Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Topic: Firm pressure required on brakes! Nearly the entire system has been replaced; WTF? (Read 2634 times) previous topic - next topic

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

July 19, 2016, 12:07:16 AM

I’ve got a ’87 5.0 that has been my daily driver for the past 10 years. Since I got it, the brakes never felt right; they don’t begin to really grab until the pedal is fairly far down, and at that point, require a lot of pressure.

Brakes are one thing I don’t do myself. I’ve paid shops to replace the master cylinder (twice actually, as the first one was defective), lines (they blew out on me once), regular pads+shoes+slave cylinders+hardware as needed, and finally, new rotors and drums. The shop said they were incredibly overdue, which is true as they needed replaced years ago.

For the first 3 or so days after having new rotors, drums, shoes, and pads put on, the brakes felt like a new car for the first time. That ended thereafter, and I’m back to needing a heavy and firm mash on the pedal to get the car to stop normally; emergency stops are very… not confidence inspiring.

What gives? I don’t think the brake booster is problematic but I only believe that as I can’t find any vacuum leaks. Also, when the brake lines blew and dumped the fluid all over the road, the brake light did NOT flash as I believe it should. Any ideas?

edit: furthermore, the brake lights do not come on until some firm pressure has been applied, and then flicker. The amount of pedal travel before it firms up varies every time, but sudden brake stomps tend to ‘bite’ and become firm with less pedal movement first. I’m not sure if the brake light switch detects pedal movement or fluid pressure.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #1 – July 19, 2016, 12:51:50 AM

The brake light switch is on the pedal, it is a mechanical switch and easily replaced and plentiful at a junk yard, this switch lights up the actual brake lights on the back of the car. Almost every car I've had the wires were messed up. Splicing in a new connector or price of wire usually fixes it no problem.

The low pressure light in the dash is a sensor located on the bottom of the master cylinder. It is usually swapped with the master cylinder, although all of mine have worked.

The brake boozer is easy to rule out. Plug the vacuum line and see if it feels the same when braking. Obviously be careful if you decide to drive it this way, you will still have brakes, but no power assist. If it feels noticeably firmer after, you can rule it out.

After the car is shut off, you should also have some assist, at least one pump before it bleeds off and gets harder. If you have no assist, either the diaphragm is leaking or the one way vacuum check valve has failed. It is designed to keep vacuum in case the engine dies.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #2 – July 19, 2016, 01:43:36 AM

I get a few presses after the engine is off before it is obvious there is no vacuum left. I’ve also had my vacuum tree break, so I know what it’s like without power breaks! This is why I don’t think it’s the booster, than at the fact that it felt new after the recent replacements for a couple days. I want to know what might have happened since then. Splitter thingy perhaps?

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #3 – July 19, 2016, 04:20:05 PM

Have you replaced all rubber lines front and rear yet? A collapsed rubber line can reduce braking.

How about a fluid flush? I am sure when you had a line blow out that flushed most of it! Sound scary, I've yet to have to deal with that and hope I never do....... Stay safe and good luck with this one. I'll be following along to see the fix.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #4 – July 20, 2016, 09:09:01 AM

So what I am getting out of this is that the car has excessive pedal travel prior to the brakes engaging to a point that you feel is satisfactory under normal stopping conditions and if you were to have to panic stop you have very little confidence. Is that correct?

Items that have been replace are as follows:

Master Cylinder (twice)
Front Calipers
Front Rotors
Front Brake Pads
Rear Slave Cylinders
Rear Brake Shoes
Rear Drums
Brake Lines (not sure if this is all of them or just the one that blew)
Hardware (assuming this would be a hardware kit for the rear brakes)

If the pedal travel is excessive you are looking at a couple of potential issues:

Incorrectly bled master cylinder prior to installation
Another bad master cylinder that is allowing fluid to bypass the piston
Air in the lines due to improper bleeding to the brake system
As mentioned previously, the rubber lines from the hard lines to the caliper and the one in the rear of the car from the hard line to the rear end
Brake booster rod adjustment (not a novice thing to attempt but very achievable with some research)

Burnt brake fluid will only decrease the ability of the fluid to handle higher temperatures due to a decreased boiling point. It can become corrosive and eat the soft parts of the brake system so it is always a good idea to flush the system when in doubt.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #5 – July 30, 2016, 03:55:35 AM

At this point, I might as well just bleed them and replace all the fluid. And check the low pressure switch while doing such.

Also, the rear brakes tend to lock up before the front – typically when applying increasing pressure when highway traffic abruptly stops.

I’m not sure if this is typical of all cars (but more info = more better for troubleshooting), but the rate at which I apply the brakes makes a difference. If I suddenly hit the brakes hard in a panic stop, the pedal is firm with minimal movement and quick bite. During normal stops the pedal requires more pressure gradually to maintain a reasonable slow down. It does not continue to sink (which it did when it had a faulty master cylinder).

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #6 – July 30, 2016, 04:44:48 AM

Sounds like a master to me. The give away is the improved performance on the hard hit. I have the same thing, so I've been watching this thread.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #7 – July 30, 2016, 09:08:58 AM

So this is what the internal components of our master cylinder looks like:

What's happening to us is that the leading edge of the seal for the front brakes (which are at the front of the MC) called a "cup" wears down, and when you push the pedal down normally fluid pressure can bypass around the cup into the following chamber and back into the reservoir. On a hard hit, the rapid pressure build accompanied by the quick movement causes the cup to flare out, thereby enhancing the seal integrity (improving braking power) until you back off the pressure. The rear piston is much larger, so it is worn less and performs better which is why you get rear lockup, but not front lockup. I ordered a repair kit from rockauto for less that $20 shipped. We'll see how that goes next week when I get it in.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #8 – July 30, 2016, 09:54:55 AM

My rear brakes have almost always been garbage on these cars, it's very odd for the rears to lock up at all in my experience. Usually you can get the fronts to lock up on even a moderate stop. Find a dirt road or parking lot where you won't pass anyone off and try to lock them up, then look at the tire marks. Fronts should easily lock up, even at 5mph and moderate brake preassure.

Firm pressure required on brakes! Nearly the entire system has been replaced; WTF?

Reply #9 – July 30, 2016, 04:40:31 PM

Now imagine you've got a problem with the front circuit piston cup in your master cylinder in addition to that...