Allpar Forums banner

'76 Dart trans swap

10K views 30 replies 6 participants last post by  AC TC 
#1 ·
I want to replace the A904 with a hydraulic OD. I believe the easiest choice would be an A500 made from '89 to '95. I'm going to look for one at the local help-yourself salvage. My research tells me that I'll need the support and I'll get the drive shaft in case the tail shaft is different.

Do I have it all right?
 
#2 ·
The A500 IS longer, it has the electric overdrive unit behind the transmission. So you would need a shorter driveshaft, and I don't know how the supports would change.
You also would need to figure out how to compensate for the lack of electronic control of the overdrive. Without it, it would top out in 3rd gear, which means you'd have the same gear ratios as the 904, but would have gone through a lot of grief for nothing
 
#3 ·
There are solutions to provide both torque converter lockup and to engage OD from something as simple as manual toggle switches to kits providing automatic activation.
The rear transmission crossmember has to be cut apart and a new piece fabricated since the OD transmission is larger at that part of the trans compared to the original. Some people modify or cut the floorpan for more clearance for the OD trans.
 
#5 ·
Not sure. The engines that used the A500 also have a crankshaft position sensor on the flywheel, so I don't know if clearances are the same. Someone may know if the bellhousing is compatible.

What is your goal in wanting a different transmission?
 
#6 ·
Bolt pattern is the same, everything is the same. The crank trigger stuff doesn't apply, but verify the flex plate spacing, that I do not know if it is the same. Be sure it is a 318 trans, the 360 has a great big counterbalance welded to the torque converter, which will work, you just have to make sure you cut it off clean, like a metal saw or chisel. And yes, there are kits at places like TransGo, easy couple wires and also a kickdown setup, fairly inexpensive (been a while since checking them), but there are other places to look, too. The magazines Mopar Muscle and Mopar Action, pick one off the magazine rack, lots of helpful vendors out there to fix this issue.
 
#7 ·
I'm confused about the "governor". There seems to be two types, hydraulic and electric, RH and RE. I thought I understood RH to be NOT computer-controlled, made from '88-'95; and RE to be computer-controlled, made from '96-on. Somebody please set me straight so I can be sure I'm pulling the correct transmission at the salvage yard.
 
#8 ·
That is correct.

I looked into those overdrive controller kits, and they started at $450. Ouch.
 
#10 ·
Not sure what you found, but a few years ago it was around $95, a switch for the kickdown, some wires and a push button to engage/disengage the overdrive itself.

Get a Mopar Muscle or Mopar Action, there are several companies that advertise in there for the swap, which was really big for the overdrives going behind big blocks.
 
#12 ·
Only thing I could think would be selonoid pack difference if going to MPFI on the engine and computer itself would be doubling the amount of troubleshooting information so they made it a separate book or something. Guts and body should be the same through all the years, programming might be different.
 
#13 ·
dana44 said:
Not sure what you found, but a few years ago it was around $95, a switch for the kickdown, some wires and a push button to engage/disengage the overdrive itself.

Get a Mopar Muscle or Mopar Action, there are several companies that advertise in there for the swap, which was really big for the overdrives going behind big blocks.
That's a manual control. I could build that for $20. I'm talking about a microprocessor-based box that provides automatic control of the overdrive, just like OEM.
 
#14 ·
A simple toggle switch will suffice on a RH tranny..
Note that its 727 cuisin the A518 or 46RH is also avail, slightly bigger thou.
The input shaft may be changed to get rid of lock up TC on booth of em, however running an od tranny
with a low numerical rear will make lots of heat from the turbine.
 
#15 ·
The A500 is my choice because it is lighter. I've done the research and I see where others have successfully automated the control of both the LU and the OD by using two pressure switches and one vacuum switch. It totals about $100. No stinkin' computer controls for this old hot rod. The point of the OD is to run a larger number in the rear gears to make it hop from a standing start. The stock 2.06:1 (or whatever it is) just won't get it.
 
