Brake issues on the e21

So, getting back to the old beast, flushed fluid, bled brakes, and they're still not what I perceive they should be. 

The pads and shoes are "new" so my pedal action should engage right at the top, but it doesn't.

In fact pedal feels a little worse than it did before I'd changed pads/shoes and MC, and it  definitely needed front pads when I did it. 

Thinking about it, old shoes were hardly worn when replaced (not unusual, I know...). 

So, is it that maybe the MC needs bled again?  Or would the recent flush and bleed have cured that?

Maybe a bad check valve for the front/ rear split? Would that lead to a pedal softness issue?

Feels marginally better if I double tap the brake pedal before full application.

It should just be better than it is, and it drives me bananas. 

What other things can I do/check to get the pedal feel firm at the top of engagement?

how old was the fluid you used when you bled it?

stuff has a poor shelf life

when you say "shoes" i imagine rear drums, is that correct?   if so, please adjust the rear shoes so that they lightly drag on the drum.

Yeah, if the rears aren't adjusted you'll never get good pedal feel.

If the flexible lines are old they might be part of the problem as well.

Lines in good shape, shoes well adjusted, fluid new in the last 4 months...

How did you bleed? Pressure? Pedal pump? Gravity?

In reply to 02Pilot :

Pedal. 

HOWEVER. 

This doesn't seem right to me:  I noticed tonight while driving, well, at a stop light, that tapping the brake pedal that it would put air in the manifold and my rpm crept up!

Wed. Thu. Fri.!!!

So did it at next stop light, same thing, bumps rpm up 5-800!

So, while I thought I had the vacuum check valve pointed the right way between the manifold and brake booster, either I don't, or that thing is defective, yes?

Seems to me that bumping the brake pedal shouldn't push air in to the manifold...

Yes, the check valve is not working properly.

I'd suggest you rebleed the system. My preference is for pressure bleeding, but gravity works well too (but takes time). I'm always a little leery of using the pedal pump method on anything but a brand new M/C for fear of damaging the seals. And don't get me started on the frustrations of vacuum bleeders.

How old are the flexible lines in the system?

Pull the handbrake on, then step on the brake.  Pedal better?  Adjustment is out.  Are the drums worn or cut oversized?  Shoes will need to wear in.

Engine revving up when stepping on the pedal is a bit normal, but 800 rpm is too much.  That sounds like a leaky booster sending too much air.  Check valve in backwards will just make no power assist.

Did you replace or machine the rotors for the new pads?  If the old rotors are worn concave across the face, the pads will only touch on the edges, 

Gravity bleed each bleeder for a minute or so.

Last, are you one of those guys that:. A- stands on the pedal with all his might with the car stopped, hoping for a rock hard pedal?  Stop that.

Or B: you are one of those guys that think Germans can build functional drum brakes?

In reply to Streetwiseguy :

New rotors, I remember for sure, but I don't recall on the drums - which probably means I turned them - which would have been colossally stupid even then....

Rear brake adjustment is right there, no issues with that. 

 Please, 'splain "leaky booster" - that has me a bit puzzled!

Oh, and damned Germans couldn't have at least done like Datsun and had nice finned   aluminum drums?  

Criminy, for what the damned thing cost new, it should've had 4 wheel disc anyway...  grumblegrumblegrumble.....

Streetwiseguy is totally correct that big idle fluctuations would not be caused by a bad check valve - I wasn't thinking too clearly, apparently.

Think about how the system works. Intake provides vacuum to the booster, so it pulls air from the booster; the check valve is there to maintain the vacuum in the booster regardless of fluctuations in the manifold.

The booster is supposed to be sealed. If the diaphragm is ruptured or the case seal failed, vacuum will not be maintained. If it's the former, pressing on the brakes moves the rod that passes through the booster, likely expanding the leaking area and allowing air to dump into the intake, hence the idle change.

This is relevant to my interests as I am dealing with the same problem right now on my mkii Focus with the same setup (rear drums). I'll start a new thread though :)

OldGray320i said:

In reply to 02Pilot :

Pedal. 

HOWEVER. 

This doesn't seem right to me:  I noticed tonight while driving, well, at a stop light, that tapping the brake pedal that it would put air in the manifold and my rpm crept up!

Wed. Thu. Fri.!!!

So did it at next stop light, same thing, bumps rpm up 5-800!

So, while I thought I had the vacuum check valve pointed the right way between the manifold and brake booster, either I don't, or that thing is defective, yes?

Seems to me that bumping the brake pedal shouldn't push air in to the manifold...

Sure it does.  When you have the brakes not applied, there is vacuum on both sides of the can.  When you apply the brakes, air is allowed into the pedal side, and the pressure difference helps push the master cylinder.  When you lift off the brakes, the two sides of the diaphragm are allowed to equalize again - meaning, air goes from the booster into the engine.

Anyway, as a rule, new pads and new shoes will feel like crap until they bed in.

In reply to 02Pilot :

If there's a leak inside the booster/diaphragm/rod seal, wouldn't all vacuum go away?

In reply to Knurled;

 Similar to above, except/and the rpm rises when pedal is depressed - letting off the pedal sometimes decreases rpm slightly, sometimes not. 

I'll do some more trouble shooting tomorrow, check for vacuum leaks (generally and specific to booster hose).

Since the booster runs off vacuum, and I'm getting more pedal softness than I expect, I must be pulling air in to the system somewhere. 

The clutch line may be a weak spot, and I'll see if any of the brake lines are a little lose or leaking. 

When I swapped wheels I didn't see anything leaking fluid, but I'll look at the upper/inner attachment points, as well. 

OldGray320i said:

In reply to 02Pilot :

If there's a leak inside the booster/diaphragm/rod seal, wouldn't all vacuum go away?

Not if it's only opening up when you press the pedal. If you have a vacuum pump with a gauge you can attach it to the booster and see if it holds vacuum.

The booster runs off vacuum.  If it leaks too much, your pedal will be harder than normal.  A soft pedal will have absolutely nothing to do with the brake booster.  Move on.

In reply to OldGray320i :

The booster won't make the pedal feel soft.  They generally fail in the "no assist" direction, although I have had them fail in the "applies brakes all the time" direction.  Either way, it won't cause a low or soft pedal.