I think I Need Higher Gears w/o Changing Ring and Pinion.

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Hilndr1701

Hilndr1701

10 Year
Joined
Apr 4, 2013
Threads
17
Messages
107
Location
Wyoming
I have a 68 FJ40 that came with a s***ty 350, I mean Chevy 350, an SM465 with the original transfercase with an advanced adapters kit from who knows when, and I believe 4:10s. I don't know much about gearing and such so if asked any hard technical questions, I probably don't know.
With that said, I'm looking for a way to, I guess, change the ratio so I can keep the low-end gears offroad but still do 55 without having the engine run at 5500 RPMs or more. Does that make any sense?
I want to get an NV4500 for the Chev but they are extremely hard to find in my area, and when they do pop up, they're 2k to 3k used. The Dodge ones are the same.
I know, back in the days of yore, they had a sort of doubler/overdrive system for the old Willys and other trucks.
What I want is a way to keep the setup I have now with and an extra shifter to get that "5th gear" if possible. Or an inexpensive NV4500...
Any ideas??

Thanks

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5,500 RPM at 55 MPH doesn’t sound like 4.11 gearing, do you know for certain that your diffs have 4.11’s?
 
I have the same drive train as you, while I don't have any real answers I'll be following this thread.
 
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5500rpm at 55mph? You sure you're not in low range. I don't know your tire size, but at 55mph with 33" tire and 4.11s your rpms would be around 2400rpms. Minimal rpms for a sbc. You might be able to find a Fairey overdrive unit. They were offered a long time ago, so they are scarce. They might not be able to handle sbc power though. An nv4500 or ax15 would be decent overdrive trannies. Both won't have as low 1st gear as you have now. Early gm nv4500s had a 6.54:1 1st gear, 94 and later, gm and dodge ones weren't as low. I think Ax15's was around 4:1 in 1st. You could go to a h55 toyota 5 speed trans but 1st won't be as low as the sm465. You could install used 3.70 3rd members in the diffs. Plug and play. You will lose a little crawl ratio and gain some highway gears. You could go up in tire size for a rubber overdrive too.
 
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Mark a tire and your rear driveshaft. Roll the tire one full turn. This is rolling the vehicle on the ground. Count how many times the driveshaft rotates. 4.11s would be just over four full rotations. 3.70s would be just under four. 4.88s would be just short of five. Easier done with two people. Be sure going straight and both wheels roll an equal amount.
 
Living in the Past said:
Mark a tire and your rear driveshaft. Roll the tire one full turn. This is rolling the vehicle on the ground. Count how many times the driveshaft rotates. 4.11s would be just over four full rotations. 3.70s would be just under four. 4.88s would be just short of five. Easier done with two people. Be sure going straight and both wheels roll an equal amount.
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OK, as soon as I make a friend I’ll try this, lol. I’ll just have to try it with a camera.
 
Tape a piece string then count the number of times it wraps around the driveshaft. Then you just need to know which the shaft is turning to know if it's before or after four turns. Growing up before the digital age had to figure low tech ways to get things done.

Thread the string thru a heavy nuts to keep some tension on the string.
 
pb4ugo said:
5500rpm at 55mph? You sure you're not in low range. I don't know your tire size, but at 55mph with 33" tire and 4.11s your rpms would be around 2400rpms. Minimal rpms for a sbc. You might be able to find a Fairey overdrive unit. They were offered a long time ago, so they are scarce. They might not be able to handle sbc power though. An nv4500 or ax15 would be decent overdrive trannies. Both won't have as low 1st gear as you have now. Early gm nv4500s had a 6.54:1 1st gear, 94 and later, gm and dodge ones weren't as low. I think Ax15's was around 4:1 in 1st. You could go to a h55 toyota 5 speed trans but 1st won't be as low as the sm465. You could install used 3.70 3rd members in the diffs. Plug and play. You will lose a little crawl ratio and gain some highway gears. You could go up in tire size for a rubber overdrive too.
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Thanks, I’m sure I’m not in low. I think I’m going to try a new tachometer and do one of the suggestions below of counting the tire rotation.
 
Hilndr1701 said:
Also, now that I think of it, I’ve always wondered if my tachometer was a POS it doesn’t work correctly.
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You dont need a tach to tell the difference between 2500rpm and 5500 rpm, assuming you're not hearing impaired. I suspect the 5500rpm comment is just an over exaggeration?

