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  • 99 300M low brake pedal

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 #288934  by skywarp
I am working on my Sisters 1999 300M, that my Mother purchased in 2001 with 34000 miles. The car has just turned 120,000 miles and I just did a Timing belt, tensioner, water pump, and dropped the trans pan and installed a new filter. When I drove the car for the first time since 2010 it seemed like the pedal went way to far down. At a stop light, I could not get my left foot under the pedal and if I pressed down even more it would go completely to the floor. So I bleed the brakes at all four wheels and it made no difference. At this point I decided to replace the master cylinder. I purchased a A1 Cardone new master cylinder complete with reservoir at Advance Auto Parts. The master cylinder came with a bench bleed kit and that was used to bleed the master cylinder before installing on the car. The original master cylinder was rusted onto the power brake booster as it had been leaking out the rear and was stuck on there pretty good. Once the new brake booster was installed, I bleed the two brake lines at the master cylinder by cracking them open then depressing the brake pedal to the floor then tightening the lines. I did this about three times to get the air out of the lines. Then I bleed the brakes at all four wheels. I still seem to think the pedal is too low and sort of spongy. Anybody have any advice on bleeding the 300M brakes? Can you get your left foot under the brake pedal at a stoplight? Is this normal?
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 #288948  by 300maximilien
A few have experienced this and there is an adjustment to the booster that can be made (should have had notes on the tag).
 #288980  by skywarp
Since the car has been in the family since 2001, I am quite certain that the booster is still original. I don't see how it got out of adjustment. I am thinking that maybe the bad master cylinder, which was leaking out the rear, was sucking air and there is a still more trapped in the lines and or ABS unit. I drove the car on some wet payment and got the ABS to come on. Then I bleed the brakes again and got some more air out. I was bleeding in this order: RR, LR, RF, and then LF brake. Somebody on the forum said it should be LR, RF, RR and then LF as per the FSM. I could not find that information in the 2000 300M, LHS, Concord and Intrepid electronic service manual that I have in .pdf format. How far does your pedal go down while applying the brake?
300maximilien wrote:A few have experienced this and there is an adjustment to the booster that can be made (should have had notes on the tag).
 #337933  by skywarp
I am resurrecting my original post.

I own the car now, car sat for the entire 2013 year. I have done the following in this order since acquiring the car:

Replaced all brake pads and rotors.
Replaced the A1 Cardone Master Cylinder with a warranty exchange. I also purchased a rebuilt vacuum booster and adjusted the pushrod length within 0.012 of an inch from touching the master cylinder piston.

Master Cylinder was bled with A1 Cardone brand syringe bleeder to pump fluid into port for a reverse bleed. They recommend this instead of traditional clear vinyl hose from ports to reservoir.

Used Motive Products power bleeder with correct master cylinder cap attachment. Bled brakes in LR, RF, RR and LF order.

Still had issue of low pedal.

Checked accumulator leakage on ABS HCU with dial indicator and had no movement when applying the brake.
Remember the car has no ABS codes or light on( tested with Innova 3160 scanner if it can be trusted).

Installed some plugs into the master cylinder ports to isolate the master cylinder. This created a rock hard pedal and super high pedal as well with engine off or running. At the time, I thought this proved the master cylinder good.

Tested one port on the master cylinder at a time: Left one port plugged and hooked up one brake line to master cylinder and had low pedal. Reversed this and swapped plug and hooked other port. I still had low pedal, so could not isolate it down to one circuit.

Hooked up both lines back onto master cylinder and power bled lines.

Bought some speed bleeders for the front calibers and hooked up to bleed bottles to the bleeders. Raised car on jack stands and cracked open both bleeder and pumped pedal to verify function. Started car and put into gear. Front wheels start to turn and traction control kicks in and ABS unit starts pumping. (My shadetree mechanics ABS brake bleed) Pedal was no better after.

I decide to pinch off front brake lines one at a time and this does help raise the pedal. So I ended up buying both front calipers and two front brake lines.

After all of this, I still am not satisfied with the brake pedal. I go back and put plugs in the master cylinder and the pedal is not hard like first time I did this test. Feels like the pedal keeps dropping. I remove master cylinder and it is wet at the rear piston. I get another warranty replacement and this time did a traditional bench bleed in a vice with hoses hooked up to ports and I pump the piston by hand with a wooden dowel until there are no bubbles.

Power bleed again and I am driving the car but pedal is still too low. My neighbor has a 2001 300M and at a stop light with my right foot on the pedal I can stick my left foot under the brake pedal and raise it up and down. In my 1999 300M the brake pedal is pressing on my left foot and it cannot move.

With the engine running you can press brake all the way to the floor if you try hard enough. With engine off the pedal is hard way before that and it will not go down any further. My mother bought the car 2 years old in 2001 with 24,000 miles on it. I am 99.9% sure the brakes were not like this back then. Unfortunately, I haven't driven the car much in the last eight years to have a feeling on how it was.
 #387871  by 58Desoto
I know this is an old post but I have the very same problem in my 1999 300m with 56k miles . What did you find to be the fix ?