Hydraulic pump
From Knowledgebase
Some call it a hydraulic pump, some call it a power steering pump, some call it "that thing that drips green/red oil everywhere". In any case we are all talking about a belt driven pump that pressurises a hydraulic fluid for use in the power steering system, and where applicable in the hydraulic brake assist system.
Contents |
Types and Identification
Audi's have used various pumps over the years. In the mid 80's and early 90's many models (especially turbocharged models) used the pump not only for power steering, but also to provide high pressure for the power brakes. In the early 90's there was also a re-designed system with a new, much more compact, pump versus the older version. Certain models didn't get the hydraulic power brakes, so they got a 'normal' power steering pump. Around mid to late 1990's Audi went away from the hydraulic brake assist and all models had pumps that were only for power steering pressure.
Early style w/ hydro-assisted brakes
This pump is driven by a V-belt, and usually mounted high on the engine to the drivers side of the cylinder head. It will have 3 hoses fitted to it by banjo bolts.
This style pump is seen mounted on a 1986 5000 Turbo engine in the following photo (external link - use your browsers back button to return here). It is in the lower right corner of the photo, and the only visible object that is belt-driven. Hydraulic pump
Later w/ hydro-assisted brakes
Most of the 20 valve 5 cylinder cars used a smaller, more compact pump. The urS4/urS6 used this style pump, and while visually nearly identical, it was valve for a slightly higher pressure output. Also the urS4/urS6 pump was driven by a 5 rib serpentine belt instead of the v-belt still used on other 20v cars.
Without hydro-assisted brakes
[Input needed]
Repair Info
Early style w/ hydro-assisted brakes
[Input needed]
Later w/ hydro-assisted brakes
Originally posted to the 20vList by Brian Powell, Jan 22, 2004:
The PS Pump on the 20v and urS cars is the same with different belts. The rebuild is straight forward and not complicated. The only difficult part is removing the pulley from the shaft (it is of triangular shape) and finding a hydraulic press to push the pulley back on. Purchase a seal kit from Audi, Part number 035 198 049A. This may be listed as for the s-car, but, as stated, it is for a 20v'er as well.
To remove the pulley from the shaft, I used a standard pulley puller and pig iron to allow a straight puller to attach to a triangular shape. Heat up the pulley with a torch (you don't care about that old seal anyhow) and start using the puller to get it off. It takes a little time, but, it will come off. Replacement of the shaft seal is straight forward during the rebuild of the internals (see below) as the shaft slides out from the interior. Once you get everything rebuilt, do not reattach the front half, you need to press the pulley back on by securing the shaft and using a hydraulic press (believe me, you need about 20 tons of pressure to get it back on).
To rebuild the internals, Richard Hoffman gave me this excellent writeup:
If you aren't noticing any noise and didn't run the pump dry, then there will be no wear on any of the metal parts. Should cost $45-$60. I did the disassembly in my metal drain pan as the pump is full of hydraulic fluid and this saved extensive bench clean-up.
Just so you know, the S6 PS pump uses the same rebuild kit and the internals are identical to the CQ pump. The difference is in the mounting, the pulley, and the hose connections. It helps to loosen the front/center section of the core support just to get a little more room to work on the pump. Removal is straight-forward - loosen the mounting bolts, then it has a tensioner. The belt is a tight fit between the shroud and pulley. The fittings are 19, 22, and 25mm for the hoses (if I remember correctly)
Once you've got it out, the pulley should come off first. I jammed a screwdriver through the pulley holes and used the appropriate allen wrench (5 or 6mm) and it was no problem.
Now you can take off the big mounting bracket/shroud. 3 10mm bolts
Now comes the messy part. I believe there are 4 10mm bolts holding the whole thing together. Pull apart the front section with the X-plugs first. Pull gently and gradually. Inside this section, you can see a brass ring and see the pistons as they are driven by the eccentric lobe. Try to keep the ring in there, its somewhat hard to put back. I cleaned everything out with spray carb cleaner.
At this point, position the pump so that the surface you just exposed points up. The center piece can be lifted upwards but is held on by 4 additional bolts. You'll notice a large round O-Ring here and inside you will find the RSFH. That is, the rubber seal from hell. It's shaped like a big malformed letter H and has a nylong support. It sits in a rather odd piece of aluminum. This is where it gets a little fuzzy for me. The important thing is that you note the orientation of the aluminum piece with respect to the center section. These parts can all be cleaned in carb cleaner dip or with the spray. Brake cleaner also works but smells worse.
The very bottom section now contains the vane pump for the power steering. The vanes can be pulled out and cleaned but you must put them back in the correct orientation. They can only go in 2 ways and one of them is right Basically they must sit flush with the top and bottom surfaces of the vane carrier. They look square but are in fact rectangular. It's easy enough to tell which is correct. If you put them in incorrectly, you will destroy the pump. Just take your time, make sure its good and clean, and inspect everything very closely.
Reassembly is easy. The RSFH and its support go in fairly easily. Put just a drop of pentosin on the seals and smear it around. This helps keep them soft and keeps them from perma-bonding to the sides of the pump. The large o-ring has to be stretched into its little groove as you tighten the pump down. Then, when re-installed, fill the fittings with pentosin and turn it a few times by hand to get the pump "primed"
To purge the system and ensure it is fully bled, turn the steering wheel lock-to-lock a few times with the motor shut off. Repeat with motor running, then top up the fluid. Repeat again and you should be good.
Cheers, Brian
Bernie Benz adds:
FME, my further advice would be not to change the shaft seal unless it is leaking. Symptoms being external leaking, or air entering the hydraulic system (which also can be the fluid supply hose from the reservoir). This seal is under very slight negative pressure so has a low failure rate.
The most likely failure point would be one of the cylinder head O-ring seals on the front half, power brake end of the pump, which can be changed in situ. (A generic 2-018 O-ring, $0.10) Clean the pump and find the leak before deciding to R&R. DFI if IAB!
Tom Saltino adds:
Just to ensure that people don't get confused. The urS and 20v cars do not use the same pump. They are almost identical in design, but the S4 uses a high pressure. The urS pump is 110psi I believe and the 20v is 90psi.
Ivan Demkovitch adds:
Had hard time figuring part numbers for oil hose rubber O-rings used in my 93' S4. Here they are:
N-904-054-01 - thats o-ring for hose P/S -> Bomb (was $1 each, you need 2)
N-904-222-01 - thats o-ring for hose P/S -> rack. This one wasn't in ETKA for 93' S4 car. Dealer matched my old one and then we found it's for 92 A10Q Those were $5 each, good idea to get pack of 10 at McMaster
