Fluid Drive Not Downshifting. What To Check?

[White Spyder]

Took the car out today for a quick drive to make sure that the work on the cooling system was good. When I got up to speed and let off the gas it up shifted as normal. When I stopped at a stop sign it did not down shift as expected and when I started to go I could tell it was in the wrong gear.

I stopped again and shifted to neutral. When I started forward it again worked as it should and up shifted at the right time. Stopped again and it did not down shift and stayed in the upper gear.

Where should I start to identify and fix the problem? Electrical, Trans, fluid?.?

Thanks for your help!

[Dodgeb4ya]

The  shifting solenoid on the trans is not being energized and letting it downshift. It opens an oil port and bleeds off the 40lbs of oil pressure. That lets the direct speed rail and sleeve pull back and out of high range and shift back into downshift low range.

So... why no coming to a stop down shifts? Several items to check.

Too high an idle speed will delay downshifts and upshifts. Idle speed needs to be at 450-500 RPM .

The M-6 "Prestomatic" system needs 6 volt power to downshift. There is a 20 Amp relay on the air cleaner bracket. Make sure you have 6 volts at it. Now once the governer (it's on the top right side of trans) points close coming to a stop @ either 5-7 MPH Low or 10-13 high range that completes the ground circuit for the solenoid to operate. Those contacts under the governer (cover has four screws) you might find oil covered contact points. Clean them carefully with contact cleaner. They are made of soft silver material. Make sure to reassemble the contact and spring parts exactly the same way if you remove them.

Next thing that needs to operate properly is the six sided interupter switch-two phillip screws/wires on top of it. It kills the ignition for a split second as the shift rail under it pulls back and closes the non servicable switch contacts inside. This relieves torque on the direct speed clutch sleeve teeth so the trans can pull back into low range on downshifts. Pull the wires off the interupter switch and remove it with a 1-1/16" wrench or socket. Use an OHM meter to test it by pushing the spring loaded ball on it in and out. The meter should show continuity and open as you operate the ball.

Remember if you took all the transmission wiring out of the car it will act exactly as your car is doing! Always upshifts but no downshifting. So what I am saying is the M-6 needs 6 volt power at the solenoid and at the proper times to be able to downshift correctly

 There are online Mr Tech films to watch and a factory service manual is a must  when working on the M-5 and M-6 transmissions.

Hope some of this helps..Bob

[White Spyder]

The shifting solenoid on the trans is not being energized and letting it downshift. It opens an oil port and bleeds off the 40lbs of oil pressure. That lets the direct speed rail and sleeve pull back and out of high range and shift back into downshift low range.

So... why no coming to a stop down shifts? Several items to check.

Too high an idle speed will delay downshifts and upshifts. Idle speed needs to be at 450-500 RPM .

The M-6 "Prestomatic" system needs 6 volt power to downshift. There is a 20 Amp relay on the air cleaner bracket. Make sure you have 6 volts at it. Now once the governer (it's on the top right side of trans) points close coming to a stop @ either 5-7 MPH Low or 10-13 high range that completes the ground circuit for the solenoid to operate. Those contacts under the governer (cover has four screws) you might find oil covered contact points. Clean them carefully with contact cleaner. They are made of soft silver material. Make sure to reassemble the contact and spring parts exactly the same way if you remove them.

Next thing that needs to operate properly is the six sided interupter switch-two phillip screws/wires on top of it. It kills the ignition for a split second as the shift rail under it pulls back and closes the non servicable switch contacts inside. This relieves torque on the direct speed clutch sleeve teeth so the trans can pull back into low range on downshifts. Pull the wires off the interupter switch and remove it with a 1-1/16" wrench or socket. Use an OHM meter to test it by pushing the spring loaded ball on it in and out. The meter should show continuity and open as you operate the ball.

Remember if you took all the transmission wiring out of the car it will act exactly as your car is doing! Always upshifts but no downshifting. So what I am saying is the M-6 needs 6 volt power at the solenoid and at the proper times to be able to downshift correctly

There are online Mr Tech films to watch and a factory service manual is a must when working on the M-5 and M-6 transmissions.

