Re: Changing the Bomb

[Alex Kowalski <akowalsk@shrike.depaul.edu>]

Al Powell wrote:
> 
> First and most important, do not confuse hydraulic oil (Pentosin) and
> ATF. They are not the same thing and ATF in the hydraulic system will
> ruin the seals. This WILL lead to leaks in the steering and possibly cause
> the check valves in the accumulator to stick. This leads to power brake
> loss unless you have a particularly good pump working for you.
> 
> There are reports that  ATF is used in some systems. It seems to
> depend on the car, so check your owner's manual AND read the label on
> top of the hydraulic reservoir carefully!!!!!!!

> 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.

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

Best Wishes,

Alex Kowalski
'84 4KQ