No brakes after replacing brake power booster

Tiny
JACKIE LYNN MATTINGLY
  • MEMBER
  • 2005 DODGE CARAVAN
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 225,310 MILES
Replaced master cylinder about 3 months ago. Brakes have been okay. Then about a month and a half ago one of the caliper bolts on driver side came out, replaced temporarily with makeshift then the other bolt (or guide pin) came out and both were replaced properly. About 3 weeks ago pedal started acting funny. It would alternate between working fine to requiring pumping in half pumps or it would go to the floor. Did my research (extensively) as I have with everything else and determined it to be the brake power booster so had it ordered and a couple days ago my husband replaced it. Now even after multiple and I mean multiple rounds of bleeding in the correct order we have no brakes at all. I have done even more research and the only thing that comes back is possibly the vacuum line from the master to the booster. Am waiting at the auto parts store for the brake like switch as the clamp has broken on it and my brake lights are stuck on. I really need to figure this out as I can't drive with only an emergency brake. If it is the vacuum how do we fix it? If not what else could it be at this point. I am lost. Thanks in advance for any assistance.
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Monday, September 7th, 2020 AT 3:36 PM

6 Replies

Tiny
JACKIE LYNN MATTINGLY
  • MEMBER
A bit of history in case it helps. In the past 6 months these parts have been replaced: Passenger side: sway bar link x2, wheel hub, and shock/strut assembly.
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Monday, September 7th, 2020 AT 3:57 PM
Tiny
ASEMASTER6371
  • EXPERT
Good evening,

First, the booster will not cause a fading or no brake pedal at all. That is all hydraulic.

This has all the sounds of a bad master cylinder again. When you change the master cylinder, did you flush the system of all brake fluid?

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

I posted below the procedure for bleeding if you have ABS. It is required to use a scan tool to bleed the ABS unit itself or you will not get a pedal.

Roy

Standard procedure - Antilock brake system bleeding

The base brake's hydraulic system must be bled anytime air enters the hydraulic system. The ABS though, particularly the ICU (HCU), should only need to be bled when the HCU is replaced or removed from the vehicle. The ABS must always be bled anytime it is suspected that the HCU has ingested air. Under most circumstances that require the bleeding of the brakes hydraulic system, only the base brake hydraulic system needs to be bled.

When bleeding the ABS system, the following bleeding sequence must be followed to insure complete and adequate bleeding.
1. Make sure all hydraulic fluid lines are installed and properly torqued.
2. Connect the scan tool to the Data Link Connector. The connector is located under the lower steering column cover to the left of the steering column.
3. Using the scan tool, check to make sure the CAB (MK20e) or ABM (Mk25e) does not have any fault codes stored. If it does, clear them using the scan tool.

Warning: when bleeding the brake system wear safety glasses. A clear bleed tube must be attached to the bleeder screws and submerged in a clear container filled part way with clean brake fluid. Direct the flow of brake fluid away from yourself and the painted surfaces of the vehicle. Brake fluid at high pressure may come out of the bleeder screws when opened.

4. Bleed the base brake system using the standard pressure or manual bleeding procedure.
5. Using the scan tool, select anti-lock brakes, followed by miscellaneous, then bleed brakes. follow the instructions displayed. when the scan tool displays test completed, disconnect the scan tool and proceed.
6. bleed the base brake system a second time. check brake fluid level in the reservoir periodically to prevent emptying, causing air to enter the hydraulic system.
7. fill the master cylinder reservoir to the full level.
8. test drive the vehicle to be sure the brakes are operating correctly and that the brake pedal does not feel spongy.
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Monday, September 7th, 2020 AT 4:21 PM
Tiny
CARADIODOC
  • EXPERT
This is not a power booster or vacuum problem. That entire system simply makes the brake pedal easier to push. If the vacuum supply is missing or the booster isn't working, the brake pedal will be hard to push and feel the same as when you push it multiple times with the engine not running. The brake systems on all cars are designed to operate sufficiently to bring the vehicle to a safe stop if the engine stalls. To test the booster, right after running the engine, turn it off, then apply the brake pedal multiple times. You should get a minimum of two power-assisted pedal applications, (three or four is not uncommon), then the pedal will become much harder to push. One exception to this is when you have anti-lock brakes, and that system also supplies the power assist. For example, my 1993 Dynasty has the Bendix-10 system that uses an accumulator to store brake fluid at up to 2200 psi. With that system, you get unlimited power assisted stops as long as the ignition switch is on, even if the engine has stalled, and around 40 pedal applications once the ignition switch is turned off.

