2007~2015 CX-9 Replacement brake booster - Beware

delucat2

Member
:
CX-9
I had the brake booster on my 2009 CX-9 go bad.
Bought the Cardone reman unit for $130.
Turned out the non-adjustable MC rod was 5mm too long.

I really looked at this out of the box new, but did not detect the 5mm difference, and since it wasn't adjustable, let it go.
Ooops!

This caused 2 weeks of nightmare for me...trying to figure out why the brakes were dragging.
The dragging brakes overheated the fluid...causing the brakes to apply and eventually lock up.
Once cool, it was drivable again.

I finally figured this out over a Tecate with the old guy next door who has wrenched for years.
Said it had to be the rod. This used to be a standard adjustment in the 50s and 60s.
An improper reman doomed me to chasing my tail and thinking i had electrical / ABS problems.

The extra 5mm caused the MC piston to be sitting slightly compressed...enough to close off the return ports.
System remained pressurized and it only got worse as the brakes were used and the calipers overheated.
I used a cutting disk to take 5mm off.
Problem solved.

This was one of those times when the aftermarket took its chunk out of me.
I needlessly replaced: 2 ABS sensors - $60, front calipers - $ 180, master cylinder - $130
About 15 hours of head banging.

What was needed: $130 booster ($260 for new), ABS module $800 programming of ABS by dealer $200.
 
:
18 Mazda CX5 AW
I had the brake booster on my 2009 CX-9 go bad.
Bought the Cardone reman unit for $130.
Turned out the non-adjustable MC rod was 5mm too long.

I really looked at this out of the box new, but did not detect the 5mm difference, and since it wasn't adjustable, let it go.
Ooops!

This caused 2 weeks of nightmare for me...trying to figure out why the brakes were dragging.
The dragging brakes overheated the fluid...causing the brakes to apply and eventually lock up.
Once cool, it was drivable again.

I finally figured this out over a Tecate with the old guy next door who has wrenched for years.
Said it had to be the rod. This used to be a standard adjustment in the 50s and 60s.
An improper reman doomed me to chasing my tail and thinking i had electrical / ABS problems.

The extra 5mm caused the MC piston to be sitting slightly compressed...enough to close off the return ports.
System remained pressurized and it only got worse as the brakes were used and the calipers overheated.
I used a cutting disk to take 5mm off.
Problem solved.

This was one of those times when the aftermarket took its chunk out of me.
I needlessly replaced: 2 ABS sensors - $60, front calipers - $ 180, master cylinder - $130
About 15 hours of head banging.

What was needed: $130 booster ($260 for new), ABS module $800 programming of ABS by dealer $200.
Glad to see it's corrected. Thanks for sharing your insight on the real cause and solution.

For others here, another cause of locking brakes(when can't find any other cause) may be bad brake lines. They may look good on the outside but come apart on the inside and start to block brake fluid similar to a check valve.
 
:
2009 Mazda CX-9 GT
This is why you always compare old parts vs new. I used to give my techs a hard time whenever they cut this corner.
 
Last edited:

delucat2

Member
:
CX-9
This is why you always compare old parts vs new. I used to give my techs are hard time whenever they cut this corner.
No corners cut. These are brakes.

I spent 15 minutes looking at it when i came out of the box. I had expected to measure and adjust the rod / mc clearance or at least check it. Careful inspection determined it was not adjustable, no locknut or threads. The protrusion with respect to the face of the booster...probably off by 3mm given the fact that I trimmed 5mm, and my engagement is a bit farther into he pedal stroke than i would like.

Even factory parts appear in "new and improved" versions.