Booster causing brakes to hang?

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QMopar

QMopar

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On my 74 Dart, I’ve noticed the brakes not releasing for about a second or so. We traced it to the booster. Jack up the car, have my buddy turn the front tire by hand and then press the brake, wheels won’t turn for about a second and then it releases. Get rid of all the vacuum in the booster and tire releases as soon as you're off the brake pedal. Put vacuum to the booster and get the delay.

I pulled it part to see what I can see and found the rod not really attached to anything. It fits in the hole but is not tight. Should the rod be more stationary in the booster to release as soon as the pedal is released?
 
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There is a check valve in the vacuum line right there at the booster. Make sure the valve is not sticking.
 
Rod adjustment is to long.

Check the manual and re-adjust to spec. It’s a fine line to good brake performance and keeping the master cylinder applied! If it is to long you will overheat and have a bad day! I speak from experience!
 
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Demonic said:
^^ This. The adjustment is very fine. A half turn in - shorter - might be a good start.
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I adjusted it to far one day in the 80’s and it cost me a nice one piece fiberglass front end! Never again!
 
Yes they should come right out like that. When I got mine back from Booster Dewey restored he had a piece of tape over the hole holding it in.
 
The rod is attached to a manual master cylinder but just sort of floats captured behind a booster. I can't imagine the rod adjustment changed on its own. So if this is a new issue in a vehicle you have driven for a while there must be something gone wrong with the booster.
If you replace the booster you'll need to check/set that adjustment.
 
I bought this last year and started driving it in June. I replaced the (leaking) calipers and thought maybe the hoses were collapsing so those are new too. Booster has a reman stamp on it but it sure seems wonky. I'll try an adjustment for now but am leaning toward replacing it or maybe sending it out to be rebuilt. Thanks again for all the input - you guys (and girls!) are a great help.
 
QMopar said:
I bought this last year and started driving it in June. I replaced the (leaking) calipers and thought maybe the hoses were collapsing so those are new too. Booster has a reman stamp on it but it sure seems wonky. I'll try an adjustment for now but am leaning toward replacing it or maybe sending it out to be rebuilt. Thanks again for all the input - you guys (and girls!) are a great help.
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If someone replaced the booster and didn't check the rod setting, that may be the problem.
Info should be in factory service manuals. Good luck with it.
 
Repeat the test but this time instead of bleeding the vacuum down; just loosen the master cylinder about 1/16inch all round; this will do same as backing off pushrod.
If the pushrod is too long it will prevent the brake fluid from returning to the reservoir, keeping the brakes on. Same will happen if the brake pedal is not returning to it's parking spot up under the dash. Same will happen if solids build up on the firewall side of the piston between the piston and the stop, or if the compensating port is restricted by rust or solids.

I really doubt this is a booster issue
 
AJ/FormS said:
Repeat the test but this time instead of bleeding the vacuum down; just loosen the master cylinder about 1/16inch all round; this will do same as backing off pushrod.
If the pushrod is too long it will prevent the brake fluid from returning to the reservoir, keeping the brakes on. Same will happen if the brake pedal is not returning to it's parking spot up under the dash. Same will happen if solids build up on the firewall side of the piston between the piston and the stop, or if the compensating port is restricted by rust or solids.

I really doubt this is a booster issue
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I tried your recommendation of loosening the master and it still was sticking. I was by myself so I just went back and forth in my driveway, I didn't jack it up and have someone turn the front wheel(s).

To go further, I pulled off the master, adjusted the rod in little increments 3 different times and it was still sticking.

What about the the brake pedal not returning and the other items you mentioned? How would I check if the pedal is/isn't returning? There's no return spring - just the master that 'pushes' it back, right?

Could that be affected only when the booster is operational?

I'm going to find a service manual and get this thing figured out. Thanks for your help
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Yes the spring inside the M/C pushes the pedal back up against it's stopper under the dash. Put your toe under the pedal and physically lift the pedal up as high as it goes. If that changes nothing, then Ok so it's not the booster nor the pushrod length.
You are gonna have to jack up the 4 corners and see which wheel(s) is/are dragging.
If the rear brakes are dragging, you may have a problem in the Proportioning valve or a failed rear hose or sticking wheel cylinders, or an obstructed C-port..
If the fronts are dragging, you will have to prove the Compensating port is open. The only way for the brake fluid to return to the M/C is thru the compensating ports; see the holes in the bottom of the reservoirs?; that's them. Make sure yours are open and not obstructed by the pistons. The hole(s) are very tiny, do not drill them out bigger.

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AJ/FormS said:
Yes the spring inside the M/C pushes the pedal back up against it's stopper under the dash. Put your toe under the pedal and physically lift the pedal up as high as it goes. If that changes nothing, then Ok so it's not the booster nor the pushrod length.
You are gonna have to jack up the 4 corners and see which wheel(s) is/are dragging.
If the rear brakes are dragging, you may have a problem in the Proportioning valve or a failed rear hose or sticking wheel cylinders, or an obstructed C-port..
If the fronts are dragging, you will have to prove the Compensating port is open. The only way for the brake fluid to return to the M/C is thru the compensating ports; see the holes in the bottom of the reservoirs?; that's them. Make sure yours are open and not obstructed by the pistons. The hole(s) are very tiny, do not drill them out bigger.

View attachment 1715370957
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That's helpful. I'm fairly certain it's the fronts that are dragging. If that's the case (compensating ports), then we're talking master, correct?
 
The C-ports are in the M/C per the image I stole off the internet. You can shine a light in the reservoirs and see the ports. Then just push a wire thru the holes. The bore will be 7/8" or larger and the floor of the reservoir is perhaps 3/16(guessing) thick, so the wire should penetrate about 1 inch or more. If it doesn't, then it may be that the piston is in the way, indicating that the pushrod is too long. Sometimes the flashlight will reflect off the piston and you can see the shine, but those holes are pretty small.

There is a sure test for open C-ports but unless you have silicon brake fluid I can't recommend it.
The test is to cover all your precious paint with blankets and such.
Then get a helper to pump up the brakes about 3 or 4 strokes then hold the pedal down with mild pressure. Now carefully lift up the cover but keep it over the reservoir. Next, have the helper slowly, slowly, slowly release the pressure bit-by-bit until the pedal comes to the top. In a properly functioning system you will be able to see the fluid returning as roiling in the reservoirs, or even a fountain, depending on the helper's control. If you make a mess, remember brake fluid eats paint, clean it up right away.
If yours doesn't do this, it may still be a different problem. But if it does do this then the C-ports are open for sure,lol.
 
First look I would question the master. It looks very old and had years of use. Crud can build up and block the CP ports.
 
QMopar said:
Yep, I’m going to order one.
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Just a follow up on my brake issue. I tried a brand new master cylinder and the brakes still hang up. Parked it for the winter and last month got my booster rebuilt by Booster Dewey. Took it for a test drive and it appears the issue is rectified. Problem solved!
 
I'm having the same issue!
Did Dewey's say they seen any issues inside the booster?
 
sammie said:
I'm having the same issue!
Did Dewey's say they seen any issues inside the booster?
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It is sometimes the crappy rebuild masters and specs that may cause a fine unit to become bad afterwards. Booster Dewey is the tops and usually delivers a spot on unit!
 
This is a old post though!
 
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