I'm having some steering issues in my '83 bobber (very erratic, loose, darty), so while checking my tie rod/knuckles/etc I noticed my birf is leaking. I'm not super familiar with birfs, but I'm guessing based on this photo that I'll need to rebuild it. I bought new wheel bearings so far to see if that would correct the steering issue, but noticed the birf just yesterday. Would a leaky/blown birf contribute to erratic steering as well? I'm wondering if maybe the worm gear in the steering box is missing teeth, but first I want to try these things. Thanks for your help.
1 - You don't rebuild Birfields. You rebuild the steering knuckles.
2- Worn trunnion (steering knuckle) bearings can cause funny issues with steering, especially "death wobble".
3 - Checking the TREs is a good place to start.
4 - I'm assuming stock push-pull steering, so also check out the drag link bits. Just rebuild it.
5 - The leaking is from worn axle seals. Knuckle grease gets diluted with diff oil and leaks out. Get the
kit from Marlin (<-link) and use his super-duper seals. Get
his tool (<-link) too to install them.
Plenty of information online on rebuilding steering knuckles. Plan on a day or two in the garage your first time. I HIGHLY recommend taking the truck to a self-serve car wash and blasting those knuckles and getting them real clean. Those are really ugly. I would blast them as clean as you can then hit them with engine degreaser, then blast them again. Use lots of quarters and get them spotless, including from the top and bottom to get the nuts clean. You will understand why if you don't. Also, see if you can find an online version for the factory service manual. Any truck/4Runner 1979-1985 will work, as will any Land Cruiser 1979-1989. They all use the same parts.
Consider doing brakes while you are in there. Shoot, consider upgrading to V6 calipers/master cylinder/LC rotors while you have it all apart.
One last thing ... those damn cone washers holding on the hub are a royal pain in the butt. Get yourself a brass hammer, place it on the stud, and give them a smack with a BFH (Big-Fing-Hammer). That will usually knock them across the garage floor.
Several of us have been through this so come back with questions.