The following is a public service message to anyone considering replacing the
pressure differential valve in the brake lines of a TR-6. Be forwarned that the
replacement part is definately not OEM. Some background: In the process of my
restoration of my 6 I found that my old valve was leaking through the warning
switch that is attached to the valve unit. A call to The Roadster Factory to
check on a replacement nearly floored me when I found out the price, $170.00
since this is the only part that is preventing me from driving a car that has
been sitting in my garage since 1984 and has just undergone a 2 year frame off
nut and bolt restoration I decided to bite the bullet and ordered the valve by
2nd day air. What came is a monstrosity, first it is no longer made of brass
but instead made out of cast metal. I could live with this howeve, the size of
the thing is twice the size of the old unit which means is no longer fits where
it is supposed to be mounted without moving the speedometer cable, where is runs
through it's lower grommet. Even at that I fear that the firewall will be in
the way. Finally, to add insult to injury they have switched the ends that the
front and back pipes thread into. For those who are not intimate with this
valve let me explain. There are two different tread sizes on a TR6, a large
thread for the front brake pipes coming from the mastercylinder and entering and
exiting this valve and a smaller thread size for the back brakes. The way the
original valve was made the larger front threads match an inlet that is toward
the side of the valve that contains a large bolt which is part of assembly and
partially restricts the front brake pipe flow through the valve. On the new
valve this is completely backwards the smaller threads that are required for
the rear brake pipes are on the side with the bolt. Now I don't know exactly
how this bolt figures into the workings of this valve (is does appear to
partially restrict the fluid ), but I can't help but feel there is a reason for
the use of two different sized thread patterns on the front and rear brake pipes
and that this is related to allowing only 1 orientation of the original valve
assembly so that this bolt was part of the front braking system. The fact that
the new valve has it as part of the rear system makes me nervous. I called TRF
and they said send it back and we will look at it but they didn't sound all that
suprised. But enough ranting on my part, I have some questions for those of you
on the list.
Where can I find a new original valve for my car?
If none are available can I fix the old on?, I have been told that the valve has
O rings in it that are the cause of my leak. Does anyone sell replacement O
rings?
Any help will be appreciated, I am desperate to get some miles on this car
before the snow flies and am considering just putting the old one back in with a
bolt and gasket in place of the switch so that I can drive the car.
Thaks for letting me get this off my chest.
Kevin A. Strait, Ph.D. voice: 612-624-5150
Assistant Professor of Medicine email: strai001@maroon.tc.umn.edu
and Cell Biology/Neuroanatomy fax: 612-626-3840
Box 91 UMHC
University of Minnesota
Minneapolis, MN 55455
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