Hope some of this helps..Bob

Lots to think through. Thanks for the info. I will be tracing it down soon. The relay on the air cleaner bracket, how big is it? Edited September 5, 2013 by White Spyder

[Dodgeb4ya]

I meant "circuit breaker" not relay.....thats located with in that little square box on the 6 cyl air cleaner bracket. The resister for the trans is also in that little box above the CB.

If the trans worked fine before your previous repairs maybe you disconnected a wire or changed something?

 Odd that now it won't downshift. Oil level is not your problem either unless you put 90W in the trans! Pics of the CB and resister box for both  six and eight cyl cars W/ descriptions.

Bob

[greg g]

Orcham's Razor would suggest checking the obvious stuff first.   Idle speed to high??? needs to be 450 to 500.  Go to the imperial club site repair section, and review the material for the semi auto trans, if the Idle is OK.  Your problem is in the transmission not the fluid drive.

[Dodgeb4ya]

Please note Greg.. 1st item mentioned to check--idle speed. Getting directly to the first thing to check!

[greg g]

Hmmm, musta missed that sentence.  My eyes begin to cross at 1:00 AM.  No snub intended.

[White Spyder]

Idle checks out good.  fluctuating between 450 and 465.

 

I do not have any thing that looks like your photos.  It is a '48 Windsor.

 

see photos below.

 

 

Air cleaner bracket

 

 

on driver side inner fender

[Dodgeb4ya]

Whoopsie. Was thinking you had a 50 chrysler. 1946-8 chryslers are wired differently with slightly diifferent controls. I'd first check the 6 volt feed  fuse in the smaller little black relay box by the voltage regulator. It could be blown but most likely not making good contact. You will see a little push down and turn fuse holder on the BAT terminal on that trans relay box. Make sure the fuse makes good contact in the holder.

[De Soto Frank]

Failure to down-shift is usually an indication of an electrical issue.

 

1) Open circuit in wiring

 

2) Blown Fuse (find-out why)

 

3) Relay failure

 

4) Governor points dirty or not closing

 

5) Solenoid not working

 

 

 

Make sure wiring between relay & transmission is in good condition, and all terminals are clean and tight.

 

Also, run some tests on the relay itself.

 

Do you have a shop manual on this vehicle (either MoToR's or Factory) ?

 

The fact that it up-shifts as normal suggests that the mechanicals and hydraulics are working.

 

Thanks for mentioning the year / make / model in #8 - that was going to be my first question !

[Dodgeb4ya]

The very important 1946-8 Chrysler and DeSoto transmission relay and  fuse. It controls the shifting solenoid operation. Also pics of the components on the M-5 "Hydraulically Operated" transmission. The points in the governer can get oily as already mentioned. Should be cleaned of oil with contact cleaner.

[De Soto Frank]

Regarding the Governor Points:  they are silver-plated (soft!)

 

NEVER, EVER file them or use emery-paper or other abrasives on them !

 

It is not uncommon to find some oil in the points chamber. It is not a sign of trouble.

 

 

Take a look at these links when you have a chance...  they are based on the '49-53 M-6 tranny, but all the principles of operation are the same.  The controls & wiring were revised slightly to eliminate the relay.

 

 

[White Spyder]

I think I have a bad relay. Ever since I had the car I could hear it clicking as I slowed down and I no longer hear that. I did watch the second film strip and heard what they said about clicking but when I did a test light on the relay I got nothing, no light with the ignition on. I clipped one end to the junction in the middle of the Side with the fuse and grounded the other end with no light. I also checked the fuse and it looked to be good. However, it was very warm to the touch.

Any thoughts?

[Dodgeb4ya]

First thing-There needs to be 6 volts to the "BAT" screw terminal on the relay. If not that is the first thing to figure out. If there is 6 volts at that screw-not the fuse holder I think You should try cleaning the fuse holder with 320 sand paper wrapped around a pencil and make sure the proper . I have seen several over the years not make good contact because of corrosion. Make sure the correct 30Amp fuse is used. It's long at just over 1-3/8" .

A picture of whats inside of the relay-two sets of points.

