Hey Yotatech. Recently been encountering an issue with my braking system. Whenever i brake, between speeds of 40-120(km/hr), my vehicle pulls extremely sharply towards the left. This just started happening randomly and i don't recall anything happening before hand.

Have a 2." lift with Balljoint spacers.
My front/rear brakes were rebuilt a few months ago.
I jacked up the front and got someone to apply pressure to the pedal while i spun the front 2 wheels by hand, nothing seemed noticeably off. Also took the wheels off and visually inspected the front brakes & cleaned them as well, they all seem fine.
New(ish) Upper/Lower balljoints, Idler Arm, Pitman Arm, Outer Tie Rods.
The only thing that looks off is a single outer tie rod boot on the left is kinda coming off, and grease is spilling out. I don't think this alone could cause the issue though.

Going to be looking into the rear drums after work tomorrow, and see if anything funky is going on in there. What else could be causing this?

 

I would guess your right caliper is not closing. With a "few months" of driving, I suspect that if you remove the pads, there will be perceptibly less wear on the right pads.

Or, the right caliper is not sliding on the pins, so only one of the two pads is applying.

So I'd remove the pads and look at them. If the caliper isn't sliding, it might be due to insufficient grease on the pins, but more likely a bent pin. You should be able to move the caliper by hand.

If the caliper isn't closing (you can try to pry the pads apart a few mm with a screwdriver, then gently apply the brakes to see if they move), you could have a bad caliper, or sometimes a bad flexible hose.

 

You think it's a seized caliper? When jacking up the truck and applying brake pressure both wheel stop pretty evenly. Another thing I just noticed is that one of my sway bar links bushings is kinda smushed.

Another think I just remembered is one of my wheel bearing nuts isnt properly torqued on, however this was a thing before these braking issues arose.

 

First and second gen IFS 4Runners have rigidly mounted calipers that have hydraulic pistons under both pads. The calipers do not slide on pins. I do not know about other models.

Floating calipers are used where hydraulic pressure is applied to only one pad.

For one pad to wear more than the other on a '91, there must be an issue with the calipers hydraulics. A stuck piston perhaps.

 

Id check the caliper first too.

Any steering issues you have would be present while driving, not just braking.

 

I agree with most of what has already been mentioned, I just thought I'd boil this down to it's essence for you.
either:
#1 the right side brake isn't working as well as the left side.
#2 something in the steering/suspension is shifting position when you hit the brakes.
I'm betting on either the brake caliper having a stuck piston or the brake hose collapsed internally and isn't allowing much pressure to the caliper.