3 speed to 4 speed swap

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May 23, 2022
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Fairview
I have a 1966 FJ40 with a F engine 3 speed on the tree and vacuum shift assembly. I wanted to get away from the vacuum shift and go with floor shift. I ran into a good deal on a 1975 FJ40 4 speed with transfer case and bell housing. I was told that I just need to change the bell housing and lengthen or shorten the drive lines. The more I read I understand that I can stick with the original flywheel or I can use a F2 flywheel and I can use the type of clutch for the different flywheels.
I am beginning to think I would be better off to swap the vacuum module on the transfer case to the floor shifter type and call it a day.
I do see that the 4 speed housing is 3 inches longer than the 3 speed the transfer cases seem to be the same length.
Does anybody know what items need changed if I go with the 1975 4 speed? Flywheel, Clutch, drive lines.
 

Skreddy

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I believe you’d just use the 4 speed bellhousing (bellhousings are specific to 3 speed or 4 speed). Clutch slave cylinder should bolt to either side or use the mounting ears from 3 speed bell?
Driveline flanges are different (I think) but you can swap the ones from your 3 speed on (again, I think). Shorten and lengthen drivelines. Cut a couple holes in the trans hump, make sure you get the transfer case shift linkage.
Either flywheel works as long as you use the clutch for that flywheel. May need to add small spacer under the front engine mounts to tilt the whole package to avoid e-brake and crossmember interference.
Why get away from the vacuum setup?
 
Joined
May 23, 2022
Messages
17
Location
Fairview
I believe you’d just use the 4 speed bellhousing (bellhousings are specific to 3 speed or 4 speed). Clutch slave cylinder should bolt to either side or use the mounting ears from 3 speed bell?
Driveline flanges are different (I think) but you can swap the ones from your 3 speed on (again, I think). Shorten and lengthen drivelines. Cut a couple holes in the trans hump, make sure you get the transfer case shift linkage.
Either flywheel works as long as you use the clutch for that flywheel. May need to add small spacer under the front engine mounts to tilt the whole package to avoid e-brake and crossmember interference.
Why get away from the vacuum setup?
I am concerned about reliability I am 62 and my wife will kill me if i get us stuck in the mountains or snow. Both of the hard lines between the firewall switch and the actuator have holes rusted in them, I also noticed when I changed the oil in the transfer case had a couple of small needle bearings stuck to the plug magnet. I just was thinking it would be nice to do the swap and have both levers on the floor.
Have you had good luck the vacuum system, I have read they can be a real pain.
Thanks for your input

20190811_183556.jpg
 
Joined
Apr 21, 2005
Messages
21,413
Wouldn't worry about your wife killing you. She is going to count you to get her home. It's once that happens I would worry about. At that point you will probably wish she had killed you, LOL.,

Still have the vacuum shift in my 1970 FJ40. It works better than the one in my FJ62. The FJ40 has only been in AZ and rust is not a problem. Regardless what you do about the type of shifter your transfer needs to be rebuild or replaced if you found needle bearings. I would not be driving it period in fear of doing more damage.
 

roadstr6

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Apr 10, 2013
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I've seen some of these old vacuum-actuated systems that looked like they had been at the bottom of a lake for 100 years. Guess what? They still worked perfectly. I wouldn't go out of my way to go full mechanical. Mr. T got the vacuum system right IMO.
 

mrboatman

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Oct 21, 2016
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I did that swap a while back. I kept the vacuum 4wd switch and under dash H/L shift. You can use either flywheel/clutch combo you want but you will need to use the throw-out bearing and throw-out fork and pivot ball for the respective flywheel/clutch combo you use. you can mount your clutch slave in the exact same location that it is on the 3 speed set up. You will need to shorten the rear drive shaft the bolt flange at the emergency brake hub is larger and the flange on the drive shaft will need to be changed to match that. The front drive shaft will need to be lengthened and the flange at the transfer case will need to be matched to the transferase. This sounds complicated but it's not. Take a piece of paper or cardboard and make a template of the flange and emergency brake hub pattern and tell the driveshaft shop to match it. They will just install a new matching universal flange on both drive shafts and your good to go. Then you will need to lower the rear of the engine to install the trans/transfer unit because of the location of the round cross brace also on the bottom of the tub their is a short 1x1 brace welded to the tub that the transfer case shift lever might hit on. I cut it out also. The transmission hump is not tall enough for the 4 speed trans. you will need about 1/2" of more room to clear I cut the top of the trans hump and welded a small cover with nut seats so it bolts on. Great improvement but don't expect any top end speed change 4th gear is the same ratio as 3rd gear so same rpm and speed.
 
