727 transmission to a 518?

[pausma]

I have a 91 D350 with a 727 and non-lockup TC. I've been playing around with the idea of swapping it out for a 518 because of the overdrive. I'm tired of running the engine near redline to go more than 65 mph and would like to bring the rpms back down where the engine will be happier. I've seen on the forum here that some guys have swapped in a 47rh as well. I'm leaning towards the 518 because its a little cheaper.

I understand that I'll need to make a switch to control when the overdrive engages. Any other modifications or parts I will need? Different driveshaft, transmission crossmember?

Also wondering about the TC. The 518 w/ stock TC I'm looking at has 140,000 miles on it at a salvage yard for $950. Where all TC on the 518s lock-up? And how would I control the lock-up function since my current TC is a nonlock-up?

 

[DonFitzwater]

I could be wrong but don't you just need to install a new torque converter and valve body as well as a front pump?


And I don't think that having lockup is going to drop your cruise RPM........maybe a touch. You should be changing ring and pinion to drop rpm's. Good luck!

 

[cerberusiam]

The 518's are a non-lockup transmission. You will get the benefit of the .69 OD but no lockup. I *think* the 518 is a bolt in for the 727, never done one so not positive.

Most of the time we just go to a 618 (47RH) for the lockup and better parts. It requires more parts, like a new engine adpater and starter and one more switch. The rear DS will work on either the 518 or 618 swap.

A better TC for the 518 is a must if you have any power in the engine. The stockers are pretty sloppy once you go beyond stock HP.

The big problem with the 518's, and the 47 RH's, was all the aluminum planetaries in the trans. So many miles with the vibrations and torsional harmonics if the 6BT puts slop into the interface. Makes al kinds of whines and slack in the drive train. Depending on hard it was used the 140k is on the border of good\bad.

 

[Simplysmn]

I would see if you can find a better deal for a Core Transmission 518 then have it rebuilt and put a Lower Stall torque converter in it . as for the OD if your truck has the 727 .All you would have to do is Set a switch up to control the OD setting and you will be ready to go . The Cross Member should be the same as what you have now .

 

[pausma]

I'll look into an aftermarket TC for a 518 bc I plan to continue to increase HP. How will the lockup function be controlled?

I've seen some vendors online that have performance built 518s. Anyone know any good vendors as far as that idea?

 

[Simplysmn]

518 doesn't have a Lock up converter . How far do you want to push the truck ? you will be good to about 400 HP with a Built trans . And Trust me with that muh HP you should be Happy .

 

[cerberusiam]

I'll look into an aftermarket TC for a 518 bc I plan to continue to increase HP. How will the lockup function be controlled?

518 is a non-lockup transmission, 618 is a lockup transmission. If you do a lockup trans then a mystery switch is easy to install.

Lots of places have a better TC for the 518 but you almost want to have one built to your specs. The over-the-counter offerings are just not that great.

 

[pausma]

Only turned up the VE pump so far, maybe advance timing, exhaust manifold, and injectors. Nothing super crazy. Who makes the engine adapter for the 47rh?

 

[cerberusiam]

The engine adapters can be had thru Cummins or Dodge. Price is better thru Cummins.

 

[Higgie]

I know this is an old thread, I’m looking to see if I have to change engine adapter plate if I go from a TF727HD to a 47RH

 

[Simplysmn]

Yes you do Because 47rh is Second gen

 

[Paul Herioux]

Yes you do. The converter on the 518 is a lock up style which sticks out of the trans approximately 5/8" more than the non lock up one in the 727. The 94 and up adapter plate is deeper to accommodate this.

 

[Fastback67]

I have the TF727HD with a Gear Vendors Overdrive on my 90 W250.

 

[Simplysmn]

Yes you do. The converter on the 518 is a lock up style which sticks out of the trans approximately 5/8" more than the non lock up one in the 727. The 94 and up adapter plate is deeper to accommodate this.

NO the Diesel 518 is NOT lock up and you don't have to change the adapter .On the Diesel they didn't use lock up converter until 1994 and 1995 Before this the 518 just has OverDrive . the 47RH does require a second gen adapter and Starter .