View Single Post
Old 05-04-2003, 04:19 PM
EricSilver's Avatar
EricSilver EricSilver is offline
Registered User
Join Date: Mar 2000
Location: Fairfax, VA
Posts: 1,322
Smile Did It!

I completed the reseal this weekend. The procedure for my ZF pump was different than described above, so I assume those instructions I had were for a different brand of PS Pump, or a different model ZF.

Simply put, the ZF pump is a very simple, well-made device that a child could put together.

I began by disconnecting the radiator hoses. Then I lifted the serpentine belt up and off of the water pump pulley, then off the PS pump pulley. (My belt is properly tensioned, yet still allows me to do that. It's a terrific timesaver.) Then I disconnected the two fluid hoses going to the pump -- the top one which enters the lower part of the reservoir, and the bottom one that connects to the pump body.

Removing an oily PS pump pulley is tough to do without losing some skin on your fingers. After it was off, all I essentially had to do was remove the pump's 5 mounting bolts -- 3 in the back and two in front. One of the front bolts is the 13mm belt tensioner bolt. The other is a long bolt that passes through the pump housing where it enters a nut on the back.

**When reassembling the pump, I reversed this since I felt it was preferable to drop a nut in front of the pump, where I can easily see and retrive it, versus dropping it in the rear where I would proibably never find it again.**

Before doing the 13mm belt tensioning bolt, I loosened the big 19mm bolt that goes through the belt tensioner itself. The pump itself has 4 bolts which should not be touched.

After removing the pump, put the mounting bolts back into their respective holes, This will save time later -- you won't have to recall where everything goes.

Once off the car, removing the 4 pump bolts splits the pump into 2 sections: Rear, which you can set aside, and Front, which contains the pulley shaft and impeller.

Tapping the front will release the impeller housing -- if it does not fall out by itself -- which is a round disk with an oval cavity that the impeller spins in. The housing is connected to the Front by two pins.

The impeller is a round disk with 10 slots that small, silver, rectangular vanes sit in. These vanes, about half the size of a piece of Chicklets gum, and approx .5mm thick, are what propel the PS fluid when the pump is spinning. They basically slide out of their slots unter hydraulic pressure, and are forced back in when they encounter the narrower ends of the oval cavity the impeller spins in. When extended, they pump fluid. When retracted, they don't. Very clever.

Once the impeller housing is out, the vanes will fall right out of the impeller slots. The only remaining challenge is removing a very small, very strong, split metal ring -- shaped like the Greek letter "Omega" -- that locks the pulley shaft into the front housing. There is a groove at the end of the shaft that this piece rests in, and locks the shaft in place.

At first glance, it would seem some type of spreader would be needed to remove this ring, but the ring is too tough. Instead, you need to carefully pry one half of the ring out and upwards from the groove, using a probe or other fine pointed, strong, tool. Once one half of the ring is up and out, prying the rest out will be easier.

**I recommend doing this in a bare, enclosed area, or perhaps covering the pump with a towel. The ring will fly away with great force once free, and you want to be sure you can find it after it does.***

With the ring off, the shaft will slide out of the front and the seals will be exposed. I say "Seals" because on my pump there was a normal looking, metal core seal like the replacement I bought, and on top of that, acting as an apparent buffer, was a second one -- concentric rings of a braided fiber core material encased in rubber.

The main, proper seal was in great shape, except for some minor brittleness around the thin edges - sufficient to allow fluid to leak through. The second, buffer seal was in bad shape -- totally deteriorated.

I am beginning to suspect that this extra seal was a cheap hack by the previous owner, after the main seal began to leak. Seems to have worked very well though (for at least 5 years).

Now, the fun part. The rerplacement (dark green) seal I bought was for a Vickers pump. It will not fit, I discovered, a ZF pump. So in a sort of repeat of the PO's hack, but with superior materials, I trimmed down the Vickers seal to make it thinner, inserted an O-ring (Home Depot #15 O-Ring from plumbing section) into the channel between its outer, metal ring and the inner rubber ring, and simply seated that against the good seal already in the pump. It's nice and tight, and should hold until I get a proper ZF seal kit and do the job again.

Putting the pump back together was easy, once that blasted ring was reseated. Force one half into the groove, and then the other.

Next, the vanes have to be replaced. I noticed that some seemed to fit snugly in some slots and very loosely in others. Just to be safe, make sure that you only insert a vane into a slot that it falls easily out of. You don't want to have them sticking when the pump is running.

Once the vanes are in, carefully cover the impeller with its housing. As I said earlier, it is seated with two pins. They are different diameters, so you need not fear putting the housing on backwards.

**Keep the housing away from any strong magnets after dismantling the pump. If it becomes magnetized, it will attract the vanes and make reassembly a bit annoying. Dont ask me how I know this. ****

Once the impeller housing is back on, join the back and front section of the pump and bolt them together. If you spin the shaft, you should hear some faint clicking. That is the vanes falling in and out of their slots. If you hear no clicking, I recommend checking to make sure they are in properly.

With the pump reassembled, except for the pulley, you are ready to reinstall it. Rebolt it, doing the back bolts first, then the fronts. Don't forget to re-tighten the 19mm belt tensioner bolt.

Next, reattach the pulley - far easier than getting it off. Then the belt. In my case, I lifted the serpentine belt onto the A/C compressor pully, over the PS Pulley, then onto the water pump pulley.

Reattach the top and bottom hoses. Add new PS fluid -- but leave the top of the reservoir off.

Double check all bolts and the belt.

Take a deep breath and start the car. Turn the steering wheel. Panic momentarily when nothing happens. Turn a little harder and power will return with a sudden jolt.

About half the reservoir fluid will be gone. It may also be mixed with old fluid regurgitated from the steering box. Refill and turn the wheel lock to lock to bleed the system of air. Replace the top of the reservoir and go for a test run.

If your car was leaking through the front seal as badly as mine was, allow suffient time to dry / burn the oil residue from the belt. Spray some brake parts cleaner onto the pulleys to help clear the oil and gunk from them.

Also, examine any rubber components that may have deteriorated because of prolonged exposure to the PS fluid that was slung around the engine bay. ( I have already replaced sway bar bushings and will need a new foam rubber hood pad.

Interestingly, my A/C compressor pulley, which unfortunately sits right below the PS pump, was so lubricated that it simply did not work. After a good cleaning, it smoked for a few minutes after I turned on the A/C, as the oil and other crap in there apparently burned off.

If you have a ZF pump that is leaking, and are considering a do-it-yourself repair, go for it. I do not recommend any stop leak products since there does not seem to be enough rubber on these seals to enable those products to work.

Finally, the seals and repair kits for ZF and Vickers pumps are not interchangeable. Make sure you have the proper materials.
2008 E350 4matic / Black/Anthracite

Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

Last edited by EricSilver; 05-04-2003 at 05:25 PM.
Reply With Quote