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A727 to A518 Trans Swap In B150

Discussion in 'Vans' started by ccrider77, Aug 13, 2012.

  1. ccrider77

    ccrider77 New Member

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    Just thought I'd post up the results of the recent transmission upgrade in my 1985 Dodge B150 passenger van. The 300,000+ mile vehicle is on the 2nd 318 engine and the non-lockup A727 3-speed automatic was starting to slip pretty badly when cold and at speed. The cost to rebuild the stock trans was $850 and it would've worked fine, however with gas prices continuing to rise, I wanted to get the mileage up.

    Being a California smog vehicle, I was stuck with the stock 2 into 1 exhaust, EGR, 2-bbl carb and low-tech computer engine managment. I considered a carb-approved FI system as well, but the price was outrageous.

    I opted to replace the stock 3-speed with an A518/46RH 4-speed auto with lockup torque converter. After doing some research, I found that this was definitely possible and contacted my local transmission shop to build the unit for me. I picked out an excellent 46RH core, a low mileage OD unit and a tailshaft which uses the standard cable-driven speedo cable instead of the speed sensor.

    After some wait for them to finish the basic trans, I picked it up and installed it. Here's what to expect:

    1) The trans and engine bolt up perfectly - no problems.
    2) The stock 1985 flex plate and starter worked perfectly.
    3) The torque converter for the 318 has no balance weights because the 318 engine is internaly balanced. If you use a 360, you'll have to get a torque converter which is balanced for the 360 engine.
    4) The lockup torque converter will drop RPM's about 200-300 more so it's definitely worth it. Your 46RH core should have a short smooth end on the input shaft before the splines. This means it's designed for a lockup converter.
    5) Find a tailshaft with a cable-driven speedometer port. If the tailshaft comes with an unplugged hole for the speed sensor, plug it. You can use the stock speedo cable if you re-route it a little bit.
    6) Some people do this conversion by adding a switch to manually switch the OD on and off. PACT makes an $85 kit that makes the trans work completely automatically without any manual switches. They us a vacuum switch to turn power on and off to the solenoids in the transmission and two pressure switches - a 44 MPH switch for the OD and a 52 MPH switch for the lockup. The wiring and plumbing is pretty simple and it means you simply put the trans in Drive and it will operate without any other driver input.
    7) The transmission crossmember will have to be modified for the lower and wider tailshaft. I took careful measurements, cut the original crossmember into pieces and brought them to a welder to fabricate the new piece. This was the "hard" part, and you can always bring the van to a muffler shop to let them fab it. I added an additional rubber bushing under the mount to help support the weight, as the factory donut bushing on older Dodge vans tend to fail pretty quickly causing a rattle.
    8) When fabing the crossmember, remember that on Dodge vans, the drivetrain is offset about 4 inches to the right, so take that into consideration.
    9) The driveshaft will need to be shortened and rebalanced. Some recommend shortening it by as much as 3.5 inches, but I took careful measurements and found it to be 3.34 inches or 85 mm. If the driveshaft is too long, it will damage the transmission when the suspension is fully loaded. If it is too short, excess stress and play on the yoke will cause wear and vibration. Now is a great time to replace the U-joints. The A727 yoke should fit perfectly into the A518 transmission.
    10) On the 727, the second lever near the selector lever is the kickdown lever. On the 518 this lever is the throttle valve, which will not only kick the transmission down, but also determine the shifting characteristics based on throttle position. Because of this, you need to either use a cable or set up the kickdown linkage so there is no free play. That is as soon as you start to depress the throttle, this lever will move immediately.
    BTW - With the transmission removed, now is the perfect opportunity to replace the rear main seal and oil pump on the engine if you need to do that. It can be done on full-size Dodge vans without lifting the engine.

    The cost for the A518 transmission was about $1375 with the rebuilt lock up torque converter. Prices will vary. The PATC kit was $85, the crossmember welding was $60, the driveshaft work and U-joints were $180 and 11 quarts of synthetic ATF+4 was $77. The total cost wasn't cheap, but if you're going to keep the vehicle for years, this modification can pay for itself in 1-2 years in gas savings alone. Since the 46RH is basically an A727 transmission body with different valving and an overdrive gear added, it will be nearly as reliable as the tried and true A727.
     
    Leslie Clemens likes this.
  2. 135SoHc

    135SoHc Active Member

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    With a few edits this should be added to allpart article section. I was considering doing such a conversion and this did answer a few questions.
     
  3. TWX

    TWX DO NOT FEED THE TROLLS!
    Level 2 Supporter

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    I'm going to sticky this. Much of this applies to any A5XX retrofit behind any small block in any vehicle...
     
    PCRMike likes this.
  4. Leslie Clemens

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    Hello!
    Is there any way we could get a pic of that modified transmission mount? I am thinking doing the same thing with a '77 B-200.
    Thanks!
     
  5. Bearhawke

    Bearhawke Things happen for a reason

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    In all fairness: since the B series van didn't change that much from 1970 to 2003; some of the ca. 1997 down B van parts i.e. crossmember, etc. may've worked as well. :)
     

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