Hello,
I ´ve got a nice `88 B250 with 318 TBi and a 904(?) with lock-up converter, but i have thoughts about getting an overdrive gearbox (maybe an A500) when cruising at highway speeds.
At 55 mph. the tach reads about 2000 rpm. How much will an OD reduce the rpm?

At which speed does the OD engage, and is it a reliable unit?

How does it work, hydraulic or electric - or combined?

Is there any changes to be made to the electrical system, driveaxle or other, before mounting an overdrive gearbox?

Any information about the overdrive option, and your experience with it, is more than welcome.

 

Overdrive reduces RPMs by 30%. So in your example the RPMs would go down to 1400.

Read this page regarding swapping to an OD tranny:
http://www.transmissioncenter.net/SwapInformation.htm

 

I have an a500 in my '89. I've heard the overdrive is the weakest link in the tranny. I had my tranny rebuilt at 130k miles.

Under the lightest throttle accelleration, my overdrive will kick in about 35 mph, and the torque converter will lock up at 47mph, according to my Speedo, which reads 3.5 mph fast at 60mph.

The ECM controls the overdrive and lock up depending on inputs from the speed sensor, so you would need an ECM from a van that came with an a500 or a518 for it wo work automatically.

These guys make underdrive/overdrive units for all sorts of trannies, but are not cheap.
http://www.gearvendors.com/ag3s.html

http://www.gearvendors.com/d2wd3s.html

 

OK, i'll see if i can figure out something with a ECU & gearbox from an OD vehicle. I'll be back!

 

OK, back again, it's been awhile but i haven't switched my A999 to an A518 yet... and the neighborhood gas station has my picture on their wall with the sign "customer of the year" under it.

I've read alloro's link which seems to be a smooth task, although i'm more into buying a parts car from Sweden (they have a country full of Dodge vans) and install the entire driveline from an OD car.
Has anyone tried that before? Do i have to replace the entire wiring system, or the ECU / engine wiring system only (except for the OD switch on the dash)?

 

The RPMs are about 2,000 at about 90kph? Our Caravan minivan does those RPMs at that speed with OD activated.

What is the rear axle gear ratio on the van??? That may be a bigger improvement than swapping the tranny.

 

Update...
I was lucky to get hands on a rusted-out, but fully functioning & well-driving ´89 B250 with A518.
Now, there's two ways to go, as i see:

1: Replacing the gearbox only (and install button in the dash). Is my '88 (in fact, build in december 1987 according to the tag) prepared for that in the wiring harness & computer? I know about the swap guide from transmissioncenter.com but i want to keep it factory.

2: Replacing the entire driveline incl. computer & wiring harness.
Is it a straightforward process to install the entire wiring harness? Or, how much of the harness do i have to change? And what's the easiest way to pull the engine?

What would you do?