Hard brakes?

[1LowLeSabre]

I have a vacuum conversion on my '87 T. My brakes feel hard when depressed all the way. In rain they lock and I skid. I have to gradually depress them. In an emergency situation they are crap. What might be the problem?

 

[Turbo6inKY]

You need better tires.

 

[1LowLeSabre]

Ok.



Next guess.

 

[Turbo6inKY]

Ok.



Next guess.

It wasn't a guess.

Hard when fully depressed? Normal.
Locks up at the drop of a hat and terrible on wet pavement? Your current tires don't have enough grip, the brake torque overwhelms the contact patch, and they lock up.

Get better tires.

 

[1LowLeSabre]

The tires are brand new BFG Radial TA's. They don't lock up at the drop of a hat. In normal use on wet ground they are fine. It's when the engine is under load, not a ton, just when ou need to come to a real fast stop, it's like the vaccuum is just not what it should be. Could it be an adjusment problem?

 

[Turbo6inKY]

A bit more detail makes all the difference.

What you have is normal for a vacuum conversion. If you stomp the brakes right after being in boost, you'll have very little power assist.

But as soon as your foot comes off the gas, the engine pulls vacuum and not too long after you hit the brakes, the booster comes on and you lock all the tires.

There are three remedies: better tires, a better check valve and vacuum resevoir on your brake booster, or both.

It's part and parcel of a boosted car and vacuum brakes.