Soft Pedal, suspect rear drums

[DaveR]

In my car I can push the brake pedal about 1/3 to 1/2 of the way down before much of anything happens, at that point the brakes feel pretty normal and behave well and predictable (in my limited experience). I am trying to figure out if and why I should have such a gap in the pedal travel before the business starts to happen. I suspect the rear drums and their adjustment.

Here is some backstory:

1971 240z

New:
master cylinder
rear cylinders
front caliper/pads
Rear hardware

Old:
Rear aluminum drums
rear shoes

Master Cylinder was successfully and convincingly bench bled. Pedal Push rod and slop are adjusted and minimal. The moment you push the brake pedal the MC starts to actuate.

All corners fully bleed. (pushed a ton of liquid through it)   Order followed   Driver rear, pass rear, pass front, driver front.

Master cylinder is aftermarket (Sanyco)  Front/Rear circuits successfully swapped. Front circuit now closest to the firewall.   Both outlet ports of the MC have Residual pressure valves. I have no idea of what Value (I know ideally front should have 2psi and rear should have ~10psi)

So I believe the problem is in the rear corners. Here are some things that worry me:

E-Brake grabs, but fairly high in the travel. I know I have not properly adjusted the rear shoes outward far enough.
This car sat for 30 years (in storage but still) so the rear drum surface is far from pristine.  I have not turned them and had a fresh surface exposed yet. I need to check the material and see if there is enough.

Rear shoes should be fine, but may be grooved to match their drums over time.

 

So I'm fairly certain its a matter of adjusting the rear click wheels, but its a hard thing to do. This problem is made worse by my not perfect rear drums that give uneven wear surfaces and make it hard to evenly adjust the cylinders. I tried to do some reverse E-brake yanks to try and get the self adjuster to work but didn't have luck.

I was considering maybe pulling the E-brake to about halfway up and adjusting the cylinders until they are very tight, and the backing the E-brake off.

I drove around a bit with the E-brake at like halfway up in and attempt to try and wear down the drum surfaces and smooth things out, but I haven't inspected yet.

Any tips would be very welcome. Next step is to pop the drums back off and check how much material is left and maybe try to tighten them back up. Very hard to figure out a good way to adjust them.

Thanks

Edited May 15, 2017 by DaveR

[Zed Head]

You should differentiate between air in the system or system needing adjustment.  Pump the pedal.  If it gets higher and harder, there's still air in the system.

The rear cylinders are so small that it's more likely that there's air in the front calipers, if you're getting 1/3 to 1/2 travel before contact.  Calipers installed on the wrong sides is the common source of the problem.  The bleed screw ends up on the bottom.  They're interchangeable, left and right.

And your e-brake is a good indicator of where the brake shoes are.  If they contact within about 6 clicks, they can't be adjust much tighter.  If you're making contact at 1/2 way on the handle, odds are it's air.  Volume doesn't get rid of air during bleeding, where the bubble sits is what does it.

[DaveR]

Okay did a little more troubleshooting.

First off, the movement of the brake pedal. It moves the first 1/4" pretty easily, and the next 1 inch with some resistance but not a ton. After that its very firm.  Pumping the brakes does nothing to stiffen it up, its always the same.

Front calipers are installed correctly with bleeder up. 

When I bled the system bubbles did finally make there way through originally. Besides in the calipers or the MC I'm not sure where bubbles could reside. But given what I wrote about the pedal I think i'm probably pretty okay as is. I think I was overstating how much the pedal moved softly, I was surprised the measurements were relatively short at 1" before it was very firm.

Other info:

The rear drums aren't great, but they aren't too too bad for now. Def out of spec but maybe the shoes will even them out. If i get vibration back there under braking then i'll know.

Tightened up the rear drums a bit more. Now with 3 clicks on the E-brake the wheels are hard to turn.  4 clicks I can't spin them by hand with the wheel on.  With the E Brake off I can get about a 1/4 rotation before they stop on their own. I'll give it a shot like it is.

[Zed Head]

4 hours ago, DaveR said:

1971 240z

New:
master cylinder

Could be that the rod from the booster just needs to be extended.  Too much play between the booster rod and the MC seat.  Not sure why it would change but you never know with aftermarket parts.  If it was good before and all you changed was the MC that would be where "new" play could be introduced.  If the car is new to you it might be that there's extra play between the pedal and the booster.  If the air is out and the parking brake is tight then mechanical play is the place to focus.  Get rid of the play.  You might even gain some benefit just by adjusting the pedal stop, but there are several adjustment points in the train.

