Cooler and lines for Torqueflite upgrade to overdrive

[Headintheclouds]

I'm replacing a Torqueflite 727 behind a 318 Poly with a 42RH. As far as I can see the earlier transmission uses 5/16" lines and the later 3/8". I'm not sure about transmission cooler capacity to dissipate heat but would be grateful if anyone has any info.

I'm a bit puzzled by the seeming need to shift more heat. The overdrive unit with lockup should improve miles to the gallon by about 25% and this suggests my 42RH shouldn't need as big a cooler as the 727. Should I stick with the lines and cooler I already have or do I need to go large?

 

[Professor Fate]

They switched for a reason, go large.
Also be aware that you may have issues with the torque convertor- early motors (pre-'68) had a smaller recess in the crank flange, this was enlarged in later years when they increased the diameter of the nose of the torque convertor in '68.

 

[Headintheclouds]

If anyone knows the reason I would like to know!

Fortunately the crank recess on my '66 Canadian Poly is the right size for the 42RH converter, but thank you for the heads up.

 

[65 Dartman]

They switched for a reason, go large.

Agreed! I will be using the 42RH behind a stock 66 273/235 Charger 273 in my 65Dart. I had the folks at Dynamic Converters rebuild my 42 and asked that very question. Their reply was to use the 3/8th’s lines with the larger cooler in the radiator or if you must use the 5/16th lines, they recommended an external transmission cooler as well

So i will be used a Be Cool cooler with the 3/8th fittings and 3/8th lines throughout with 3/8 adapter fittings at the OEM radiator cooler

 

[Headintheclouds]

A bit more reading suggests that the non lockup 727 has cooler pressure of about 10psi but the 42RH is likely to be over 80psi. I currently have a single unit water radiator and transmission cooler. I guess I need to either disconnect the transmission cooler part and add a separate modern cooler or get a new combined unit made.