When you have a low brake pedal, there has to be air in the system or a fluid leak. The fluid leak can be internal or external. An internal leak is due to a ripped lip seal inside the master cylinder. When you press the brake pedal, fluid bypasses that seal instead of being pushed under pressure down to the wheels. The clue is you will not be losing brake fluid from the reservoir. The level will go down if there is an external leak. Those are found by looking for the wet area, and following it back to the source. Slow leaks are commonly caused by leaking rear wheel cylinders if you have rear drum brakes. Rusted steel lines leak faster and will leave a puddle on the ground right under the leak. The fastest leaks are caused by ruptured rubber flex hoses. Those almost always go from no leak to a low brake pedal instantly with no warning.

Remember too that since the late 1960's, all vehicles have their brake systems split hydraulically into two parts, so even if a major leak occurs suddenly, you will still have half the brakes, but the brake pedal will be lower than normal, and the red "Brake" warning light will be on.

If your van has anti-lock brakes and air got into the system, it will usually be necessary to use a scanner to bleed that air out. If you try to bleed at the wheels, you'll force the air to travel through the system and it will get trapped in the ABS hydraulic controller. The scanners have a procedure that commands the ABS Computer to open two valves to let the air be expelled from two chambers, then it can be bled out at two of the wheels.

Bleeding at the wheels is not necessary when replacing the master cylinder as long as the new one is properly bench-bled before it is installed. When you replaced it, was that a rebuilt unit from an auto parts store, or a used one from a salvage yard?

There is one more thing that can cause a low brake pedal if you have rear drum brakes. That is brake shoes that are badly out of adjustment. The first clue is the low pedal comes on gradually, as in over a period of many months. The second, and bigger clue is you'll get a higher and harder brake pedal if you pump it one or two times first before holding steady pressure on it. With each pump the shoes get pushed out closer to the drums, but return spring tension retracts them so slowly that they are still part-way out when you press the brake pedal again. Each time you press the brake pedal, the shoes get closer to the drums, until they make contact, then pedal pressure will feel normal. When you release the pedal and wait a good four or five seconds, the shoes will have time to fully retract, then on the next application, the brake pedal will be low and mushy again.

Also take a look at this article related to a low brake pedal:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Don't overlook the work that was done on the front caliper mount. If the guide pins are not holding the caliper square to the rotor, excessive piston travel to get the pads to contact the rotor can result in excessive brake pedal travel. This is a variable we can only talk about in general terms until we actually see what is happening. Watch how much movement is taking place when a helper presses the brake pedal. When the brakes are applied, those caliper pistons only come out, then retract, a few thousandths of an inch. Not much more than the thickness of a few sheets of paper.
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Monday, September 7th, 2020 AT 4:54 PM
Tiny
JACKIE LYNN MATTINGLY
  • MEMBER
It was a rebuilt from the parts store. From what you explained in thinking that it could just be bleeding to be fled properly with the scan tool. Going to see if parts store has a loaner or how much on will cost. Thanks so much for the info will update as soon as I find out.
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Monday, September 7th, 2020 AT 5:34 PM
Tiny
JACKIE LYNN MATTINGLY
  • MEMBER
Okay, so got the switch and he replaced it. Now no brake lights at all and with switch plugged in won't shit out of park. Take plug out and it will shift just fine but still no brake lights. Weird thing is that before he put new one in with the old one in and out we had brake lights and it shifted out of park just fine. By the way; haven't been able to get a scan tool that has the abs bleed capability yet so, standby.
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Monday, September 7th, 2020 AT 7:45 PM
Tiny
ASEMASTER6371
  • EXPERT
Why did they change the brake light switch?

They should have never touched that as it had no bearing on the issue you have.

Worse case scenario is to call a mobile mechanic to come to you with his scan tool and bleed the brakes for you.

Roy
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Tuesday, September 8th, 2020 AT 3:34 AM

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