Re: Changing the Bomb

[raf40@oes.amdahl.com (Richard Funnell)]

>Al Powell wrote:
>>
--snip--

>
>> The hydraulic pump is really two pumps in one. One runs a circuit for the
>> power steering, and the other circuit is for the brakes.
>
>Yes, absolutely correct, and you can differentiate the two systems
>because, on the one hand, the power steering and brake systems both
>depend on the high-pressure hydraulic (Pentosin-driven) pump, and on the
>other type, they don't.

This isn't quite true.  My urQ has hydraulic assist on the brakes, what
you're calling a linked system, and it calls for ATF.

>
>The '84 4KQ that I have has power steering and power brakes.  Although
>the front-mounted steering pump looks to all the world like the same one
>at the front of other Audis, with great big hex nuts and all, its
>reservoir cap specifies ATF as the fluid and I have never had any
>problems with it using such.  The brakes on my car are operated by a
>normal, VW-looking <<vacuum-assist servo>>, master cylinder, and fluid
>reservoir, with NO cross-connections.
>
>My dad's '86 5k wagon, on the other hand, has the linked system which I
>believe runs at a higher pressure (see David Head's archived
>information about high-pressure nuclear-reactor coolant pumps on
>our aircraft carriers for enlightenment as to why so high a pressure)
>and, at least on his car, has leaked on several occasions.  I can only
>conjecture that this setup was introduced by Audi to correlate the
>steering and brake feel to each other more exactly

I'm not sure why they use this system.  It may be related to the large
number of cars that use turbo's, almost all in the 5000/200 series, and the
fact that a turbo engine under boost doesn't supply vacuum.

>, and on a non-leaking
>car, it works very well to impart a sense of harmony between the steering
>and braking effort.

I don't know about the harmony concept.  I suspect it's just a case of
wanting to use a common power source (the high-pressure pump) for more than
one function.

>
>Best Wishes,
>
>Alex Kowalski
>'84 4KQ

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL