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Triumph TR6 - brake servo problems

After a major interior restoration I have got my TR back on the road. The car beeing stopped for nearly 5 month generates problems in the brake servo. Before I started on the interior job the brake servo functioned well.

During driving conditions both servo chambers are subject to inlet manifold pressure. Applying the brake should leave the forward chamber at inlet conditions whilst the rear chamber is exposed to atmospheric pressure. As a result the diagram should move forward assisting to operate the main pushrod of the master brake cylinder. So far the theory.

Depressing the brake pedal one can hear a hissing sound inside the footwell. The hiss remains for the time the brake pedal is pressed. The servo is clearly not functioning, hughe brake pressure needs to be applied.

I think the valve (?) seperating the chambers does not close.

Does anyone have experience whith repairing servo's ?
Are there any tricks to fix this ?
Is overhaul a feasible option ?

Any advise welcom,
E. Creyghton

Hi Erik

No experience myself. They rarely fail on any car. From the hiss you have a problem. Did you change anything or have problems hooking up brake pedal clevis? Don't run out and buy one something seems wrong after only 5 months. I don't have a good understanding of exactly how valves work. But I would check vac. at line and one way valve first.

Used ones are fairly easy to get at least here. And are likley best bet.


Bill Brayford

The link below is to Buckeye Triumph's page. The article here is to rebuild the servo. I didn't read it, but its written by the same guy who did the article on carb rebuilds and brake systems. He must be an engineer, a teacher, or both. Really does a good job explaining things.

Let us know how it works out, and good luck.

Mark H


Thanks very much for the link, it looks like an interesting artical. I did not yet decide to pull everything apart. Because the servo functioned well before and nothing was altered in the brake system I assume something is stuck inside. I still hope to be able to free-up whatever is jammed without starting a major brake system overhaul.

E. Creyghton


Hiss heard inside means blocked air filter. Air filter should let air rush in no hiss and let vacuum assist brakes.

Air filter may have gotten paint clogged when you were doing interior. Its under the rubber cap behind clevis at pedal connection..

Sorry, Must be getting old should have spotted your hiss comment.

Bill Brayford

I carefully studied the brake servo experience, and decided to have a go at it. I got the servo out on the workbench and bolted some heavey steal profiles to the studs to mount it in a bench vise. What ever mussel I applied, it would not open. I do not have a sledge hammer like described in the document, I did however gave it a big whack with a heavey hammer without result.

I have now installed a new one (Lucas ?!) and will try again to refurbish the original over next winter period.

E. Creyghton

Eric-According the instructions in the Haynes manual, the servo should be hooked to a vaccum source (manifold or pump) when trying to seperate the 2 halves. Has anybody had their servos rebuilt by Partco for $85, as suggested in the Buckeye article?

This thread was discussed between 11/05/2003 and 24/05/2003

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