My 1990 240 wagon vibrates through the steering wheel at high speeds.
Here is what I have done:

1. new Brembo rotors in the front, (lug nuts are torqued at 85 lbs)
2. the rears rotors are true,
3. no calibers are stuck,
4. tightened down the bearings (finger tight and no play on the tires),
5. rims are straight (I spun the tires and watched out for run out),
6. the rubber on tie rods seem fine,

The only thing left now is to bring the tires in for a balance. I know they are due for a balance, but I can't fathom how unbalanced tires can lead to vibrations while braking. I can understand that it would lead to vibrations all the time.

Could worn bushings cause problems?

If it vibrates all of the time, and not just while braking, your culprit will invariably be imbalanced tires. The most common speed for imbalanced tires to start causing vibrations is around 40-45 MPH.

You can have looseness in other steering components that will cause clunkiness, but it is rare that loose bushings, ball joints and such will cause an even, pulsating vibration. Worn suspension or steering components will make the vibrations of imbalanced wheels sound and feel much worse (and imbalanced wheels will in turn hasten the demise of failing weak suspension/steering components), but they won't in themselves set up vibrations.

If your car only vibrates while braking at high speeds, imbalanced tires are not the culprit. Neither are your calipers or wheel bearings. Usually it's the discs. How do you know for sure the rear discs are true? And just because your front discs are new doesn't guarantee that they weren't dropped in shipping or manufactured incorrectly. These things are not common, but not unheard of. Get all of your discs checked for run out before you do anything else.

Just curious... were the hubs really really clean before the rotors were installed.. it does not take muck more than a few specs of rust and sand to throw off rotor aliginment. You can build in a nice wobble easy.. Mac

First things first. An unbalanced tire has a 'critical speed' above and below which the vibration is reduced. You can always "drive through" an unbalance.

An out-of-round tire will feel a lot like an unbalanced tire, but as speed increases the vibration and harshness will increase and never decrease. An out-of-round tire can be hard to diagnose by eye.

Front wheel vibrations are typically felt through the steering wheel, and rear wheel vibrations are felt through the seat.

If your vibration only happens when you're braking, then the prime suspect is brake rotors. However, you say they're new, so other looseness needs to be investigated (although over-torquing can warp even new rotors). Loose or worn wheel bearings can be the culprit; you said you tightened them by hand, but you really need to seat the bearings with a torque wrench and then back off a flat or 2 on the castellated nut.

I would re-check the bearings and also the ball joints. Perhaps the place you go to get your tires balanced can check them for you.

Way down on the list of things to check would be front suspension bushings, since they usually contribute to harshness when they're worn, not vibration per se.

Unbalanced tires will vibrate at speed whether braking or not.
Sounds like your bearings might be a little short of tight enough
unless your fingers are pretty strong.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma