A-500 transmission OD and LU controls.

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Clelan

Clelan

Inferno Red Duster
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I have seen a few good ways to control the overdrive and lock up on the A-500/42RH transmissions when swapped into older cars, and I hope I learned a bit from all of them while coming up with my own plan. So here it is. What do you think?

Forgive me for the schematic diagram, but that is the way my mind works!

Cley
Capture.PNG
 
Yes. I'm not exactly sure what the on logic was but it replaces that with speed sensing and timers.

Cley
 
I'm using a simple 3-step (OFF-ON1-ON2) toggle switch mounted on the center console.
OFF = no overdrive
ON1 = OD
ON2 = OD + LU


e876_1_4.jpg
 
Then you need a pressure sensor and vacuum switch tee'd in a transmission's oil pressure port.
 
BigBlockMopar said:
Then you need a pressure sensor and vacuum switch tee'd in a transmission's oil pressure port.
Click to expand...

That is what i described in the drawing and functional description in post 1. Actually I think I'll use 2 vacuum switches, 1 for LU and 1 for OD. And possibly the B&M trans controller instead of the pressure switch.

Cley
 
The problem is nobody can read the text in your diagram
 
I know someone has posted this before- COMPUSHIFT MINI hgmelectronics.com looks like the way to go.
 
89on35s said:
I have seen a few good ways to control the overdrive and lock up on the A-500/42RH transmissions when swapped into older cars, and I hope I learned a bit from all of them while coming up with my own plan. So here it is. What do you think?

Forgive me for the schematic diagram, but that is the way my mind works!

Cley
View attachment 1715108691
Click to expand...

Overcomplicated.
The governor pressure in lbs is real close to road speed in mph, so normally off adjustable pressure switches can be used to activate OD and LU.
This way there is no need for an electronic speed sensor, as the governor supplies speed sensing in psi.
NOS fuel safety cutoff switches work great for this, as they are designed to disable the NOS if there is insufficient fuel pressure. (so normally off, but contact when the pressure is high enough)
Plumbed into the governor port and set at different pressures gives you an adjustable speed range where OD and LU engage.

Then a normally on adjustable vacuum switch can be used to kickdown on heavier throttle by breaking the ground for the relay that controls the respective solenoids in the trans when intake vacuum drops below your set range.
If you build the system with power to the trans whenever the ignition is on it's easy to use ground switching for engaging disengaging OD and LU.

My own 42RH is set to go into OD at about 55mph, and LU at 70 completely automatic, but if I turn the ground off to one or the other of the control solenoids with the switches on my shifter it disables it.
If I have the OD switch on inside the car the trans automatically goes into OD at 55mph, but if the lockup switch is off then LU will not come on.
If I have the OD switch off and the LU switch on the trans will skip OD and then LU at 70mph in 3rd.
This means I can run it in 3rd with lockup, OD with lockup or OD without LU but I have never seen any real use for doing it.

Oh, and I plumbed those two pressure switches up to the back of my intake on a mounting bracket so those speed adjustments can be done from under the hood instead of under the car like some do.
 
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I know my drawing came out hard to read. I'll try and fix it on the next one. I am still considering the pressure switches because I guess I likely won't be adjusting after the system is set up. Now that I see the prices of the timing relays I chose, I am rethinking the entire thing. @TrailBeast do you ever have issues with hunting on OD or LU shifts where they shift in and out when your speed is close to setpoint? That was my reason for the timers, to avoid that. Also, does your kick down vacuum switch disengage OD and LU?

Cley
 
89on35s said:
I know my drawing came out hard to read. I'll try and fix it on the next one. I am still considering the pressure switches because I guess I likely won't be adjusting after the system is set up. Now that I see the prices of the timing relays I chose, I am rethinking the entire thing. @TrailBeast do you ever have issues with hunting on OD or LU shifts where they shift in and out when your speed is close to setpoint? That was my reason for the timers, to avoid that. Also, does your kick down vacuum switch disengage OD and LU?

Cley
Click to expand...

Good questions.:D
I don't get a hunting problem because I won't let the speed sit right there, but if for some reason I had to hold that speed I would just switch OD off at the shifter switch for the time being.
Same with LU, but I have never had the need really.
As far as the vacuum switch it is only set up to disengage LU and if I also wanted out of OD while above 55mph I can switch it off at the shifter.

One thing I noticed in setting mine up was that the brake switch disengage didn't matter either, so I don't have that.
The car comes down below 70 where lockup will disengage WAY before it produces a drag on the motor.
The thing is, that fully automatic is nice for longer cruises but if one was serious about putting power down you probably would just want OD and LU manually turned off anyway.

BTW, you are going to LOVE your new fuel economy when you get er done.
My mild cammed headered 4 barrel 5.9 gets a little over 25mpg on the hiway at 80mph at 2,100 rpms.:D
This is how the manual override inside the car is set up.

ShifterArt.jpg
 
TrailBeast said:
Overcomplicated.
The governor pressure in lbs is real close to road speed in mph, so normally off adjustable pressure switches can be used to activate OD and LU.
This way there is no need for an electronic speed sensor, as the governor supplies speed sensing in psi.
NOS fuel safety cutoff switches work great for this, as they are designed to disable the fuel pump if there is insufficient NOS pressure. (so normally off, but contact when the pressure is high enough)
Plumbed into the governor port and set at different pressures gives you an adjustable speed range where OD and LU engage.

