Need Drivetrain advice

[dkmdvm]

I have recently purchased an 85 CJ7 . From what I can tell it has a six inch suspension lift, 2 inch body lift, Dana 30 front with disc brakes, and AMC20 rear (2.73, open differential, 2 piece axles, drum brakes), 35 inch tires with a 3 speed Transmission and Dana 300 Transfer Case . I will probably use this jeep pretty light to drive back and forth to work, some dirt road, some state hwy use, deer lease, etc. No rock climbing or hard trails or deep mud, and probably no interstate or long trips. Does it make sense to strengthen the rear with one-piece axles and re-gearing to 4.10 with what Transmission I have? Or is this going to give me some weird Frankenstein drivetrain that is worse than what I have. I would like to keep the tire size and the automatic Transmission if possible, but don't feel like it is really a good combo the way it is now.

I forgot to mention the engine is a AMC 258 i6 / 4.2l 6 cyl.

 

[tarry99]

I have recently purchased an 85 CJ7 . From what I can tell it has a six inch suspension lift, 2 inch body lift, Dana 30 front with disc brakes, and AMC20 rear (2.73, open differential, 2 piece axles, drum brakes), 35 inch tires with a 3 speed Transmission and Dana 300 Transfer Case . I will probably use this jeep pretty light to drive back and forth to work, some dirt road, some state hwy use, deer lease, etc. No rock climbing or hard trails or deep mud, and probably no interstate or long trips. Does it make sense to strengthen the rear with one-piece axles and re-gearing to 4.10 with what Transmission I have? Or is this going to give me some weird Frankenstein drivetrain that is worse than what I have. I would like to keep the tire size and the automatic Transmission if possible, but don't feel like it is really a good combo the way it is now.

The Bigger / taller tires are what is killing it............with the 2.73 gear ratio......lower gears like the 4.10 would help its low speed performance but will kill your gas mileage..........If your not going to use it off road , your just caught in the middle.................No off road save your money fixing that axle!

 

[Torxhead]

The later CJs oem manual Transmission were only 4 and 5 speeds. That gear/tire combination can really be hard on your clutch also.

 

[mstar]

I really don't think going to 4.10 gears is a deal breaker as far as mileage goes. With those size tires you may actually improve. Lugging that engine
with tall gears and large tires is doing nothing for you.I realize fuel is costly but if you did the math you might be suprised.Not to mention it's probably about as much fun to drive as getting a root canal. mike

 

[Lumpy Grits]

Yes on 1 piece axles!(Moser!)
Go to 4:56 R&P.
I run 33" tires and run 4:88 R&P with my 5 speed tranny. Look at installing power lock, Limited slip diffs as you're going to have to change the carriers anyway.
I also suggest you get a tranny cooler installed ASAP.
LG

 

[dkmdvm]

I meant to say 3 speed automatic. Not worried to much about gas mileage and I agree it may even do better geared lower. Wouldn't it be easier on the tranny? I guess that is my question.

 

[Lumpy Grits]

Yes as 'easier' on the tranny.
Extra tranny cooler goes along with that mind set too.
LG

 

[Hedgehog]

Yeah, no question about it, setting your road Jeep up like it's a rock crawler will be easier on the Transmission , especially when driving to work on paved roads. You never know when you'll need a good locker to get you into the grocery story parking lot.

On this forum I believe most will advise to go with bigger gears, tougher differentials and bigger skid plates. It really doesn't matter what your intended use will be. How does your jeep handle your commute now? Is it strained? And yes bigger gears might actually get better mileage. That is if your Jeep is in the power circuit while on the road.

I can't blame you for using your Jeep as your daily driver, I used to do exactly that. Driving it shows that you really like your Jeep. A Jeep can be more than a mud slinger and a rock crawling wonder, it can be part of your everyday life.

 

[73CJ]

Yes on 1 piece axles!(Moser!)
Go to 4:56


For sure 1-piece axles and gears.

4.56s work well with 36s & 38s for me

Lots of lift. Do you have a double cardigan rear drive shaft? If not you might eat u-joints.

 

[dkmdvm]

Doesn't have the double cardigan drive shaft. The pinion Is pointing towards the Transfer Case but not enough. I need to replace that drive shaft and get a little more angle there as we'll. thanks for the advice everyone. I think I will strengthen the axle and re gear in addition to changing drive shafts. Not sure if it is 4 or 6 inch lift. The PO welded extensions into the sway bar links that measure 6 inches. I think it is a tuff country lift and they only sell a 2 or 4 inch kit. Is there another way to measure? I may drop to 33 inch tires.

 

[starcommtrey1]

I run 33s. I have a V8 and 2.72 gears. My tranny is great for what I got. Chrysler built my tranny with a semi low gearing in 1st and 2nd gear. Third gear is only a 'highway' gear built with gas mileage in mind. I actually get damn good gas mileage up at 55-60 because im turning very few rpms. Im just cruisin. Now around town, I stay in 2nd and everynow and then bump up to third. Ive had it up to about 80 mph and its a little scary at that speed, so again with my setup and driving style im great. IF I decide to get offroad and play, my high range is a 1.1 ratio. If I need to get some serious power, low range is 2.61 to 1 ratio, which really makes up for the high gears every where else....I have a NP208 Transfer Case an A999 tranny. Which tranny and Transfer Case do you have????

 

[dkmdvm]

I believe it is stock TF 999 and a Dana 300

 

[starcommtrey1]

You should be good. A lot of people with the TF 999 run them with V8s with no problem. As long as you dont tow alot of weight or put an engine like mine into it, you should be good to go. And you'll really have to work at it to break that Dana 300 .