Apparently an old engine may lack the vacuum to drive the brake booster enough to release the brakes. In my case, the brakes were really held tight. Today I had to open the bleed valve on both sides to be able to move. The car drove fine the rest of the day.
What puzzles me is that I thought the vacuum assisted the brake. That is, less vacuum would mean less braking. It looks as if more vacuum is less braking.
My next step is in the manual. Measure the vacuum to determine if it’s the engine or the booster. My question is, why does less vacuum mean more braking?
Gee, my link didn’t work and I don’t know why. Well, I don’t think my question needs the link. I got to it my searching CarTalk newspaper columns with ‘brake booster’
The fellow who had that problem had an 82 Honda. It was published in April 1996.
They are vacuum assisted brakes.
When there is no vacuum the brakes are very hard as there is NO assist.
The vacuum does not release the brakes, it helps to apply them.
The problem you described in the OP is NOT what car talk is discussing.
Your problem (Locked brakes) could be caused by (in order of likely hood)
[ul]
[li]Sticking caliper[/li][li]Mis-adjusted booster rod[/li][li]Binding or non returning brake pedal[/li][li]Bad master cylinder[/li][li]ABS problem[/li][/ul]
Can you tell which wheel(s) are locking? All four or just one or two?
If it is all four, then I would look at the booster rod, the brake pedal, or a master cylinder. If only one or two wheels are having the problem, then a sticking caliper, or ABS problem.
Yesterday when it happened, I relieved pressure on both front wheels to get rolling. I’ll be more selective in the future. I’m getting more suspicious of the master cylinder. I understand there’s a tiny little hole in it to relieve pressure. If it’s plugged, the brakes stay on.
When it happened, the car didn’t pull to the side, so I suppose both sides are locking evenly.
Add a failing brake hose to the list of possible causes.
If you want to deal with this efficiently, you’ve got to raise the car so you can try to turn the wheels by hand. The first thing I would do when I perceived the brakes were staying on would be to raise the back of the car and rotate the rear wheels (don’t forget to release the handbrake). If they turn, but the car still won’t move, I know the problem’s in the front. Next I would raise the front wheels and see if either one turned. If only one is stuck, it’s got to be the caliper or hose on that side.
If the stuck wheel turns after the bleed screw is opened (and there’s a gush, with the fluid obviously under pressure), it’s a hose on that side collapsing internally. You generate enough pressure with the pedal to force fluid through the restriction and apply the brake, but then not enough fluid can get back out to let the brake off.
Today I had to open the bleed valve on both sides to be able to move.
Are you absolutely certain you had to do it to both sides? If, say, only the right side was sticking, but you first bled the left side, it could have fooled you. Lack of pull is not sufficient evidence to prove both sides were hanging up.
After driving a while, then sitting a while…
Are you saying that it first has to sit? You drive it, and when you park, the car will roll, but after it sits the brakes apply? If so, this is a weird problem and I don’t have a guess off the top of my head.
I’ve had this happen twice. I drive a few miles no problem. I park for an hour or few, I drive a few miles and the brakes get ‘auto-applied’ harder and harder until I have to pull over. I pull out my handy 10mm box wrench and crack the bleed gizmo on one side. The brakes are still applied. I open the bleed gizmo on the other side and I can drive with no further problems.
I may be confused and really only one side is sticking. My next attempt will be to bleed at the master cylinder. If these symptoms remain consistant, I’ll finally replace the master cylinder. I just can’t imagine what else would do this. Of course, I’ll be looking at the hoses and I’ll find a place/time to raise the wheels during failure.
And I was wrong about bleeding both sides. Only the passenger side was tightening up. I could only go a few miles before the car would be dragged down as the right brake tightened up.
There was a layer of powdery looking black guck at the bottom of the master cylinder. I’m confident that goo was blocking the relief channels.
Possibly a good fix would have been to clean the tiny hole out with a tinier wire. (or maybe not.)