Maxima rear brakes and 280zx MC

[383 260z]

So i recently finished my brake upgrade, i converted the rears to maxima brakes,and installed a brand new 280zx MC and 280z brake booster, i do have low vacuum at idle (10 inches) , its a 383 SBC. My brakes go all the way to the floor, and the stopping power really is not that great. Ive bled the brakes with the car running above idle so it exceeded the needed vacuum for power brakes and bles them with the car off. I never changed or removed the proportioning valve. 

 

Any suggestions??

[LLave]

Did you bench bleed the master cylinder? Air bubbles can be really difficult to get out if you don't bench bleed. 

 

Have you checked for vacuum leaks at the booster? Sounds like you may also have a leak, or a bad booster. 

 

Also, check the booster / reaction disc. It may be that the disc fell out. 

[Miles]

Does the pedal have long travel and the the brakes come on suddenly?

 

Did you adjust the booster push rod that pushes on the MC piston?  If it is too short you will have a long pedal. If it is too long it will cause the brakes to lock up after a few pumps of the pedal.

 

Suggest you research the following HybridZ topics before doing anything more:

 

• Booster reaction disk falling out. There is a specific write up on the in the brake or FAQ sections. It is under (next to) your post in the brake FAQ.
• How to bench bleed  a master cylinder.
• Brake booster push rod adjustment.

Edited July 6, 2018 by Miles

[NewZed]

2 hours ago, 383 260z said:

 rears to maxima brakes,

 

It's very often the bleed valve orientation.  A bad booster won't cause the pedal to go to the floor.  You either have bad seals in the MC, air in the hydraulic lines, or a mechanical misadjustment.

 

The standard test for air in the lines is to see if the pedal will "pump up".  Pump the pedal quickly several times and see if the pedal gets higher.

[Miles]

35 minutes ago, NewZed said:

 

It's very often the bleed valve orientation.  A bad booster won't cause the pedal to go to the floor.  You either have bad seals in the MC, air in the hydraulic lines, or a mechanical misadjustment.

 

The standard test for air in the lines is to see if the pedal will "pump up".  Pump the pedal quickly several times and see if the pedal gets higher.

 

On Maxima and 240SX calipers you have to make sure that the bleed valves are pointing straight up to get all of the air out. You can unbolt one side of the caliper and point the bleeder up. You must block the pistons from moving or you will blow them out of the cylinders when you step on the brake.

[383 260z]

Thank you everybody for your input.

 

So im thinking its the pushrod,i never did adjust it.

 

I did bench bleed the MC. And i re-bled the system again yesterday and got quite a bit of air out . the pedal is very long,and it only just starts to kind of stop at like 1/2- 3/4 the way down. 

 

Most of the time i can get the pedal to get firm when bleeding but when I add vacuum to the system the pedal goes all the way. Im going to pull the booster, and check the rod/reaction disc! 

[NewZed]

First glance says that you have a bad MC.  You'll get a firm pedal at first then the pedal drops when pressure blows fluid past a bad seal.  The booster gives that extra force to blow the seal.

 

Edit - I wrote something about how "new" reman's are often bad out of the box but it didn't get through for some reason.  Weird.  Anyway, there it is.  "New" doesn't mean good.

Edited July 8, 2018 by NewZed