65RFE to 66RFE swap for more towing and drivability

[Wild one]

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

Check post #8

 

[Steve White]

So I checked the tailshaft of the 66 to the 65 and that is the biggest difference in them. The tailshaft on the 66 is alot bigger then the 65. That is going to be the biggest problem i run into. I currently have contacted advanced adapters to see if they can help so you dont have to change t-cases and also the driveshafts. If i cant get this conversion to work I will have a freshly rebuilt 66RFE that I will be selling. But i will keep everyone updated on my progress.

 

[Steve White]

These are pictures of the 66 RFE that I have torn apart currently.

 

[Jeepwalker]

Would a revised transfer case bolt in (that would fit a 66RFE)? Seems a transfer case out of a 3/4 ton would somewhat easy to get (used). Driveshafts can be dealt with. But like you say, then the project suddenly got bigger.

BTW, besides it being a more robust transmission, what (if any) improved driveability would a guy gain going from a 65 to a 66? I see the gear ratios are different, but.. do they shift better, or tighter/smoother? I'm just curious (not being a jerk)..

 

[DILLIGAF]

This is great info.

 

[Steve White]

So after the weekend I tried to contact Advanced Adapters in California and they said that at this time they are no doing anything to help with this conversion. So I have done some more research and found that the 66RFE output shaft is a 29 spline and is 1.4670" in diameter. The 65 RFE is a 23 spline and is smaller. I do not have the measurement for the 65 diameter as I am finding that unless you use the t-case from a 66 and then change driveshafts as well. The problem you run into with that is the size difference between the two t-cases is pretty substantial. The physical size is also bigger and dont think that it would work in a 1500 frame. If someone knows of a machine shop that would take the input gear for the BW 44-45 t-case and machine it to work with the 66 tailshaft then it would work. or if someone could take the output shaft for the 66 and take it down to the 65 rfe shaft size and splines. That is the only way that i see this conversion could work. I know alot of people are talking about doing the 8 speed conversion but I am not going to do that as then you have to change the cooler lines, cooler, and transmission wiring. So I do not believe that this conversion is going to be possible at this time until someone has the money or a machine shop that would be willing to take on this challenge. Hope this helps as I was really hoping to try it but I dont want to change t-cases and driveshafts. If it was a 2WD then the conversion would be pretty straight forward as you dont have to mess with much and only change the rear drive shaft yoke. Then it is possible. BUT for us with 4WD it is currently not possible.

 

[Steve White]

Would a revised transfer case bolt in (that would fit a 66RFE)? Seems a transfer case out of a 3/4 ton would somewhat easy to get (used). Driveshafts can be dealt with. But like you say, then the project suddenly got bigger.

BTW, besides it being a more robust transmission, what (if any) improved driveability would a guy gain going from a 65 to a 66? I see the gear ratios are different, but.. do they shift better, or tighter/smoother? I'm just curious (not being a jerk)..

I dont think that there would be any driveability differences going from the 65 to the 66. I would think the biggest thing you would notice is reverse of course and then maybe a little better fuel mileage with the deeper 6th gear.

 

[Wild one]

So after the weekend I tried to contact Advanced Adapters in California and they said that at this time they are no doing anything to help with this conversion. So I have done some more research and found that the 66RFE output shaft is a 29 spline and is 1.4670" in diameter. The 65 RFE is a 23 spline and is smaller. I do not have the measurement for the 65 diameter as I am finding that unless you use the t-case from a 66 and then change driveshafts as well. The problem you run into with that is the size difference between the two t-cases is pretty substantial. The physical size is also bigger and dont think that it would work in a 1500 frame. If someone knows of a machine shop that would take the input gear for the BW 44-45 t-case and machine it to work with the 66 tailshaft then it would work. or if someone could take the output shaft for the 66 and take it down to the 65 rfe shaft size and splines. That is the only way that i see this conversion could work. I know alot of people are talking about doing the 8 speed conversion but I am not going to do that as then you have to change the cooler lines, cooler, and transmission wiring. So I do not believe that this conversion is going to be possible at this time until someone has the money or a machine shop that would be willing to take on this challenge. Hope this helps as I was really hoping to try it but I dont want to change t-cases and driveshafts. If it was a 2WD then the conversion would be pretty straight forward as you dont have to mess with much and only change the rear drive shaft yoke. Then it is possible. BUT for us with 4WD it is currently not possible.

8 speed swap

Figured I would throw together a brief list of info for swapping in the 8hp70 in early 4th gens… I couldn’t find a lot of this out there so some was trial by fire and then leaning on others (thanks to Alex LaBrash), as they were the biggest help. The process would be similar in earlier models...

www.ramforum.com

 

[mtofell]

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

I suppose I can see if it doesn't cost you much but beware, the 66rfe is kind of crappy tranny. As they age in these trucks there are starting be a lot of reports of valve body failures. Also, the ratios suck if you will be towing heavy. The ratios are borrowed from from the 68rfe that goes in the Cummins and are really meant for a diesel with the low end torque.

The biggest problem is the gap between 1 and 2. With the 3.73 rear end in my truck and hauling my 5th wheel (11,000#) up a winding grade I'm either at 5000RPMs in 1st or if I let it drop into second it can't hold it and slams back to 1st. Basically, there's a "no man's land" between about 30 and 45 up a hill pulling heavy. Once over 45 where it can hold second it's a beast but it just kind sucks at lower speeds. Granted, and 11K 5th wheel is pretty much pushing the limits of the truck but all reports are the 8-spd is another world entirely.

 

[Hemi395]

Would a revised transfer case bolt in (that would fit a 66RFE)? Seems a transfer case out of a 3/4 ton would somewhat easy to get (used). Driveshafts can be dealt with. But like you say, then the project suddenly got bigger.

BTW, besides it being a more robust transmission, what (if any) improved driveability would a guy gain going from a 65 to a 66? I see the gear ratios are different, but.. do they shift better, or tighter/smoother? I'm just curious (not being a jerk)..

The main difference in drivability between the two is the 66 shifts through all 6 gears in sequence. The 65 shifts 1-2-4-5-6 and only goes into 3rd during certain kickdown situations. You can tune the 65 to shift in sequence but the 2-3 shift isn't spaced as nice as the 66 is.

Other than that I doubt you would notice too much difference besides the much shorter reverse ratio.