bomb rebuild - the thread that wouldn't die

[Mike Arman <armanmik@n-jcenter.com>]

Bomb recharge thread - more (gack!)

Found some gen-you-wine Audi sales info from 1986 vintage, and there was a
cutaway and operation description of the famous Lemforder bomb.

1. Drawing clearly shows a threaded plug at the mounting end of the bomb.
On the 89 100 bomb I have on my bench, this plug (if present) is under the
mounting stud which is spot-welded to the dome, and thus probably
inaccessable (chisel?). Earlier model bombs (1988 and down) may not mount
this way, so the plug may be accessable - fairly easy recharge here, if
this is the case! Anyone got an older bomb to look at the plug? Suggestions
on remove and replace the mounting stud to access the plug?

2. Operation: Pump feeds a tee. One leg of tee has a relief valve set at
150 bar (2205 psi) which goes back to the reservoir. Other leg of tee has a
relief valve set at 144 bar (2116 psi) which feeds the pressure accumulator
sphere AND feeds the brake booster.

When the brakes are not applied, accumulator filled with pentosin to 150
bar, whereupon the 150 bar valve opens and vents excess pentosin to the
reservoir. (Accumulator never exceeds 150 bar.) System is stable.

Brakes applied, pressure in booster line is reduced, accumulator tries to
restore pressure (volume of incompressible fluid) to booster line. Pump
supplies some pressure, accumulator supplies the rest. With repeated brake
application (or low bomb pressure), eventually the accumulator is exhausted
and the pump only supplies (inadequate) pressure (volume) to the booster.
(Autocheck goes berserk, wallet tightens up, visions of Chevrolets cross
mind of Significant Other.)

Since the pressure is now under 150 bar, the relief valve to the reservoir
closes, and all the pentosin goes to the booster and to recharge the
accumulator.

Brakes released: Pentosin flow is to accumulator until 150 bar is reached,
whereupon relief valve to reservoir opens again. The system is stable again.

Function of the 144 bar valve seems to be to prevent the accumulator sphere
from depressurising should the 150 bar valve stick, and to maintain a
stable 144 bar in the sphere while waiting for the next brake application.
(Keeps the brake effort consistent - if the pressure varied, sometimes the
brake effort would be light, sometimes heavy.)

3. Checked in Burden's Surplus Hydraulics catalog (1-800-488-3407), found
the following:
	pressure accumulators, 10 cu in (11" long) and 29 cu in (16" long), 3000
psi max, fill with schrader valves (!), $79.95 each, new.
	relief valves, adjustable from 1500 to 2500 psi, $12 to 20 each, depending
on exact style. Also new.
	Lots of hose fittings, tees, etc. cheap.

Anyone got too much time on their hands and want to pursue this further?????

Could we build an easily rechargeable bomb retrofit kit for less than $150
using these parts?


By the way, this is off the Alfa list - interesting!

>P.P.S.   Saw a 164 <Alfa, not Volvo> with a rusted-out right rear quarter
panel >Saturday.  Very disappointing for a car with a galvanized body.  You
never see any rust >on galvanized-body Audis, even in Minnesota, home of
road salt <snip>
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Best Regards,

Mike Arman