Soft Brake Pedal on new brakes

[Miles]

Just finished complete 100% rebuild of front and rear brakes on a 72 240Z including a new master cylinder using all stock parts. Noted that brake pedal was soft with original old brake parts.

 

The pedal is still soft with all new parts. I know the pads and shoes will have a springy feel for a few hundred miles.

 

I bench bled the MC. I have checked all connections for leaks and found none. The pedal is still soft and pumping does not stiffen the pedal up. Perhaps I did not bench bleed the MC correctly. What is the procedure to bench bleed the MC?

 

Thanks

 

Miles

[Guest jwelch]

Hi Miles;

 

Do a search on "Bench Bleeding" in the this forum. I found 4 matches that had info in them. Good Luck.

Regards,

[Dave]

Hi Miles,

A couple months ago I upgraded to the 15/16" master Cylinder in my 71Z.

and could not get the pedal feel where I felt safe with it. I went back and

bleed the brakes again except this time I did it this way.

 

I used the master cylinder bleeder kit but fit the tubing over the bleeder

screws. Then I looped each short hose back into it’s own reserve bottle

with the end below the fluid level. I opened both front and rear bleeder

screws and slowly pumped the pedal to bleed the master and fill these

loops with fluid. I did this slowly so the fluid would not aerate. I let it sit

for a few minutes then did this again, this allows any bubbles to gather

together so they come out easier.

 

After this was done I started to bleed out the system. I closed the rear

bleed screw on the master, but left the front one open. This will allow

pressure to bleed the rear circuit, but leaving the front open will prevent

the pressure differential switch and proportioning valve from messing with

you. Normally when you are bleeding the rear circuit the front circuit will

be fighting you and you will not get a full pedal travel while bleeding.

 

I bleed the both rears and then swapped the master bleeders. This time I

closed the front bleeder and opened the rear bleeder. This will prevent

the rear circuit from building pressure while you bleed the front cylinders.

Now I bleed both front cylinders. After all this I had the pedal back where

it felt safe.

[Mike C]

In my experience, adjustment of the rear brakes on an early Z has a HUGE effect on pedal feel. You may have them bled perfectly, but will never get the pedal to firm up. Adjust your shoes out as far as you possibly can without any real drag as you rotate the drum and try that out.

[Guest Drewz]

The pedal feel is directly effected by the adjustment of the rear shoes on a rear drum front disc setup and it also effects the height of the brake pedal. Just a note here.....GM's manual states that with any major brake replacement that they suggest a minimum of 1 litre of brake fluid per wheel be bled out. I think that is extreme but after all it is your braking system.Also the front calipers are know to trap small amounts of air so I also do a gravity bleed and sometimes tap on the side of the calipers to release the trapped bubbles. My $0.02 here

[Guest kc6wfs]

I just did my MC and vacume booster today.

I bench bled mc by filling it and plunging till fluid comes out the bottom.

installed it and installed the 2 lines.

Bled the 2 valves front first then rear, then went to the rear disks and bled them 12 shots each.

refilling the resvor every 3 times.

 

Then did the fronts in the same maner.

 

Brake pettle now is nice with almost no travel!! feels great!

 

Dave

 

[Miles]

I bled the brakes on our72 V8 240Z using the above procedures, but the pedal is still spongy. Adjusting the rear brakes manually helped bring the pedal up, but I am having trouble getting the right and left sides adjusted evenly such that one wheel will lock up. I am going to back the adjusters out and readjust the shoes again.

 

Hard stops from 25-30 mph will not lock up the fronts only the rears. I assume this is partly due to the new pads or the proportioning valve.

 

My Haynes manual says that if you can't lock the front brakes at 30 mph the proportioning valve should be replaced. I note on my other stock 72 240z daily driver that I can not lock the fronts either. Is this normal for 240Zs? I am considering replacing the proportioning valve in the V8 Z with an adjustable unit from MSA or Summit, but don't have a clue how to connect it to the stock hard pipes. If someone has installed an adjustable proportioning valve in a 240Z I could use your input.

 

Thanks for all of your input. I'll just keep grinding away at this til I get it right. Hope to have the brakes resolved soon so we can make it to the next northern California (Rio Vista?) Hybrid meet in July.

 

Miles

[Guest Drewz]

If the brake pedal is fairly good than I would suggest a break in period for the front pads. This is done by 8 to 12 slow stops with moderate pedal pressure to preheat the pads and rotors. after that a few (4 to ???) harder stops with more pedal pressure to finish it off. Than return home to rebleed the fronts since it is obvious there is some air in there still. It may be the prop. valve too but if the brakes are safe enough to do some light driving I would break them in and rebleed to be sure there is no trapped pockets still there.Keep up the effort

[Miles]

Brakes are working. Put some city miles on them and they stiffened up. Bled them one more time and got a few bubbles out of the right front and right rear.

 

Now that the brakes are done we were finally able to open it up and experience the full potential of a V8 Z. What a ride!

 

Thanks again for your help.

 

Miles

[Guest Drewz]

Glad it all worked out for ya. Just keep an eye on the fluid and for leaks since this was a bit of a rough go it may not be over yet. Way to stick with it!!!