Mushy brakes 4 life...

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The shoes most definitely fit flush on the backing plate. I pulled the drum off almost in frustration and cocked one of the shoes. You push it flat with your hand and it stays put. As for the backing plates... buried in the thread I show the dimensions and they seem to have been confirmed as indeed 11x2.5. The drum also is shown and marked 11” bla bla bla. When I get back over to the shop I have new drums I’m going to try for giggles and grins. Long work days and I will be back at it and post up.
 
AJ/FormS said:
I have never seen shoes flip up like that unless they were too wide, or the backing plates were in the wrong plane. If the pushrods from the W/Cs are in any position but parallel to the centerline of the car, then you have a mismatch of parts, that has nothing to do with the axles..........yet.
If the shoes flip up by themselves......something is wrong, and they will flip up after the drum is on, and SHAZZAM there is your mushiness.
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Well said this is what was in my mind
 
67Dart273 said:
Well said this is what was in my mind
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The shoes sit flush with the backing plate pads without issue. I just banged it cocked when I pulled the drum off. The WC and WC pushrods also run parallel with the plate as they should. I’ll be back on the car soon. I’ll try the new drums and see
 
Mopar92 said:
I have never bench bled a MC in my life. ...
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Long post, but I still suspect this is a problem. Watch youtube's. It can take 50 pedal strokes to sweep all the air bubbles out. I always "bench" bleed w/ MC installed in car, then I can use the pedal and don't worry about fluid dribbling out when connecting the car's tubes. Might get a small air bubble at each port, but that doesn't go into the MC and gets swept thru in bleeding the corners. That is one reason the tube ID is so small.
 
BillGrissom said:
Long post, but I still suspect this is a problem. Watch youtube's. It can take 50 pedal strokes to sweep all the air bubbles out. I always "bench" bleed w/ MC installed in car, then I can use the pedal and don't worry about fluid dribbling out when connecting the car's tubes. Might get a small air bubble at each port, but that doesn't go into the MC and gets swept thru in bleeding the corners. That is one reason the tube ID is so small.
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Is that would could be causing this extreme interference?
NOTE: the mechanical interference has absolutely nothing to do with bench bleeding a master. I appreciate the reply but that’s not the issue thus yet. Of the 20-30 masters I’ve replaced over the years... I’ve yet to have one that didn’t bleed in 2 minutes of pressure bleeding.

900A1C2C-F5B6-43D5-B78B-7E134950E103.jpeg
 
Replaced 100 or more,bench bled every one. As per manufacturers instructions.
I still dont think drum is the issue.
Crank brakes up tight with adjusters and try pedal. Zero clearance should mean hard pedal.
Backing plate rubbing in only one spot,plates bent?

Soft pedal,maybe reverse bleeding. Pressure bleed from each wheel pushing fluid up to master. I have never had to do this,especially on domestic. 75%are usually successful just gravity bleeding.
 
Tooljunkie said:
Replaced 100 or more,bench bled every one. As per manufacturers instructions.
I still dont think drum is the issue.
Crank brakes up tight with adjusters and try pedal. Zero clearance should mean hard pedal.
Backing plate rubbing in only one spot,plates bent?

Soft pedal,maybe reverse bleeding. Pressure bleed from each wheel pushing fluid up to master. I have never had to do this,especially on domestic. 75%are usually successful just gravity bleeding.
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I hope you are just kidding. With the rear wheels tight, you cannot turn the wheels. Period. Period. So yeah the drums are the first issue. Did you see the pics where the paint has been burned off and the backing plate friction? It’s more than a rub. It’s hardcore into the backing plate. Both backing plates are rubbing in about 4 spots very consistent to each other. Unlikely they are both bent in the exact same 4 locations per side. 28 bench bled master cylinders on the car will not fix this issue. Again I appreciate the comments and suggestions here... I really do... I just think some are reading the title and replying. You might have to scroll up a little to get caught up. Metal on metal has absolutely nothing to do with Pascals law here.
 
I have been reading from the top.
Didnt realize 4 spots rubbing.
So adjusting is moot,as you cant tell whats rubbing. Shoes on drums or backing plates. The whole idea behind my suggestion of tightening adjusters was only to check for hard pedal. Thats it.
 
I’ve pointed out where the drum is making contact on the backing plate. I’ll get back on it in a few days. Works getting in the way of play.
 
That is becoming more of a problem,all work and no play makes frank a grumpy boy....
 
Guess a man has to work to play. It is what it is. After all they are just toys. I’ve never been angered by a car but they can frustrate a man. Especially race cars.
 
I was yelling at gm engineering on thursday. How hard should it be to replace a starter? Gotta tangle it up in there with tubes and wiring harnesses.
 
I can't help with the rear drum situation but once had a problem with crappy brake performance and overheating and found the culprit to be the adjustable aftermarket push rod where the heim joint end rubbed on the brake pedal.
 
