[Fot] Type A OD pressure test

Tue Mar 6 09:03:04 MST 2018

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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