I have a 1990 inline 6 (4.9L 300 ci) 4x4

1) I want to upgrade my tires to a 31x10.5r15 from a 255/70r15 but I've been told by a few people that when you put bigger then factory tires you have to change the transmission and gear down the rear end to compensate for the bigger radius on the tires and wheels. Has anyone done this already (bigger tires)? If so then how did it effect/affect the power of the truck, fuel mileage, shifting and etc.

2) I want to level my truck and possibly a 4 inch lift. I've heard that it ruins the ride of the truck, is this true? I've did some research and Daystar claims that the factory ride will be maintained. Has anyone noticed a difference in the ride?

3) I want to change my Automatic Locking Hubs over to Manual Lockers. I don't know that much about the four wheel drive systems. What all would have to be replaced to make the change. Also does anyone know if these trucks are vacuum shift or electric shift for the four wheel drive?

4) I have a slight miss when the truck it is in Park and Neutral. When you put it in Drive or Reverse it's fine and there is no miss, I have already replaced: Plugs, Wires, Distributor Cap, Rotor Button, Air Filter and a newer fuel filter. I'm not sure what else it could be.


Thanks for all the help.

Going to just 31's you'll be fine no need to change trans or rear axle gear unless you want better acceleration. Your speedometer will be off slightly but you'll just need to change the speedo gear to fix it. The bigger tired and the stock gearing will lower your highway rpm.. I run 30's on my 4 cylinder jeep and still have decent power so 31's with the straight six your good

Highway mileage will go up slightly It shouldn't really argent shifting

That size came on trucks . You probably Have 3:08 gears I running that now . didn't even effect my MPG much .

As for level kit . They are just taller springs and hardware . I run F350 2x4 upper duty coils My self and they do ride rough (like a truck ) . But most kits ride ifne . The newer lift kits also ride close to stock for the better kits . But I have not had one since 90's Rancho 3" lift

Get Stock or Warn hubs . Just the plain stock type .I have had all types hubs and also premium Warn . But stock type are easy to turn in with glove on.

But everything should be in kit (may need some parts hub washers ect but easy to do . I'd get related tools needed and go to upull . remove youself take pics so know how gose together and get everything you need for $15 or so (here) plus the knowledge of how come apart with out loosing your truck .

As for miss some do . I had a new 94 300-6 back 5 times for it dealer never fixed it . had 179000 when I sold it .

Check this guy's '98 6 inline, pretty nice set up:
https://www.youtube.com/watch?v=QNJUmziwibQ

It's got a 6 inch skyjacker lift kit, a propane system for daily driving, shift kit, accel ignition kit, 16x12 Michey Thompson wheels and 37 Creepy Crawler Maxxis rubbers.

Click to expand...

Those are aggressive good looking tires you might want to see. Start with choosing good lift kit, see good one's here: 4Wheel Lift Kits