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New brake pads install but car barely brakes. Why?

Hi. I own a 1989 Honda Prelude 2.0 Si (automatic). In my car’s dash board the “lamp brake” turned on and its been like that for a few months now. So today I changed the brakes and installed brand new brake pads for front and rear. But now the brake pedal sInks in too much and the car barely brakes. I try flushing out the brake fluid for a bit and still the car won’t brake much and the brake pedal goes in too far. What can I do to fix this major problem???

If you have rear disc brakes, you probably have spin-back calipers. Did you spin the piston into the caliper, or force it in without spinning it (if not, damage to the calipers is likely)? Did you ensure the pin on the rear pads was aligned with the notch on the piston? Did you adjust the rear calipers after installing the pads? This is done by actuating the parking brake mechanism at each caliper until it will allow the pads to compress with minimal movement of the actuating arm.

Also, if your brake light is still on, your proportioning valve may be stuck, which would make bleeding the brakes successfully impossible.

Hmm yeah I did aligned the pin with the notch on the rear pistons…but I will now try the actuating the parking brake part. This part i did not know about. And once my mechanic has some free time i’ll ask him to check the proportioning valve for me. Thank you very much for your help and information mark9207. I will look into this answer tomorrow!!

When you replace old pads with new ones you lose braking power if you didn’t smooth out the current rotors or replace the rotors with new ones. Reason, the old pads left grooves in the rotors and the new pads are smooth. It takes time for the new pads to “wear in” and you will have poor braking performance until it happens.

In this case it seems you also have hydralic problems too. It might be the master cylinder at this point that is failing. The piston seals in the master could be moving over areas where some dirt “ridge” accumulated and now the master isn’t building and holding pressure when you hit the brake petal. This can happen in a pro brake job, but is even more common on a DIY job.

I second UncleTurbo on it being a bad master cylinder. If you pump up the brake, then keep firm pressure on the brake, and if the peddle slowly sinks it is either the master cylinder or a hydraulic leak.

Along with those good suggestions, if it ends up being the master cylinder, be sure to bench bleed it before installation (google that procedure). It is nearly impossible to get all the air out if you don’t.

Since it is a 1989 model, a weak master cylinder is entirely possible. However, if the brake lines are not properly bled, there could be air left in the system that causes a spongy or very soft pedal.