can the rear axle gears be swapped with ones taller for more top end speed, or do they make such a thing? And if not. What rear axle could I use to put in the originals place? what axles would fit? Mind you it doesn't have to be a Daihatsu hijet axle.
I am not aware of separate gear and pinyon sets for the Hijet. They had several different ratios depending on which transmission, and what the options were. The trucks with a 5-spd would have the 6.666 ratio, because the overdrive would let them get the max speed, so they had the higher numeric axles to have better acceleration when loaded. The 4-spd would have the 6.285 ratio. On the Vans, the ratio can be: 5.571, 5.875, 6.285, or 6.666, depending on which transmission, and the engine options. The automatic was more frequent in the vans, and they also had optional turbochargers.
I suppose the bigger question is to whether you could bolt in (lets say) a 5.571 gear set into the 5-speed truck that has the 6.666 gears to obtain a nice cruising highway speed if your not carrying heavy loads all the time eh.
Yes, if you had a 4-sod donor, you could trade in a lower numeric axle/ differential and get a higher max speed. But that is a maybe. These little trucks have an air drag coefficient somewhere close to that of a brick. They just aren’t very streamlined, and don’t have much to clean up the air flow underneath. The power required to go a given speed, with a given air drag, cubes as the speed doubles. If it takes x-horsepower to go 30-mph, it takes 8 times as much horsepower to go 60-mph. So, you might spend a chunk of change, to get a 5-mph faster top end, and hurt the acceleration and responsiveness at lower speeds. The engineers at the factory, are trying to build a vehicle to a certain set of performance characteristics. What is the top design speed? From that you work out the aerodynamics, and the torque and horsepower curves of the drivetrain at the wheels. In the US, they used to design cars to go 150-200-miles between fill ups. If your truck gets 10-mpg, you get a 20-gallon tank. 7-mpg, a 30-gallon tank. My Dad had an F250, with high numeric axles. Best case scenario was 7-mpg, you might get 8-mpg downhill with a forty mph tailwind. that beast had 43-gallons of fuel tanks. if you want to run above the design speed of the truck, you have to come up with more horsepower, or reduce the air drag somehow.
Also if the 4 speed has the smaller rear ratio I suppose I could purchase a rear axle assembly from a 4 speed and swap it into the 5 speed and just see eh?
Jigs-n-fixtures, I was planning to post a new thread but this one is close enough to my topic question and you always seem to have the answers. I’ve got a 5 speed with rear locker but I don’t drive it on road and would really like to put some taller gears in. My property has steep, muddy timber tracks and in 4WD it just bogs down even in 1st so I have to use 4WD low all the time. I don’t care about top speed, I’d just like more torque and curious if there is a gear option for the diffs that is taller than the 6.666:1 that they come with? Thanks!
So far as I know the 6.66 is the lowest set they came with, in the EF s series engines. The EB series engine trucks might have something lower/higher numeric to compensate for the lower horsepower.
Thanks Jiggs. I figured 6.66 is as tall as I’m going to find. I’ll probably get 23” tires to replace the 24” I have and that will hopefully help a little bit. I suppose I need to remember also that it’s only 40ish HP so throwing 600lbs of people and gear in it and trying to climb steep dirt roads may just require 4low no matter what!
Another option might be a supercharger. Motocheez on YouTube, did a install on his Hijet. At 12-psi boost, he should have been getting about an 80% increase in torque.
Jigs, I saw that and was really considering. May be slightly above my fabrication level but he sure makes it look easy. Plus I’ve got a Jumbo so access is a lot tougher. I did get the Amazon carb and per your advice in another post picked up a timing light with RPM and advance to get it dialed and it’s like a different truck. Runs and drives so much better. The factory carb is just tired and wore out. I appreciate your guidance in that other post on how to set it up. Learning this carburetor thing slowly.
As an option to taller gears, you could go to shorter tires. Not sure that you would want to loose the ground clearance though.
Yea, I was thinking about dropping down to 23” from the 24”. Won’t make a huge difference but it will help. Plus the tires I have are not radials with a 7PSI max so they’re very soft and inefficient. I’m sure they create a ton of rolling resistance on anything other than mud so getting a smaller radial that I can put 16-18lbs in will hopefully help.
So I have a couple of questions on my s83p, I don’t have a locker but my rear end is a posi. Did they come from the factory stock like that or did some pull the member out and weld it? Next question I have a 4 speed with transfer case, I can I find a 5 speed transmission for a 4x4 and swap to two out or would I have to use the transfer case from the 5 speed?
Transfer Case and transmission are to the best of my knowledge single units. That said climb under and see if there is a split between them. And I’d guess that the difference between a 4-spd, and the 5-spd, might be a shift rod blocker, and a missing gear on the cluster. Toyota did that in the 70s, with the transmissions behind the 18R. And Daihatsu did it with the transfer case and transmission of the “Off Road Utility Vehicles”, they imported in the late 80s. There were C-clips in grooves on the shift rods, which prevented the T-case from getting to high range, and the 3-4 rod in the transmission had a C-clip to block 4th gear. Couple that with a solenoid, which vibrated in and out of the main jet at 25-mph, and they were accepted by the EPA, as not being able to exceed 25-mph.
So being a solid unit could you just swap a 4 speed out for a 5 speed and is it worth it. Are you gaining that much difference?
