Help diagnosing soft brakes?

Elkins45

Elkins45

Joined
May 7, 2018
Messages
2,668
Location
Northern KY
I drove a 2012 Mazda5 (2.5L MZR engine) today. It has a lot of plusses (one owner, 83k miles, good service history, close to home) but one big minus: the brake petal was very soft. It would stop fine but you had to push the pedal a lot farther than anything I’ve ever driven. It felt like how it feels after you’ve changed pads and are pushing the pistons back out to seat the pads. The salesman said they just replaced the master cylinder and had actually sent the first one back because they thought it must be defective.

Assuming they did an OK install of the new master cylinder, what else should I look at to diagnose the issue? Maybe it just needs to be bled completely? Vacuum leak? It had plenty of fluid. He made me an offer but I would like a better idea of how much work I might need to do before I decide if I need to make a lower counteroffer or just walk away. With enough of a discount it might be a decent project just to throw parts at LOL.
 
It might need the anti-lock brake pump bled. If you get air in it, you can bleed the brakes till the cows come home, but you'll never get all the air out the ABS unit unless you use a scan tool to cycle/bleed the pump. I had to do this with our Expedition not too long ago after changing the master cylinder.

I think you can use ForScan on Mazdas? ForScan is free and can use a inexpensive Bluetooth module as the OBDII interface.
 
First, bleeding is needed using the OBD tool. There are probably bubbles in ABS module. I'm not sure how Mazda does it, but the BMW procedure is to connect the pressure pump, 10-15psi, open each caliper one after another (LR, RR, FR, FL), and run the ISTA (software) bleeding procedure. When I was upgrading brakes and installing M3 master cyl. I did 3 times this procedure using ISTA.
So, do that before starting to disassemble things.
Also, what pads they installed?
 
I have a 2012 Mazda 5. Your soft brake problem is air in the ABS. I have had this happen 3 times. If you have an Ancel610 you can fix it easily. Hook the tester to it and go to abs system adjustment. Pump the Pedal several times to get it hard and activate abs hydraulic pump. The pedal. Will drop first and then come up hard under your foot. It happened to ours and you would swear it was a bad master cylinder. I changed ours and bled brakes and still the same. Get the tool and fix it. Great car by the way.
 
I tried using Forscan to bleed brakes on BIL's Fusion. It was NOT an available option for that particular car.

This is a pretty big red flag-- their best mechanic worked on it, probably threw parts at it, and they're giving up.
 
I just had the brake fluid replaced on my '07 Accord as a routine maintenance item by a reputable local shop. The brakes came out exactly as you describe. The brakes worked but the pedal was soft and way down. Took it back the next day and they found "a lot of air" in one brake line. So it happens. They bled all the lines again and it's back to perfect.

I didn't do the job myself because I was afraid of getting air in the ABS.

It doesn't sound like the Mazda needs parts (maybe never did). It most likely needs to be properly bled including and especially the ABS system. I have to think a reputable Mazda dealership would know how. But it could be expensive. And if it's not that, well ....
 
eljefino said:
I tried using Forscan to bleed brakes on BIL's Fusion. It was NOT an available option for that particular car.

This is a pretty big red flag-- their best mechanic worked on it, probably threw parts at it, and they're giving up.
Click to expand...
I’m not certain saying their best mechanic gave up is actually saying much. Brakes are a fairly simple system, there’s only so much that can go wrong. I can buy the scan tool @vwmaniaman used for $100 and bleed the ABS, then bleed the entire system myself. If not, my local mechanic is really good and quite reasonably priced.

If I get the car for $1000 less than market value and he charges me $1000 to fix it then it’s all good. I’m encouraged by everyone saying it’s probably just air in the ABS.
 
Sounds like they need to be properly bled.
My primary mechanic who does good work reasonably, and is honest as the day is long, is woefully deficient in this skill.
I always check them before I leave.
 
I have a 2010 Mazda 3 2.5. The brake pedal has a lot of travel / not a ton of brake boost compared to some cars. I've owned it since new and you get used to it but it's weird when you switch out of something with bitey brakes like a BMW. Switching back to OEM pads can help also, the OE formula was high dust and high bite. The bite is not good at all with most aftermarket / ceramic type pads. Over time, I have grown to like the linearity of this brake setup. Hard to say if that car is normal or not though based on the description.
 
Last edited:
ecotourist said:
I just had the brake fluid replaced on my '07 Accord as a routine maintenance item by a reputable local shop. The brakes came out exactly as you describe. The brakes worked but the pedal was soft and way down. Took it back the next day and they found "a lot of air" in one brake line. So it happens. They bled all the lines again and it's back to perfect.
Click to expand...
Slight sidebar from the OP's question, but I can guarantee you that this is what happened:

https://bobistheoilguy.com/forums/threads/dot-3-in-a-honda.381347/post-6848691
 
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