52 Custom Saga #3: Transmission does not upshift -- (now upshifts but does not downshift without help)

[Justin Pease]

Good morning all! Happy day-after-the-Fourth-of-July. I got my 52 Custom up and running with loads of help from you guys, and it now starts right up, warms up, idles, and goes into gear. I did change the engine oil but didn't pull the oil pan or open the trans cover yet. I've driven it about a little bit, just basically across the street and in the parking lot where I work on it, but I noticed that the transmission does not shift from 3rd to 4th in Drive/high gear. The car speeds up to about 20-25, and sounds like it's ready to shift, so I pick my foot up off the gas, but it doesn't shift for me. This condition exists the same in Low gear, where the car is in 1 but does not shift to 2. I don't dare speed up any more past 25 or so in Drive because I know that's about where the shift point from 3-4 is and don't want to overrun the engine.

 

I have a good understanding on how the transmission works (thanks to my shop manual and @keithb7): Where is a good place to start looking at failure points? I suspect wiring, as the wiring on this car is rather... terrifying. I have four connections in the engine compartment that are disconnected - two that go to the carb, and two that go to the coil. Do all of those need to be connected for the transmission to shift? I was under the impression that the ones to the carb were the kick-down shift, telling the car to shift back into 3rd under 40mph when the accelerator is pushed to the floor. What do the ones to the coil do? Would connecting them allow the trans to shift? Or is a more likely scenario that the transmission solenoid, governor, or wiring between the two has failed? Could it perhaps be the trans oil pump?

 

There are so many potential points of failure on this wildly complicated transmission - I'm basically just looking for what might be the most likely to fail and where to start looking, or whether those wires to the carb and coil need to be connected to shift UP. Thanks all! Have a safe weekend!

Edited July 5, 2020 by Justin Pease (see edit history)

[Justin Pease]

Update - got the car moving a little bit faster and I believe the transmission may have shifted, but I wasn't sure. Certainly sounded like it did, but by that point I was going about 35-40 and being that the car currently only has rear brakes, no plates, no insurance, and my turn was rapidly approaching, I didn't keep it going in what might've been fourth for more than about 5 seconds. I'll try again tomorrow evening perhaps and see if I can't get it to shift again.

[keithb7]

Start by confirming that your oil is SAE 10W, and that the tranny is full. Proper oil and pressure are vital to the hydraulic shift, when you lift your foot off the gas at 20 or so MPH faster.

 

The wire to the coil: When you are in 4th, travelling about 35 mph or slower, when you floor the gas pedal, it will downshift to 3rd. When this happens power to coil is sent to ground momentarily so none of the spark plugs are firing. This takes all load off the tranny input pinion so synchro gears can speed match very quickly and the tranny can downshift to 3rd.

 

The wires on the carb.  A dashpot that controls the throttle closing too fast when you let your foot off the throttle to initiate an upshift. If the throttle closes too fast apparently the engine can stall. So the electric dash pot controls the throttle to close a little slower. Other wires on the carb travel down to a kick down switch on the tranny. When you mash the gas pedal, it connects this switch. Power is cut off at the interrupter switch, grounding the main spark coil as mentioned above. This interrupter switch is screwed into your tranny with wires to it. It's right atop of the larger 6V solenoid on the tranny.

 

This is all explained in the manual. There are wiring schematics and also charts showing hydraulic flow. If you don't have a manual, I highly recommend. 

I'd rule out the tranny oil pump until a last resort. All the wiring needs to be checked for continuity, also ensuring all proper connections are true. Rotating governor points need should be cleaned. Proper voltages should be checked with a digital multimeter at all various points, when switches are activated.  If the wiring you have it shoddy, I'd say that the wiring is highly likely to be your problem. The coil screwed into the transmission should be tested to ensure it moves the pin in and out, when power 6V is applied to it. 

