727-518 or 47re

[mykal41]

I had posted a question a while back in regards to a transmission swap. My 727 has issues and the 3 speed is killing me. I would like to swap to an overdrive unit. I know the early overdrives were 518s and the later were 47rh. FASTMAN performance offers trannys and Dan is going to help me work some bugs out of my stroked and supercharged 98 ram, . I would like to have him build me a 47rh. However I dont know if it a direct swap. If anyone know whats involved pleas let me know.

 

[Philip]

Would you post all the spec's of the truck and drive train! You threw a year model out there but no engine. Plus the trans you listed wasn't a option in 98. So tell us what you built and what you plan on doing with it.

 

[fox]

The hard parts interchange, so the best can be put into any of those cases. The differences are this.

727 of course is a good strong 3 speed.

518 is the same with an OD ( 4th ) and Od needs 12 volts. Some have a lock up converter that needs 12 volts also.

The 47re is more electronic controls. ( 4 speeds).

Shorten the drive shaft, use a 518/618 with a couple of ****ches to get od and lock up.

One more thing, the 518 was for a gas engine, 618 was Diesel application. These are different cases, needed to bolt up to the engine.

 

[mykal41]

thanks for the input. The vehicle I am working on is my 89 250,727,205 dana 60 locked dana 70 307 ring and pinion 68,000 original miles. The truck is bone stock. I have just completed a full body resto. All new metal. My next step is power so I figured I would start with the transmission.

How do I list my vehicle info with my posts.

If I swap the 618 in can I supply the overdrive with 12 volts from a switch.

 

[Mcarcerano]

How do I list my vehicle info with my posts

go to the user control panel and edit signature

 

[fox]

With 3. 07 gears you will really have low RPM in OD. This can tax the trans, so be sure it is built right.



Now, for OD you will need to wire in a switch that you can engage OD when you want it, but it needs to drop out when you slow or coast. It will only disegage when power to it drops.

Also with a lock up converter, it will need to have 12 volts the same way. Must unlock ( remove 12 volts) when slowing down to a stop, or it will stay locked and in a high gear. Thus killing the motor.



Can you say TOP speed??

 

[Philip]

The 518 was used in diesels. Most of the 91. 5's and up used them. There are supposed to be some late 93's with 618's in them. But I haven't seen one yet.



There is a two wire plug on the tail housing. One wire is hot when the key is on. The other wire is the ground which would go back to the PCM if your truck had one. The ground is what the PCM controls for OD to work. It just grounds it to engage OD.



Which ever trans you decide on. The 3:07's with OD make a good package if you don't tow heavy. In OD your looking at 1550 RPM at 60 MPH.



The 518's for our trucks are noted for loose converters from the factory. There are replacement converters on the market. But your still looking at slippage at all RPM ranges. With a 618 and lockup. You get around that. But the stock converters are only good for 350 or so HP. So a updated converter would be needed for it also. Eather way the OD trans would be a good choice. Grab which ever you can find at a good price. While your looking the V10 trucks used the same bolt pattern as are our cummins. I don't know if there is any differences inside the trans.

 

[zstroken]

you might be able to play with two differential pressure switches to get your OD and lockup. Theoretically you could use the relationship between throttle pressure and governor pressure to determine OD and Lock up scenarios. If you wanted to just cop out and go the easy way you could just put a pressure switch on Gov pressure and when say gov pressure hits 45 it goes in to OD and when it hits 55 or so it goes in to lock up.