[s-cars] Hydraulic Pressure Accumulator aka "Bomb" lessons learned...

[Peter Schulz]

Guys:

I recently replaced a pressure accumulator on our green S6 avant 
because the brake light was flickering after multiple stops and it 
took a long time to charge after first startup.

Sure enough, it failed the bomb "test'- ignition off, count how many 
times you can depress the brake pedal until it gets hard...a "good 
bomb" should be something over 15 pumps...

I had a old spare bomb recharged by Dave Kase (who now has Russ 
Southerlin's rig) for recharging the nitrogen bomb bladder.

It took me all of 30 minutes to remove and replace the accumulator...
Things seemed fine at first. The next week however, noticed that the 
car was loosing brake assist, to the point where I had to rev the 
engine to get ANY assist, and then the brake pedal would get hard and 
actually stutter on the travel down to the floor.

I also made sure to clean the screen on the banjo bolt for the line 
to the pump ( "J" hose)

I suspected a bad hydraulic pump, or worse, having to replace the brake servo.

I tried to remove and replace the old hydraulic fluid from the 
reservoir to see if it would help ( it didn't), and yes the old fluid 
was dirty.

Sanity prevailed however, and I first decided to replace the rebuilt 
bomb with another rebuilt 7a 20v bomb I also had...

Long story short - full assist has returned, brake light only stays 
on for a moment on the coldest mornings....

Seems that the pressure valve on the "bad" rebuilt bomb was 
compromised...so even though it had a new nitrogen charge,  the 
pressurized hydraulic fluid coming from the pump lost pressure there 
on its way to the brake servo, so no assist.. Dave said he doesn't 
currently have the capability to test the valve, perhaps sometime in 
the future.

so lessons learned:
o R&R fluid if the old stuff is dirty
o Clean all the screens as they can reduce flow
o Bad check valve means no pressure to the servo
o a B3/Coupe Quattro bomb will bolt right into a 95 S6

For me the cost of the recharge from Dave was worth the gamble of a 
bad check valve
...others in the past have bought new bombs that already had a low charge
( shelf life is critical, the nitrogen bladder is a glorified balloon 
and it WILL leak over time.)
_________________

-Peter Schulz
Chelmsford Ma, USA
http://www.naaclub.org/

1995.5 S6 Avant Emerald/Ecru
1995.5 S6 Avant Silver/Platinum

1991 200 20v Q Avant Titan Grey
1991 200 20v Q Avant Indigo Mica (for Sale)
1991 90 20v Q Red

1990 CQ silver  (sold)
1991 CQ silver  (eS2 recipient)