Jumping bean fenders and shaky steering wheel!

[CaliCajun78]

Hey fellas,
Have a problem I think I have a decent bead on, but would love some expert analysis!

1978 Continental 4-dr with the Hydro-Boost disc brakes in front (boost runs off the power steering pump, sans vacuum booster), drums in back. Worked on the car for a man 4 years ago, before I recently bought the car from him. Had same symptoms back then - apply brakes - front end of car jumps up and down and steering wheel shakes violently left to right. Not knowing about the Hydro-Boost system at the time (have to admit I'm sort of a shade-tree mechanic, but a good one, darn it, but hadn't yet encountered Hydro-Boost). Considering the car had mostly sat for about 5 years, I figured his front calipers were bad, and they did drag like hell. Replaced them with rebuilt calipers, had rotors turned. This took them down to minimum spec.

Fast forward 4 years. I buy car, need it immediately, take it on 5 mile test drive and plunk down the cash. Brakes work perfectly.

Begin to drive it from California to Louisiana and the same shaking problem returns. Funny thing is, the longer I drive on the highway w/o touching the brakes, the WORSE the front rotor warpage/jumping/steering wheel shimmy is. Drive it around town 5 minutes, use the brakes, no prob. After 10 minutes, get ready. Drive 75 mph and don't touch them for 2 hours, apply them, and get ready for the Lincoln jumping bean.

Get this now. Before I made the 2,000-mile drive, I put it up in the air, and noticed both front calipers were dragging heavily, and evenly.

My conclusions: Rotors are down to minimums and prime for warpage. But that's the symptom. Here's my hypothetical cause: Either the master cylinder or Hydro-Boost is holding the front caliper pistons in the applied position. The violent shaking after a long stretch w/o touching the brakes suggests continuous application and heating of brakes by a hanging-up M/C or leakage through the Hydro-Boost applying constant pressure. Remember, both calipers were replaced at once, and the wheel drag is identical for both front wheels.

The terrible gas mileage cross-country was another indicator.

Has anyone any experience with the Hydro-Boost seal failing and applying constant pressure to the master cylinder? Any ideas how to economically proceed? The M/C is $16 from Autozone, so I could just play swap the parts, on the chance the M/C is sticking, but the rebuilt Hydro-Boost is $129+ and I don't have that cash to go on a guess....... especially since I know know I have to buy new rotors.

Thanks for any input! :)

Steve C.
Lafayette, Louisiana

[CaliCajun78]

Forgot to mention - before driving the Linc cross-country, (nice, cushy ride - the first time I arrived without lower-back pain!) I took it to the shop I used to work at and put it in the air. We shook everything. The only parts worn were the stabilizer bar end bushings. Everything else was tight as a tick. ;)

[Steve Moran]

I have been asking some wrench turners about this one and I am still coming up with a blank. I hated not to post something because I wanted to give some help, but it seems help has not arrived.
the only thing I can say is I wonder if the P/S pump is getting bad or if the fluid is warn out or very dirty.
I will toss an idea out but I am on sure of it.
Give a try at putting in some P/S conditioner.

[LSRX101]

This is almost a classic example of delaminated brake hoses. The inner lining breaks loose and acts as a check valve, keeping pressure on the brakes.

You can check for this, when the brakes are tight, by opening the bleeders. If the calipers releae, the brake hoses are highly suspect.
You can verify this by opening the lines at the master cylinder when the brakes are tight. If the brakes don't release, it's the hoses. If they release, it's the master.
My money is on the brake hoses.