foam =air in the steering box.
Undo the nipple on top of the box.
Fit 5 mm clear vynil line to the nipple and make 100% sure it's tight.
run the line to the power steer reservoir and use a cable tie to hold it tight in the reservoir .
Start engine. DO NOT REV IT UP!
fill the reservoir and watch the fluid as it returns.
leave the engine idling until the fluid comes back clear.
Then slowly WITH WHEELS ON THE GROUND turn the steering slowly lock to lock while the clear line is watched.
When it ceases to have air bubbles in the fluid the steering box is clear of air.
Keep the engine idling. Tighten the bleed nipple. Remove the hose .
fill the reservoir to the mark and fit the lid .
Done.

Ron, I did all that already as you can imagine. If I bleed the system without running the engine (by gravity) I can see bubble going up the line and then clear liquid. Then I start the engine. The first few seconds liquid is clear and then it stats foaming, even when I don't operate the steering. It is as if air is being sucked somewhere in the system during operation, and only when engine is running. No matter how well I bleed the thing, I'm having foam in the line after a few seconds when I start the engine.

I bleed these things by having the front wheels off the ground. I don't run the engine at all and simply turn the steering back and forth until all of the air is purged out. If you still get foam then there is a leak somewhere as already stated.

If you want to bleed with the engine running then you should attach a line to the bleed screw on top of the steering box and run it to the supply tank. This may in fact be the best way to do it but sometimes the bleed screw ( just like a brake bleeder ) wil be seized and it's best to leave it alone if it is.

Benz Dr. I will try the way you suggest. My bleed screw is not seized and when I attach a line I get clear liquid that becomes foam as soon as I start the engine. So air is being sucked in during operation, I just don't see where from.

Thanks for the advice.

Gael,the steering box will not work or bleed as the BenzDR suggests, He is talking through a hole in his foil hat. (HTF does he honestly expect the steering box to bleed out air if no pressure is being applied ,jeez talk about stupid.
Do it the way i suggest and let it run with clear vynil hose until ZERO bubbles appear. It can take up to 10 minutes before the fluid runs clear . Slow and easy is only approach. I just did one this morning which took 10 minutes at 700 RPM idle to run clear .
IF you are still getting bubbles you have either a defective pump or the steering box itself has a seal in the gut pack leaking.
You will not suck air,it's impossible with the pressure these things run at(812 PSI) . You will however have a leak in the small line ,thats the pressure line. My advice is to get the pump overhualed first if you can't get the fluid to run clear. The large line is the return and it doesn't matter if itl eaks just replace it. It has hardly any pressure when operating.
just to make things clear here is the relevent page from the manual.

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thanks i will recheck the pipes and joints
mak

__________________
mark

Don't get mad with me for giving W123 related advice but for the Vickers type 24 power steering pump (W123 Vickers type 24 power steering pump questions) I've found it useful to put the front wheels on slip plates and bleed by turning the wheel lock to lock with the engine off.

So far I've not had a problem.

So far after starting the engine I've not had to top up the system.

(Different pump / different steering box - but perhaps of a similar breed?)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Well, if I'm so stupid why does it work for me? I use the other method too but generally only use the method without runnng the engine. If the bleed screw is broken off that's about the only way you will ever bleed it.
You don't need pressure going through the box to get the air out. Try it and find out before you call me names, OK?
After 30 plus years working around these cars you might think I'd know something about them.........

Oh, do you mean that just by lifting the front and turning the wheels lock to lock the system will bleed itself without the engine running and without the bleed screw being undone? I was assuming you still had to have the bleed screw undone and a line going to the reservoir as I noted the system was bleeding itself this way, at least to a certain extent, without the engine runing.

Yup,
that's what I'm saying. Every time you turn the steering wheel a small amount of fluid will get pushed through the box. This stuff will return to the canister and you will see some fairly large bubbles come out. As they do the fluid level will go down in the canister and you will need to top it up so it doesn't draw in any air.

( you need to have the front wheels lifted so there is no weight on them )

Keep the steering wheel mostly centered and move it from side to side. Go lock to lock once in a while just to make sure all the air comes out.

I often use this method even before I start the engine if I've done a full rebuild so that I don't end up with the usual foaming problems from running the canister low on fluid.

Trust me, it works......

Most likely.
i think it would be difficult to detect but easier to simply replace the hose with low pressure .
thanks
mak

__________________
mark

I did. still foaming. Is this the only low pressue area in the circuit? I guess a pinhole in any high pressure area would translate into a leak under operation, not sucking air.

Check, replace front pump seal maybe?

On a 65 220SEb M127 old style pump had a leak in the front seal which allowed air in when running, light fluid drip when not.