Brake Booster Tech
#2603459
01/08/19 03:31 PM
01/08/19 03:31 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
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Hey guys, I need to consult the brain trust on what I think is a booster problem.
73 Barracuda Power disk/drum, adj prop valve.
I have been completely through the brake system, new rotors, drums, shoes, pads, rebuilt calipers, new style wheel cylinders with residual valves, 1 1/32 AL MC listed for a Gran Fury, parts store reman booster, PR clearance set at .020" using a tool.
The hydraulics are fine, properly bled and functioning.
So, my factory brake booster died, but before it did, the pedal got very soft and would travel about half way before any meaningful braking started, and then I let off the pedal and I have immediate braking when pushing the pedal. Then the booster failed completely.
Parts store reman booster, same pedal behavior. I don't doubt that my rebuilt booster could be a POS, but my inner A&P loathes throwing parts as a troubleshooting measure.
I have tested the booster using the FSM method and methods I found on the interwebs. It seems to pass those tests, but I dunno.
Can anyone put a finger on what would cause these symptoms? I am befuddled. Faulty booster is where I'm at...
Thanks
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Re: Brake Booster Tech
[Re: BcudaChris]
#2603502
01/08/19 05:16 PM
01/08/19 05:16 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
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Yep, when the booster bleeds its reserve, nice high, hard pedal. Also removing vac nets a super hard pedal, but no need to let off and take another "bite" (if you will).
On the air in the hydraulics, that was my first check on the old and reman boosters. I've pulled a couple of quarts of fluid through at all four corners using vacuum pump. I am confident of no air in the lines or MC. Nice solid jets of fluid. With air in the lines, multiple pumps gives you better performance. In my situation, letting off the brake after application nets a high hard pedal for the next push, with no improvement in subsequent pushes.
It is the stock style booster for a 73 E body and it feels to me like the volume of the booster might be mismatched to pedal travel/MC stroke?? Its like the booster needs a re-charge after initial application. Could a small internal diaphragm leak cause this?
I will add that in reverse, I get a nice initial bite, going fwd, mush pedal with a Flintstone's level initial bite. I have watched the actuation at all four corners and I can feel braking happening when I touch the pedal, just not much.
I probably should have stated this in the OP, but it is outside my experience and seems unlikely to me. I have overheated my pads to the point of smoking two times in all of this. On the initial bed in I was having so much fun getting from 20-60 that I did it until things heated up and when I came to a stop, brake stink and white smoke. Did the same a few weeks later while adjusting the prop valve. In the pre-overhaul setup with the same symptoms, I had organics front and rear that had been seriously abused and installed were installed without dressing the drums/rotors.
The pads are EBC reds, which I've loved on several other cars, but could I have smoked my pads? They didn't appear to need it, but I roughed the pads up on a flat plate with 180 and blew them clean, I also used some 120 to scuff the rotors. No change. Also, performance doesn't change when the brakes are cold or hot (unless heated until they go away).
I'm with you on ruling out the booster 469, but I can't think of anywhere else to troubleshoot. And, that said, my intellectual curiosity has failed me when it comes to more than just high lever brake booster theory.
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Re: Brake Booster Tech
[Re: BcudaChris]
#2603599
01/08/19 09:38 PM
01/08/19 09:38 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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As said, cap the MC with with 2 plugs from the Edelman cabinet at your parts house & with it idling, if the MC is (1) good (try easy pedal & stomping) (2) bled out (3) pushrod clearance OK (4) booster and or check valve OK: then the pedal should be rock hard with virtually no travel.
live every 24 hour block of time like it's your last day on earth
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Re: Brake Booster Tech
[Re: BcudaChris]
#2606503
01/14/19 04:25 PM
01/14/19 04:25 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
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Gents, by way of an update, I re-bled and tested the MC. Passed. I checked shoe movement on retract, does not appear excessive. Tightened up rear adjustment. No change.
Yet another Vac pump bleed. No change. Traditional pedal bleed, no change.
It has to be air in the system....
Did an overnight gravity bleed on the rears, and the fronts are bleeding today. I'll let you know.
One other thing I touched on, but I had been running an old MP adj prop valve on the rear output side of the funky 73 prop valve with the shuttle valve in it. I replaced that mess with one of the Willwood adj prop valve/distribution block combo units. It gives far less adjustment on a per-turn basis than what I had. I have it set to max rear flow for the gravity bleed.
Also, to install that wilwood valve and my big exhaust, I had to get a couple of 10" prefab brake lines and bend them to my will. I checked and verified the integrity of the bends, but I theorize given my routing, they could potentially be an air trap. Hopefully the gravity bleed will deal with that, if it is the case.
Sure would be nice to have access to a hydraulic brake mule like I had when I worked in hangars.
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Re: Brake Booster Tech
[Re: BcudaChris]
#2606546
01/14/19 06:11 PM
01/14/19 06:11 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
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Circle Track
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what about capping the forward MC port with a plug & see if it is now high & tight useing the next to the firewall port for the fronts. this would elim everything rearward & you'd be dealing with the easier to deal with (shorter lines/no prop valve) front brakes (tho discs can be hard to bleed out).
live every 24 hour block of time like it's your last day on earth
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Re: Brake Booster Tech
[Re: BcudaChris]
#2606954
01/15/19 03:04 PM
01/15/19 03:04 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
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Great Idea, thanks Robert, I'll add that to my troubleshooting chicken scratch notebook. Isolate the circuits like electrical troubleshooting.
That said, success! My confidence in my bleed was misplaced. A 12hr gravity bleed on the rear, then one on the front took care of it. High, hard pedal. I do have some Popeye arms now from unsuccessful vac pump bleeding, and the traditional pedal bleed didn't get it either. Gravity is your friend.
A tip to pass along, the Bosch 3,4,5.1 high temp fluid gives much improved brake "feel" and doesn't hemorrhage out the MC cap vents when you make the fronts go away with extreme use.
Thanks all, I learned a lot going down rabbit holes troubleshooting a basic problem. Once again the KISS principle proves its self once again.
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Re: Brake Booster Tech
[Re: BcudaChris]
#2606980
01/15/19 03:49 PM
01/15/19 03:49 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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You sound pumped (enjoy it while it lasts!)
live every 24 hour block of time like it's your last day on earth
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Re: Brake Booster Tech
[Re: BcudaChris]
#2607529
01/16/19 03:23 PM
01/16/19 03:23 PM
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Joined: Mar 2005
Posts: 403 Colorado front range
BcudaChris
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Posts: 403
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Pumped, I see what you did there Robert Negative on the calipers on the wrong side John, and no offense taken. All thoughts and advise welcome and wanted. And, I have done that before. 469, EXACTLY! It is highly frustrating to spend time searching and find a thread on point, with good info and the OP leaves you hanging. There outta be a sticky at the top requesting that people post their resolution instead of taking the money and running. It's just good form.
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Re: Brake Booster Tech
[Re: BcudaChris]
#2607586
01/16/19 04:20 PM
01/16/19 04:20 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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Pumped, I see what you did there Robert Yeah but it took you awhile!
live every 24 hour block of time like it's your last day on earth
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