Interesting thoughts and observations on OD transmissions

[TrailBeast]

In my specific situation I have a 42RH Dodge transmission in my Dart, and have had it in there for 6 or so years and it has been flawless.

Recently I have an issue where it doesn’t stay in converter lockup consistently.
It will drop out and re engage randomly.
My setup is fully automatic using governor pressure to determine shift points using adjustable pressure switches.
The lockup normally engages at about 65mph, and disengages when under 65 if the switch inside the cabin is in the Auto position.

I used a jumper wire to bypass the adjustable pressure switch to start diagnosing the intermittent on/off of converter lockup, then go to the relay that actually switches it if needed.
The question was, is the problem the pressure switch, the relay, or the solenoid inside the trans?
Well, bypassing the pressure switch solved the problem and in that process made lockup totally manual depending on the switch inside the car. (Which I expected)
Of course the problem is the most expensive part of the shifting system.
Those pressure switches ain't cheep.
I hardly use lockup except for extended 80mph and up drives, but it would be nice to have it all working as designed.

Anyway, here’s the interesting part.
I knew OD only works off the 3rd gear oil, meaning OD won’t engage unless the trans is already in 3rd gear.
Well during the lockup diagnosis I also found lockup will only engage once in 3rd.
With the pressure switch bypassed I can manually engage lockup at any speed I want as long as the trans is already in 3rd gear.
(Kinda fun to play with, but no practical use)

Now here’s the actual interesting thought based on how this trans works.
Imagine doing 80+ in OD with converter lockup and manually downshifting to second gear.
Converter lockup, OD and 3rd gear will all drop out at the same time.
Depending on the rear gears this could be a real problem.
I have a ratshit shifter, so this could easily happen accidentally.

Interesting.

 

[67Dart273]

When I had the old White Whale I think it was the 3/4T I had a pair of toggles. More than once, LOL, I came brainless rolling up to a red light and forgot to drop it out of lockup

 

[Demonic]

Not to hijack the topic, but the 90-95 A518/47RH seem to be scarce around here. Anyone near Maryland have one to sell?

 

[4spdragtop]

Not to hijack the topic, but the 90-95 A518/47RH seem to be scarce around here. Anyone near Maryland have one to sell?

 

[mbaird]

How many rpms did you drop locking up the torque converter?

 

[TT5.9mag]

If you had a turbo you’d really like being able to control the lock up in lower gears. The diesel guys have figured out how to do it.

 

[TrailBeast]

How many rpms did you drop locking up the torque converter?

Lockup drops about 300 rpms.
One big thing about using lockup besides it’s obvious no slip connection to the trans is that it eliminates the heat generated by the converter.
That 300 rpm slippage creates heat in the fluid.

 

[67Dart273]

One unfortunate thing about the OD Torqueflites is that 2nd over and 3rd under amount to approximately the same ratio

 

[RustyRatRod]

You wouldn't have to worry about all that with a third pedal.

 

[mbaird]

Not sure what that means.
Can you elaborate?

 

[mbaird]

One unfortunate thing about the OD Torqueflites is that 2nd over and 3rd under amount to approximately the same ratio

Thats was for Del…. 2nd over and 3rd under ?

Lockup drops about 300 rpms.
One big thing about using lockup besides it’s obvious no slip connection to the trans is that it eliminates the heat generated by the converter.
That 300 rpm slippage creates heat in the fluid.

300 makes more of difference than one would think . My car turns about 3k at 80 . 2700 would be much better .

 

[67Dart273]

Not sure what that means.
Can you elaborate?

With manual control (toggle) of the OD you can put it in OD in 2nd. But at least with the 727 based ones, the difference between 2 gear in OD or 3rd without OD amounts to nearly the same thing.

I'd have to look up the ratios. I don't remember "whut" anymore.

 

[273]

Thats was for Del…. 2nd over and 3rd under ?

300 makes more of difference than one would think . My car turns about 3k at 80 . 2700 would be much better .

