65RFE to 66RFE swap for more towing and drivability

[Steve White]

So I have been contemplating doing the 65 RFE to 66 RFE conversion on my truck and am looking for some tips if anyone has actually done it or not. Programming wise it should be pretty easy as it was available on the 3500 dually with a 5.7 in 2014 as well. So with that being said I am going to be posting what the differences are between these transmissions as I am at the dealer and happen to have a spare 66 RFE laying around and am rebuilding currently.

First big difference between these transmissions that i have found is the gear ratios are completely different.
65 RFE 66RFE
1st 3.00:1 1st 3.23:1
2nd 1.67:1 2nd 1.83:1
2nd gear prime 1.50:1 3rd 1.41:1
3rd 1.00:1 4th 1.00:1
4th 0.75:1 5th 0.81:1
5th 0.67:1 6th 0.62:1
REV 3.00:1 REV 4.44:1

I have looked up in the parts catalog as I have that access (which is nice to have), There is no difference from the torque converter to the center section of the transmission. Everything that is different for these transmission is the same in the input clutch hub. Same Valve body, torque converter, and transmission pump. The biggest difference is when you get into the planetary's of the transmission. The 65 RFE has 5 pinion plaentary gears as the 66 has 6 pinion planetary's. there is two more clutch disc in the 4c clutch and the Low reverse also has two more clutch disc in them.

I know from experience that the week point of the RFE transmission is the input clutch assembly. This is where all the clutches burn up and I am almost positive that it is caused from either lack of maintenance or someone just not caring when there vehicle is overloaded. Anyway. I will post pictures later but was curious what everyone was thinking on this change.

 

[Wild one]

So I have been contemplating doing the 65 RFE to 66 RFE conversion on my truck and am looking for some tips if anyone has actually done it or not. Programming wise it should be pretty easy as it was available on the 3500 dually with a 5.7 in 2014 as well. So with that being said I am going to be posting what the differences are between these transmissions as I am at the dealer and happen to have a spare 66 RFE laying around and am rebuilding currently.

First big difference between these transmissions that i have found is the gear ratios are completely different.
65 RFE 66RFE
1st 3.00:1 1st 3.23:1
2nd 1.67:1 2nd 1.83:1
2nd gear prime 1.50:1 3rd 1.41:1
3rd 1.00:1 4th 1.00:1
4th 0.75:1 5th 0.81:1
5th 0.67:1 6th 0.62:1
REV 3.00:1 REV 4.44:1

I have looked up in the parts catalog as I have that access (which is nice to have), There is no difference from the torque converter to the center section of the transmission. Everything that is different for these transmission is the same in the input clutch hub. Same Valve body, torque converter, and transmission pump. The biggest difference is when you get into the planetary's of the transmission. The 65 RFE has 5 pinion plaentary gears as the 66 has 6 pinion planetary's. there is two more clutch disc in the 4c clutch and the Low reverse also has two more clutch disc in them.

I know from experience that the week point of the RFE transmission is the input clutch assembly. This is where all the clutches burn up and I am almost positive that it is caused from either lack of maintenance or someone just not caring when there vehicle is overloaded. Anyway. I will post pictures later but was curious what everyone was thinking on this change.

Gave any thought to doing the 8 speed swap instead,even better gear ratio's ,and if you're towing,it's hard to beat the 8 speeds stump pulling 4.71:1 first gear,and closer gear ratio's.A lot less rpm drop between gear changes,and your 2014 could of been had with the 8 speed,so it makes it a pretty easy swap to.

 

[Steve White]

The main reason I thought about doing it cause I have a free 66RFE that i only need to put about $300 bucks into.

 

[Jeepwalker]

That's very interesting information. Do they look the same physically ...where it should just bolt in?

 

[Socalramfan]

This thread certainly has my attention. I’m guessing that the driveshaft is the same length provided the Tran is physically the same size.

 

[runamuck]

actually the 8hp75 8 speed in my '19 has 5.0 first gear. even better

 

[Jeepwalker]

A guy could still pull stumps with the 66RFE ....just use 'reverse' LOL

 

[Steve White]

This setup is basically a direct bolt in as the transmission case, pump, valve body, and torque converter are all the same. The actual cased of the transmission is the same all the way back to the 45 and 545RFE transmissions from the 2000's era. I need to check the tailshaft of the transmission to see about for the transfer case.

 

[Wild one]

actually the 8hp75 8 speed in my '19 has 5.0 first gear. even better

Nobody has been able to adapt the 75 in yet.There's been a couple guys who tried and Russell at Sound German hasn't been able to make the 8HP75 function properly.You can make the 8HP70 and 8HP90 work though

 

[Jeepwalker]

OP, is your pickup a 2x or 4x4?