Too much brake pedal travel

[iinca]

I was under the impression springs controlled all that and that the Residual Pressure valve is built into the system.

 

But this is the first time dealing with a low pedal so wtf do I know.

 

I will say again the brakes do work great it's just too much travel to drive fast safe. It's about 40% then they engage..

 

I spend half the time using the engine to brake

 

Also the booster is not new. Bought from a person who swears by the Baby Jesus and Mother Mary it's working perfectly...Once again that 

could be an issue and just a 'bag of jakes' by a seller who's worried I'll kill him it's defective

 

I think Im going to power bleed bleed bleed before I start tearing into the booster, master or calipers

Edited July 23, 2019 by iinca

[iinca]

ok I finally noticed I don't have a fitting for that pressure valve on my master!

 

I think it might be an E21 master,,,sonabitch!. I have no #4 Pre Pressure Valve on my master.

 

Previous owner installed the Master right before I got the car...another suspect part!

 

 

http://www.realoem.com/bmw/showparts.do?model=2552&mospid=47140&btnr=34_0804&hg=34&fg=25

Edited July 23, 2019 by iinca

[dlacey]

The pre-pressure valve tries to correct for slack in the rear brake adjustment, stopping the shoes pulling back too far. but you said with handbrake on your long pedal is unchanged...so rear brake adjustment is not your issue.

[Hans]

Does an E21 master have enough outlet holes?

Did you replace the plastic bushings where the push rod connect to pedal?

I'd be bleeding again. Give the rears a good run.

I vaguely recall that if you put your foot on the pedal with engine off, then start it, you should feel booster kick in.

[iinca]

Those bushing seem tight. There's no play there but I think I'll order them for peace of mind for the next 46 years

 

Here's a pic of the Master. Shouldn't there be a brass fixture/valve in the middle on top?

 

I guess I could get an aftermarket valve inline'

 

 

Edited July 23, 2019 by iinca

[Tommy]

9 hours ago, dlacey said:

The pre-pressure valve tries to correct for slack in the rear brake adjustment, stopping the shoes pulling back too far. but you said with handbrake on your long pedal is unchanged...so rear brake adjustment is not your issue.

I still feel that this might be the culprit in the case. The valve is there specifically for that reason, to decrease pedal travel. Could the pistons retract some distance even handbrake applied? Since the master doesn't have provision for one an external valve could be fitted. e.g. https://www.wilwood.com/MasterCylinders/MasterCylinderValves

 

Another question is the master dimensioning?  Is the diameter same as what is used as stock with the calipers? Smaller master will cause longer travel.

[dlacey]

11 hours ago, iinca said:

 

Beware of using fuel hose for the low pressure brake fluid lines, DOT3/4 may "sweat" thru that rubber & damage paint.. 

[Hans]

Seems to me E21 has remote rear pressure valve.

[rstclark]

Despite your best effort to bleed the system especially the calipers. The calipers can trap small air bubbles Have you tapped them with a brass of plastic hammer to see if you can get anymore air out ?  Having had a similar feel before I drove the car for about a week and it cleared up because I think air was finally forced out of the calipers. I guess i'm saying  maybe drive it carefully and see if it doesn't get more peddle 

 Sorry I can't add to the discussion about the pre pressure  valve.  

['76mintgrün'02]

Does pumping the pedal eliminate the play?

[Guest_anonymous]

Its not a matter of holes in the MC it is the size of the port for the rear brake line where the Pre pressure valve mounts. The e12 MC does not have the Pre pressure valve either, Wilwood makes an inline 10lb pre pressure valve. I run the e12 master and have the gap in pedal feel where I did not have with the standard MC with the same brake set up.

[Einspritz]

Just a thought; you might want to find out if fuel hose is compatible with brake fluid......I think not.

 

18 hours ago, iinca said:

ok I finally noticed I don't have a fitting for that pressure valve on my master!

 

And the OE master cylinders didn't have those valves, and work just fine if all the air is out of the system.

 

Are your shoes arced to the drums? Additional play can come from the difference of the shoe contacting just at the ends vs. full contact when you press down hard.

 

In addition, if you have replaced with an E21 M/C the larger diameter of the pistons allow for an increase of travel to get the same movement at the pistons F/R.

 

The booster does not affect the amount of play in the linkages.

 

Try using a pressure bleeder at the rear to backfill the system in hopes of dislodging air through the system. At the front, the piston chamber that points UP is a usual suspect, so try bleeding that again.....

 

Check your linkages for play by having someone depress the pedal and looking at the movement (or non movement) at the bell crank going to the M/C. Those pivots all wear and make for a sloppy pedal travel. Unfortunately, unless you fabricate bronze bushings at every pivot ( and the OE clevis' don't have enough meat there to do that), there will be some slop, but usually no more than 2 pedal thicknesses before a firm pedal. You can also use a precision ground shoulder bolt (Mc Master-Carr PN: 90323A254) to take up some minute slack at the clevis', but it is not much, more of a refinement. The pedal ratio is 4.44 so any slop will be magnified by that amount.

[iinca]

first that fuel hose is on the list. I'm still cleaning up the mess from the prior owner. 

Thanks for the reminder though. No excuse just overwhelmed with details.

 

Pumping the brakes does nothing. It's actually a nice feeling pedal once you get to that point. I can def' lock 'em up if I have to

 

Real OEM schematics shows pre squaretail 2002's to have that valve in the Master but I understand the system can work without it if it's air free. I ordered a Wilwood RVP anyway. 20 bux...It's not a hard job and it's peace of mind

 

The peddle box seems to have been addressed somewhere along the way. Not much slop at all when I hit the pedal.....despite that it's gonna be done soon. I promised myself early on that every mechanical part will be dealt with.

 

I'll go through the power bleed again and again..... AND I'll "bang" on the calipers. If I

have to blow through a gallon of fluid so be it.

 

I'm not sure if it's an E21 master..just guessing. I've never dealt with an E21 Master cylinder..

I just have to deal with it or find an OE with the valve built in. I chose to  deal with the

current master cylinder but if I find an OE I can rebuild it...

 

please keep badgering me with suggestions and observations. I'm sorta desperate to drive it this summer..

Edited July 24, 2019 by iinca

[iinca]

Ok I changed my mind. After talking with Blunt I'm goin with a new unit.  I don't 

trust the prior owner(s) with replacement parts. The master on there can go in the

spare parts boxes.

 

 https://www.blunttech.com/shop/replacement-parts/brake/brake-hydraulic/1410btkt

[Hans]

I thought E21 had single circuit front calipers. Hence my puzzlement as to how PO got five pipes into three or four holes.  I believe diameter is same as 2002, but I guess we're beyond that point.