300 rpms is like going from 3.55 to 3.23 on the highway, definitely a decent drop and don't have to sacrifice gearing to do it.

 

[mbaird]

I had no idea the OD could engage in any gear except 3rd.
Makes sense I guess .
I have the solenoids for my 46rh . Should be in the car by spring ..

 

[Scody21]

You wouldn't have to worry about all that with a third pedal.

No truer words could be spoken…

 

[autopar3000]

In my specific situation I have a 42RH Dodge transmission in my Dart, and have had it in there for 6 or so years and it has been flawless.

Recently I have an issue where it doesn’t stay in converter lockup consistently.
It will drop out and re engage randomly.
My setup is fully automatic using governor pressure to determine shift points using adjustable pressure switches.
The lockup normally engages at about 65mph, and disengages when under 65 if the switch inside the cabin is in the Auto position.

I used a jumper wire to bypass the adjustable pressure switch to start diagnosing the intermittent on/off of converter lockup, then go to the relay that actually switches it if needed.
The question was, is the problem the pressure switch, the relay, or the solenoid inside the trans?
Well, bypassing the pressure switch solved the problem and in that process made lockup totally manual depending on the switch inside the car. (Which I expected)
Of course the problem is the most expensive part of the shifting system.
Those pressure switches ain't cheep.
I hardly use lockup except for extended 80mph and up drives, but it would be nice to have it all working as designed.

Anyway, here’s the interesting part.
I knew OD only works off the 3rd gear oil, meaning OD won’t engage unless the trans is already in 3rd gear.
Well during the lockup diagnosis I also found lockup will only engage once in 3rd.
With the pressure switch bypassed I can manually engage lockup at any speed I want as long as the trans is already in 3rd gear.
(Kinda fun to play with, but no practical use)

Now here’s the actual interesting thought based on how this trans works.
Imagine doing 80+ in OD with converter lockup and manually downshifting to second gear.
Converter lockup, OD and 3rd gear will all drop out at the same time.
Depending on the rear gears this could be a real problem.
I have a ratshit shifter, so this could easily happen accidentally.

Interesting.

I find it interesting that you have your OD set up to lock so late. What differential gear are you running?

I had that same type of pressure switch setup in my car with a 46rh. I had the pressure switches adjusted for "normal" acceleration, so it went into OD at about 50 mph and lockup at about 55 mph (3.23 gear, 26" tire). Of course, if I was going to do any sort of spirited acceleration I would have to manually shut off OD and LU ahead of time, otherwise I would be shifting to OD and locking up as soon as it shifted into 3rd gear, which could be way too early.

But mine wouldn't unlock at those same speeds. It unlocked when I hit about 50 mph (about 1500 rpm), and it wouldn't drop out of OD until I hit about 45 mph (about 1300 rpm). I guess that's just how my pressure switches worked; the pressure to close the circuit was X and the pressure to open the circuit was X minus a bit.

I'm running factory Magnum EFI, so I eventually got rid of the pressure switches and wired the computer to control the OD and LU. I was pretty surprised how quickly the computer would tell it to go into OD and LU during light acceleration. During light acceleration 3rd only lasts about 1 second, it will shift into OD almost immediately and put the RPMs at about 1200. If I keep accelerating gently or start cruising it will lockup and end up at about 1300 rpm (about 45 mph). I thought that was super low and there must be a problem, then I found this in the 1995 service manual:

 

[mbaird]

Mopars transmission programs suck upto at least 03. My 03 ram does same thing . You have to floor it to get out of OD and then it drops to 2nd !

 

[TrailBeast]

With manual control (toggle) of the OD you can put it in OD in 2nd. But at least with the 727 based ones, the difference between 2 gear in OD or 3rd without OD amounts to nearly the same thing.

I'd have to look up the ratios. I don't remember "whut" anymore.

