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Ecklers AutoMotive
Username Post: Can a power booster leak off all vacuum?        (Topic#354471)
vabeach56wagon 
Valued Contributor
Posts: 3133
vabeach56wagon
Loc: Chesapeake,VA,
Reg: 04-22-02
12-20-18 08:49 AM - Post#2755116    

Engine vacuum reading is way below 6.5hg...way below.

All vacuum lines from carb are without leaks.

Vacuum line to power booster is fresh and manifold fittings are sealed.

Compression in the engine on all cylinders is within 10% of #4 Cylinder:


Lowest figure is 185psi.

I've sprayed to find any leaks at manifold/carb base...nothing obvious, nothing leaking. But keeping the engine running for any extended period of time for additional testing is tough because the power valve is hanging open at such low vacuum.

So my question is: can the booster be so blown as to bleed off all the vacuum in this engine? This evening I plan to plug the booster's vacuum fitting on the intake. I just find it amazing that this could be the cause of the problem.

paul

Original builder of the Gobstomper - '56 210 9 passenger wagon now in other's hands. Current Ride is '69 X33D80 Z28 Camaro



 
Ecklers AutoMotive
Rick_L 
Honored Member
Posts: 27602
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
12-20-18 11:59 AM - Post#2755121    
    In response to vabeach56wagon

It sure can, but the check valve would have to be blown too, unless the vacuum leak symptoms were noticeable only when the brake pedal was applied.



 
acardon 
Ultra Senior Member
Posts: 11181
acardon
Loc: DFW TEXAS
Reg: 03-25-05
12-20-18 03:46 PM - Post#2755136    
    In response to vabeach56wagon

  • Quote:
But keeping the engine running for any extended period of time for additional testing is tough



Why not plug the booster hose and all other vacuum lines? Is there a transmission modulator?

Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


Edited by acardon on 12-20-18 03:47 PM. Reason for edit: No reason given.

 
55MAS 
Senior Member
Posts: 1488

Loc: North Coast, Ohio
Reg: 12-19-01
12-21-18 07:32 AM - Post#2755186    
    In response to Rick_L

  • Rick_L Said:
It sure can, but the check valve would have to be blown too, unless the vacuum leak symptoms were noticeable only when the brake pedal was applied.



The vacuum booster itself can can also have an internal leak at the diaphragm. Sometimes one can detect ans audible "hissing" under the dash where the plunger rod passes



 
vabeach56wagon 
Valued Contributor
Posts: 3133
vabeach56wagon
Loc: Chesapeake,VA,
Reg: 04-22-02
12-21-18 12:30 PM - Post#2755208    
    In response to acardon

No modulator: 4 speed...I have replaced the booster check valve, all vacuum lines, checked and double-checked the flared fitting in the rear of the intake...

So just to be sure I decided to double down on the spray testing. Last night as I sprayed brakleen at the back left carb base, it killed the motor, bam...."aha", said I, "found it"....




then I smiled, turned off the lights and went back in the house and fell asleep, dreaming of sugar plums, a nice steady idle, snap response to throttle and clean plugs. I'll attack the intake carb base sometime before Christmas....

Merry Christmas

paul

Original builder of the Gobstomper - '56 210 9 passenger wagon now in other's hands. Current Ride is '69 X33D80 Z28 Camaro



 
4dr 57 
Valued Contributor
Posts: 4576
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
01-05-19 11:22 AM - Post#2756634    
    In response to vabeach56wagon

Carburators don't need much manifold torque, just a 1/8 past snug, like an oil filter only less.Otherwise the carb will warp...everywhere after constant tightening, snugging up just a bit, more...maybe add a new gasket this time.


It's all good. mostly




 
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