87 300 td - suspension - rear sag
 

Hi -

I am prepping for a number of fixes to my 87 300 td to be the family vehicle and I know I need suspension work. The rear sits low - sags basically. I do know there is leaking in the SLS system and I plan to track that down.

In reading through a number of posts - they indicated that SLS woes are often the accumulators (first place to look) but also that if the rear is sagging it is more than the SLS system - but the coil springs.

What I want to know is to overhaul my rear suspension am I looking at likely replacing the coil springs, shocks, and likely accumulators? How does the point system work with sizing the coil springs?

In what I have read I am not real clear on when the shocks need to be replaced - but basically the ride is a little rough and I would like to improve it all around. I am also going to replace the front struts and I guess might need to look at those coil springs too.

Any advice appreciated.

does your sls pump run? see if the fluid is circulating while the engine is running. also consider maybe the adjuster arm thing at the rear axle is not adjusted correctly, it is what controls the hyd pressure i believe.

de-grease and clean everything possible to find any leaks.

Accumulators are a really good place to start. They will definitely help the ride quality. Though I'm guessing it won't help the sagging much. Unfortunately the SLS valve in your car is not rebuildable, like the earlier models. But the valves are the first place to look for leaks. You may find a leak that is allowing fluid to leak externally, but more likely the valve is leaking internally. The SLS and springs maintain the unloaded ride height. So if either is subpar you'll can get sagging. Does the rear lift when you load it down and the car is running? If so the pump is doing it's job. If not, you likely have a bad pump. The possible leaks spots are the rear struts, the connections of all the hard lines, and the pump. Make sure the reservoir is full as well.

I am not sure if the pump runs or not. I know the hydraulic fluid is low and needs to be brought up, and that the system leaks, but not from where. I plan to degrease everything, top the system off and start looking for leaks.

If the pump is the culprit and it not being rebuildable - what do you do? Is there a retrofit?

Also - won't replacing the coil springs and shocks help out the sag a lot?

Probably not. Almost always, the problems lie elsewhere. Pressure in the system maintains the ride height. Loss of pressure=sag. Only look at hydraulic cylinders (they're not shocks) and springs after everything else is up to snuff.

So should I be getting 4 liters of the febi 2615 fluid and a suspension filter (SLS) to do a fluid flush to clean out the system?

I figure I degrease all the components then flush the system with new fluid and check for leaks on all the components. Is that basically it?

That fluid is somewhat costly, i think i would verify that the pump is at least circulating fluid when the engine is running by removing the cap on the reservoir and look in there, if its working you will see a small stream of fluid coming in from the small steel return pipe that attaches to the cap. Then do your cleaning and leak finding and after the repairs are made flush and fill with new fluid.No point putting in the new fluid then having to take the system apart and loose half of it. Don

My dealer told me that 2liters is enough to fill the system if drained, ... I only bought two. I hope he's right.

The 4matic takes considerably more.

2 liters sounds about right. i bought a gallon of hyd oil and did a total flush. disconnected the return line and attached a clear hose into an old jug. pumped all the old ATF out.....and then added hyd oil to the tank. the drain hose ran clear after only about a quart. kept flushing for good measure. ended up with about a quart left and that's after a complete flush and probably flushing out 1/2 to a quart of new fluid as well.

is this the same fluid that the 123's use? I have nearly a gallon of fluid left from my 123 repairs! I think I will be flushing the fluid in my 87 soon.

My only thought is that the system is low right now because of the leaks - I think I am going to have to add fluid to really see if it is working at all. Then will I have enough to test everything out, check for what is leaking, fix it, and drain and refill with clean fluid?

as long as there is some fluid in the tank, then your system should function. your fluid will run hotter but all should still function. just the tank being low or half full should not result in a sagging rear end. as long as there is some fluid for the pump to suck in and pressurize all should work...

same as low engine oil...if the pickup tube is still picking up oil, it's enough...but no room for error either.

Reply
 

I think yes. I flash the fluid in my 87. I think you can do it too.

i JUST fixed the sagging rear in the 83 TD I have. I never saw any leaks in the rear, but the front was covered with oil and such. I rebuilt the low and high pressure hoses, and flushed the fluid. it's been holding level ever since (2 days so far) and I've not lost any fluid. I set it about 1" above the high line, and it's held there for 2 days.
I've noticed the 87 uses crimped connections on the high pressure lines... bummer. so in order to rebuild, you have to cut them out, or order new lines from source. or buy replacement fittings that are rebuild-able...

Finally back to this project
 

Slow to get back onto this project - had to get the A/C working first for the hot weather!

Okay - I put the rear end up on jack stands to start checking on the SLS - and I think my pump is shot, or the SLS valve. The SLS fluid is low (I have it on order) but even low - there is fluid in the resevoir, but no fluid returning.

I marked the fluid level on the resevoir and got underneath and removed the nut holding the fill/empty lever and first lifted it to fill and checked the resevoir level mark, then moved it to empty and did the same - no movement in the resevoir fluid level.

I assume this means the pump is not pumping at a minimum, but other components could be shot too.

Any advice? Anyone know where to get this pump? (this is a w124)

Also - my Haynes manual says that the SLS helps in the loaded condition, but the hydropneumatic shocks should keep the car level when unloaded. I have seen differing opinions on this forum. I ask this because even thought the rear shocks do not appear to be leaking - the rear sags tremendously now that I changed the front struts. If the SLS is to improve the performance from the regular shock, and I have severe sagging - I would assume the non hdropneumatic parts of the shock are shot.