View single post by Mark Rosenbaum
 Posted: 04-06-2005 11:40 pm
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Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
The TR6 conversion was the master cylinder only.

If brake fluid is leaking into the servo from the master cylinder, the master cylinder is defective and requires replacement as soon as practical.  A very large percentage of rebuilt British master cylinders seem to fail almost at once, perhaps due to counterfeit parts that some years ago were discovered in the distribution system, so I'd opt for a brand new master cylinder whenever possible.

A 'firm feel' to the brakes sounds normal.  With the car moving slowly in a non-traffic area such as a disused parking lot, you can test the servo by determining the amount of leg force needed to just lock the brakes with the vacuum line to the servo (a) connected and (b) disconnected and capped off at the intake manifold.  The latter case should require a very considerable increase in force -- perhaps 5 to 10 times as much.

If you think you have a vacuum leak, the servo can be tested while still on the car.  Simply apply a vacuum of about 20" Hg to its inlet and see how long it takes for the vacuum to drop.  A serviceable unit should maintain perhaps 15" Hg of vacuum for 10 minutes.  A really good one will hold the full vacuum for much longer than an hour.

I will note here that, unlike passenger cars with mild street camshafts, the JH with stock cams produces only about 15" Hg of manifold vacuum at idle.

In the event your servo won't hold vacuum, check the one-way inlet valve and its gasket before condemning the servo itself.

There's a truly excellent article on the Buckeye Triumphs website (don't have the URL, sorry, but a Google search should work) that is highly recommended to anyone interested in the topic.  The attached drawing has been borrowed from there.

Attachment: Brake servo internals.jpg (Downloaded 620 times)