Changing Brake Booster insights

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CX9 Grand Touring
I normally work on my own cars, 2 weeks ago due to time restraints I took the CX9 into Mazda to change the transmission fluid. I did one at 55, 85 and now the odometer is at 115,000. surprising it cost $125.00 (I had paid $65 a qt when I did it myself). Today I lost the power brakes and a quick check at the brake level show none and I found the cap was just sitting on top of the reservoir. I called Mazda back because they did a 20 point check which included fluid checks. They told me to bring it in. It has been diagnosed as a bad booster and master cylinder. I have never changed out a booster, retails between $85.00 and $165.00. Any words of wisdom from anyone out there to watch out for? I did see the back reservoir line is a little b**** to thread up, Mazda has quoted me 6 hours and $1650 bucks for the repair.
 
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I am not sure what year your vehicle is, but do you qualify for the brake booster recall? Mine did and the job was done under that recall. I have a 2012. I'm not sure if your mileage is too high but it may be worth having a discussion with them about any options you may have.
 
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Mazda CX-9 Grand Touring 2016
"...the brake level show none and I found the cap was just sitting on top of the reservoir. I called Mazda back because they did a 20 point check which included fluid checks. "

This is very suspicious. How could the cap be "just sitting on top of the reservoir?" How did it get loose? I've never seen one shake off. Were there splashes of fluid on the area around the loose cap? The fluid went somewhere, and there should be indications of where it went. I'd suspect the mechanic of failing to tighten the cap when he looked into the reservoir to check the fluid level. I'd suspect the service writer of needing a bigger commission check this month.

I'd top off the reservoir to the full line, correctly tighten the cap, and get a second opinion. I agree that the level sensor switch in the reservoir should have given you a warning light of the low fluid level.
 
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CX9 Grand Touring
Not a big job, Im in it for 2 hours, The only thing I am having trouble with is metal water line on the firewall is in the way of removing the Power Booster, 2 lines run about 3 inches on the left side. I need to take off the intake to loosed them. 2013 CX9 112,000 miles. The dealer did not charge me to isolate but did say Master Cylinder was bad too...I show no leaks on the MC. Did have to drain coolant which needs to be changed anyway.
 
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CX9 Grand Touring
Not a big job, Im in it for 2 hours, The only thing I am having trouble with is metal water line on the firewall is in the way of removing the Power Booster, 2 lines run about 3 inches on the left side. I need to take off the intake to loosed them. 2013 CX9 112,000 miles. The dealer did not charge me to isolate but did say Master Cylinder was bad too...I show no leaks on the MC. Did have to drain coolant which needs to be changed anyway.
Originally, the dealer gave us a free 20 point check. Everything was good, fluids OK. That's how the cap was loose, nothing to do with the Power booster.
 
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CX9 Grand Touring
Cake, may have done more than I needed but glad I did. First, Battery and airbox, next, water lines in the way (though you really don't need to, Mazda placed the Pitcock as easy as they could have ) with 112,000 miles, I needed to change antifreeze anyway. fewer hoses in the way made the job easier...a plus. You don't have to do anything with the cowl. Don't touch it!. You do have to remove both nuts holding a small heater hose manifold on the firewall, 2 nuts. I just took off the intake made it a lot easier, might as well change the spark plugs, makes moving the lines away from the Power Booster. Completely remove both brake lines front and rear from the Master and the pump 14mm. Yes, that's it! I removed the vacuum lines in 2 pieces but you could keep them together. Bought a new brake bleed system for the compressor for 24.00 Amazon and the Power Booster from Autozone for 148.00...better that the $1600.00 quoted from the dealer.... 6 hours total.

Had to add: After everything is completed I had no pressure from the Master Cylinder, Youtube vid had a great way to bleed the MC. "Hold the brake pedal down, loosen the connection at the MC to bleed, then tighten, do it 3xs. I used paper towels to catch the fluid. BINGO, works like a charm.
 
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CX9 Grand Touring
One more POST problem, Car ran like crap after everything was done. At first I thought it may be that I reused the intake manifold gasket..pulled that and checked all vacuum lines again. Everything check OK, I sprayed the Throttle Body which was pretty dirty. Still crap. The give away was that the brake lights stayed on. I checked the switch at the pedal and light went off... drove about a mile and again ..crap. Sure enough, brake lights on....The switch has an adjustable pad..twist push in and twist again to lock. I now have a small air gap.. sure enough runs like a champ. New Vacuum booster has a tighter spring. Brake switch must have been telling the computer I was riding the brakes.
 
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