'79' 450 - Accumulator replacement

[BMW850]

Hi there...

I am replacing 4 accumulators on a (79) w/ 17.000 miles on it. I was wondering if there was a (sticky thread) or a post topic for servicing the hydraulic suspension ? The vehicle was stuck on very stiff on the front suspension and the rear would leak down over night but the rear seemed to be functioning. I found no hydro leaks under the rear of the car but one leak on the right front accumulator.

I have replaced the one leaky accumulator so far which has depressurized the system, today I am going to try to raise the suspension and wanted to know if there is a bleed 'procedure' ? Someone mentioned I could just start the car and it would pump up on its own but trying this had no effect.

thanks for any leads...

(I am just servicing this ride, shes not mine but I figured I would ask around before getting into this cherry classic. Will take some pics for you guys when I get her back up in the air, the interior is like it rolled off the dealer floor)

[Big_Richard]

that sounds like a 6.9 if im not mistaken, although full hydraulic suspension was indeed optional (though almost never taken up) on ALL w116's.

[BMW850]

6.9 indeed...  I am going to check the pump this morning but I am sure it was working.

[Big_Richard]

if all is tight and there are no severe leaks and the tank has enough fluid in it AND the control disk is in the home position,  the pump may be air locked. If it is, it will never recover and you will need to bleed out the air from its discharge line while it runs.

[BMW850]

thanks Patrick,

I have the car rise up after I bled the pump into the tank... After finding the proper manuals in a thread I was able to read up on the subject and gained a little more understanding of this system (beautiful in its simplicity) I am having the same problem with the front not adjusting, it is very hard and seems to be risen all the way up (car is level when I pull the lever all the way out) but it is very stiff unlike the rear. When I select a position with the lever the rear drops but the front stays in the same position at all times. I will try to clean the leveling valve to remedy this...

The warehouse the accumulators were ordered from sent me (Pentosin Hydro Fluid 7.1) 'green fluid' and it says it is for hydraulic suspension systems (what do you think about this fluid in the system) am I going to have to flush it out while I am servicing the leveling valve ?



I wonder why I can not find the manuals for the 6.9 in the sticky post ? its only showing a 5.4 selection for the 79... the tag in the door says 116 though.


whatta car ! it'll possibly give my 8'er a run for its money

[s class]

If you are sure that both front accumulators are good, then it sounds like the front circuit is 'locked up'.  This has happened to me when debugging 6.9 suspensions, and it is caused by creating a set of circumstances (not achievable in normal driving) where the pressure in the front accumulators is now higher than in the regulator circuit (5th accumulator).  This locks up the front level control valve and prevents fluid return.  the solution is to safely support the car, and then bleed off the excess fluid from the front circuit.  There is a bleeder screw fitted to one of the tees under the battery tray for this purpose.  You should use care and wrap a rag around the bleeder, because the fluid will come out at a ridiculously high pressure. 

[koan]

I wonder why I can not find the manuals for the 6.9 in the sticky post ? its only showing a 5.4 selection for the 79... the tag in the door says 116 though.

There isn't an M100 engine manual in the library, it was never available in a scanable printed form, only on micro fiche and the scans of that end up with very poor negative images.

As for the body and chassis just use the 450 section, most of it's the same and it covers hydro suspension. Can't think of any differences.

koan

[BMW850]

If you are sure that both front accumulators are good, then it sounds like the front circuit is 'locked up'.  This has happened to me when debugging 6.9 suspensions, and it is caused by creating a set of circumstances (not achievable in normal driving) where the pressure in the front accumulators is now higher than in the regulator circuit (5th accumulator).  This locks up the front level control valve and prevents fluid return.  the solution is to safely support the car, and then bleed off the excess fluid from the front circuit.  There is a bleeder screw fitted to one of the tees under the battery tray for this purpose.  You should use care and wrap a rag around the bleeder, because the fluid will come out at a ridiculously high pressure.  

I replaced the 4 accumulators with lemforder replacements although the ones I took off I am sure were good. I found that the leak was actually coming from the brass crush ring on the banjo bolt to the RF bomb was loose... There is factory paint on most all nuts&bolts on this car and the accumulators I removed look new as the car looks, the pump appears to be working just fine (its dated 79 with red paint mark) The pump operates the rear suspension as it should, I have depressurized the system several times just so I can keep re-bleeding in an effort to free up blockage that I am assuming it to be (the car obviously just sits w/ 17000 on the odometer)

for some reason I am suspecting that valve under the vacuum block at the firewall (connected to the swaybar) I will release the pressure from the bleed valve under the battery on monday when I get back to work.


I guess I have a set of bombs if anyone is interested...

[koan]

for some reason I am suspecting that valve under the vacuum block at the firewall (connected to the swaybar) I will release the pressure from the bleed valve under the battery on monday when I get back to work.

The (sway bar connected) leveling valves have axial movement as well as rotary movement. The axial movement is what gives low and high suspension positions.

I've had the situation where the front suspension won't return to low when the knob is pushed in.

Make sure the control disc and cable on suspension tank is fully clockwise, disconnect the linkage to the front leveling valve and then with engine running at a fast idle operate the leveling valve in both a rotary (a max of +/- 45 degrees) and axial direction.  The axial movement is only about 5 or 6 mm.

koan

[BMW850]

well I am riding on air, (or should I say waterbed)   seems like my main problem may have been air in the line ? I am not sure... I removed the valve connected to the front sway bar soaked it in brake clean over night and blew out the passage ways with air, reinstalled and bled the air from the front bleed valve under the battery (this took quite awhile to get all the fine bubbles out of the stream) finally the front and rear are nice and soft... the car rides like a dream and is sitting proper stance, but I have not worked up the nerve to pull that lever as of yet   it is the first time I have had the car unstuck up in the front since it has been in the shop so today I am going to put a few miles on her and let the system work doing its thing before I go and pull that lever...

thanks guys for the help with this system, I wonder still if I should get that pentosin hydro fluid out of the system or if its ok.  any thoughts on that ?

[BMW850]

as promised...






everything turned out great, shes is a joy to drive an look at... I serviced/evacuated all the fluids in this car along with a major tune up and valve cover gaskets (a tightening would have done the trick but the customer wanted all new)

more interior shots to come... I have worked on this one as time permitted because it recieved a little extra special treatment and the owner now has a technician who has researched his car to the hilt read every digital service manual I could find and with my present 20 yrs experience he is in good hands...

seems like the last guy to service it did not set the control valve to service position before jacking the car ?

[pompy]

Stunning car!
Are those 15" wheels on there?

[s class]

Glad to hear it all worked out.  I'd be grateful if you could give the last 4 digits of the VIN.  Thanks

[BMW850]

I will check the wheels today, I didn't take notice when I was setting the tire pressure...



# (6979)

[wbrian63]

Ask the owner if they are aware of the M-100.cc website. It's the web presence of the International M-100 owners club. Taking nothing away from this fine forum, M-100.cc is ALL about the M-100 powered MB's - the 600 Grosser, 300SEL 6.3 and the 450SEL 6.9, of which the car you're working on is a stellar example.

Part of the reason for the question, is the M-100 site maintains a registry of 600's, 6.3's and 6.9's. The owner does not have to be identified, but the existence of the car is nicely documented in that section.

Please send along some more eye candy when you have the chance. There are lots of nice 6.9's out there, but I never tire (or is it tyre?) of looking at another one....