Soft brake pedal (BBK install)

[MildSeven]

Yes that needs to go to the rear brakes it prevents the shoes from retracting to far from the drums to reduce brake pedal travel, switching the lines will help your problem, 

 

Thanks. Does the e21 MC have it "built in" because the thread width/size on the low-pressure valve won't fit on the e21 MC?

 

I found it on the diagram...

https://www.realoem.com/bmw/enUS/showparts?id=1731-EUR---E21-BMW-318i&diagId=34_0195

 

Part # 34314650332

 

But seems like it's the same part as 2002 so i already have it, thus thread will be to big for MC

 

 

 

[Son of Marty]

Yeah the e21 had 2 sizes for some reason the part you may need 34311121798, but if you have one on the cyl you have that's for the rear brakes no need for one on the disc's

[MildSeven]

9 hours ago, Son of Marty said:

Yeah the e21 had 2 sizes for some reason the part you may need 34311121798, but if you have one on the cyl you have that's for the rear brakes no need for one on the disc's

 

Thanks again for you help!

 

There was no pre-pressure valve included on the e21 Master Cylinder + the one I had on my 2002 is a different size.

 

[Einspritz]

After all these machinations, it begs the question "how do you define soft?".

 

If you search, this is commonplace with owner's "upgrades" to a BBK, and incidentally the same as in the E30 (M3) community.

 

How far does the pedal go before you get resistance if any,and then do you get a firm pedal?

 

Is it sporadic?

 

What condition is your linkage in?

 

I ask because I have done a few simulations of these systems (no one but me cares) and the resulting effects, but lack hard dimensions to be certain. Many times it's the linkage slop from wear that manifests as a "Soft" pedal, or thinking that a larger diameter MC is "better" without looking at the effects of each of the components as a part of the whole system.

 

[MildSeven]

1 hour ago, Einspritz said:

After all these machinations, it begs the question "how do you define soft?".

 

If you search, this is commonplace with owner's "upgrades" to a BBK, and incidentally the same as in the E30 (M3) community.

 

How far does the pedal go before you get resistance if any,and then do you get a firm pedal?

 

Is it sporadic?

 

What condition is your linkage in?

 

I ask because I have done a few simulations of these systems (no one but me cares) and the resulting effects, but lack hard dimensions to be certain. Many times it's the linkage slop from wear that manifests as a "Soft" pedal, or thinking that a larger diameter MC is "better" without looking at the effects of each of the components as a part of the whole system.

 

 it's soft almost like it feels like it's not pushing anything. Not much resistance.

 

Before upgrade, pedal had a nice feel, brakes were applied pretty high up on pedal.

 

Sporadic... maybe 2% of the time, if i pump up it will firm up when the car is not in motion.

 

Linkage and everything was refreshed in 2016-17 using IE bushings, etc. never gave me a problem.

 

thanks

 

 

[Einspritz]

3 hours ago, MildSeven said:

Linkage and everything was refreshed in 2016-17 using IE bushings, etc. never gave me a problem.

 

Ok great. That eliminates one  source. So much of this diagnostic is not "what it is" but "what it is not".

 

The normal movement of the pedal linkage system when new or properly refurbished is about one pedal thickness before firmness.

 

Did you only change the MC and the front calipers? Are the calipers mounted with the bleeders UP? What condition are the hoses? Are there any kinks in the hard lines, e.g. at the strut when you bent them for the BBK?

 

As far as bench bleeding, I have never done it, just slow filling of the resivor, tapping to remove the bubbles.

 

An alternative to just the pump-hold-bleed, first try "back filling" wherein you attach your pressure bleeder to the bleed screw, open it under pressure, then observe if there are bubbles coming from the MC into the resivor. Do this for the rear and the front. It will take a while and remember to remove some fluid from the resivor so it doesn't overflow.

 

Check the operation of the booster vacuum valve and the hose connections. Sometimes they fail. If after running the engine, wait a few minutes, then you remove the hose between the valve and the booster; if you get a rush of air replacing the vacuum (in the booster) then all probability it is OK. IF there is no vacuum rush, then it is either the valve or the booster itself.

 

And finally, did you change the brand of brake fluid? Are you using RedLine or other similar? good old Castrol LMA is fine or ATE TYP 600.

[arminyack]

I have a similar problem with my car right now; the e21 MC worked fine for about 3 years...then the car came in to the garage for an engine swap, and the the brake system was dry for about 8 months. I upgraded my braking system from the old, remote booster system on the 1600-2 to the 02 style MC/booster assembly, the brake pedal goes to the floor....after bleeding everything (including bench bleeding the MC) Asking questions to various people has led me to believe the MC going dry for that time has ruined the seals, as the quality of the new e21 MC's are all over the place. I've ordered a new e21 ATE cylinder, and as I wait for it, I'm going to pull the newish MC off my Alfa Berlina, and see hos it goes with that. I know of a few people who have had bad e21 MC's when they were brand new!

[MildSeven]

17 hours ago, Einspritz said:

 

Ok great. That eliminates one  source. So much of this diagnostic is not "what it is" but "what it is not".

