Drivetrain decisions (1 Viewer)

[CruisinGA]

@EWheeler I find that with H42, 1:1 high in split case (I considered under drive) and 4.11, 38" tires I'm about right for the highway. Just need more powa for long inclines
The downshift to 3rd with the H42 is so much better for onramps than when I had a SM420 (which was about the same as downshifting to 2nd with the 3spd trans).

 

[EWheeler]

Curious if anyone has used a rubber overdrive and setup the drivetrain gearing and diff gearing such that an H55f 5th gear is the same as the 1:1 h42 and 4.11 you are running @CruisinGA . Say swap in an h55 and 4.88’s, you would cruise at the same rpm as you do now, but have a much lower 1st, and maybe better splits for highway cruising at speed? I need to play with my gearing spreadsheet. I like the idea of having the 5 speed but not using as a true OD as most do with smaller tires and factory diff gearing.

 

[EWheeler]

@EWheeler I find that with H42, 1:1 high in split case (I considered under drive) and 4.11, 38" tires I'm about right for the highway. Just need more powa for long inclines
The downshift to 3rd with the H42 is so much better for onramps than when I had a SM420 (which was about the same as downshifting to 2nd with the 3spd trans).

Yes, waiting on the 4 on the tree adapter from Chase @red66toy and the 3 speed will be ditched for an H42 in the truck i mentioned earlier. Have another truck i want to put an h55f in to make it more flexible for wheeling and also highway driving.

 

[pb4ugo]

Whats the consensus on a target cruising RPM and target cruising highway speed for an F/2f engine? None of my 40’s have tachs…. We only have so much HP, and are driving a brick down the highway, its really annoying to have to shift down at every slight incline because it takes all the HPs to keep the truck at speed and there isnt any power left to climb a small hill. This is a result of my form over function setup of a 3 spd trans, 4.11 diff gears and 37” tires, but curious what an ideal setup is to stay in the “power band” of these old tractor engines.

Maybe consider what was stk when it came off the lot. What size tire did it come with? Obviously 37" tires leaves you under powered. It sounds like a shifting machine. It reminds my of a friends YJ with 3.08 diffs. He went from stk tires to 33's never used 5th gear again, until he went to 4.88's, then he went to 35's and still can hold 5th on some hills.

 

[Living in the Past]

Maybe consider what was stk when it came off the lot. What size tire did it come with? Obviously 37" tires leaves you under powered. It sounds like a shifting machine. It reminds my of a friends YJ with 3.08 diffs. He went from stk tires to 33's never used 5th gear again, until he went to 4.88's, then he went to 35's and still can hold 5th on some hills.

His original post said a three speed with vacuum shift transfer case. That mean it was 72 or older on US market FJ40s. Also said has V8. My biggest complain with the older FJ40s is torque tube clearance and tub clearance. I was able to get a H42 in my 68 but that was a right fit. 73-78 had better clearance. 79-82 better yet. 83+ had the best clearance for larger transmissions. But H55F still didn't have clearance if the transfer case used a hand brake. No longer wheel base 40 left the factory with five speed because Toyota obviously did want deal with the hand brake cable on a long wheel base 40 series.

 

[pb4ugo]

On my 72 40, I put a stk 4speed/tcase w/ an SBC and left the torque tube. I just had to lower the back of the driveline to remove Tranny/tcase. My 75 w/the NV4500/stk 1 piece t/case, the PO removed the torque tube. My trail rig with a 76 frame now has SM420,Dana 20 case w/ center rear output and the tube was removed. My crossmember takes it place.