New gears and lockers for 75 CJ5

I am fixing to buy new gears and lockers for my 75 cj5 its got a 304 t-15 and d-20 i am running 35x12.50 tires. I am going to put 4.88 gears, a full spool in the rear and a spartin in the front. Would this be a good ratio to use with my set up?

 

Are you going to do any highway driving or mostly offroad? If highway, I might suggest lowering your ratio down to 4.10 or 3.73....just a thought.

 

If it's going to see hi-way miles, a higher gear (4.56) would be nice but with the 3sp and D20 that kind of limits how hi you would want to go.

I think your combo will be nice up to about 60ish and offroad.

 

This was kinda interesting...

http://www.4lo.com/calc/geartable.htm

w/ 35" tires, this chart says 4.11 for best gas milage, 4.56 for daily driver and 5.13 for the most power....don't know how accurate it is but seems just about right.

 

I will only be driveing it on gravel roads and in the woods.
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The t-15 3 speed is why i want to go low because the trany is geared so high in first gear. I have 3.73 now but its just to fast in first gear so i figure if i go with the 4.88 ratio it will help me in two and four high. I am eventually gona swap in a t-18 but the bank account wont allow it wright now and when i do swap in the t-18 second, third, and fourth will be the same as first, second, and third in the t-15. I am going into the axles to install lockers and change wheel bearings anyway so i figure it will be a good time to change the gears to.

 

another thing to consider is to change ou low ratio in you're dana 20...i read somewhere (Teraflex kit) that you can pass from 2:1 gear ratio to something about 3.15:1. This way you keep a good ratio for the road and get a very good ratio for off road...just calcul this
dana 20 standart 2:1 x ratio 4.88= 9.76
dana 20 special ratio 3.15:a x ratio actual 3.73= 11.75

So if you plan to put a t18 with the big first low see the difference you go
Actual set up
t150 ratio 1rst 2.99 X t case 2:1 x 3.73: 22.30:1
What you get with new gear ratio
T-150 ratio: 2.99 x tcase 2 x diff 4.88: 29.18
What you get with teraflex t-case kit without new gear in the diff
T-150 Ratio : 1: 2.99 x t-case(with teraflex kit) low 3.15 x 3.73 diff = 35.13:1 overal ratio
What you will get if you put a t-18
t-18 ratio: 1: 6.32 x t-case (no kit) loc 2:1 x diff: 4.88 = 61.68

So if it was for myself i'll keep the stock diff ratio for on-road on only change the gear in the t-case for offroad. The t-18 first gear is very interesting for guy who want to keep stock diff gear ratio and have a good crawling ratio but with 4.88 gear in diff you might have a too high overall ratio for what you plan to do. T-18 only advantage is the fist gear you back up one but for the other speed almost same ratio than the t-150.

 

35s are quite tall - the axle gears will help. 4.88s are ok on the street, if you have tall tires. You may have an easier time finding 4.54s. My CJ-6 has 30-31s with the same drivetrain as you. I think 1st is plenty low enough for driving on the street.

If you want crawl ratio, your best bang-for-the-buck is probably one of the truck 4-speeds with a granny 1st. This won't help you with 1st on the street though - the 1st of a T18 or NP435 is too low to start off with, and 2nd is about the same as 1st with the T15.

 

I ran 4:56s with 35s. This compensated for the larger tire size and put me slightly lower then stock gearing (it origionally had 3.73:1). For crawl gears I swapped in a 6:32:1 T-18 and Terra Low gears (3.15:1) in the T-case. This gave a crawl ratio of 91:1 and would still do 70 on the highway.

 

thanks for the info guys this site is awesome.