 

Here is what the actual manual lists about troubleshooting the tranny electrical system. Instructions for each steps are listed. I'd rather not type them all out.

 

Ignition System to Circuit Breaker Test

 

Circuit Breaker Check

 

Circuit Breaker to Tranny Solenoid Check

 

Circuit Breaker to Anti-Stall Check

 

Anti-Stall Check

 

Solenoid Check

 

Governor and Kick Down Switch Check

 

Interrupter Switch Check

 

Ignition Interrupter Resistor Check

 

Hydraulic Pressure Check 

 

 

 

 

Edited July 5, 2020 by keithb7 (see edit history)

[Grimy]

AND... ensure that the engine idles at 450 rpm or less.  The idle needs to drop to allow the upshift.

[Justin Pease]

Thanks for all this info - a little update, the trans is working beautifully (turns out I didn't have enough speed which is why it was only upshifting sometimes - give it 30-35mph and it shifts happily into 4th). I've been driving the car on the road for about 2 weeks now, and for one of those weeks it was my daily. It starts every time, runs beautifully, and I found the source of my evil oil leak (I joke that this car is like a feral cat - sometimes it dislikes new people, you must approach it slowly, and it marks its territory). 

 

The transmission will not downshift, though, from 4 to 3 when I come to a stop (I must come to a full stop and I have to put the clutch in and release it to force the car to shift back into 3rd). I think this likely has something to do with the thickness of the oil that I'm using (I have been using very thick oil in the engine as the car was burning a lot of it due to rings - the rings have now seemingly rejuvenated and it now burns no more oil than would be normally acceptable for a car of this vintage. I am going to start moving the oil back thinner and thinner to bring it back to a more acceptable, thinner oil).

 

I have to replace the wiring for the dashpot and the coil interrupter wiring before I dare connect it - those wires are very, very frayed and a giant fire waiting to happen if I were to run any power through them. I have been driving the vehicle without the aid of the kickdown in the meantime.

[keithb7]

The engine oil thickness has nothing to do with the down shifting of the transmission. 
 

The tranny has its own oil. The oil pump for the tranny is driven by ground speed. As your tires rotate, the driveshaft turns too. It drives the tranny oil pump. It creates about 40 psi pressure at a certain speed.  When the conditions are right, this pressurized oil forces a piston to move inside a cylinder bore. Creating a shift.

 

When you slow down for to a stop, if your tranny is not downshifting, maybe the governor points are dirty and not making contact when they slow down? When the governor points close, the 6V solenoid on the drivers side of your tranny, becomes energized. The solenoid moves a rod, it seats a ball valve. That ball valve relieves oil pressure from the hydraulic shift cylinder. The drop in oil pressure as planned, then allows an internal spring to force the shift cylinder back. Then your tranny downshifts from 4th to 3rd.  Another issue might be electrical wiring along the side of the tranny between the governor points and the solenoid. Could be crispy, insulation missing, self grounding? Or the actual 6V solenoid could be acting up. I'd be inclined to clean up the governor points first. Then see how the tranny acts.

Edited August 12, 2020 by keithb7 (see edit history)

[Justin Pease]

Hey Keith,

 

I have a pretty good understanding on how the trans works thanks to your videos (though I was under the impression that the trans and engine shared oil... realizing now that they do not, but the trans does use engine oil, just not shared engine oil). I'm curious if the governor points causing the trans not to downshift can be possible in this case... It was my understanding that the governor is responsible for both upshifts and downshifts, as the oil pressure cannot flow without the displacement of the ball valve. The governor hits the sweet spot (35), cuts power to the solenoid, which actuates the rod and displaces the ball valve, allowing oil to flow and move the shift collar. The inverse happens as you lose speed, the governor loses contact, the solenoid is de-energized, and the ball valve is seated. Oil pressure drops on the work side and the collar is pushed back. But if the governor is working one way, shouldn't it be working the other? Upshifts are working just fine, and without fail, but downshifts only happen when the clutch is put in. I'm missing the connection between the clutch and the oil pressure - how does putting the clutch in (which increases engine rpm since it is no longer under load) make any difference?

