Re: 5000 brake booster (servo)

[Andrew Duane USG/PE <duane@zk3.dec.com>]

> I've found that failed hydraulic boosters are a fairly common problem. I bet
> lots of folks are driving around with marginal boosters. I also "think" that
> replacing the pressure accumulator will make a marginal booster look good due
> to the higher hydraulic pressure available.  
> 
> Anyhow, the telltale booster test is to disconnect the return line from the
> booster (the one that goes back to the reservoir). If _any_ hydraulic fluid is
> dribbling out of this line when the brake is not applied, the booster is
> marginal. The higher the leak rate from the return line, the more "bad" the
> booster. Since this is an internal leak, it's easy to understand why folks may
> not know they have a problem.
> 
> Symptoms of a bad booster are: a bit higher pedal effort (but not too bad) and
> lack of pressure reserve. Try pumping the pedal hard 5-10 times while the car
> is idling. Can you make your brake warning light come on? Suspect the booster,
> especially if the pedal effort seems to remain normal.  Be careful that a bad
> accumulator can create similar symptoms. If the booster leaks all the time, the
> pressure accumulator may never reach full pressure. Old accumulators that are
> OK, but are holding less pressure are "bothered" more by booster leaks.

Hmmmm.

This rings a bell. Angela's 1990 90Q recently had these symptoms exactly.
The dealer replaced the accumulator under warranty, and the problem
sort-of got better for a while. But, the brake light still stays on
for a long time (30 seconds), and the pedal effort seems noticeably
higher than my 1989 100Q. After a short park, the pressure is OK.
Overnight, pressure leaks out, and we have 30 seconds of brake light
again.

I think maybe this weekend we will take a look, and see if we need the
booster replaced under warranty, too.

Where is the booster located in a 90Q (20V) ?

-- 

Andrew L. Duane (JOT-7)			duane@zk3.dec.com
Digital Equipment Corporation		(603)-881-1294
110 Spit Brook Road			http://www.zk3.dec.com/~duane
M/S ZKO3-3/U14
Nashua, NH    03062-2698

Only my cat shares my opinions, and she thinks brakes are for wusses.