Lets figure a faulty fuse or holder!

[White Spyder]

Called Baurnbaums and they do not have any relays. Ay ideas on where to fing one?

[De Soto Frank]

Fuse is an SFE-30.  Try Dodgeb4ya's suggestion of cleaning teh fuse holder and socket.

 

I had relay failure in my '48 New Yorker somewhere around 1989.

 

Couldn't find a replacement, so I got creative and took the cover off, and found that  the "reed-spring hinge"  on the armature of the heavy relay had broken due to metal fatigue.

 

I repaired it with a small brass cabinet-hinge, about the size you'd find on a small jewelry box.  Got that from a hardware store.

 

Secured the hinge with some tiny machine screws & nuts (#0 or #2 ?), and peened the ends of the screws over the nuts, so that the nuts couldn't back-off.  I made a flexible jumper lead out of desoldering braid, and soldered that between the armature and its support, to insure good continuity.

 

It worked.  For at least 40,000 more miles  (when I retired the car).

 

If cleaning the fuse-holder and replacing the fuse doesn't help, remove the cover from the relay and see what you find...

Edited September 5, 2013 by De Soto Frank

[greg g]

This thread need to be saved to the tech forum.  It seems to pretty much cover the care and feeding of the Semi Auto trans.

[White Spyder]

Having to do my paying job is getting in the way of fixing this! I saw that it was a 30 amp fuse bought some and found out the hard way that the needed one is long. Off to the store in the morning.

I did get power at the screw that is on the fuse holder. I was trying at the one in the middle. Helps to be able to see things in the photos. I could not read the markings on mine.

Edited September 5, 2013 by White Spyder

[White Spyder]

De Soto Frank, you have any photos of your work?

[De Soto Frank]

De Soto Frank, you have any photos of your work?

 

I wish I did, Spyder.

 

That was way back in 1989, when I was a starving college senior, and my only camera was a 1950's Kodak Retina (actually a good camera, and I still have it!).

 

I was in a crunch to get the NYer fixed as it was my main transportation at the time, so I didn't think to take pics.

 

The fuse you need is an SFE-30 ( it is longer than most glass Buss-fuses ).

You might do well to tag the relay wires, remove them, and remove the entire relay from the car, and open it up, to see what you have.  If the relay armature is intact, then you can proceed with electrical tests.  If the hinge has broken, then you know you need to fix that.

 

I'll see if I can sketch-up how I engineered my fix, scan, and post.

 

Unfortunately, the NYer, that relay, and a spare that I later found are all 200 miles away at Mom & Dad's... so I cannot grab them to shoot some digi-pix.

[White Spyder]

Thanks.  I did get the right length fuse and it still would not down shift.  I am going to remove the relay and open it up for a peek.

[White Spyder]

Pulled the relay.  in this photo you can see there are little 6 tangs that hold the cover on.  2 for each side

 

 

Side one and two.  All looks good.

 

   

 

 

Now the question is how to test this thin while out of the car.  I have a 6volt lanter battery but which leads to touch with the test wires.  I know that the on near the fuse is power.  That leaves 4 other terminals. here is my thoughts.  Apply constant power to the one at the fuse.  with the base grounded apply a jumper from the fuse screw to the screw next to it and entergize the magnet and see if it pulls the arms of the relay down.

 

Any suggestions?

Edited September 6, 2013 by White Spyder

[Dodgeb4ya]

Yep, But hopefully you have a meter too.

With your 6 volt battery leads ground the relay base, 6 volts to the BAT terminal. Ground the "TH" terminal. Points should both close. With one volt meter  lead grounded other lead connected to "SOL" terminal- should show 6 volts.

With "TH still grounded- both points closed- use the ohm meter across "PRI" and "INT" terminals. Should show continuity.

Basically if the points close the relay probably is OK as long as the points are good and clean.

Bob

 

Edited October 22, 2013 by Dodgeb4ya

[Don Coatney]

Bob, Does your Fluke seporate?

[Merle Coggins]

Bob's got all the cool toys. I've seen those Flukes with the detachable display. They are way cool.

Merle