You have a nice looking 40. Cheapest route would be to step up to a tall skinny 35” diameter tire. Any other route will cost multiple thousands of dollars….unless you have 5.29 gears in the diffs and want 4.10’s or 3.70’s, Im sure you’ll find someone willing to trade
 
Hilndr1701 said:
I have a 68 FJ40 that came with a s***ty 350, I mean Chevy 350, an SM465 with the original transfercase with an advanced adapters kit from who knows when, and I believe 4:10s. I don't know much about gearing and such so if asked any hard technical questions, I probably don't know.
With that said, I'm looking for a way to, I guess, change the ratio so I can keep the low-end gears offroad but still do 55 without having the engine run at 5500 RPMs or more. Does that make any sense?
I want to get an NV4500 for the Chev but they are extremely hard to find in my area, and when they do pop up, they're 2k to 3k used. The Dodge ones are the same.
I know, back in the days of yore, they had a sort of doubler/overdrive system for the old Willys and other trucks.
What I want is a way to keep the setup I have now with and an extra shifter to get that "5th gear" if possible. Or an inexpensive NV4500...
Any ideas??

Thanks

View attachment 3601036
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Hilndr1701 said:
OK, as soon as I make a friend I’ll try this, lol. I’ll just have to try it with a camera.
Click to expand...
Well, since you went there first... Try to be sure this new friend has a bit of mechanical knowledge. That can be pretty handy. ;)

Seriously though, you do need to find a local to you knowledge source. When you are starting way down on the tree, it can be tough to learn what you need to know via internet forums. It can be tough to even communicate to others what it is you want/need. Often you really do not know what you need in the first place. And there is only so much that even those who are eager to help can really do. Not to mention the difficulty of weeding through bad advice too.

When you find that friend, try and have him be a mechanic. Or, better yet, try and have her be a mechanic. ;)

Pretty much everything in Wyoming is few and far between. But there *might* be a few Cruiser enthusiasts or even some sort of off road vehicle club in your area. Even if they are not actual experts... they will physically be in the same place as you and your rig. Big plus. especially if you can buy them beer, mow their lawn of something to give them motivation. ;)

Kinda answering your question(s) now... There are no overdrive units on the market any longer for older cruisers nor are there overdrive gears for the older T/Cs.

If you are turning those kind of RPMs at 55... you ARE in low range. Check again. Unless maybe you recorded those numbers while you had go cart wheels on your rig for some reason?

Most aftermarket tachs can be set for 4,6 or 8 cylinder engines. Make sure yours is not set for a 4 cylinder powerplant.

If you have the OEM 4.11:1 gearsets in your diffs, the most you will gain if you do decide to swap out the gears will be 10% lower rpm with a set of 3.70:1 gears.

"rubber overdrive" (taller tires) does not look to be an option for you unless you lift the rig more, and that is a great big boatload of additional factors, concerns and complications that you really do not want to dive into simply to lower your highway rpms.

Anyway, while the rpm that you think you are seeing on the highway is simply impossible... unless you are in low range... you ARE gonna have to live with a rig that is not really designed for highway runs and will always be turning faster than your average grocery getter. :)

Mark...
 
Whenever I'm considering a driveline swap I make up ratio charts. 1st I make one chart for my current driveline set, then a chart for each setup I'm considering. I can then compare each setup to what I have now. Across the top of the chart ref the individual gear ratios of the trans 1st thru 4th or 5th of your current trans. Vertically on the chart ref high range and the low range reduction ratio. In doing the math include the diff ratio your considering. For example my nv4500 1st gear is 6.54, the tcase is 1.99:1 and diff is 4.11. 6.54x4.11x =high range. Low range is 6.54x1.99x4.11=crawl ratio. Do this for each individual gear. You can find an rpm calculator on the internet to determine what the rpms are at certain speeds for highway cruising. Be sure to actually measure your tire height.
 
It does not fit with your original statement but 3.73’s, 33’s and an Orion will drive at 70MPH to the Rubicon, run the trail with grace and then get you home. Not the cheapest option but is a 100% bolt in with no fab work or butchering required.

Look at an H55 split case combo if you really want a five speed…
 
Hilndr1701 said:
I have a 68 FJ40 that came with a s***ty 350, I mean Chevy 350, an SM465 with the original transfercase with an advanced adapters kit from who knows when, and I believe 4:10s. I don't know much about gearing and such so if asked any hard technical questions, I probably don't know.
With that said, I'm looking for a way to, I guess, change the ratio so I can keep the low-end gears offroad but still do 55 without having the engine run at 5500 RPMs or more. Does that make any sense?
I want to get an NV4500 for the Chev but they are extremely hard to find in my area, and when they do pop up, they're 2k to 3k used. The Dodge ones are the same.
I know, back in the days of yore, they had a sort of doubler/overdrive system for the old Willys and other trucks.
What I want is a way to keep the setup I have now with and an extra shifter to get that "5th gear" if possible. Or an inexpensive NV4500...
Any ideas??

Thanks

View attachment 3601036
Click to expand...
I put a R2.8, H55 with split transfer case that has a 3:1 low range in my 78 FJ40. I also have 4:11 gears. According to Cummins with 35" tires at 80 mph I should be turning 2650 rpms.
It is not road ready so can not verify if that is correct. With the 2F and 4 speed it was wound pretty tight starting at 55 but would top out at 80 mph.
 
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as others have said get some good numbers on your ratios and RPMs.
 
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