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Discussion Starter #1
I have a 2004 Touring currently at the shop where they replaced the master cylinder and brake booster. They're telling that after replacing the parts, they can't get pressure build up in the system to bleed it. What gives?


I have been taking my vehicles to this shop for over 15 years and I have never had an issue with them - I know they are competent. Here's a history of what's happened:


I bought the car 2 months ago. When I bought it, it had been parked under a tree for almost a year. The brakes had been run to the ground, the cylinder had popped out of the right rear caliper and all the fluid had drained out. I had the shop replace both rear calipers, all brake pads & rotors and do a thorough brake fluid flush. Upon getting the car back, the pedal felt soft and like it took a little more effort than normal to bring the truck to a stop. Mechanic assured me he did the multiple "panic stops" as part of the bleeding procedure.


Last weekend, I was driving and made a hurried stop when a red light caught me off guard. I used firm pressure on the pedal, but not enough to constitute a panic stop. At the moment I expected the truck to come to a complete halt, the pedal gave a bit, meaning it suddenly sank a little, the brakes lost pressure and the truck suddenly rolled a little further. This caused some concern, so I tested doing some more hard braking, which re-created the incident a couple of times. On my way back home, it happened one more time, catching me by surprise and I came within a hair of tapping the car in front of me.


On Tuesday I dropped the car off at the shop. The mechanic concluded it was a failing master cylinder. At the end of the day he called me to report that in the middle of bleeding the system with the new master cylinder, the brake pressure suddenly gave and the pedal sank to the floor. Upon removing the master cylinder, something fell out of the brake booster and thus he needed to order a new booster.


Mechanic called me again today, reported that upon failure to build pressure, he ordered another master cylinder believing the first replacement was defective, replaced it again, yet he still cannot build up pressure in the system. He explained that it begins to build pressure but eventually loses it completely.


Anyone have an idea of what the issue may be? Thanks in advance.
 

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The bleeding procedure can be tricky. Anti-lock systems can complicate it. Sometimes a pressure bleeding system is what it takes, and not all shops have one.

I had a customer tow his car into my shop. He had been doing his own brake work, and could not get a solid pedal. Turns out that he had swapped the left and right front calipers. They were the same mechanically, except for the position of the bleeder screws. Rather than being on the very top of the caliper, they were now lower down, causing air to be trapped inside the caliper. You might suggest to your shop to check this. It's a long shot, but maybe one of the new calipers was boxed wrong and is creating this problem.
 

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Pedal going to the floor are symptoms of the master cylinder and/or booster failings so your mechanic seems to be making the right call. Air in the system could be suspect too. That it's still intermittent (or was intermittent) seems to indicate something else. The rear calipers were replaced, but how about the front? The fronts give you about 60% of the stopping power. When the brake fluid drained out and the X sat, moisture getting into the system could have created rust and the front calipers might not be working correctly being "sticky". If they weren't checked, think it's worth at least checking the front. Maybe a second bleed too or at least check with the bleeding screws that the brake lines are indeed still clear.

Good luck!
 

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Discussion Starter #5
Quick update. Both master cylinder and brake booster were replaced. My mechanic originally got the replacement parts from O'Reilly Auto Parts and for some reason they didn't work. Once replaced with genuine Acura parts everything is good now.

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The bleeding procedure can be tricky. Anti-lock systems can complicate it. Sometimes a pressure bleeding system is what it takes, and not all shops have one.

I had a customer tow his car into my shop. He had been doing his own brake work, and could not get a solid pedal. Turns out that he had swapped the left and right front calipers. They were the same mechanically, except for the position of the bleeder screws. Rather than being on the very top of the caliper, they were now lower down, causing air to be trapped inside the caliper. You might suggest to your shop to check this. It's a long shot, but maybe one of the new calipers was boxed wrong and is creating this problem.
was this an acura?my 03 mdx appears to have right and left front calipers.
 
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