1960s Harsh Gearchanges on a '67 Sedan DeVille HT

[mbracing]

Hallo my '67 Sedan DeVille HT, bought recently, has an harsh gear change specially from 1st to 2nd in the left "Drive" position, if I move to the right "Drive" selection then gearchanges are smoother. Gearbox oil and filter has been changed recently by the previous owner, and the car has a low mileage. There might be an additive or something else to try before thinking about an eventual transmission overhaul?
Kindest regards from Italy.
mbracing

[Alan Harris CLC#1513]

1. Is your fluid level OK? 2. What kind of fluid did the previous owner use? I do not know what kind of fluid is sold in Italy or if Dexron fluid is commonly available there. 3. Does the fluid smell burnt? If it does, you might have a serious problem. 4. A rough shift could be a problem with the vacuum modulator. Make sure that you are getting vacuum at the line into the modulator and that no transmission fluid is in the line. If there is fluid, it means that the diaphragm inside the modulator is leaking. Buona Fortuna!

[mbracing]

1. Is your fluid level OK? 2. What kind of fluid did the previous owner use? I do not know what kind of fluid is sold in Italy or if Dexron fluid is commonly available there. 3. Does the fluid smell burnt? If it does, you might have a serious problem. 4. A rough shift could be a problem with the vacuum modulator. Make sure that you are getting vacuum at the line into the modulator and that no transmission fluid is in the line. If there is fluid, it means that the diaphragm inside the modulator is leaking. Buona Fortuna!

Thanks Alan, I will check the level, the previous owner (a friend) told me it was OK but better to do this again! Fluid used is ATF Dextron, so it should be OK. I will also check that vacuum line to the modulator. Is it visible from underneath the car? I will check on the workshop manual.
mbracing

[James Landi]

If you let off the accelerator between the first and second harsh shift, does it shift smoothly?  You describe the shift as harsh... does it create a shudder that you can feel?   I mention this because I had the  problem I described with a '67,  and it ran with the shudder many, many years even after I tried replacing the modulator and the transmission "governor" ... it was diagnosed as a "crack in the casing at the coupler," and I was told by Cadillac service that rather than a master rebuild, it would need an entire transmission because the internal part of the case was cracked and leaking hydraulic pressure. Apparently, a former owner  had seriously abused the transmission, so I'm hoping your problem is not what I experienced. 

[mbracing]

If you let off the accelerator between the first and second harsh shift, does it shift smoothly?  You describe the shift as harsh... does it create a shudder that you can feel?   I mention this because I had the  problem I described with a '67,  and it ran with the shudder many, many years even after I tried replacing the modulator and the transmission "governor" ... it was diagnosed as a "crack in the casing at the coupler," and I was told by Cadillac service that rather than a master rebuild, it would need an entire transmission because the internal part of the case was cracked and leaking hydraulic pressure. Apparently, a former owner  had seriously abused the transmission, so I'm hoping your problem is not what I experienced. 

Thanks James, yes if I lift the accelerator just before the change it shift a bit more smoothly. The strange thing is that if I move the selector on the right hand side "Drive" position the problem is almost non existing. Let's hope is not bad as you say.
Cheers
mbracing

[Big Fins]

Grasping at straws here because I don't know for sure, but the '67 has a switch pitch converter in it. I wonder if the electrical controller might be stuck in one position or another.

@Bruce Row could weigh in on this one. He's the resident switch pitch expert.

[bcroe]

Mauro Borella,

The TH400 has bands that are engaged for deceleration or backing
up, these are not engaged for normal shifting.  While 2nd might be
selected from speed for engine braking, shifting from 1st may not be
as smooth. 

OR, is your trans still all original?  While lower miles may preserve all
the hard parts, the rubber seals on the pistons will still age.  I recommend
replacing theses with the $40 soft kit (but installation is the same as an
overhaul) every couple dozen years, keeping all the original hard parts if 
in good shape.  Better than replacements from across the ocean. 
Otherwise a blown seal can cause slipping and ruin a good trans. 

All the TH400s here are Switch Pitch.  They use an electronic controller
to delay change to low stall until shifting is completed, set for 14 seconds
here but adjustable.  This makes the trans smoother and more responsive. 
The factory control has no timers or torque detection.  But this may not be
the best answer to a different problem. 

I am lately locked out of posting to the forums latest software, since I use
an Apple computer.  At considerable inconvenience, I can post using a PC
that is accepted.  I have sent numerous emails to our web management,
but nothing is done about it. 

Bruce Roe  CLC 14630   bcroe@juno.com
++++++++++++++++++++++++++++++++++++++++++++++++++
mbracing  Mauro Borella   
CLC Number: 34608

Today at 08:32:35 AM

Thanks James, yes if I lift the accelerator just before the change it
shift a bit more smoothly. The strange thing is that if I move the
selector on the right hand side "Drive" position the problem is
almost non existing. Let's hope is not bad as you say.
Cheers
mbracing
++++++++++++++++++++++++++++++++++++++++++
Big Fins Today
Grasping at straws here because I don't know for sure, but
the '67 has a switch pitch converter in it. I wonder if the
electrical controller might be stuck in one position or another?

bcroe@juno.com   Bruce Roe could weigh in on this one. He's
the resident switch pitch expert.