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
>
> Sent from my iPhone_______________________________________________
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