Makes sense. Subsequently, is compressed air a viable means of testing seals
that normally run gear oil?
> On Mar 6, 2018, at 10:17 AM, Charly Mitchel <charly at mitchelplumbing.com>
> wrote:
>
> 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
>>
>> Sent from my iPhone_______________________________________________
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>>
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>>
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