I did a quick search, and it doesn't look like this problem was discussed recently.

I had to make a sort-of-panic stop today, when coming up to a light, somebody with ABS and all-season tires decided to slam the brakes for a red light. Now, I have winter tires and no ABS (the roads were good though), so I slam my brakes really hard, and I notice that my driver's side front wheel is the only one that locks up. (Although, for what it's worth, the celica behind me couldn't stop in time, and skidded around me and through the intersection, red light camera, lol) Now, I noticed this a lot on the ice, but I always dismissed it as one side of the road being icier than the other.
So, here's what I know.
Our cars have a brake balance controller, that is not perfect, for this reason, the front brakes lock up first. (?)
So, the question turns into, why does my left wheel always lock up, and my right wheel never does?

The calipers were rebuilt in april by a questionable shop, but they don't leak, and it seems to me they are pretty hard to get wrong, and not have them leak.
The pads look about the same on both sides, but I haven't pulled them and measured them or anything like that, but they are both the same brand and type.

the rotors are below spec, and badly warped. But both front ones are about the same in both size and warp. I don't have the funds to replace the rotors, and I don't believe they are at risk of failing, just warping worse, so I plan to drive it until I can replace them. And, if at all possible, I would rather not buy new calipers, because I don't have money for that either.

 

This is only slightly related but:
if your rotors are warped now, and you don't replace them, soon you'll be replacing worn out components of the steering linkage (tie rods, tie rod ends, possibly the rack), suspension (***** joints), etc.
I suggest you place the rotors at the top of your list, and borrow money if you can't afford now.
Sorry for this bad news...
P.s. I bought the front ones for CAN$59 ea.

 

... and coming to your question, here are some of the possible reasons:

1. the right rotor is warped more than the left, and the vibrations during braking delay the lock-up.
2. air and/or air-leak in the lines
3. severely left-right unbalanced car. if this was the case, you would probably see a noticable difference in the left vs. right ride height. Also a dynamic unbalance could be caused by a damaged (binding) front shock. This could be tested by pushing down the front with your body (above a wheel), and checking for smooth and consistent operation.
4. are you sure this is not related to severely cambered road?

 

Hmm.. rack was rebuilt 5 months ago (by me), tie rod ends are new, one new ball joint.
Shocks are new, ride height is even (I had a passenger).
The pulsation is about the same side to side. I am worried it is indeed something wrong with the calipers.
The rotors aren't warped too bad, can feel the car pulsate on braking though.

 

I think you answered your own question! With badly warped rotors, your braking ability is greatly effected and reduced!

How do you know that it's just the driver's side that locks up? If the car pulls to one side, that may mean other things (improper wheel alignment, work suspension or rack...etc).

Replace the rotors and see what happens: I suspect your braking issues will go away.

Just my $0.42,
-Z-man.

PS: My rotors lasted me a really long time: matter of fact, the fronts are below Porsche spec, and I still have absolutely ZERO warping! (Then again, I've got the 951 brakes on my 944S2: big difference.)

 

I know it's just the driver's side, because it's the one the screeching sound was coming from =)
Usually when it locks up, I can hear the wheel skidding (my door doesn't seal right).
Since both rotors were warped pretty equally, I presumed it would affect braking on both sides equally. When I get a few bucks I will replace the rotors.

 

Yeah, with warped rotors, you can never get consistant braking... so having one side lockup before the other can most likely be blamed by that. Replace the rotors (see if any Rennlisters have a spair pair) and replace the pads with it. Warped rotors give uneven pad wear. While you're at it, bleed the brakes! I'm almost positive you'll have lockup on both sides. You'll also be VERY confident braking in it again as the violent shaking will stop. Just make sure you bed the pads for 50-100 miles when you do all this, and you'll be straight.

-Kevin

 

Heh, now I just have to find money to fix them. The shaking is not violent, but it just causes some minor jerking when stopping. The brakes have no air in the lines, and were bled about 2 months ago. However, I will probably have to remove some fluid and push the calipers back in if I replace rotors and change pads. While I'm in there, I might as well change wheel bearings, the rear ones are getting loud, and I just adjusted the fronts, and they are still loud.
See how fast it gets expensive?