[DML] Brake booster/Servo troubleshooting

["Ed B." <mr.pants@xxxxxxxxxxxx>]

A few question about the brake booster/servo:

My braking is the pits: I can slam the brakes on, hold with all my force 
and I will not lock the wheels up.  The car does stop, but it's nowhere 
near what it should be in terms of rate of deceleration.  This is at 
around 15mph in my driveway.  At higher speeds, I do slow down, but 
again, it seems really poor and I have to apply a LOT of pressure to get 
decent braking.  I'd be screwed if I had to do a panic stop at speed.  
All brake components are good/new: master cylinder, calipers, rotors, 
pads, fluid, all is properly bled, no air in the M.C.  I know the 
DeLorean brakes are not the greatest, but this is terrible. 

Would a bad servo cause weak braking?  I removed the vacuum hose from 
the servo and there is nice suction from it when the engine is running.  
I also did a crude test of the check valve by connecting separate, short 
hose to the check valve inlet and I cannot blow through, but I can draw 
(albeit with difficulty and not freely), indicating the check valve is 
functioning, right?  I do hear a faint hissing around the servo, but it 
doesn't sound like a leak - more like the vacuum noise inside the hose.  
What else can i check?

How do I check if the actual servo/booster itself is good?  The manual 
does not seem to be much help here -  it doesn't even show where the 
other end of the vacuum line goes in the engine bay...

Thanks...
- ed

-- 

1982 DMC-12 [11594]
1986.5 928S
1990 Coupe Quattro 20V




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