I have a 91 Maxima SE with 75k easy miles on it, bought new.
I have been havinr brake problems. I just put a new master cylinder, bled & flushed all lines really good. I put dealer purchased rear pads in, fronts 2/3 like left. Flexible lines all look good-no cracks, leaks etc.

The pedal is nice and firm with very little travel when the car is off. When I start it I get alot of pedal travel and a mushy pedal. What's up here???

(the rear pads were a headache- I had no anti-squeel shims to reinstall and the 'nub' that centers or locates the shim on the inboard pad back was interfering with the caliper piston..I had to adjust the piston perfectly vertical so that the slots were in a clocklike 12-3-6-9 pattern - so that the 6 oclock slot fit the nub on the pad back. Strange.)

Any thought fellas??

 

well, your car isnt on therefore, you dont have any power going to your brakes, thus you cant push em in...when the car is on, you can push all the way down...something to that affect?

 

Jamsan is correct. It's called a brake booster. You have no power assist when your car is off. Once the engine is runnig, the vacuume boost assists you while you push the pedal down. Always "feel" your brakes while the engine is running. This is how they feel when you drive as well.

Is your mushy pedal bad enough to indicate a problem? Or are you just feeling the difference? Your a 91, the rubber lines may look good, but there 12 years old now. Might want to look into replacing them is you can't get a nice firm pedal back.

 

Yeah, I suspected those flexible lines. I have stainless stell/kevlar lines in my 944 and the pedal is rock hard (with all other compenents being refreshed as well)

Do you think I have a bad vacuum check valve or something else wrong with the booster?

 

You should hold some vacuum after the engine is off. Maybe one or two pushes of the pedal, then it's hard again. If thats the case your booster and check valve are ok.

 

When I rpelaced my brake lines with SS on my 98, the brake feel went from somewhat mushy to straight solid. Do the SS upgrade, your brakes will love you for it

DW