 

The normal movement of the pedal linkage system when new or properly refurbished is about one pedal thickness before firmness.

 

Did you only change the MC and the front calipers? Are the calipers mounted with the bleeders UP? What condition are the hoses? Are there any kinks in the hard lines, e.g. at the strut when you bent them for the BBK?

 

As far as bench bleeding, I have never done it, just slow filling of the resivor, tapping to remove the bubbles.

 

An alternative to just the pump-hold-bleed, first try "back filling" wherein you attach your pressure bleeder to the bleed screw, open it under pressure, then observe if there are bubbles coming from the MC into the resivor. Do this for the rear and the front. It will take a while and remember to remove some fluid from the resivor so it doesn't overflow.

 

Check the operation of the booster vacuum valve and the hose connections. Sometimes they fail. If after running the engine, wait a few minutes, then you remove the hose between the valve and the booster; if you get a rush of air replacing the vacuum (in the booster) then all probability it is OK. IF there is no vacuum rush, then it is either the valve or the booster itself.

 

And finally, did you change the brand of brake fluid? Are you using RedLine or other similar? good old Castrol LMA is fine or ATE TYP 600.

 

Lines look good, only changed MC and front calipers. also the hard lines on the struts are both no longer needed with the kit.

 

Last night, i bench bled the MC while it was in the car.what a mess, since fluid was already in it... (I should've pumped it out in retro-spec ;p)

 

i swapped the passenger front with rear line, since i messed that up, but didn't finish bleeding yet, wanted to wait for a partner.

 

16 hours ago, arminyack said:

I have a similar problem with my car right now; the e21 MC worked fine for about 3 years...then the car came in to the garage for an engine swap, and the the brake system was dry for about 8 months. I upgraded my braking system from the old, remote booster system on the 1600-2 to the 02 style MC/booster assembly, the brake pedal goes to the floor....after bleeding everything (including bench bleeding the MC) Asking questions to various people has led me to believe the MC going dry for that time has ruined the seals, as the quality of the new e21 MC's are all over the place. I've ordered a new e21 ATE cylinder, and as I wait for it, I'm going to pull the newish MC off my Alfa Berlina, and see hos it goes with that. I know of a few people who have had bad e21 MC's when they were brand new!

 

iiish... well if this doesn't work, I'll try my old 2002 MC with 2 ports plugged.

 

I follow your projects on IG btw

 

thanks everyone.

Anthony

[rcf925]

During my 68 restoration I switched over to E21 system, I just slightly opened bleeders on all four corners and let gravity do it's job, Tighened up bleeders when they were all dripping and had a nice pedal

 

[AustrianVespaGuy]

The classic symptom of a bad MC is the the pedal continuing to sink down under constant foot pressure.  Should be able to do this with the engine either on or off, but obviously a good bit more pedal pressure is needed when off to compensate for what the booster provides in order to get the same rate of 'sinkage.'  If this is the case, then yeah I'd probably try a different MC.

On the other hand air in the lines results in a spongy pedal that still firms up once all the air is compressed, albeit after longer travel of the pedal.  If this sounds more like your symptoms, then I recommend yet another good bleeding session. Sometimes you can suck some air in through the bleed nipple threads, or have a bubble trapped in the caliper that's just stubborn to get out.

What I'm getting at is, really paying attention to the pedal feel and clearly defining your symptoms can go a long way at taking out some of the guesswork and really pointing you in the right direction.

[MildSeven]

So last night, I bench blead the e21 MC.
+ I swapped the passenger and rear brake lines, since I messed those up.
Tonight, I re-blead the lines.
I tested it without driving it.

I can still floor the pedal without it braking substantially .

I even started the car up (with wheels off + up on jack). I was apply to give some gas and a lot of brake with the wheels still spinning problem free .

I will try my old 2002 MC with 2 port blocked tomorrow.

I really hope it's a bad MC because I'll be extra frustrated if it's not.

Thanks again everyone,
Anthony

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[arminyack]

My new e21 MC just arrived today (early), and i put it it, bled everything.....and the pedal still goes to the floor. 

 

Im new to this particular brake set up (the standard 02 with the actuating rods the press on the booster, then the booster on the MC. What could go wrong at this end?

 

I'm not trying to hightjack a thread...it just seems that we both have the same problem now, and maybe the same solution

[arminyack]

Ok< I got mine sorted out. I removed both front calipers, and turned em upside down. I slide them on the rotors so the pads wont push out too far, and then bled them. Big air bubbles, followed by a flurry of small ones, then no bubbles at all. Bingo, a working brake pedal.

 

GO figure.

[M3M3]

The three common reasons for soft brake pedal on a 2002 are....

 

1/ front calipers installed upside down.   The bleed valves go UP.  Think about where air goes.....

 

2/ air in system.  Pedal pumping doesn't cut it.  Gotta have a pressure bleeder on the reservoir while pumping pedal slowly.  Especially if major brakes system parts were replaced.

 

3/ rear shoes not adjusted properly.

[Dudeland]

Dammit just read this I thought I would be all smart and say, “ flip the callipers” . Glad you got it sorted out.




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