[Healeys] fuel in Brake Booster

Bob Spidell bspidell at comcast.net
Wed Dec 30 17:58:47 MST 2015


I'm having trouble following your description because:

1) there should not be a 'vacuum hose' going into the stock air 
filters.  That is actually a (slight) pressure hose for venting 
crankcase fumes back into the induction system for combustion

2) there IS a vacuum hose from the brake servo--with a check valve at 
the servo or possibly fitted inline in the hose--and it should never be 
installed anywhere but on the nipple on the intake manifold

3) if you want to run a vacuum line from the crankcase to the intake 
manifold you need to install a PCV valve inline

Anyway, the only possible way to get fuel in the servo is from the 
intake system downstream of the carburettors; if 2 cylinders were 
not/mis-firing that unburned fuel would end up in the crankcase and oil 
(and possibly some evaporated back into the induction system). So, yes, 
some fuel could get into the servo via the vacuum line on the manifold, 
but if it was more than a trace your engine would likely be flooded out.

I'm not sure what the servo rebuilder was talking about (unless you 
talked to the tech that did the rebuild he could have been blowing 
smoke).  There is no 'baffle' in the servo; the large air/vacuum piston 
has a rubber/leather seal around the perimeter, and this can get brittle 
contributing to poor operation of the servo.  The typical failure 
mechanism--the one resulting in brake fluid being drawn into the 
air/vacuum cylinder--is the aging and embrittlement of the 'gland seal,' 
a small, circular rubber seal that seals the shaft of the air/vacuum 
piston; on one side is manifold vacuum and on the other is the brake 
fluid in the servo's 'master' cylinder.

If all your hoses, etc. are connected properly to their proper locations 
I would not worry about getting fuel in the rebuilt servo.


On 12/30/2015 3:07 PM, R. Price Lindsay wrote:
> Listers -
> A couple of weeks ago my brakes were acting funny.  It turned out that all of the fluid was out of the brake/clutch reservoir.  I sent the brake servo into be repaired at the suggestion of the list.  I just talked to the rebuilder and he said the baffle in the servo was swollen because of a large amount of fuel present in the booster.  He mentioned this is not unusual with TR6”s.  I guess this can cause the servo to fail and  draw the brake fluid into the servo.
> Now that the servo is fixed, I don’t want a repeat the problem and am searching for a cause for the presence of fuel.  A few months ago I was having a problem with fuel starvation.  It turned out to be a pinched fuel line.  During my long search I made a number of changes including installing a new distributor cap and wires.  Somehow I switched a couple of wires and could not get a spark in cylinders 5 & 6.  I found the problem after quite a bit of trying to get the car to run smoothly and driving it for 20 - 30 miles.  Also, maybe a contributing factor or maybe not, a year or two ago I moved the vacuum hose to the induction manifold because I installed air cleaners without a connection point for the vacuum hose. (Before the fuel starvation issue I reinstalled the original air cleaners and moved the vacuum hose back up to the air rear cleaner.)
> Now for my question: Could the presence of fuel in the brake booster have been caused when I was not getting spark and not burning fuel in 5 & 6?  Could the unspent fuel have been sucked into the servo through the induction manifold a while ago, or through the air cleaners recently?
> Thank you so much for your collective thoughts.
> Price Lindsay
> 67 BJ8

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