In a message dated 7/11/00 9:04:08 AM Central Daylight Time,
owner-6pack-digest@autox.team.net writes:
<<
Sam, I just took my PDWA apart from my 1972 TR6 and the piston looks
torpedo
shaped on both ends as you described. The markings on my PDWA are: 4324/641
and 4L21. Mine measured:
groove inside diameter = 0.194"
groove width = 0.084"
bore diameter = 0.312" (so effective groove depth = 0.059")
I've read that o-rings should have a 10% diameter squeeze to seal,
so we need an o-ring with a minimum cross-section of 0.059" x 1.1 =
0.0649".
A "0" series o-ring has a x-section of 0.070" +or- 0.003" (0.067"-0.073"),
so a "0" series o-ring should provide an adequate seal.
Possible "0" series o-ring sizes are:
- -008 uniform dash size: id = 0.176" +or- 0.005"
- -009 uniform dash size: id = 0.208" +or- 0.005"
The -008 size is slightly smaller than the shaft and would be stretched out
slightly resulting in a snug fit on the shaft. While this will reduce the
x-section diameter slightly, the change should be very small and not cause
it to be less than the minimum required for a good seal.
The -009 size is slightly larger than the shaft and would be a loose fit.
This will require the o-ring to be compressed more when inserted into the
bore. The additional compression may be a problem when assembling the PDWA.
As the piston is inserted and the o-ring passes under the switch hole in
the PWDA body, the o-ring will want to squirt out the hole. If care is not
taken a small chunk of the o-ring will be cut from the o-ring.
I don't know which is the correct one to use. But I've decided to use the
- -008 size (in Ethylene Propylene of course).
Can anyone tell me if I've made the correct choice.
Wayne Whippo (Digest mode)
Boulder, CO
72 TR6 CC81472UO >>
Wayne;
The 008 size is the one I went with. Although they only have a
cross-sectional area of .070 (1/16") and the width of the groove indicates
that a .096 (3/32) is the correct size. Unfortunately, the .096 is
unavailable. I really don't think it will matter. I lubed up the rings with
silicone fluid, which is what I use, and slid the piston into the bore with
minimal resistance, tightened the plug in the end and put it back on the '6.
I used a MityVac and mason jar arrangement to bleed the system (one man
operation) and took the car for a 10 mile drive last night (with lots of
stops) and, so far, there is no more locking of the brakes. If the brake
light is on when you get done with the installation all you have to do is
remove the switch from the top of the PDWA and center the piston with a small
diameter pin punch.
Samuel R. Clark
Green Country Triumphs/Jaguar Enthusiast's Club of Oklahoma
VTR South Central Regional Coordinator
TS45355L O
CC82030U O
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