1-2 shift too soft

[81dmc]

So after my 3.0 install, I've noticed the 1-2 shift is rather soft while the 2-3 is harder. This translates to violent slipping 1-2 under mild-heavy part throttle acceleration. I don't want to glaze the clutches.

Does this sound like a symptom of different power under vacuum, or some other problem?

Could I just turn up the vacuum modulator to compensate?

[DMCMW Dave]

So after my 3.0 install, I've noticed the 1-2 shift is rather soft while the 2-3 is harder. This translates to violent slipping 1-2 under mild-heavy part throttle acceleration. I don't want to glaze the clutches.

Does this sound like a symptom of different power under vacuum, or some other problem?

Could I just turn up the vacuum modulator to compensate?

Before you change the modulator setting, put a pressure gauge on the trans (instructions in the manual). Then you can change the pressure if needed without flying blind on it. You should also have a vacuum gauge teed in at the modulator to see what it's trying to respond to. The modulator doesn't "care" what gear you are in; it only responds to engine vacuum. Hight vacuum = soft shift, low vacuum = hard shift. If you disconnect the vacuum line, it will shift "hard" all the time. The shift point (RPM/speed) is not impacted by the modulator.

I kind of suspect other issues, but I'd start here. If the pressures seem per spec, you probably are about to have the clutches fail anyway.

[81dmc]

Before you change the modulator setting, put a pressure gauge on the trans (instructions in the manual). Then you can change the pressure if needed without flying blind on it. You should also have a vacuum gauge teed in at the modulator to see what it's trying to respond to. The modulator doesn't "care" what gear you are in; it only responds to engine vacuum. Hight vacuum = soft shift, low vacuum = hard shift. If you disconnect the vacuum line, it will shift "hard" all the time. The shift point (RPM/speed) is not impacted by the modulator.
I know pressure is supposed to be 113psi, but is there supposed to be a vacuum spec? I was thinking I could use some sort of vacuum restrictor like old Mercedes diesels use.




I kind of suspect other issues, but I'd start here. If the pressures seem per spec, you probably are about to have the clutches fail anyway.
Not what I want to hear obviously. What another issues do you think could be suspect?

[David T]

Obviously check the line pressure and the vacuum but I found the shifts too soft also. That's why when I rebuild a transmission I use stiffer springs in the clutches for faster, harder shifts. That way the clutches don't slip as much and will last much longer too.

[81dmc]

Obviously check the line pressure and the vacuum but I found the shifts too soft also. That's why when I rebuild a transmission I use stiffer springs in the clutches for faster, harder shifts. That way the clutches don't slip as much and will last much longer too.
Stiffer springs in clutches? Usually that would mean increased pressure is needed for piston application.

Or are you perhaps talking about something in the valve body?

I haven?t had a DeLorean trans apart, so I don?t know too much about it.

[David T]

Stiffer springs in clutches? Usually that would mean increased pressure is needed for piston application.

Or are you perhaps talking about something in the valve body?

I haven?t had a DeLorean trans apart, so I don?t know too much about it.

The springs in the clutch packs hold the clutches. The hydraulic pressure is what releases them. As long as your line pressure is within specs, stiffer springs just give you faster, firmer shifts. The vacuum modulator REDUCES line pressure to give you softer shifts. The valve body also has built-in delays so as to let the clutch packs slip so when one clutch pack is engaging the other is releasing. The more the clutch packs slip the more they wear and the more heat gets generated. Faster, firmer shifts will add some more shock load but the clutch packs will last a lot longer. Think of it like a "Shift Kit" for a Renault automatic transmission. To get faster, firmer shifts without changing the springs, just block off the vacuum line to the vacuum modulator. It will give you slightly firmer shifts. The most important things are to have clean hydraulic fluid at the correct level and the correct line pressure. You can also experiment with the cable from the throttle spool to the shift governor (aka shift computer) to affect the timing of the shifts.

[Ron]

The springs in a clutch pak are for piston return -- Hydraulic pressure against the piston(s) is what makes the clutches hold.

