How Big A Tire For Stock TJ Axles?
Q. I have a 2003 Jeep Wrangler Sport. I want to install a 2-inch budget lift and 33s. My Jeep is primarily a daily driver that gets to see mild off-roading and mud on the weekends. In order to keep drivability, and to make sure that I still have some decent gas mileage, I understand that I need to change the axle gears. So what gearing should I be putting in the front and the back? Since my axles are stock, can I go up to 33s? O is that pretty much guaranteeing me disaster?
Chad Wilson
Wilsey, Kansas
A. For what you're going to use the Jeep for, you can most likely get away with the 33-inch tires, at least for awhile. I am pretty sure your rearend is a Dana Model 35, which is pretty notorious for being, well, a weak link. The differential cover has a rounded shape, somewhat like someone squished a circle a bit, while the much more desirable Dana 44 has an unequal shape with peaks at the top and bottom. I have known people to put over 100,000 miles on their Dana 35s without a problem, and others break the axle or bend the housing with 31-inch tires within 10,000 miles.
There are upgrade kits available from several of our advertisers that use a larger-diameter axleshaft that must be used with either an ARB Air Locker or a Detroit Locker. It's not exactly cheap, at about $1,000, but it's less expensive than a complete rearend swap to a Dana 44 or Ford 8.8. I would also recommend a swap to about 4.11:1 gears to put the rpm range back to where it was before the larger tire swap. The gears will cost you about $200 a set plus the installation. Plan on spending another $1,000 or so for making the gear swap.
Yes, you're going to lose some fuel mileage. The reason is due to the added rolling resistance of the large tires, and to a height increase, exposing more of the underside of the vehicle to "dirty air."
Wants Granny-Low 4-Speed For K-10
Q. I own a 1977 Chevy K-10 with a 400ci V-8, TH350 trans, 4.10:1 axles and 39.5-inch tires. I want to swap out the transmission for a four-speed with a granny-low gear. I have the chance to buy a donor truck that's the same body style with the four-speed, but it has a 350 small-block.
Is this a bad idea or not? What about wheeling with the granny low, or staying away from a certain model tranny? How hard would it be to do the swap? I know I would probably have to buy a new flywheel and clutch.
Brett Applegate
Via fourwheeler.com
A. Well, you're wise in coming up with a complete truck to make the transmission swap, as there are lots of parts that you will be needing from it.
To start out with, the 400 engine, I don't believe, ever came with the four-speed manual transmission. All of them, to my knowledge, used the automatic and the NP203 full-time transfer case. The only four-speed offered was the SM 465 with gear ratios of 6.55:1, 3.58:1, 1.70:1 and 1.00:1. The transfer case was a part time NP205, which is the preferred transfer case.
You're lucky the donor truck you found was in the same year group as your truck, as there was a spline count and pattern change in the later years.
Now as to the swap, the 400 small-block is an externally balanced engine, so you're going to have to find a manual-trans/TH400 flywheel or have the 350 flywheel balanced to the 400's specifications. Naturally, you're also going to have to use the clutch linkage from the donor truck, as well as the crossmember, driveshafts, and transfer-case shift linkage.
While you're at it, you'll want to take the locking hubs off the donor truck's front axle and install them on your present axles. This way, you can eliminate some parasitic drag of the rotating components when in two-wheel drive and even pick up a mile (or so) per gallon increase in fuel economy.