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Re: 5000 brake booster (servo)

Ljubisa Stevanovic (stevanov@crd.ge.com) wrote:
> This weekend I found out that hydraulic brake booster (servo) on my 87 5000TQ 
> needs replacement. The symptoms were same as those experienced by others with 
> failed presure accumulator (initial loss of brake assist after overnight 
> rest), except that my accumulator is good. The next step was to disconnect a 
> return line at the servo where, much to my dismay, I observed fluid leaking 
> out at a slow, steady rate. 

I haven't had a problem with the brake booster yet :-) (same car as yours)
but have replaced the pressure accumulator and brake master cylinder recently.
Just curious, how do you know that the pressure accumulator is good and
that the booster is bad? Did you do the pressure tests described in
Bentley? Or is it because of the leak at the return line? May be that leak
can be fixed by replacing the return line fitting (much cheaper, I would

> The new part is available from Carlsen only and it costs $510, but before I 
> order it I would like to hear from those of you who have had to repair this 
> before. Is there a kit for rebuilding these things? How effective it is? Is 
> it easy to perform (nothing that saves $500 should be too difficult)?

May be you can try Shokan (800-ALL-AUDI) to see if they have a used one.

> Should I expect any problems when separating/reassembling the booster and 
> the master cylinder? 

Not w.r.t the master cylinder. As I mentioned, I replaced the brake master
cylinder recently and it was straight-forward. There are two plugs under
the cylinder that can be removed to drain the fluid. Disconnect the brake
lines, and remove the two bolts holding the cylinder to the booster.
Reassembly is just as simple. You may have to adjust the length of the
plunger (I'm not sure this is what its called) in the booster that pushes
against the master cylinder piston, since you will be changing/rebuilding
the booster. I recall seeing something to this effect in Bentley. A mis-
adjusted plunger can cause brake drag or excessive pedal play. I didn't
adjust this plunger since I was only replacing the brake master cylinder.

Hope this helps. Let us know how you make out.

87 5000 TQ

Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