Let me set the stage for you:
Summer time. Minnesota. 2007 Chevrolet Tahoe 4×4.
Wait, I did say, “Summer,” and “Minnesota,” didn’t I?
There we go. Much more fitting.
So, this Tahoe has the 5.3L V8 Flex-Fuel engine with 109,591 miles and the JL4 RPO code, which is the active brake control/Stabilitrak option.
We had done some brake work on the rear of it and performed a suggested brake fluid flush with it. After the flush, we had no brake pedal. What the H-E-double hockey stick is going on here?
As it turns out, bleeding the brakes on this truck (and most newer GM trucks) can be quite challenging if air is introduced into the brake system.
First, you must bleed out the ABS (Anti-Lock Braking System), which requires the use of a scan tool which engages the ABS pump in a sequence as you pump the brake pedal, like this one:
I’ve stumbled across a secondary method which remains untested at our shop:
- Fill the master cylinder and pressure bleed the brakes like always, in this order: Right rear, left rear, right front, left front.
- Then take a short test drive over 15 mph, and brake hard enough to make the ABS engage during braking. ABS all the way to the stop. A gravel road works well for this, as does the snow if it’s winter time, or even wet grass. Do that 3 times in a row, then return to your shop/garage/carport/driveway/whatever.
- Refill the master cylinder again, and pressure bleed the brakes again, in the same order.
- If your brakes are still spongy, go do the ABS stops again, and bleed the brakes again.
Now, after we bled the ABS using the scan tool, we still had a very spongy brake pedal, and a lot of air in the front lines.
What worked best for us, was to have the truck running and the master cylinder cap removed. We then bled the brakes as the above procedure stated and ended up with a firm brake pedal and no MILs (Malfunction Indicator Lamps) after over an hour (total time including ABS bleeding). You can imagine how great my right leg/hip felt the next day.
Now, I’ll “brake” down…get it, BRAKE instead of BREAK…
…how to manually (pressure) bleed your brakes:
First, start by making sure your master cylinder reservoir is full of brake fluid.
In the interest of not making a mess, you can get yourself a neat little bleeding tool like this:
The hose fits onto the bleeder screw so that the brake fluid that comes out will go into that reservoir and not on your driveway/garage floor.
Have a friend/neighbor/spouse/sibling/offspring (someone that reach and depress the brake pedal) sit in the car.
You’ll want to start at the wheel furthest away from the master cylinder, which will be the right (passenger) rear.
Have whomever is in the car press and hold the brake pedal, then open your bleeder screw (either on the brake caliper for disc brakes or behind your wheel cylinder for drum brakes) until the pedal is all the way to the floor, then close the bleeder screw.
Have them pump the brake pedal back up three times, and hold it down as you open the bleeder screw again. Do this until you see a steady stream of brake fluid with no bubbles/foam in it.
Repeat the process for the remaining wheels in this order: left rear, right front, left front.
Note: It’s a good idea to randomly check the fluid level in your master cylinder reservoir as to not let it go below the “MIN” (minimum) line, because you could then introduce air into the system, negating everything you’ve been trying to do thus far.
All said and done, you now have a nice, firm brake pedal that doesn’t fade away when you hold pressure on the pedal. If the pedal fades off, you’ve got a leak somewhere. If the pedal doesn’t get firm, there’s still air in the system or you may have a bad master cylinder.