I had no idea the OD could engage in any gear except 3rd.
Makes sense I guess .
I have the solenoids for my 46rh . Should be in the car by spring ..

OD and lockup both are able to engage only after the trans is in 3rd gear.
They both get their apply oil from the active 3rd gear circuit.

I find it interesting that you have your OD set up to lock so late. What differential gear are you running?

I had that same type of pressure switch setup in my car with a 46rh. I had the pressure switches adjusted for "normal" acceleration, so it went into OD at about 50 mph and lockup at about 55 mph (3.23 gear, 26" tire). Of course, if I was going to do any sort of spirited acceleration I would have to manually shut off OD and LU ahead of time, otherwise I would be shifting to OD and locking up as soon as it shifted into 3rd gear, which could be way too early.

But mine wouldn't unlock at those same speeds. It unlocked when I hit about 50 mph (about 1500 rpm), and it wouldn't drop out of OD until I hit about 45 mph (about 1300 rpm). I guess that's just how my pressure switches worked; the pressure to close the circuit was X and the pressure to open the circuit was X minus a bit.

I'm running factory Magnum EFI, so I eventually got rid of the pressure switches and wired the computer to control the OD and LU. I was pretty surprised how quickly the computer would tell it to go into OD and LU during light acceleration. During light acceleration 3rd only lasts about 1 second, it will shift into OD almost immediately and put the RPMs at about 1200. If I keep accelerating gently or start cruising it will lockup and end up at about 1300 rpm (about 45 mph). I thought that was super low and there must be a problem, then I found this in the 1995 service manual:

View attachment 1716316071

Thats odd.
My switches are adjustable and I have 3.55 gears in the back.
To me the rpms of the shifts are more important than the speed, and I like 2,000 - 2,500 or so.
About the same for the 1-2 and 2-3 shifts.

Maybe I should do a video of it out on the road just for fun.
Although for now lockup is manual on or off since that pressure switch is dead and currently bypassed.

 

[TrailBeast]

You wouldn't have to worry about all that with a third pedal.

I had a third pedal for years and I’m over it.
This car was never intended to be a hotrod, though it is fairly capable.

 

[autopar3000]

OD and lockup both are able to engage only after the trans is in 3rd gear.
They both get their apply oil from the active 3rd gear circuit.




Thats odd.
My switches are adjustable and I have 3.55 gears in the back.
To me the rpms of the shifts are more important than the speed, and I like 2,000 - 2,500 or so.
About the same for the 1-2 and 2-3 shifts.

Maybe I should do a video of it out on the road just for fun.
Although for now lockup is manual on or off since that pressure switch is dead and currently bypassed.

Yeah, 2000 rpm makes sense. Assuming a 26 inch tire, the math says you're at 2050 rpm at 65 mph when after the converter locks, so probably around 2300 under light acceleration at 65 mph. Is your torque converter stock?

Those 3.55's must be nice! The 3.23 is way low (high?) for me, but I just picked up another center section and will be putting in a set of 3.73 gears.

I would love to see a video. Maybe I'll get my car out tomorrow and do a video too (it's raining today).

 

[mbaird]

I had a third pedal for years and I’m over it.
This car was never intended to be a hotrod, though it is fairly capable.

I have an a/t in my Barracuda and a 4 speed in my Swinger.

The Barracuda has a mildly built 5.9 with a 221/229 .540 lift cam , IMM EQ ported heads and 2.76 gears . I enjoy the auto in it . It’s pretty much my daily driver .
I will drive it anywhere so the 46rh with 3.55s will give me better off the line excelleratiin and the ability to cruise at 80 on the freeway whiteout turning 3200 rpm and some asshole tailgating me .

The Dart has a 408 W2 solid 246/250 .648 roller and it’s more of a fun/race car . Although it has yet to see the track . It’s fun to roll through the gears once in a while ! Plus I love the look of a stick shift popping up from the floor !

Every loves pics ….

 

[mbaird]

Gotta paint those wheel wells black ….