1987 300E gear box seal problems - PeachParts Mercedes-Benz Forum

#1 01-07-2002, 12:30 PM

I have had the steering gear box seal replaced 4 times in the last several months. It does not seem to be a problem with something nicking the seal. Dealer now wants to replace the power steering pump, but can't tell me why. I am thinking that there might bee too much pressure which is blowing out the seal. Has anyone seen this before or have any suggestions?

dpetryk · #2 01-07-2002, 01:47 PM

You say "gear box" I assume you mean "steering gear". What seal is failing? There are two large seals that must be replaced. One on the steering shaft and one on the pitmann arm shaft. There are several smaller ports that use O rings to seal. So my question to you is what seal is failing?

I have seen corrosion (rust) on the shafts which will cause the seal to wear out. I cannot see why the pump needs to be changed. There might be some sort of restriction in the return line which might cause excessive steering gear case pressure. This pressure might cause excessive leakage.

I overhauled all three of my steering gears and had no problems with leakage since. Maybe they are putting some "stop leak" in the fluid and not really overhauling the steering gear.

#3 01-07-2002, 01:55 PM

It is the Steering gear box. It is the seal on the bottom of the unit. After it is replaced it is fine for a few weeks. Then it just doesn't leak, it blows out out the fluid comes out as fast as it can be poured into the power steering unit. I couldn't see how it could be the Power steering unit either, but then I didn't know if there is some kind of check valve or something else in the Power Steering unit that could build up pressure in the gear box.

dpetryk · #4 01-07-2002, 02:01 PM

Like I said there might be some sort restriction in the return circuit. There is a filter in the pump. It might be clogged. That would certainly make for some back pressure. Have you replaced the rubber section of the return line?

dpetryk · #5 01-07-2002, 02:04 PM

To remove the filter, take off the lid and unscrew the nut holding the plastic thing and spring on. Slide the plastic and spring off the threaded rod and using a needle nose pliers lift the filter out. Has it ever been changed?

dpetryk · #6 01-07-2002, 02:05 PM

There are seals inside the steering gear as well. Maybe you need some inside seals replaced as well.

#7 01-07-2002, 02:08 PM

I will check those things. I am the 3rd owner of this car and it has 270k on it. I am guessing the the filter has never been replaced

#8 01-07-2002, 06:23 PM

I was wondering if there is a check valve inside the Power Steering pump, that if stuck might lead to high pressure being put on the steering box seals ?

dpetryk · #9 01-07-2002, 07:59 PM

I dont believe there is a check valve anywhere in the pump. If there was one I didnt recognize it. There is a pressure limiting device on the output side of the pump which has a natural check valve function but it is not designed to function as a check valve. The pumps are very simple. There are not many components inside.

#10 01-07-2002, 08:00 PM

Ok I checked the filter and the return hose and they are both ok. So I guess I am back at the beginning. It seems that all the pressusre is on the front end and not on the return?? I'm up for any other suggestions.

dpetryk · #11 01-07-2002, 08:08 PM

Im out of ideas. Something must be wrong inside the steering gear box itself. Where exactly does the seal fail? Is it between the shaft and seal or between the housing and the seal. Dosent make sense cuz the seal on the steering shaft should see the same pressure. Is the pitmann shaft nice and smooth and free of corrosion ?

Kebowers · #12 01-07-2002, 10:23 PM

Something is seriously wrong inside the gear box. There should not be any measurable pressure against either the worm or pitman arm shaft seals. those seals are to keep oil from dribbling out.

Time to get a 'new' steering box from your friendly parts recycler (junkyard)

It is mighty inconvenient when a steering gear quits steering--and it's about to.

dpetryk · #13 01-08-2002, 11:32 AM

Why dont you try to rebuild it. The kit is available from MB for about $30.

#14 01-08-2002, 11:35 AM

It was more or less rebuilt when the seals blew. The rebuild kit is just seals and o rings, which is what they replaced before. Maybe it is time to replace the whole gear box.

dpetryk · #15 01-08-2002, 11:41 AM

But there is a large teflon seal that is deep inside. I have never replaced that myself, I have only done the external seals. But I can imagine that if that seal is leaking high pressure could be in placesz where you dont want it. The worst that could happen is that you screw it up and the fact is that it needed to be replaced anyway. So you dont have much to loose.

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