95 lesabre brake trouble.

I have a 95 lesabre that has a brake pedal i can't live with. In the morning or after a long wait the pedal, car off, will slowly go to the floor. After a pump I get some pedal. good firm pedal. sStart he car and the pedal goes way down. Almost to floor. I replaced the master cylinder. Bled the brakes numerous times. before and after the master cylinder replacement. Seems slightly better after the $50 master cylinder. Just very frustating. Any help will be appreciated. It is an ABS vehicle.

Hold the pedal down and start the car. If the pedal drops it shows the booster is working. I'd still check the vaccuum source and hoses. Make sure the bottom of the booster isn't wet. Was the old master wet on the rear where it goes into the booster? Does this car have rear drum brakes? If so the rear brakes might be way out of adjustment. Did you bleed them in the proper order?

booster was dry. the rear drum brakes were slightly out of adjustment. adjusted them. I did bleed inorder of rr,lr.rf,lf. I'm just thinking i have a lot of air in the system. Seems like I never have a great deal of luck bleedig brakes.

Have you tried a vacuum pump, such as "Mighty Vac" for bleeding? Vacuum bleeding works much better than the traditional peddle pump.

A bad brake booster won't make the pedal sink to the floor, it will just make the pedal effort really hard. If pumping the pedal several times temporarily restores the pedal feel, it's my guess that the replacement master cylinder is bad. Did you use an ACDelco master cylinder? Rockauto's ACDelco master cylinder is $80. $50 doesn't sound like the cheapest one, but perhaps not the best one either. I'm not a mechanic so I cannot judge the quality of the different brands, but I've had enough trouble with aftermarket stuff that I generally get OEM stuff now.

I went to harbor frieght and got a vacuum bleed kit. So I'm going to keep at it. guess I better get more fluid also. The master cylinder came from advance auto, and probably was the cheapest. Does anyone know if the ABS pump can cause trouble without an ABS light?

If you got air in the abs unit you will need a bidirectional high line scanner to bleed the abs.

I just bought a 95 lesabre with exact same issue... I haven't had time to check it out yet, but was wandering if you ever fixed your problem...