Transmission pressure measurement

[FresnoBob]

I connected an oil filled gauge to what I believe is the correct transmission port (see photo), sealed off the vacuum connection (see photo), but at 750 rpm whether in gear or park, the gauge reads 40 psi.  When i push the kick down switch, the pressure increases to 60 psi.  I never see any pressure below 40, and I believe I'm supposed to have 10 psi at idle.  Am I performing the test correctly?  Does the adjusting screw only adjust pressure at idle or increase (or decrease) the pressure across the range? 

[FresnoBob]

By the way, I earlier verified my 3 position solenoid was moving the linkage correctly from the rear to middle to forward positions. 

[ja17]

It should read 10 psi when the linkage rod moves to the rearmost position, 40 psi in the center position and 67psi in the frontmost position. The venture switch should move the transmission linkage rod to the rearmost position at idle. Make sure that it does so.

[FresnoBob]

Thanks Joe,
The 3 position solenoid was working a few weeks ago, but I now found it remains in the middle position across the throttle range, but does move forward when the kick-down switch is activated.  The lever moved freely to the rear position, so I checked the Venturi switch which was not working.  After disassembly, I was able to file and clean the contacts as you suggested elsewhere, and it started working again.  Now I was able to increase the modulator pressure to precisely 10 psi at idle, 40 psi at between 1,100 rpm and 1,400 rpm (depending upon rate of throttle increase).  However, I was only able to observe 63 psi with the kick-down switch activated.  Is that a sign of an aging transmission, or is it possible to independently increase the kick-down modulator pressure?

Thanks again for all your helpful advice.  The car is running so incredibly well now. 

[teahead]

It should read 10 psi when the linkage rod moves to the rearmost position, 40 psi in the center position and 67psi in the frontmost position. The venture switch should move the transmission linkage rod to the rearmost position at idle. Make sure that it does so.

I'm confused.

Tech manual says:  "Check the modulator pressure at the test port to make sure you have around 4 bar at idle with no vacuum."

4 bar = ~60psi.

[Pawel66]

Yes, when I did my measurements i found out there were mistakes i n units in some of the descriptions.

[FresnoBob]

I have mine now set to 10 psi at idle, 40 psi above idle and 60+ psi when the kick down switch is activated.  All with the vacuum line disconnected at the manifold (and then seal the manifold with metal tape).  My transmission shifts smoothly with no clunks and revs as high as I desire before shifting. 

[ja17]

Think about it logically, when the car is at idle (venture switch activated) modulator pressure is reduced to (approx. 10 psi.).  The low pressure will create a smooth final downshift when you let off the gas pedal. When you press the gas pedal the increase in pressure to (approx. 40 psi.) prevents slipping of the transmission during acceleration. Fully depressing the gas pedal activates the "kick down" and additionally increases modulator pressure to (approx. 67 psi.) causing the downshift.

[teahead]

Think about it logically, when the car is at idle (venture switch activated) modulator pressure is reduced to (approx. 10 psi.).  The low pressure will create a smooth final downshift when you let off the gas pedal. When you press the gas pedal the increase in pressure to (approx. 40 psi.) prevents slipping of the transmission during acceleration. Fully depressing the gas pedal activates the "kick down" and additionally increases modulator pressure to (approx. 67 psi.) causing the downshift.

And that's all with the vacuum line disconnected (and plugged on the engine side)?

[FresnoBob]

Yes, I completed my measurements with a piece of aluminum tape covering the intake manifold opening as you can see from the photo.  Good luck!

[teahead]

Also, do you check the pressure w/the car jacked up and the transmission in "drive" (4, 3, or 2)?

Or can it all be done while in P or N?

[ja17]

For the first reading it can be done in "P" at first at idle. For the second reading, you will have to come off idle enough to move the trans linkage to the middle position. Next, with the linkage still in the middle position,  you will have to reach under the accelerator pedal and push down the kick-down for the last reading when the linkage moves to the front position.With this procedure  you do not have to over-rev the engine to test kick-down.

[teahead]

Right, but for all 3 readings, the trans can stay in Park?

[ja17]

Can't remember for sure, but I believe so.

[teahead]

Just curious, but what RPMs does YOUR transmission normally shifts at?

Smooth acceleration on a flat surface, mine goes from 2->3 at around 2900 RPM, and then 3-->4 around 2500 RPM.

That normal?

Of course, if I step on it, 2-->3 is around 3300RPM, and the latter around 2900 RPM (IIRC).

[Tom in seattle]

FresnoBob:  my view of the photo did not show the connection of the pressure gauge until I scrolled side to side and then saw it.  I do not see where the adjustment screw is.  Can you describe it to me ?.  Also, how and what materials did you use to set up your gauge?

[teahead]

FresnoBob:  my view of the photo did not show the connection of the pressure gauge until I scrolled side to side and then saw it.  I do not see where the adjustment screw is.  Can you describe it to me ?.  Also, how and what materials did you use to set up your gauge?

If Bob won't mind, I can lend you HIS after I'm done with it.

I'm not that far from you.

[Tom in seattle]

If Bob will allow the sharing of the gauge I will be very grateful.  Yes I can drive to you to pick it up and will pay any postage involved in its return to Bob.

[teahead]

That adjustment screw thing won't turn?

Does one have to push it in?  Still won't turn.

I removed the locknut and man, that adjustment screw (which I can barely get a hold of either with needle nose pliers or a crescent wrench) won't turn that thing!



Not a very good picture close up of the adjustment screw thing.

[ja17]

It is probably jammed all the way or out. You might have to remove it to get it un-stuck. Try needle nose vice grips first (turn clockwise)

[teahead]

Well...it shifts OK, but now I have no kickdown.

Even though it pegs to like 60psi w/the button pressed, so I screwed something up.

*sigh*

[ja17]

Check the fuses, check the kick-down switch, check the ignition timing (effects vacuum), then you can adjust the turnbuckle on the transmission linkage rod slightly to get your kick-down back. You can do this in the car, through the opening. Count the turns , so you can get it back to the starting point if the adjustment does not work.