Home > Trog > Brakes again…Picture explains some things

Brakes again…Picture explains some things

March 19th, 2009

One of the brake fluid reservoirs keeps emptying, and I’ve been scratching my head trying to figure out where the brake fluid goes.   It does soak into the concrete and evaporate, so a slow leak could go unnoticed.

However….this pic shows where the mystery fluid went.


That’s the upper brake servo.    Upon opening it 1 liter of brake fluid came gushing out!    Ooops.

Alternating brake fluid colors between blue and yellow lets you know when you have completely bled the system when replacing all the brake fluid.


I suspect moisture in the brake fluid caused the slave cylinder walls to corrode, allowing brake fluid to sneak past the cup seal and into the vacuum chamber on the right.   Fluid could have also slipped by the reaction piston as well.  Surprisingly the rubber bellows and seals seemed to be in great condition.

Here’s a pic of a more modern slave and reaction piston.


Slave piston on top, reaction on bottom.    The reaction piston in Trog only had 1 O ring seal – a failure point addressed with the double seal in later revisiion….so that could be the culprit.   (Pic stolen from the website linked below)

Here’s a page on a rebuild of the servos

I could have possibly had the cylinder sleaved with chromed inserts, but given that the whole unit is 30 years old and it is an essential safety feature, I think replacement is prudent.

The new replacements from SNG Barrat USA have a higher boost ratio as well at 4.25:1 vs 3:1 of the old servos (I’m not 100% sure the old ones are 3:1).  This means the braking power will be increased.

Will the brake saga end here?    There is a 30 year old master cylinder that I haven’t dug into yet….

UPDATE (3/11/2010):   The old boost ratio is “approx 4x” according to the service manual. A reader pointed out that the vacuum shell, slave and reaction cylinder diameters are the same on the LR18230 as on the stock servo (8″, 5/8″ and 3/8″ respectively).   So it makes sense the boost ratio would be the same.

  1. Daniel
    May 30th, 2010 at 13:20 | #1


    i am rebuilding 2 of these vehicles and im having trouble finding parts for the servos.

    can you order parts from lockheed?
    how did you solve this problem?
    WERRY nice project!

    regards Daniel

  2. wesc
    June 2nd, 2010 at 18:55 | #2

    I ordered replacements from sngbarretusa. see post for URL.

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