Then a normally on adjustable vacuum switch can be used to kickdown on heavier throttle by breaking the ground for the relay that controls the respective solenoids in the trans when intake vacuum drops below your set range.
If you build the system with power to the trans whenever the ignition is on it's easy to use ground switching for engaging disengaging OD and LU.

My own 42RH is set to go into OD at about 55mph, and LU at 70 completely automatic, but if I turn the ground off to one or the other of the control solenoids with the switches on my shifter it disables it.
If I have the OD switch on inside the car the trans automatically goes into OD at 55mph, but if the lockup switch is off then LU will not come on.
If I have the OD switch off and the LU switch on the trans will skip OD and then LU at 70mph in 3rd.
This means I can run it in 3rd with lockup, OD with lockup or OD without LU but I have never seen any real use for doing it.

Oh, and I plumbed those two pressure switches up to the back of my intake on a mounting bracket so those speed adjustments can be done from under the hood instead of under the car like some do.
Click to expand...
That sounds like it works well.
 
toolmanmike said:
That sounds like it works well.
Click to expand...

Yea, but it took months before I got used to those extra shifts being there.
A slight momentary panic happens when third lets go before you realize again that it's because it's shifting into overdrive.:D
 
OD at 55? Why so late...?
What gears do you have in the rearaxle?
With my 3.55 gears and easy driving I usually switch on OD at around 30mph already.

I believe the PATC OD-kit switches on at 40-45mph, which seems more inline with the factory setting I believe?
 
BigBlockMopar said:
OD at 55? Why so late...?
What gears do you have in the rearaxle?
With my 3.55 gears and easy driving I usually switch on OD at around 30mph already.

I believe the PATC OD-kit switches on at 40-45mph, which seems more inline with the factory setting I believe?
Click to expand...

In our 93 Dakota with 3.55 gears, OD kicks on about 45-50 and locks up about 55 - you can feel each one and also see by the tach. It's been this way since we bought the truck brand new with 35 miles on it.
 
Thanks for the info.
Could probably be explained by a difference in tire size perhaps between pickups and passenger cars?
 
Not quite knowing how the factory did it, I tend to disagree 'bout that.

I had my switch wired wrongly at the beginning and it would engage LU in 3rd, then upshift to OD, but the resulting jolt in the driveline told me this can't be right and imo the LU should be disengaged before the shift to OD.
 
BigBlockMopar said:
Not quite knowing how the factory did it, I tend to disagree 'bout that.

I had my switch wired wrongly at the beginning and it would engage LU in 3rd, then upshift to OD, but the resulting jolt in the driveline told me this can't be right and imo the LU should be disengaged before the shift to OD.
Click to expand...
I was thinking GM .
 
BigBlockMopar said:
OD at 55? Why so late...?
What gears do you have in the rearaxle?
With my 3.55 gears and easy driving I usually switch on OD at around 30mph already.

I believe the PATC OD-kit switches on at 40-45mph, which seems more inline with the factory setting I believe?
Click to expand...

BigBlockMopar said:
Not quite knowing how the factory did it, I tend to disagree 'bout that.

I had my switch wired wrongly at the beginning and it would engage LU in 3rd, then upshift to OD, but the resulting jolt in the driveline told me this can't be right and imo the LU should be disengaged before the shift to OD.
Click to expand...

I have 2:73 rear gears.
If I let it shift sooner it would almost be at an idle.:D
Most of my shifts are at about 2,100rpms driving normally, and of course higher if I step in it more.

Yea, having lockup come on before OD I could see that being a problem.:D
3rd gear fluid is what supplies the OD, so it's not possible for OD to engage unless the trans is already in 3rd, but lockup can come on whenever it is supplied with a ground. (any gear at any speed)

I played with that for awhile just for fun and at one point ended up idling down the street on cam lope at 35mph in 3rd with lockup.
 
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AJ/FormS said:
If you were to imagine it, could you put 250 ftlbs into the lock up?
Click to expand...

I personally don't know what the converter can actually deal with and usually don't push it too much seeing as how it's designed to be a cruise gear basically.
I do know I can pull pretty much any hill on freeways that comes up without leaving lockup. (the 5 miles of 6% grade on I17 near Black Canyon City for example)
Chasing a Corvette on I40 at 120 should have put a little power through it though, but that was only about 2,400rpms so it wasn't into the cam power range yet.
 
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TrailBeast said:
I personally don't know what the converter can actually deal with and usually don't push it too much seeing as how it's designed to be a cruise gear basically.
I do know I can pull pretty much any hill on freeways that comes up without leaving lockup. (the 5 miles of 6% grade on I17 near Black Canyon City for example)
Chasing a Corvette on I40 at 120 should have put a little power through it though, but that was only about 2,400rpms so it wasn't into the cam power range yet.
Click to expand...
Well I think that settles it; 2400 in a warm 5.9,(say a 220ish cam with matching compression), could easily be 200. Thx TB
 
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