Brakes: second pump squishy, thrid OK

[xferboy]

I haven't started digging into this yet, I'm putting out some feelers from people with more experience that I have on this than I.  Winter is coming to an end and this will probably the first thing I want to address.

 

My searching has not found anything similar (doesn't mean I didn't miss it, or used the wrong terms)

 

Symptom: When coming to a stop, if I lift off the brakes, and re-apply the pedal travels about 50% further than the first application.  It doesn't go to the floor, and the brakes are solid, there is just more pedal travel.  If I lift and re-apply the pedal travel is normal (high).

 

This feature is pretty repeatable.  If I don't re-apply the brakes, the symptoms will re-appear at the next stop.  If I stop in one pedal application, the next stop is normal height.

 

I've bleed the brakes multiple ways (pressure, vacuum, second person helping) and believe that is OK.  There is fresh brake fluid (several times over the years)

most hydraulic components at the wheels have been replaced (calipers, slaves, hoses, but not hard lines)

 

I haven't dug deeply into anything under the hood yet (master cylinder, booster or vacuum line). There are no leaks I can see.

 

Thoughts on what to check or more importantly whats going on?  First I'll check to make sure the vacuum line/valve to the booster isn't partially blocked or leaking.  I'm really hoping its not the master cylinder  or booster, since they are rather expensive.

 

Thanks for reading.

 

Allan

 

[ray_]

Adjust the shoes.

 

Good luck,

[halboyles]

It sounds like you do have a leaking MC.  Has the brake fluid gone down but there was no apparent leakage?  If so, the fluid is leaking into the brake booster and is not a good scenario due to brake fluid's hydrophilic properties.

[xferboy]

I'll re-check the shoes.

 

No loss in fluid.  I haven't pulled the master to see if there is any fluid in the booster.  I hope not, because that sounds like replacing both parts....

 

Oh yeah, it's a tii, so all the parts are 3x non-tii (ti?) parts...

 

 

[halboyles]

Even with no loss of fluid in the reservoir, the MC could have one or both internal seals leaking so that the liquid sometimes just squishes back and forth inside the cylinder.  And yet it works off and on.  

[Mike Self]

Also make sure you don't have a vacuum leak either in the booster or in the hoses connecting booster to manifold.  The short hose between the one-way valve (also worth checking) and manifold is especially prone to cracking as it's constantly bent, and wants to be straight.  Replace with a pre-bent hose meant for an E21 320.

 

mike

[PaulTWinterton]

10 hours ago, halboyles said:

Even with no loss of fluid in the reservoir, the MC could have one or both internal seals leaking so that the liquid sometimes just squishes back and forth inside the cylinder.  And yet it works off and on.  

 

+1

MC is not too expensive and if you have caught it in time, you can clean out your booster.

Sounds like it's time to do a peddle box RE&RE.  Very rewarding.