FWIW- For most transmissions, you turn the screw in inside the modulaor's vacuum port:
(R)ight to (R)ise) the RPM shift points.
(L)eft for (S)ooner and (S)ofter.

+1 on checking line pressure.
Check fluid color -- Dark means clutch wear=>slippage.

[81dmc]

The springs in a clutch pak are for piston return -- Hydraulic pressure against the piston(s) is what makes the clutches hold.
Yep, that's what I thought...

Under medium throttle, my 1-2 feels like it's almost hanging before it finally clunks into 2nd.

[Ron]

Yep, that's what I thought...

Under medium throttle, my 1-2 feels like it's almost hanging before it finally clunks into 2nd.
I think I may have edited my previous post while you were replying...

If it seems like it shifts a little late, you might try confirming good line pressure then turning the screw (~1/8 turn at a time) to the right (clockwise) to make it shift later and firmer.

[81dmc]

I think I may have edited my previous post while you were replying...

If it seems like it shifts a little late, you might try confirming good line pressure then turning the screw (~1/8 turn at a time) to the right (clockwise) to make it shift later and firmer.
I lost my old pressure gauge, so I tried turning it maybe 10 teeth (15psi), and it gave me a very bad slipping 3rd gear shift and really only marginal improvements with 1>2.

[Ron]

I lost my old pressure gauge, so I tried turning it maybe 10 teeth (15psi), and it gave me a very bad slipping 3rd gear shift and really only marginal improvements with 1>2.I'd put it back where it was and investigate further...
(Of course , the D's "Vacuum Capsule" is different than a modulator valve...)

[David T]

If the problem is the timing of the shifts the most likely cause is a problem with the shift computer. There are plenty of tech articles on how to troubleshoot and repair it.

[81dmc]

It?s not a timing issue. I have a DMCH computer.

Issue is the shift from 1 to 2 takes a bit of time, then it goes into gear, or it shudders into gear.

I guess I?ll have to go get a gauge. Is it 1/8npt?

[81dmc]

FWIW, there's bubbles on the dipstick, and it's at the perfect level too. Running Valvoline Maxlife synthetic ATF.

[Ron]

FWIW, there's bubbles on the dipstick...There's a red flag!...since the level seems OK, maybe: filter, vent stopped up, etc.

[81dmc]

There's a red flag!...since the level seems OK, maybe: filter, vent stopped up, etc.
Where's the vent?

I put a DMCH filter because I had some things packed, but now I can install one of the filters Michael offered. I have a box of them. Also, maybe I'll put some Allison Transynd ATF.

Anything else I should inspect in there? Should I pull the VB?

[David T]

Where's the vent?

I put a DMCH filter because I had some things packed, but now I can install one of the filters Michael offered. I have a box of them. Also, maybe I'll put some Allison Transynd ATF.

Anything else I should inspect in there? Should I pull the VB?

The transmission was designed to use Dexron III. I have no idea how it would react to anything exotic or synthetic. The gauge port is a metric thread. I can't think of any good reason to remove the VB. If it is shuddering into gear you should get a light box and see what the shift computer is doing. Maybe it is commanding 2 gears at once or it is fluctuating between 1st and 2nd. You should also go over all of the external adjustments, throttle cable and gear shift linkage.

[Ron]

I put a DMCH filter because I had some things packed, but now I can install one of the filters Michael offered. I have a box of them. Also, maybe I'll put some Allison Transynd ATF.

Anything else I should inspect in there? Should I pull the VB?
Valvoline Maxlife synthetic ATF is supposed to be usable where Dextron VI is called out. Dextron VI is downward compatible with all previous Dextron ATF. The manual calls out Dextron II...
So, your fluid should be fine.
You should be able to see anything that's wrong with the filter: loose/torn/clogged up...
The VB is the last thing you want to mess with, imho.

I can't remember exactly where the vent is...you can blow smoke into the dipstick tube and look for it near the top of the case.

[81dmc]

I decided to take a whiff of the atf from the dipstick, and I don't know if it's my nose playing tricks, but I smell gear oil.

