I believe the answer is the water molecules are larger than the air molecules,
which makes them easier to pass through the space. I think Gore-Tex work the
same way, lets the fabric breathe, but keeps the water out.
Not sure why I know this :)
Charly Mitchel
TR6 #44
----- Original Message -----
From: J Wagner via Fot
To: fot at autox.team.net
Sent: Tuesday, March 06, 2018 8:03 AM
Subject: Re: [Fot] Type A OD pressure test
I?m almost embarrassed to chime in here as I have no expertise on the inner
workings of a transmission, but perhaps it?s more of a question than an answer.
I?ve run a lot of PVC irrigation pipe in my day, particularly in the last few
years landscaping my house. I?ve noticed that whenever I turn on a new
system, the air compressed by the incoming water with force it?s way past
connections of threaded pipe, joined with teflon tape, and take a little water
with it. Just when I?m thinking that I?ve failed to tighten the pipe enough,
the leaking stops once all the air escapes.
I suppose it?s a fluid dynamics question. Will compressed air act
differently on seals than pressurized oil?
Maybe the escape of air is as meaningless as it has been in my sprinklers?
?Justin
On Mar 6, 2018, at 6:48 AM, M&M Hado via Fot <fot at autox.team.net> wrote:
Greg,
Just a couple more thoughts to add to the good suggestions already offered.
I especially liked Jack?s idea of hand-lapping in the aluminum seats with a
ball welded to a rod.
I?m guessing that most of the air you?re hearing is leaking around the
outside of the operating valve since air is much more likely to do so than the
relatively thick 90 weight oil. Just the fact that only 120 psi of air
pressure is enough to move the operating pistons tells me that the rest of your
system is relatively tight. The normal operating pressure after all is about
400 psig so you have a lot of ?fat? built into it.
One thing that might cause the operating pistons to move with a relatively
small pressure is having weak or incorrect springs pushing the cone clutch
rearward. Be sure you have the so-called ?long? and ?short? ones in the right
locations, It?s actually the coil bound length that determines which is which.
If you put a long one where a short one will be, it may bind before reaching
full movement, resulting in the cone clutch not reaching the brake ring. Don?t
ask me how I know this. To check this, I put each spring on a threaded rod and
run a nut down the rod until the coil binds. Measure the length at that point
and the long springs will be about 3/8? longer than the short ones.
Also, the seating of the balls on the aluminum seats in the casing is
indeed important but it?s also important to have a good seat between the ball
and tip of the operating valve. I had a D-type OD that was eating my lunch
with low operating pressure during engagement and the tip of the valve was
nicked resulting in a bad seal. Changing the valve solved the problem. The
oil flow is very small in the system so a leak of even the smallest area will
drop the pressure quite a bit.
Lastly, you mentioned the ?relief valve? and I?m not sure which valve you
are referring to since the pressure relief occurs when the accumulator piston
moves enough to uncover the relief holes back to the sump. Since you only had
120 psi, the accumulator piston would not have moved nearly enough to
?relieve.? I?m guessing you were referring to the operating valve.
Mike Hado
From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of barry
rosenberg via Fot
Sent: Tuesday, March 6, 2018 5:31 AM
To: Jack Wheeler; Greg Blake via Fot
Subject: Re: [Fot] Type A OD pressure test
I used to put the ball in a tap in down with a blunt punch. As the case is
aluminum and the ball hard steel, it made a very nice seat for itself. This can
be done without pulling the OD apart. Just pull the plug, spring and little
plunger.
Barry
On Monday, March 5, 2018 5:26 PM, Jack Wheeler via Fot <fot at
autox.team.net> wrote:
Hi Greg. Here is a tip for you. When I used to rebuild A-Type overdrives,
I would "lap in" the surface that the ball sits on. I had a spare ball of the
correct size, and I welded a small rod to it (about 3/16" diam.). Then I put a
bit of valve grinding compound on the ball, inserted it down into the hole,
then turned it back and forth, thus lapping the surface that the ball sits on.
This is a tip that Hardy Prentice gave me years ago, when we were both racing,
and obviously the purpose was to minimize any leakage past the ball. This may
be to late in your case, as you would have to do this while the unit is apart,
so that you can carefully clean all of the grinding compoound out of the
housing after the lapping. Maybe this will help you next time. Good luck.
Jack Wheeler
On Monday, March 5, 2018, 12:12:29 AM EST, Greg Blake via Fot <fot at
autox.team.net> wrote:
All knowing FOT
Attached is a video of my Type A OD unit ready to bolt up to the
transmission. I decided to do a pressure test with 120psi of compressed air
plumbed into the operating vale port.
The engagement seems to work well when I move the operating lever. But I am
concerned about the amount of air that can be heard leaking. I believe it is
going past the relief valve. Is this abnormal amount of leaking?
I noticed upon tear down that the nonreturn valve had a 1/4" ball instead
of the 5/16" this unit should have had. The test you see in the video is with a
new 5/16" ball. I am sure on a previous rebuild someone mistakenly used the
later style 1/4".
Just wanted opinions before I buttoned this up to the transmission for some
bench testing.
Thanks.
Greg
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