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Rebuilding the tandem-style hydraulic pump
(This procedure does not apply to the earlier system using
ATF fluid as fitted to, e.g., WR and WX-engined ur-quattros)

This is the full procedure including the shaft seal. It is in general applicable to all tandem pumps such as the long "grey casting pump" ("Graugußpumpe") fitted to later Type 44s and the box-shaped pump fitted to the MB and RR ur-quattros, Audi S2 amongst other vehicles. Be aware that a leaking power steering pump is now an MoT failure item.

A degraded brake assist pump can cause poor brake performance. The classic test is to remove the drive belt (as described below) and rotate the pump with a finger pressed onto the outside of the pulley. There should be a marked resistance - twice per revolution on earlier pumps, only once on later models. It should be necessary to grip the pulley to overcome this.

Parts required:

Special tools required:

Otherwise it is assumed that a comprehensive toolbox is available. A digital camera is useful to record, e.g., the position of the mounting brackets on the pump prior to removal from the car.

Many people have only limited success at this operation - it is a Haynes "5-spanner" item. There is nothing intrinsically difficult - care and attention to detail will guarantee success. Cleanliness is important, as is an understanding of some of the basic principles of engineering. The pump is lubricated by the oil it pumps, so all references to "oil" on this page refer to green hydraulic oil; Audi part number G 004 000 M2 or an equivalent.

Audi tandem hydraulic pump
Audi hydraulic pump split showing
Rubber Seal from Hell - RSFH

The tandem pump is actually two pumps, as its name implies. The rear section is a standard high-volume low-pressure power steering vane pump - the front part is a low-volume high-pressure pump for the braking system fed by an internal bleed from the power steering pump. The hoses are - from front to back - high pressure to brakes, lower pressure to power steering, feed from the reservoir. The latter two are normal hoses and can be replaced with made-up patterns, but the high-pressure brake accumulator hose contains a special constrictor to reduce noise.

The rear half of the pump is essentially sealed and apart from some O-rings between itself and the front portion is along for the ride in the following procedure. It stays in one piece via stiction but can fall apart and scatter the vanes on the bench if not treated with respect. The front part is somewhat more stressed. Most rebuild failures occur because one of the mating faces is damaged or O-rings are not pre-oiled when being replaced. The following procedure is for complete disassembly to replace the shaft seal - note that in this case the pistons cannot be replaced until after the pump has been reassembled.

While the pump is split into two halves, it is VERY susceptible to damage; this procedure has been optimized to reduce this time. The central body joint is metal-to-metal and the slightest burr on an edge will prevent a good seal. This joint is under considerable pressure because of the pump-to-pump feed - if it leaks, check for this first. Otherwise, an extremely thin film of Loktite 542 thread sealant may help. Yes, that is how much 50ml costs. No, they don't make smaller bottles.


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