Joined
May 23, 2022
Messages
17
Location
Fairview
I believe you’d just use the 4 speed bellhousing (bellhousings are specific to 3 speed or 4 speed). Clutch slave cylinder should bolt to either side or use the mounting ears from 3 speed bell?
Driveline flanges are different (I think) but you can swap the ones from your 3 speed on (again, I think). Shorten and lengthen drivelines. Cut a couple holes in the trans hump, make sure you get the transfer case shift linkage.
Either flywheel works as long as you use the clutch for that flywheel. May need to add small spacer under the front engine mounts to tilt the whole package to avoid e-brake and crossmember interference.
Why get away from the vacuum setup?
Thanks much for the information. I think I am going to stick with the original 3 speed and vacuum switch as long as it works when I get the two rusted steel lines replaced. I will be pulling the trans and transfer case next we to rebuild both. I will be rebuilding the 1975/76 4 speed and transfer case and get them up for sale in the next month.
Thanks again
 
Joined
May 23, 2022
Messages
17
Location
Fairview
Wouldn't worry about your wife killing you. She is going to count you to get her home. It's once that happens I would worry about. At that point you will probably wish she had killed you, LOL.,

Still have the vacuum shift in my 1970 FJ40. It works better than the one in my FJ62. The FJ40 has only been in AZ and rust is not a problem. Regardless what you do about the type of shifter your transfer needs to be rebuild or replaced if you found needle bearings. I would not be driving it period in fear of doing more damage.
Thanks much for the information. I think I am going to stick with the original 3 speed and vacuum switch as long as it works when I get the two rusted steel lines replaced. I will be pulling the trans and transfer case next we to rebuild both. I will be rebuilding the 1975/76 4 speed and transfer case and get them up for sale in the next month.
Thanks again
 
Joined
May 23, 2022
Messages
17
Location
Fairview
I did that swap a while back. I kept the vacuum 4wd switch and under dash H/L shift. You can use either flywheel/clutch combo you want but you will need to use the throw-out bearing and throw-out fork and pivot ball for the respective flywheel/clutch combo you use. you can mount your clutch slave in the exact same location that it is on the 3 speed set up. You will need to shorten the rear drive shaft the bolt flange at the emergency brake hub is larger and the flange on the drive shaft will need to be changed to match that. The front drive shaft will need to be lengthened and the flange at the transfer case will need to be matched to the transferase. This sounds complicated but it's not. Take a piece of paper or cardboard and make a template of the flange and emergency brake hub pattern and tell the driveshaft shop to match it. They will just install a new matching universal flange on both drive shafts and your good to go. Then you will need to lower the rear of the engine to install the trans/transfer unit because of the location of the round cross brace also on the bottom of the tub their is a short 1x1 brace welded to the tub that the transfer case shift lever might hit on. I cut it out also. The transmission hump is not tall enough for the 4 speed trans. you will need about 1/2" of more room to clear I cut the top of the trans hump and welded a small cover with nut seats so it bolts on. Great improvement but don't expect any top end speed change 4th gear is the same ratio as 3rd gear so same rpm and speed.
Thanks much for the information. I think I am going to stick with the original 3 speed and vacuum switch as long as it works when I get the two rusted steel lines replaced. I will be pulling the trans and transfer case next we to rebuild both. I will be rebuilding the 1975/76 4 speed and transfer case and get them up for sale in the next month.
Thanks again
 
Joined
May 23, 2022
Messages
17
Location
Fairview
I believe you’d just use the 4 speed bellhousing (bellhousings are specific to 3 speed or 4 speed). Clutch slave cylinder should bolt to either side or use the mounting ears from 3 speed bell?
Driveline flanges are different (I think) but you can swap the ones from your 3 speed on (again, I think). Shorten and lengthen drivelines. Cut a couple holes in the trans hump, make sure you get the transfer case shift linkage.
Either flywheel works as long as you use the clutch for that flywheel. May need to add small spacer under the front engine mounts to tilt the whole package to avoid e-brake and crossmember interference.
Why get away from the vacuum setup?
Thanks much for the information. I think I am going to stick with the original 3 speed and vacuum switch as long as it works when I get the two rusted steel lines replaced. I will be pulling the trans and transfer case next we to rebuild both. I will be rebuilding the 1975/76 4 speed and transfer case and get them up for sale in the next month.
Thanks again
 

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