[keithb7]

One more part to confuse readers, is my M6 semi-auto tranny in my 53 6 cylinder Chrysler has its own tranny oil. Yet my torque converter and the engine oil are indeed shared. 

 

I thought about what you mentioned too. The up and the down shifting.  I wonder if your troubles have to do with your idle speed? What is it set at? Have you by chance tweaked your carb A/F idle screw lately? Too high of idle and the tranny won't shift properly either. Don't ask me how I know this. LOL.

 

When you push the clutch in the tranny input pinion (front input shaft) slows down.  As the speed of the pinion slows down, adjacent gears may align, release any load, then shift properly.  So if you engine idle is too high, the input pinion is spinning too fast to allow for a shift. Yet pushing in the clutch, the engine can still idle high, but the input pinion on the tranny slows down as the engine speed is disconnected.

Edited August 14, 2020 by keithb7 (see edit history)

[Justin Pease]

High idle speed could be possible, though the transmission shifts up okay (though it does take about 3-4 seconds between letting my foot off and hearing it shift as the idle comes down). I felt like if I adjusted the idle down much further, the car might stall when you come to a stop in gear, which is why I haven't touched it at all.

 

I'll try to record a video of the car running (both in drive and not) so you can hear her run and tell me if it sounds super high to you... I'll also try to measure my idle today with my timing light.

[Justin Pease]

Alright, so I tried to use my timing light to measure the idle only to realize it does not have a tach on it... so that didn't work. I don't really believe that this is the issue since the vehicle shifts up just fine, and it's only struggling to shift down.

 

I've linked a short video of the vehicle running so you can decide if the idle sounds high to you or not. It was relatively warm (but probably not 100% operating temp) at the time of the video. I do show the temp gauge so you can see for yourself exactly how warm it is.

 

Additionally, I have made a miniscule amount of progress - for the first time ever, I was able to inadvertently get the transmission to shift down on its own. Not sure exactly how, I think mostly in a "perfect storm" kind of way, but I took the car for a short Italian tune-up (a 2-exit jaunt on the interstate at about 60-65 to see how she liked it - for those curious, she liked it just fine!). The exit I took was a long, downhill stretch - not so steep as to need copious brakes, but just so that she engine braked down the hill without gaining or losing much speed. As I approached my turn, I applied the brakes, then applied them with more force as my turn approached a little faster than I had anticipated. I slowed from about 60mph to 20mph (indicated speed) at a moderately fast pace and turned onto the road. As I reapplied the gas, I found that she had downshifted into 3rd and I hadn't even noticed it! I was stoked, but alas could not replicate the results on the remainder of my drive home.

 

I'm now suspicious of the hydraulic fluid - I have no idea what it's running, and I have not changed it in my ownership of the vehicle. But if it was able to downshift, then I wonder if the fluid is perhaps too thick and not allowing it to downshift unless it experiences a sudden deceleration and causes the oil pressure inside the trans to drop quickly. Thoughts? How do I check trans fluid level and confirm the type? Is it best to just change it for safety?

 

Here's the video of her running (it's hosted on Google Drive since it's too long to attach directly). It is currently still processing but should be done in a few more minutes - if anyone has trouble viewing it, let me know.

Edited August 16, 2020 by Justin Pease (see edit history)

[keithb7]

If unknown, drain the tranny and re-fill it with the correct oil. 
 

Lower hole (Red arrow) is the drain port. Upper hole (Green arrow) the fill port. After draining, re install lower plug. Leave top plug out. Refill oil into top plug until oil comes out of upper plug. Then its full. 
 

Easy and cheap piece of mind. 

Edited August 17, 2020 by keithb7 (see edit history)

[Justin Pease]

Gotcha. And this is just 10w motor oil?