Is it even possible for that to happen? I thought pressure alone would push atf into the final drive not the other way around...

In any case, I?m going to change the ATF and collect a sample to be sent to blackstone. They can tell me if something is mixing.

[81dmc]

Here's a video, it's mainly noticeable by looking at speedo during 1-2 shift. It's like a hesitation before it shifts, and it's getting worse.


https://www.youtube.com/watch?v=Fbk7areNB3g

[Ron]

It don't sound like the the engine is doing what the tach says it is, to me. Tach shows changes to late/slow, maybe??

Is the two quick bump sounds at 7-8 seconds the road/shift shutter/?

[81dmc]

It don't sound like the the engine is doing what the tach says it is, to me. Tach shows changes to late/slow, maybe??

Is the two quick bump sounds at 7-8 seconds the road/shift shutter/?
The bang you hear around 6-7 seconds is 1st gear finally catching. It slips before catching hard.


And tach is slightly behind as it runs via CAN Bus.

[81dmc]

So I?ve noticed the 1-2 slip isn?t there when cold.

[Michael]

Few things.
You can not tell if a filter needs to be replaced by looking at it. The part that usually clogs up is hidden under the clamshells.

I just replaced my shift computer with a rebuilt one. The rebuilt one was faulty pushing my car into 2nd at times with no warning and other times it would not shift out of 1st and/or second. My second shift computer works flawlessly. Point is a rebuilt computer can malfunction too.

Make yourself some shift lights and see what the computer is telling the solenoids to do. It will help you zero in on the issue.

Next time you have the pan off, inspect the wiring at the solenoid plug to the solenoids themselves just to make sure they are not visibly damaged.


So I?ve noticed the 1-2 slip isn?t there when cold.
That is a textbook symptom of a clogged filter. Not saying it is but if you have an oe filter, it's a good place to start.

[81dmc]

Few things.
You can not tell if a filter needs to be replaced by looking at it. The part that usually clogs up is hidden under the clamshells.

I just replaced my shift computer with a rebuilt one. The rebuilt one was faulty pushing my car into 2nd at times with no warning and other times it would not shift out of 1st and/or second. My second shift computer works flawlessly. Point is a rebuilt computer can malfunction too.

Make yourself some shift lights and see what the computer is telling the solenoids to do. It will help you zero in on the issue.

Next time you have the pan off, inspect the wiring at the solenoid plug to the solenoids themselves just to make sure they are not visibly damaged.


That is a textbook symptom of a clogged filter. Not saying it is but if you have an oe filter, it's a good place to start.
Had the pan off a few days ago. Wires looked good and I cut open the old filter and it was mostly clean. I replaced it with one of your filters anyways.

[David T]

If you notice that the shifts improve once it warms up the possible causes include;
Low fluid
Wrong fluid
Low line pressure
Clogged filter

[81dmc]

If you notice that the shifts improve once it warms up the possible causes include;
Low fluid
Wrong fluid
Low line pressure
Clogged filter
Opposite. Shift gets worse as it heats up.

[Michael]

At the end of the day, if your fluid is fresh and filter is clean and the shifting is fine but slipping or "flare shifting", then I would be expecting trans a rebuild in your near future.

[81dmc]

At the end of the day, if your fluid is fresh and filter is clean and the shifting is fine but slipping or "flare shifting", then I would be expecting trans a rebuild in your near future.
Yeah, I'm starting to think that may be the case. I have been driving it rather hard to get the 3.0 dialed in. I'll probably keep going until I lose it completely.

Are these things really a pain to overhaul? I've rebuilt an GM type transmission before, but never a transaxle.

Also, are there any special tools I should start looking for?

[WHO1DMC]

Forgive me if im off base but some of the symptoms are of a bad converter.
If you're going to invest in a rebuild I would include a new converter.



Dave B.

[David T]

Opposite. Shift gets worse as it heats up.


Well then;

Wrong fluid
Too much fluid
Low line pressure
Bad shift computer