Soft brake pedal

[Macklen]

Hello.

I recently started working on a truck that had been sitting for a couple of years.

I noticed the brake pedal went almost to the bottom, gotta pump it once or twice for it to get firm with the motor running.

Front pads are good, I replaced both rear drums and shoes, bled the system and it keeps doing the same.

Pedal goes too far at first, then after one or two pumps it gets fine.

It can be driven like this, but I know it's not safe, I don't think it would stop right away if I gotta brake suddenly.

What else should I look into?

Bleed again? Booster issues?

 

Thanks.

[banzai510(hainz)]

I assume the rear brakes adjust and are tight.

 

I got a toyota pick up the the MC was bad. the from your rear cyl in the maser was bad and I really only had the fromt or rear brakes working right.

 

Most likely the rear wasnt working good enough.  A guy mech told me the diaphrame wasnt holding the pressure and bleed into the other side. Thus NO leaks .

 

this is my best guess. but not a 720 expert as thery have a NLV system or soemthing like that also i think

[datzenmike]

If the booster was not working the pedal would feel like a brick was under it. The booster reduces pedal pressure. Stops faster with less effort.

 

Half way through the '81 model year the 720 switched to self adjusting brakes so continued depression of the brake pedal would have ratcheted these close enough.

 

I would suggest loosening the emergency brake cable before bleeding, then reset the cable.

 

Did you bleed the NLSV (Nissan load sensing valve) ??? It's mounted on the inside of the right frame rail under the passenger seat. The procedure is to bleed this first, then the rears then the fronts.

[Macklen]

I did not bleed that valve, I wasn't aware of it till now.

I'll do that next, thanks for the advice.

[datzenmike]

The NLSV is mounted tilting up at the front slightly. Inside is a steel ball and spring that rolls forward and 'up hill' and blocks excessive brake pressure to the rear brakes. As the truck is loaded, the back end sinks increasing the upward tilt limiting the ball's travel and allowing more brake pressure to the rears. A heavier load also increases the traction of the rear tires so they can brake harder now with less chance of lock up.