very frustrated lately with the quality of rebuilt and supposed new parts.i lost my brakes last sunday while on the approach to captree boat basin, while attempting to join any die hards out there.seems like i lost one circuit completely and the second mostly.was able to limp home downshifting and using the e brake.supposedly new master cylinder install in 2012,



ACDelco 18M72 Professional Durastop Brake Master Cylinder Assembly
by ACDelco
i have no leaks anywhere and the pedal goes to the floor even withe the engine off.dismantled it when i got home and it looked clean with no damage to any seal or the bore itself.with that in mind am i missing something?then i see my wagner brake pads with the second slipped shim only now in the front.i replaced the rear in november, when the rear failed, with monroe ceramics which have the shim built in.(much better braking action also).while under there i noticed one of the newly replaced moog sway bar rubber bushings had split in half just to add to the frustration. this is all coming on the heels of a long list of failed rebuilt power steering parts on my daily beater,including a rack.(power steering filter was installed as required).any ideas on what failed in the master cylinder?

 

1. The fluid levels in the master when you opened the cover were close to the top both front and rear?
2. Why do you have brake pads that have shims, noise reduction?
3. Did you over tighten the bushing?

 

Being a rookie I am wondering why the shims aren't designed to fit onto the caliper "cross-pin" to prevent them from slipping.

As for brakes...my wife had the same thing happen...she ended up in a store window in her personal car.

It took me most of two days to bleed all the air out of my project car brakes after rebuilding the calipers/master cylinder/replacing rubber lines/rebuilding directional valve/very frustrating...I finally used a vacuumpump.

Maybe it's the camera angle, but 2 of the piston seals seem collapsed.

 

MelWff to answer you questions yes the fluid was near the top on front and rear chambers with no apparent loss.i would guess that the shims are necessary on the wagner semi metallic pads for proper noise reduction and in the directions you are not given a choice.ok there is a possibility that i might have overtightened one side on the replacement bushings,but i don't think i did.may have got me on that one.

 

doorgunner it must be the camera angle because i removed all the seals and examined them under a strong light and they all seemed perfect.i even repeated the bench bleed procedure with plugs on the ports and it would not pump pressure.the bore was clean and burr free as i ran a cotton swab over to see if it would snag.i do not want to experience this again.perhaps they need some rookies like yourself down at wagner to improve the design as i wondered the same about why the shims are not pinned.(more metal use).

 

Bill,

Did you bench bleed it first, then plug the ports? If not, then I wouldn't expect it to build pressure because there would be a lot of air in the master cylinder.

Also, have you looked at the linkage from the brake pedal to the master cylinder?

 

Well, to me, there would seem to be two possible causes for no pressure - with no leaks.
1. The master seals or bore not pumping up. It was working OK before? Did it gradually get bad, or all at once?
2. Air in the system. Did you try to bleed the system before taking it apart? Rotor run-out could help put air in the calipers.

And to bench bleed you would need to have a way (like tubing) for the air to exit the master.

 

my 76 ray yes i bench bled it in 2012 when i installed it using the return tubes to the reservoir method and had no issues till the sudden failure last sunday.i bench bled it again yesterday after i reassembled it using the plugged port method and it would not pump pressure.i have not checked the brake pedal linkage because there was some albeit minimal braking action.i will be checking everything now however,thanks.

 

74modified some of your questions i answered in my response to my 76 ray.it happened all of a sudden with absolutely no warning.scarey stuff!

 

Could one of the cup seals be oriented incorrectly, which is very easy to do? The lower left hand seal looks a little worn to me, but might just be the photo. I have had the last seal leak into the car and it is very hard to notice the leakage. Don't forget that with all of our 16 pistons, only a tiny leak is very scary.
I have never seen pads that needed shims before. Good luck finding the problem. Lou.

 

I would follow your logic and replace the front pads with your Monroes. Double check rotor runout, verify your caliper seals, and replace your master cylinder under warranty. Then see where you're at.

 

lou the funny thing is i lost no fluid and that it happened all at once with no warning whatsoever.looking at the cup seals they seemed ok but there must be some distortion like you say somewhere in the seals.my vette will never see shimmed pads again that is for sure.

 

briankeery the monroe pads are all in and i am waiting on another supposedly new master cylinder,this time a Dorman M89160.the ac delco lasted 2 years so i figured try another vendor.

 

RATS! I hate it when the problem is right there but can't be discovered!

I hope the new M/C does a great job for a longgggggg time.

 

thanks doorgunner and you were the first to point out the seals looking distorted.i will dismantle it again and photograph the seals as it still did not pump pressure when i reassembled it the first time.went through your rebuild thread and i must say you are doing a great job and loving every minute,except when it's time to bleed the brake system.

 

Exactly! I'm glad the brakes are done (fluid was everywhere).....and I DID manage to install one seal backwards years ago on another car....the brakes worked but would bleed down at long stop=lights

Also.....it should be difficult to install the pistons into the bore with new seals in place....if not, I would wonder if the seals are too small/undersize?

 

I missed DG's comment about the seals being distorted, sorry.
I have used silicone brake fluid for about 35 years now, in my coupe, and have not had any problems with it. Lou.

 

DG i have been under the chair more than once so nobody's perfect.we just do the best we can and buy hit and miss parts as we go along.i checked to see if the bore was true to 1 1/8" and it was.the seals went in,both times,tightly so i continue to be baffled.here is a shot of the seals from both sides:

 

lou you say you are using silicone brake fluid.is it different from the prestone dot 3 stuff i am using?

 

Silicone brake fluid is DOT 5.