1978 CJ7 Gears

1978 CJ7 Gears
T

TXsoccer00

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San Marcos, Texas
Hey guys I have recently purchased a 1978 CJ7 with alot of mods on it and I want to make it a little more road friendly. I dont know alot about jeeps so I want to continue learning. Right now i can only go about 55-60 mph on the highway and the rpms are at like 3000. Here is what is done to the jeep. The engine is a AMC 304 V-8 that came in the jeep from the factory.The Transmission is a T-18 out of a 1980 ford 3/4 ton truck. It is a four speed with 1st gear granny, a 6:32 gear ratio. The frt. & rear differentials are Dana 44 `s out of a 1980 international scout. The rear has a Detriot locker & the frt.has a OX locker with 4:56 gears.
 
I would say the easiest way to get a few more MPH with a few less RPM is to change out the azle gears. 4.10:1 or maybe even a 3.73:1
 
Hello TXsoccer00!!! :chug: If you don't mind me saying so - most here would :drool: over that CJ!

Changing the Transmission really wont help you to achieve better highway sped - your 4.56 gear ratio is the major PITA! :)

I run a 4.56 but expect nothing less the great off road use - I also drive on the interstate - I have 33's so I can cruse at 70 but the mileage sucks!

The greatest thing is that you can change to 3.73 gears without changing out the carriers - if you ever decide to go lower the 3.73 your carriers cannot be used :)

What do you want with this CJ? You have a great starting stone - and many would kill for your combo - :)

What do you want?
 
Hey I want a jeep that I can drive on the interstate with no problems but also go off road and be able to tear it up. You know best of both worlds lol. Also I have 35s on the jeep right now. So what gear ratio should I be looking for and how much or what is the cost for changing that out? thank you guys
 
sounds like someone built a nice jeep.
My jeep also turns 3000 at 65 if you are going to run it off road that sounds about right. I'm not sure what you think the problem is.
 
Right now this is my only vehicle. I need to be able to get on the Interstate and going 55 and running 3000 rpms is not good at all. I want to be able to run 65 possibly 70 on the highway.
 
IMO changing to 3:73 or 4:10 will help on the highway but running 70 with a lifted cj might take more than gears depending on how well it was built. also expect less performance off road.
To get the gears changed around here would be at least $500-600 per end in a good shop.
 
TXsoccer00 said:
Hey I want a jeep that I can drive on the interstate with no problems but also go off road and be able to tear it up. You know best of both worlds lol. Also I have 35s on the jeep right now. So what gear ratio should I be looking for and how much or what is the cost for changing that out? thank you guys
Click to expand...

TXsoccer00 said:
Right now this is my only vehicle. I need to be able to get on the Interstate and going 55 and running 3000 rpms is not good at all. I want to be able to run 65 possibly 70 on the highway.
Click to expand...
I hate to the bearer of bad news but what you have now is about optimum for the tire size you are running - for off road sake...

You have a T-18 with a 1:1 final gear ratio, 35" tires and a 4.56 gear. If you gear up or down you sacrifice highway speed or a (very small amount of off-roading), the reason I say that is the T-18 has a very low 1st gear - you can chug along with a better highway gear and still have relatively good 1st gear fun... :)

Your best best is to change the final gear ratios (the diffs) - but that can get pretty expensive unless you have to right tools and the will power to work the change through. Also, because of your carrier size - you cannot go lower the a 3.73 gear...
 
It is a four speed with 1st gear granny, a 6:32 gear ratio. The frt. & rear differentials are Dana 44 `s out of a 1980 international scout. The rear has a Detriot locker & the frt.has a OX locker with 4:56 gears.
This is what the guy who sold me the jeep told me it had. So why does he say 6:32 and then say the lockers have a 4:56.? sorry but im still learning.
 
The 6:32 is the gear reduction in the granny first gear for the tranny. The 456 is the actual gear ratio for your ring and pinion in the front and rear ends. What the guys are saying is, By changing your ring and pinions to a 373,( which is the highest ratio you can fit on your carriers without having to swap them as well) You will be able to reduce your RPM on the highway a little. The 632 deep reduction in your granny gear tranny, will make up for the gear swap, and you will be fine off road as well.
 
TXsoccer00 said:
It is a four speed with 1st gear granny, a 6:32 gear ratio. The frt. & rear differentials are Dana 44 `s out of a 1980 international scout. The rear has a Detriot locker & the frt.has a OX locker with 4:56 gears.
This is what the guy who sold me the jeep told me it had. So why does he say 6:32 and then say the lockers have a 4:56.? sorry but im still learning.
Click to expand...

You dont need to be sorry at all :D You got confused with gearing is what happened basically. What the original owner was trying to tell you was you have a T-18 Transmission , which in every CJ owners eyes is the "golden Transmission " it has in first gear a 6.32 to 1 ratio which means, if you put that thing in 4 High and 1st you will be able to walk faster then that thing will go especially with that 4.56 gearing in your front and rear end. But the ratios that are 4.56 are in your front and rear ends and the 6.32 to 1 is in your Transmission . What it basically sums up to is you bought a great "off-road jeep" i personally would keep it like it is and take the sacrifice in gas, because all around the off roading will be better how it is but the highway cruising wont, unless you take the highway daily to work or commuting, then i might consider changing gears.
 
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