Transmission slipping - Modulator pressure?

[Kopie]

Let me start by saying that I have not driven this car more than a few blocks at a time and have been slowly but surely taking care of cosmetics and mechanics and i have just gotten back in to this transmission problem.  I have gone through the linkage tour and it runs and idles nicely, but the transmission slips.  i verified the function of the three position solenoid and it functions as it should. I do have a problem with the kick down switch that a good cleaning should remedy.  I removed the wires from it and when the circuit is closed it does engage the solenoid.  I decided that I would leave my test wires connected to the kickdown circuit so that i could engage it while driving.  This is where it gets interesting and I need advice.  As soon as i engage the circuit for the kickdown the slipping stops and it shifts very nicely.  Can I assume that this is a linkage problem or can there be something else at play here that I am missing?  Does anyone know where to purchase a suitable gauge to connect to the test port or what size threads are at the test port?  Any advice would be most welcome!

[JosephBach]

check and re check the wiring to the 3-pos switch, tranny , and kickdown.

sounds like you switched a few wires, in your case it seems kickdown signal is always transmitted to the tranny. so when you manually "activate" the kickdown you are actually deactivating the signal, causing the tranny to think is under normal driving conditions and giving you smooth shifts

[Kopie]

I have the cover off of the side of the transmission and am able to observe the operation of the three position solenoid.  I can actually reach down while driving (still watching the road of course) and move the lever towards kickdown and the transmission immediately stops slipping and behaves normally.  If I let go of it and allow it to return to maximum (normal driving pressure) position it immediately starts slipping again.  I have a compression gauge, but I don't think it has the adapters that would allow me to use it for modulator pressure testing.  Thank you for the reply and I value any and all suggestions.

[JosephBach]

that rod (not usually) can call for adjustment at some point in time. its like the linkage rods in the fact that they can be lengthened & shortened.
if its been altered over the course of time, it will throw off the base operating pressure of the trans.

theres compression guages with a plethora of connections, you'll find one eventually.(cant tell you exact size)
i'd say check and get your modulating pressures within specs then report!

[Kopie]

My compression gauge is designed for testing cylinder compression and checks and locks the pressure on the gauge.  Do you think this is ok for the purpose if I can adapt it to fit?  Sorry to ask so many questions, but this is new territory for me.

[ja17]

Hello,

What is the history of the problem. Always been like that?  A new problem?

You need to make sure the modulator diaphragm is not ruptured, or you do not have a bad vacuum leak. Incorrect ignition timing can cause low vacuum and shifting problems also. Make sure the fluid level is correct. 

The above basics should be checked before you jump in and make changes.

There is a turnbuckle on the trans linkage rod. You can loosen the two lock nuts, turning the turnbuckle will lengthen or shorten the linkage rod. Be careful one of the lock nuts is backward threaded.  Count the number of turns you adjust it so you can put it back if you need to. 

[Kopie]

Joe,
The car has had this problem since I bought it.  I have been working on other things that I'm more familiar with ie. paint, body work, replacing interior, etc. 
I just did a complete fluid fluid change on it following your directions previously posted.  I tightened the valve bolts while I had the filter off, but it didn't help the problem.  Fluid level is correct.  I assumed that the diaphragm would be ok since it isn't smoking at all.  Is it still possible to have a diaphragm problem without the obvious white smoke?  I just got a new timing light and plan to check the timing tomorrow.  I'll post back the results from that.  I know I saw a post (yours I think) that shows the input on the transmission for a gauge but for the life of me I can't find it again.  I need to start bookmarking these when I find them.  It gave me hope that the transmission may not be a complete loss when i moved the lever and got a good response from shifting.  I am hesitant to move that rod without a gauge present to tell me where I am as far as pressure.  I don't think I have a vacuum leak and until now I thought that vacuum was only a factor when at idling or low speed.  This is where my lack of knowledge is failing me.  Thank you for helping.

[ja17]

Hello Jim,

Yes, let us know how the timing check works out. Most likely the diaphragm is OK if it is not smoking. I will see if I still  have a picture of the test port for the modulator pressure.   

[Kopie]

Well, I checked the timing and it was 10 degrees at idle (35 at 3000).  I reduced it to 5 at idle (30 at 3000rpm).  It didn't make any difference with the transmission and I think it actually ran a little better before.  I think I'll order an oil pressure gauge and a vacuum gauge.  Does anyone know what size threads are on that test port.  I was able to find reference in the workshop manual and it indicates where that port is.  It looks tight under there, I hope I can get the gauge installed.  I tried adjusting the modulating pressure one turn (the manual says that's 2.1 psi) which i guess isn't much of a change if I'm looking for 40psi maximum pressure.  I hope I'm not throwing money towards tools that won't solve my problem.  Any thoughts?

[Kopie]

Well, I think I am getting towards the end of my problem.  I connected a pressure gauge to the test port and was getting 10 psi with no change when giving it throttle.  I adjusted the linkage rod and the idle pressure rose to about 12-13 psi, maximum pressure 20 psi, and kickdown 30 psi.  I then went to the modulator to make adjustments and the screw didn't feel right (loose and unable to stay in position).  I removed the cover plate and found that the diaphram was ok but the spring was gone, a victim of corrosion.  I'm guessing (hoping) that replacing these parts will solve my problem.  I went ahead and ordered a new diaphram as well.  Seeing the UPS truck in the neighborhood will once again have me in eager anticipation.

[ja17]

Hello Kopie,

Thats a new one on me. 
A spring rusting away is most unusual.  Sounds like your on the right track. I think your persistance will pay off !

[Kopie]

Just wanted to update the thread and thank everyone for help with this.  I installed the new diaphram, spring and sealing washer, adjusted and all pressures are in spec.  Sadly, I can't drive it yet because noticed front wheels were stiff to turn and ended up having to send off a caliper for rebuild since right front are in short supply.  I sure am getting anxious at this point.