#16 ·
I agree with you Toolman_, don't need no stinking processor and all that crup, might as well swap the whole running gear setup, put the proper computer in there and take it down and get it smog and safety tested. No, less than $100 to make new technology work with the old.

3.55 to 3.90 was stock with these transmissions most of the time, so 3.55 with a smaller diameter tire compared to a truck tire should give you some good motion and still not kill you on the highway.
 
#18 ·
Pretty sure it is too wide from the Dakota, the B body rears fit under the Dakota with a spring perch change.

Remember to adjust for he diameter of the wheels as I said, a 3.55 with truck tires is about the same as a 3.23 with street tires. A lot closer than not for the math-heads doing the calculations.
 
#19 ·
It's a lot more complicated than that to switch the transmission. Shifting into OD and lockup requires two separate switches. You can do it manually, which would be more of a pain than a manual transmission, to remember to turn the lockup and OD off and on all the time. As far as automating control, you need a lot more than pressure and vacuum inputs. OD is not to be used when the coolant is below 60F, and lockup is not to be used when coolant is below 140F. Doing so will damage the transmission. Other inputs to the shifting decisions include MAP and TPS. So, good luck.
 
#20 ·
Bob Lincoln said:
...OD is not to be used when the coolant is below 60F, and lockup is not to be used when coolant is below 140F...
That's good to know. So far there's a pressure switch that closes at about 48psi, a pressure switch that closes at about 50psi, a vacuum switch that closes at about 4psi, a temperature switch that closes at about 60F, and a temperature switch that closes at about 140F. I wonder if all these aren't on the Dakota that has the transmission?

Temperature and pressure are the critical variables in most hydraulic things. Vacuum infers throttle position. How do the other variables affect the transmission? Tell me more...
 
#22 ·
toolman_ said:
That's good to know. So far there's a pressure switch that closes at about 48psi, a pressure switch that closes at about 50psi, a vacuum switch that closes at about 4psi, a temperature switch that closes at about 60F, and a temperature switch that closes at about 140F. I wonder if all these aren't on the Dakota that has the transmission?
They are not discrete switches, the computer uses the input from the coolant temperature sensor. So you will have to have discrete switches as you mention in the last post.
4th gear (the overdrive), is not hydraulically controlled for shifting. It's electrically controlled. So there is no transmission fluid pressure input to the decision to turn that on or off. There is a solenoid pack on the right side of the valve body, which is activated or deactivated for shifting into and out of 4th, and also for the lockup torque converter. The solenoids block or open a fluid passage to accomplish the shift. These are the controls that a toggle switch will turn on or off.
 
#23 ·
#24 ·
I have an A500 and torque converter out of a '92 Dakota. I have a '92 Mitchell transmission service an repair manual. I have sources for GM pressure switches and an adjustable vacuum switch. I intend to energize OD at 40-MPH and energize LU at 48-MPH provided vacuum is above the minimum.

Studying the manual, it appears the OD and LU solenoids are the only aspects of the transmission controlled by electronics. The rest is hydro-mechanical. The manual is a little fuzzy as to whether or not the hydro-mechanical in some way inhibits either OD or LU. Does anyone understand the inner workings well enough to clear this up?
 
#25 ·
O/D and lockup are engaged and disengaged only by solenoids being switched. No hydraulics directly turn them on or off. It's a solenoid pack on the side of the valve body. The solenoids are activated and deactivated by the ECM, and the ECM bases its decisions on inputs from the MAP sensor, TPS, CTS, etc. Vacuum switches will not provide the proper decision-making alone.
 
#26 ·
Pressure switches will signal speed. The manual confirms that governor pressure (PSI) directly correlates to speed (MPH). Pressure switches used on Turbo 350's from '80-'86 are rated in increments from 34 PSI to 54 PSI. Most of them can be purchased new from Dacco. With two pressure switches and two vacuum switches I'll have essentially the same logic as any automatic transmission had before electronics. The vacuum switches are adjustable which should provide the ability to first drop-out LU, then OD, before the 3-2 downshift. Vacuum switches will be in series with pressure switches. I don't see how it cannot work...
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top