Checking back into this one with some measurements from one of my 11x2.5" brake set ups.

From the drum, inside friction surface
IMG_4923.jpg


Depth. I know I show the tape measure here, but I also measured with a set of calipers- 4.46" to the outside
IMG_4925.jpg


This where it gets a little more interesting. This is a set of Dr. Diff BBP axles in a stock A-body 8 3/4 housing, using tapered bearings.
That measurement is 2.3", also checked with calipers. Now, that's with tapered bearings and this is the passenger side, but these brakes work so...
IMG_4926.jpg


I think this is the measurement you really need to take. Face of the axle to the outer lip of the backing plate. The square is in tenths on the side being used, FYI, so, this is about 3.45". That's off the mounting surface, not the register.
IMG_4930.jpg


And last, in the thread where you ID'd the backing plates I never saw a diameter of the backing plates posted. Did you measure it? The 11x2.5" backing plates are ~12" in diameter measured to the outside edges.
 
Mopar92 said:
Is that would could be causing this extreme interference?
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It isn't unusual to have multiple problems. But, it sounds like you are the only one here (and in most of internet space) who doesn't first bench bleed an MC, and all rebuilt ones come w/ such instructions and usually plastic tools to allow that. So, our question is "why not bench bleed it like everyone else and then try again?". You only need to unscrew the 2 tubes and route temp tubes into the reservoir. No need to remove the MC from the car. If you see air bubbles sweeping thru, that suggests that was one of the problems.
 
Do these part numbers mean anything ? I got to the shop today and I’m .100” off both sides.

15B7E2BE-B09B-4D6F-AD04-18C749C75FE2.jpeg


829DB0B1-6A15-445D-B8F5-41E24FAD20F0.jpeg
 
72bluNblu said:
Checking back into this one with some measurements from one of my 11x2.5" brake set ups.

From the drum, inside friction surface
View attachment 1715141350

Depth. I know I show the tape measure here, but I also measured with a set of calipers- 4.46" to the outside
View attachment 1715141348

This where it gets a little more interesting. This is a set of Dr. Diff BBP axles in a stock A-body 8 3/4 housing, using tapered bearings.
That measurement is 2.3", also checked with calipers. Now, that's with tapered bearings and this is the passenger side, but these brakes work so...
View attachment 1715141349

I think this is the measurement you really need to take. Face of the axle to the outer lip of the backing plate. The square is in tenths on the side being used, FYI, so, this is about 3.45". That's off the mounting surface, not the register.
View attachment 1715141351

And last, in the thread where you ID'd the backing plates I never saw a diameter of the backing plates posted. Did you measure it? The 11x2.5" backing plates are ~12" in diameter measured to the outside edges.
Click to expand...


Thank you very much for taking the time to reply and try to help me sort this. I really appreciate it. The car is at my buddies shop, as he has heat and mine doesn’t. Anyway. I went today to grab some measurements for you all.

1- backing plates are 12” OD
2- new drums were exact to my old OEM
3- If i remember( left my notes) I am 3.3” from the lip of the plate to my flange. After measuring the drum from the flange side down inside the recess for the plate... I would need 3.4”. That gives the .100” that the mock up washers behind the drum also clarified.
4- the shoes fit perfect inside the drums. I removed them and verified that.
5- I confirmed my axle to backing plate depth is correct up against what dr diff said it should be.

I guess I have 2 choices here... well practical choices. I could
a- use some .190” steel wheel spacer shims I have in the race car stash between the drum and the axle flange.
B- take a chance and buy another set of “ 11x2.5” backing plates.
c- have the drum machined. I don’t want to do this in case I’m on a trip and need a drum.
D- grind .100” off the plate. This is messy and time consuming.
 
Not likely you would need a drum while away on a trip. Imagine the situation,drum would be only part on the dilemma. I say machine the drums. They dont contact the shoe there anyway.mind you, i have a brake lathe, it would be a no brainer for me.
 
Yeah I’m contemplating that. I need to find a machine shop that can swing a 12” part. Two I found have baby lathes. Only an 8” bed.
 
Usually an 8” swing is 16” diameter. Your drum is 6” swing.
You wouldnt want to spin that on a small lathe anyway. My 9” swing would handle it, but i dont like swinging big stuff, and as i mentioned the brake lathe is best.
 
Grind one. Its easy. I have used hss on my brake lathe, can grind any shape you want.
 
I told you what to do earlier. FIND SOMEONE with a brake lathe that knows how to use it and have them turn some off the open side. If you want to ship it to me (in the northern end of Idaho) I would do that for you.

This idea of "being on a trip and needing a drum" is nonsense.
 
Judging by the large picture you posted in the other thread, I think you have 11 x 2" backing plates. I have never seen an 11 x 2.5" backing plate shaped like that. I bet the backing plate was laying on the brake cable "pockets" when you measured the depth.
 
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