Air should also be forced out of the system naturally.

kerry · #7 07-24-2008, 09:54 AM

I didn't bleed my system because the bleeder screw seemed fused to the valve body. (bad idea to have an iron bleeder screw in an aluminum bodied valve in my opinion). But I've driven it at least 3000 miles since I did the accumulators and since the system is self-bleeding, I think the air should be gone.
The noise is not loud and I live on a cul-de-sac.
I have assumed the sound is normal because I've heard similar sounds while operating control valves on hydraulic backhoes.

Chad300tdt · #8 07-24-2008, 10:03 AM

Quote:

Originally Posted by kerry

I didn't bleed my system because the bleeder screw seemed fused to the valve body. (bad idea to have an iron bleeder screw in an aluminum bodied valve in my opinion). But I've driven it at least 3000 miles since I did the accumulators and since the system is self-bleeding, I think the air should be gone.
The noise is not loud and I live on a cul-de-sac.
I have assumed the sound is normal because I've heard similar sounds while operating control valves on hydraulic backhoes.

That must have made for an interesting time when taking out the old accumulators. I use that bleeder to release system pressure before servicing anything on the SLS.

I doubt you have any air left in there and believe that the noise you're hearing is normal. I am now jealous of your working AC AND your quiet cul-de-sac location.

kerry · #9 07-24-2008, 10:22 AM

When I replaced the accumulators, I released the pressure by barely cracking one of the small lines to the accumulator and slowly bleeding off the pressure. However, I didn't replace the crush washers and one side started leaking a week later just as I was leaving on a long trip and I had to replace the washers in a hurry. That was an adventure. Basically, I took a bath in hydraulic fluid when I unscrewed the banjo bolt. It's not something I'd recommend.

jcyuhn · #10 07-24-2008, 10:30 AM

My 124 wagon definately made that type of noise when the SLS was bleeding down. Can't say I've noticed it on the 210 wagon, but then I don't tend to use it as a pickup truck to the same degree.

- JimY

karmabitch · #11 07-24-2008, 10:47 AM

The sls is self bleeding isnt it? that would have to be a leak.

kerry · #12 07-24-2008, 10:51 AM

Definitely not a leak.

ds190 · #13 07-24-2008, 10:55 AM

I had the same issue with my 300TE and the bleed screw impossibly stuck in the valve. So before I did my accumulators, I repeatedly sprayed PB Blaster on it and let it soak. Maybe six times, and thankfully with a closed end 11mm wrench, it finally came loose.

Bajaman · #14 07-24-2008, 11:18 AM

I have the same noise. I believe it is completely normal, simply the sound of the fluid being released as the weight is removed. I also only started hearing it after replacing the accumulators.

Dee8go · #15 07-24-2008, 11:27 AM

Did you replace the nitrogen spheres at the same time?