Use the 72 FSM, it's easier than 71.

http://www.classiczcars.com/files/category/11-240z/

 

 

[DaveR]

The master cylinder was new as of last year, but I have always had this issue.  I have adjusted the pedal stop and accounted for slack in the pedal clevis hole, and also the booster rod and MC seat is perfectly adjusted. Went to great lengths to get the rod properly set. It had to adjust quite a bit. I know for a fact that the moment you touch the pedal you move the push rod on the brake booster, and that is basically flush or a hair off the MC piston surface. Did a test with the MC unbolted and someone feathering the pedal and watching the MC push off the mounting flange.

I have been working off the FSM, but again something isn't adding up. I'm thinking that the 1" before the super firm pedal may just be typical operation? I've never really ridden in a car where the moment you touched the brake pedal it was super firm... At least not a car with a brake booster.

Edited May 15, 2017 by DaveR

[Hardway]

I've been working on my rear brakes lately as I replaced my rear wheel cylinders.  The rear shoes should be adjusted where they are just lightly dragging on the drums.  Based on your description it sounds like you have them set this way.  The rears can hide air since the path to them is longer and the wheel cylinders are one of the lowest brake components on the car.  When you drive the car, get up to a reasonable speed and hit the brakes quick, does the nose dive hard or does it stay pretty level with only a slight dip at the nose?  How are you bleeding your brakes - 2 person method: one person pumping the pedal up and you opening the bleeder screw while they hold pressure, 1 person method: a bottle filled with brake fluid with a tube, pressured machine, or Mity-Vac?   The order in which you are bleeding your brakes may be effecting the perfomance, you should always start with the wheel farthest from the MC.  Passenger rear, Driver rear, passenger front, driver front.  Your original post has you starting with the driver side rear.  When you say your rear brakes are out of spec, does that mean the drum is turned beyond spec?  I don't think this would be contributing to your soft pedal but long term it needs to be replaced if that is the case. 

[DaveR]

Your bleed order is different than I did, so maybe I read it wrong when I looked last.  I am doing 2 person method. I did many many pumps to the rear drums and know i cleared it all out because the bubbles from the MC install made their way through.

The car does not nose dive during braking, but I will double check soon and test my further adjusted wheel cylinders.

I am starting to suspect the drums/rotors being out of spec. The rear drums are definitely out of round and not helping things. They are close to the max allowable diameter so I will probably replace them anyway. I'll do the rotors at the front as well because why not. I have a dial caliper so I may measure for grins, but I imagine I will replace them no matter what.

So yea, next step is to replace those components and see. I'm still pretty keen that its not air in the lines from the bleed operation... but I can't 100% rule it out jussst yet.  Maybe I'll rebleed the drivers rear again to correct my order just in case.

[Mark Maras]

 Do you feel a pulsation in the pedal? You might also try easing the E. brake on while driving to try to detect a pulsation in the E. brake handle. It's also possible that the return springs on the rear brakes are weak and not pulling the shoes all the way back, allowing them to drag. VOE on my 71 621 pick-up.

[Zed Head]

12 hours ago, DaveR said:

I'm thinking that the 1" before the super firm pedal may just be typical operation? I've never really ridden in a car where the moment you touched the brake pedal it was super firm... At least not a car with a brake booster.

How about the reaction disc?  It's purpose is to allow a gradual application of force.  Maybe the sharp contrast is what really bothers you, not the one inch.

You could go to the other end of the adjustment problem and run the booster rod out so far that the brakes build pressure from heat and fluid expansion and lock up because the return hole is closed.  Then back it off from that point.

 

[DaveR]

Nothing about the braking actually bothers me. This was until a fellow long time Z enthusiast drove it last year and commented that the pedal was spongey and dangerous, but I never felt that way prior to him saying that. I figured he knew what Z's should feel like and maybe this was contrary to what I felt was typical brake pedal operation.

Your comment about the reaction disc is actually something I hadn't thought about, and I would imagine its there and doing its job properly in this case. It really may be operating properly and I am just over analyzing it.  That said the  drums and rotors surely still need replacing.

Pedal pulsing isn't bad.  I actually rode a bit with the e-brake partially engaged to try and smooth out the contact surface on the drum.  Return springs on the shoes are new so I think that's in decent shape.

For now don't rack your brains any more unless you enjoy doing it, I'll scope out a few more things and hopefully get some more clear direction.

[Zed Head]

Other areas where you can get play are the shims behind the pads.  If they're bent they'll need to be compressed before you get solid braking action.  The bends will push the pistons back in to the calipers when pressure's off the problem won't fix itself.

If you get new shoes beware that some  shoes seem to be designed for oversize drums.  Mine only contacted on the edges until they wore in because the diameter was too large for the drums.

Have fun, good luck.

[grannyknot]

The D/S rear brake is actually the farthest from the M/C so you did bleed it in the proper order, also you could try the trick of giving the calipers a sharp rap with hard plastic faced hammer just before bleeding, it will help release those tiny bubbles that cling to the walls.