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.

[Big Fins]

Sorry Bruce! I didn't even spell your name correctly. 

[tcom2027]

Since you mention moving the lever eliminated the condition, possibly a linkage problem? Is the shift lever quadrant loose or does the lever flop around?

I believe there is at least one plastic bushing in the linkage along with ball and socket connections. Possibly looseness in the shifter frame. IIRC when I worked on a '66 years ago there was one. I don't know if the  '67s have the same design

I had a '67 DeVille. You could barely feel it shift so I never had to get my fingers into it.

It's probably not a good idea the use any "rebuild in a bottle" additives or "seal softeners", etc. Onr mans' opinion.

tony

[TJ Hopland]

Checked the vacuum line to and the function of the vacuum modulator?   If that isn't got vacuum or working that makes the transmission think you are fairly hard on the gas so its going to firm up and delay the shifting.  Normally you would notice that but since it sounds like this is a fairly recent acquisition normal hasn't been established yet. 

But was said above, age is also a very likely cause.  Seals in the servos and pistons are not going to be doing a good job if they are more than about 20 years old so they are not able to hold the required pressure on clutches or drums like they need to so what you are feeling is the slipping of the outgoing gear or the incoming one or both.       

[tcom2027]

TJ has an excellent suggestion about the modulator. A good vacuum supply, etc. A failing or failed modulator can mimic all manner of shifting problems, shuttering, hard engagement, slipping, etc. although the OP didn't mention any slipping problems. Just that the lever had to be tickled a little to get proper 1-2 engagement.

I would start with the shift quadrant. Make sure lever is engaging snugly in the gates and the linkage is tight. If that is ok, go on to the linkage at the transmission. IIRC it's cable operated. Use the factory manual and follow the directions to properly adjust it. I have found that manufacturers have a remarkable amount of knowledge related to the products they produce. I believe there is an electro mechanical switch in the system, Check for proper operation,, wiring, contacts, relays, etc.

Before I went ripping and tearing into the unit, I would do the above. Dumping snake oils into it isn't going to help. Even if there is some real or imagined benefits,they soon disappear. None of them make new seals or add metal to worn gears, bearing or bushings, etc.

I haven't had a lot of experience with those transmissions. My only experience was with a '66. adjusting the linkage and replacing motor and trans mounts, so take my suggestions for what they are worth.

That said abut additives  however, I have used Silver and Alumina Seal with good results but the effect was temporary.  I do add the GM pellets to our NorthStar engined DeVille and Eldo when the coolant is changed. 

Good luck finding and repairing the problem.

tony

[cadillacmike68]

Late and harsh shifts, if not due to internal issues are usually vacuum supply or vacuum modulator issues. Some "mechanic" actually switched my transmission vacuum lines with the main vacuum manifold line and the transmission wasn't getting enough vacuum. The result: late and harsh shifts, I put the lines right and it's been fine.