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FW: Triumph TR7, Brake Pressure Reducing Valve.

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Karl Schmitt

FW: Triumph TR7, Brake Pressure Reducing Valve.
« on: October 22, 2018, 01:06:36 PM »
Re: Tr-7 DHC, Brake Pressure Reducing Valve, build date, July 1979.

Present project is the restoration of the brake components with the brake
pressure reducing valve on my bench and disassembled. Condition is dirty,
gunky and the square profile rubber (?) O-ring seals have deteriorated beyond
So, what are my options?

Is a seal service kit available to purchase? If so, I have not been able to
find one.

Purchase an assortment of Square Seals from McMaster-Carr, inch or metric to
be determined, clean the components, install new seals and re-assemble. Would
cost $50 - $60 or so and I would have many surplus seals left over.

Purchase a 50/50 proportioning block from the Wedge Shop for $91, which I hear
many do, successfully. Add an RPC Inline Proportioning Valve for $71 if you
want to adjust the bias pressure.

Purchase a modified pressure reducing valve from TSI, but, the seals are the
originals furnished with the core.

Specifying and selecting O-ring seals I am somewhat familiar with from way
back when I was gainfully employed. James Tencate could probably help with
this as he is presently employed in the Engineering field.

As to why square seals instead of round O-rings, well they seal a bit better
in a static application and the movement of the pistons (plungers) is very
short indeed. Also, the Wedge shop offered an interesting comment, i.e.,
replacement valves are most likely NOS and today nearly 35 years old. Just how
good are the seals contained therein?

Your comments would be appreciated, direct at or via the list.

Thank you,

Karl Schmitt, SLTOA and the Wedge Group.

Sent from Mail for Windows 10

Benjamin Zwissler

Re: FW: Triumph TR7, Brake Pressure Reducing Valve.
« Reply #1 on: October 22, 2018, 01:29:32 PM »
EPDM is the material generally recommended for brake fluid.  Lots of places

have square and x-ring o-rings.  Do you know which they are?  the X-rings

have two sealing bumps with a valley in between.   Here's a link to a site

that popped up in a quick search:

I'd like to rebuild mine but it doesn't leak and I've never taken it apart.