It appears that after depressing the brake pedal on my '72 SS (power disc/drum), the pedal returns slowly, which leaves the brake switch engaged for a few additional seconds. Should the boost pressure return the pedal instantly? Is this an indication that I have a minor leak in booster? The car stops normally, the brake switch itself has been replaced, and the switch bracket bolted near the top of the pedal arm has been tightened.
Brake pedal slow to return
edb
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It appears that after depressing the brake pedal on my '72 SS (power disc/drum), the pedal returns slowly, which leaves the brake switch engaged for a few additional seconds. Should the boost pressure return the pedal instantly? Is this an indication that I have a minor leak in booster? The car stops normally, the brake switch itself has been replaced, and the switch bracket bolted near the top of the pedal arm has been tightened.
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1,286 Posts
The pedal returns with the help of a (strong) spring inside the booster. I don't think that any malfunction on the «vacuum side» of the booster would make any difference on pedal return (but I could be mistaken).
If the car brakes normally, I would just re-adjust the brake switch such that it lights on with the pedal a little more depressed.
If the car brakes normally, I would just re-adjust the brake switch such that it lights on with the pedal a little more depressed.
Thanks for the response. I've got it pretty close now, but pushing on it with my hand and stepping on the pedal with my foot obviously apply different amounts of pressure. I just wanted to make sure that the booster, which is reasonably new, wasn't at fault for the slow return of the pedal. I may also be able to adjust the clevis where it connects to the pedal to remove any play in the pedal.
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8,690 Posts
Weak shoe return springs.
Partially-seized calipers
Partially-plugged brake hoses or seized/partially-plugged hydraulic valving
Defective rubber seals--swollen and stiff from contaminated fluid
Defective booster
Defective return spring on brake pedal.
Of all these, the defective spring on the pedal is least likely.
I would put the vehicle in the air, have a helper hit the brakes, and see how long it takes for the wheels to turn freely after releasing the brake pedal.
Partially-seized calipers
Partially-plugged brake hoses or seized/partially-plugged hydraulic valving
Defective rubber seals--swollen and stiff from contaminated fluid
Defective booster
Defective return spring on brake pedal.
Of all these, the defective spring on the pedal is least likely.
I would put the vehicle in the air, have a helper hit the brakes, and see how long it takes for the wheels to turn freely after releasing the brake pedal.
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1,286 Posts
Even if the brakes wouldn't release (which doesn't seems to be the case here) and the m/c piston wouldn't go back to its original place, the brake pedal would come back up with the help of the return spring, as the push rod is not connected to the m/c piston (it just pushes on it).
As I said in the previous post, I don't think it is possible that a vacuum problem in the booster would prevent the pedal from returning to its position.
But I've double check with this page that explain how brake boosters work, and it might be possible (I say «might be») to have a brake pedal «slow release» problem if a spring is broken in the valve body or if there was a bad seal in one of the valve, but you would probably either have a hard pedal (booster doesn't work) or you would have a vacuum leak (the engine would suffer and you would hear a constant "whoosh" sound from under the dash when the brake pedal is not applied).
Is there a return spring on the brake pedal? The car is a 4-spd, and I've been under the dash a couple of times now, working on adjusting the switch, but didn't see a spring. That's how I noticed the slow return of the pedal. Also, while attending the Syracuse Nationals this past weekend, I picked up a new brake switch from Ground Up, thinking it may be the problem. I asked specifically if there should be a return spring, and was told no.
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Jack, Thanks for the link to the Brake Booster lesson. It is very interesting and valuable information. I'm going to separate the MC from the booster and see if I can get the booster off to inspect for dirt or corrosion inside that may be hindering the operation. The booster was replaced 8 or 9 years ago, and the MC 2 or 3, but the car sits in cold storage every winter.
I thought I had this problem solved after adjusting the clevis and taking some play out of the rod to the booster, along with adjusting the brake switch. The lights now go off within a sec or so of releasing the pedal, which seems acceptable. I've noticed now that when I'm warming up the car for a cruise and engage the emergency brake, the brake lights come on. I don't remember this happening before, and don't think it is correct?
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Sorry, I meant the rear brake lights. As before, when I pull up a bit on the brake pedal the lights go out. I had forgotten about the dash light, which isn't working. It may have a blown bulb. The little red disc is intact in the dash. The cruise/show season is almost over. It appears to be time for an overhaul of the brake system on the car.
I finally got to the root of the problem. I ended up taking it to my local garage, and they found a small leak in the master cylinder, and the booster is failing, which together was contributing to the slow pedal return and having a tough time bleeding the brakes after replacing the calipers. I'm now looking for a rebuild kit for the booster, as it is in excellent condition on the outside. Thanks for everyones help!
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