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[Fot] Type A OD pressure test

Subject: [Fot] Type A OD pressure test
From: charly at mitchelplumbing.com (Charly Mitchel)
Date: Tue, 6 Mar 2018 10:17:37 -0800
References: <7DF32ACB-8C68-45A3-9654-C743E3FB3C1A@icloud.com> <1967427720.8517669.1520273071794@mail.yahoo.com> <1123716743.11727331.1520335836458@mail.yahoo.com> <003901d3b55a$3503c540$9f0b4fc0$@att.net> <4774C90B-FECF-420A-9343-42AEE8D920F9@gmail.com>
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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