[Healeys] FW: BJ8 Brake servo problem

[Bob Spidell]

John,

I'm not familiar with the PBR per se, but AFAIK all servos--at least for 
Healeys--pull vacuum on both sides of the large piston in the vacuum 
cylinder during normal running.  When you apply the brakes, a valve 
admits ambient air at atmospheric pressure onto the top of the piston, 
which pushes against the vacuum on the underside and applies pressure to 
the fluid piston in the servo's master cylinder, which applies pressure 
through the brake fluid to the slave cylinders.

It sounds like there's a leak around the seal of the large air/vacuum 
piston, admitting air into the vacuum side and hence into the intake 
manifold (the source of the vacuum).  This would explain both the rough 
running during braking and the slight RPM increase when brakes are 
applied (esp. if you're running somewhat rich like most Healeys need to).

If the vacuum canister can be easily disassembled, then it probably can 
be rebuilt (if you can find a kit).  If it's welded or riveted or 
otherwise sealed it's probably not meant to be rebuilt (or worth the 
trouble).

bs



Rebecca Sawyer wrote:
> From: John Sawyer [johnbeckysawyer at yahoo.com] 
> Sent: Tuesday, November 27, 2007 7:49 PM
> To: 'healeys at autox.team.net'
> Subject: BJ8 Brake servo problem
>
>  
>
> I have a 65 with a servo that is not original, I think it's Australian.
> Patton's Brake Replacements (PBR).   Recently the engine runs rough when
> brakeing.  At idle the engine idle speeds up slightly when brakes are
> applied.  I think the problem is with the servo affecting the intake
> manifold.  Any one have experience with this? 
>
> Can the servo be rebuilt?   
> _______________________________________________
>
>   


-- 
***************************************************************
Bob Spidell         San Jose, CA        bspidell at comcast.net
'67 Austin-Healey 3000             '56 Austin-Healey 100M
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