Author Topic: 68 Brake issue. Input needed.  (Read 5628 times)

cwyllie

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68 Brake issue. Input needed.
« on: May 18, 2022, 02:12:22 AM »
Hey everyone.
I am having an issue with my brakes and at this point I am not sure which direction to go. Here's my situation.
Original Front disk power brakes. 396/TH400.
Caliper was leaking when I got the car so one of the first things to tackle were the brakes. Had calipers rebuilt (all new pistons and seals) and also had to replace the metering valve as it was leaking from the boot. Bench bled the Master and put it back together. Bled all four corners twice. Test drove around the block and everything seemed fine other than pulling to the right.
Took the car to work about a week later. Drove it to lunch and after sitting in the drive thru for 7-8 mins, went to leave and approaching the street.... HARD brake pedal with indicator light on. Pulled it into the parking lot next door and could not get anything better out of the pedal so had it towed home. Pulling off the flatbed and on the ground, good pedal for just a pump or two then HARD pedal with light. Next day I pulled the check valve from booster and whoosh. Still holding vac. Did the suck blow on check and it's good. Bled all four again and took for a spin. Good brakes for the fist 3-5 minutes then.... HARD pedal with indicator light..
So. Vac/booster issue or HYD issue??? Could it be the diverter valve is tripped? Could it be a bad booster even if it holds vac?
Any advice would be appreciated as I really NEED to get this car out and enjoy it with the Wife.
Thanks. Craig

william

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Re: 68 Brake issue. Input needed.
« Reply #1 on: May 19, 2022, 08:38:52 PM »
Here's a check list from the 1970 Delco manual.

Learning more and more about less and less...

GMAD_Van Nuys

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Re: 68 Brake issue. Input needed.
« Reply #2 on: May 19, 2022, 09:54:08 PM »
I had the power brake booster fail in my 1979 Trans Am and had problems similar to what you are experiencing.  I would also recommend changing your brake hoses as one on the car collapsed internally and locked the front caliper.

cwyllie

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Re: 68 Brake issue. Input needed.
« Reply #3 on: May 20, 2022, 12:45:40 AM »
GMAD.
Front hoses are new. When your booster was shot and pedal hard was braking minimal? And did your brake light come on? I suspected booster but everything I have read says that if brake light comes on it is a hydraulic issue so that is throwing me off my suspicion.

GMAD_Van Nuys

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Re: 68 Brake issue. Input needed.
« Reply #4 on: May 20, 2022, 01:36:00 AM »
cwyllie - The "brake light" did come on and as I live on a hill, I doubt if I could have stopped the Trans Am as I had a problem even pressing the brake pedal to stop the car on my driveway.  The brake booster was original and I also replaced the master cylinder when I got a rebuilt booster, which was somewhat tough to find as the Trans Am has 4-wheel disc brakes. - Mark

cwyllie

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Re: 68 Brake issue. Input needed.
« Reply #5 on: May 23, 2022, 12:36:17 AM »
I have a booster ordered but still questioning what is going on. Took the car for a spin again and brakes work fine until the engine warms up. Then, back to hard pedal with brake light on. Obviously the booster works when cold. It also is holding vacuum until the next day. Just weird.  :o

David K

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Re: 68 Brake issue. Input needed.
« Reply #6 on: May 23, 2022, 03:30:33 AM »
If you warm the engine without driving the car, does  it happen immediately or after actually driving a certain distance or brake applications?

Gars68Tux

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Re: 68 Brake issue. Input needed.
« Reply #7 on: May 23, 2022, 07:47:25 AM »
I have a booster ordered but still questioning what is going on. Took the car for a spin again and brakes work fine until the engine warms up. Then, back to hard pedal with brake light on. Obviously the booster works when cold. It also is holding vacuum until the next day. Just weird.  :o

Sorry I don't have much to offer in diagnosing the problem. But beings I know how original your car is, I highly recommend saving the booster and rebuilding if necessary. The correct police will spot a repop before the hood is completely raised... ;)

Ya sure it's not the vacuum hose to the manifold? Maybe it collapses when it gets warm.
Garth

68 RS L30 AA 749 Fred Gibb Chevrolet

cwyllie

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Re: 68 Brake issue. Input needed.
« Reply #8 on: May 28, 2022, 09:18:25 PM »
DavidK
I have not warmed completely before driving. It is the same situation every time I test it. Booster is fine, brakes fine then a couple miles up the road it acts up again. Once it starts, I will get intermittent ďgoodĒ braking on the way home.  Meaning, no hard pedal, no brake light, and working brakes.
Just pulled the proportioning valve off and it is centered so I think I can reduce that one.
After sitting for a week, I pulled the check valve and booster is still holding vacuum.
Could it be trapped air?? Iíve bled the crap out of them but have head that power bleeding is the only way to get it all out.

cwyllie

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Re: 68 Brake issue. Input needed.
« Reply #9 on: May 28, 2022, 09:20:45 PM »
Gars
I donít think so. Itís original and hard as a rock.  :)
No cracks. I checked.

GMAD_Van Nuys

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Re: 68 Brake issue. Input needed.
« Reply #10 on: May 28, 2022, 09:44:28 PM »
cwyllie - The power brake booster is designed to retain enough vacuum to stop the vehicle a couple of times, even if the engine isn't running, for obvious safety reasons.  If you have air in the brake system, it would be evident when you first tried to stop your Camaro.  I still believe that your power brake booster needs to be replaced.  Is the booster original?  When my Mini-Vac didn't have enough vacuum to bleed the front one piston calipers on my 1979 Trans Am, I bled the brakes by using the brake pedal, which ended up damaging my power brake booster. - Mark

cwyllie

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Re: 68 Brake issue. Input needed.
« Reply #11 on: May 29, 2022, 03:58:15 AM »
Mark.
Thank you very much for the info.
I think the booster is original but hard to say. No markings and not plated.
I have bled the system several time with the pedal. How would that damage the booster?
Considering a power bleeder for next go round.
Craig.

Gars68Tux

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Re: 68 Brake issue. Input needed.
« Reply #12 on: May 29, 2022, 06:02:44 AM »
The booster, if original, should have a stamped application and date code...http://camaros.org/suspen.shtml#Brakecomp
Garth

68 RS L30 AA 749 Fred Gibb Chevrolet

GMAD_Van Nuys

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Re: 68 Brake issue. Input needed.
« Reply #13 on: May 29, 2022, 03:01:01 PM »
When my Mini-Vac didn't generate enough vacuum to bleed the front calipers, I should have gotten another power bleeder.  I might have not damaged the power brake booster if I hadn't depressed the brake pedal to the floor.  They have one-way bleed valves that you can install on the calipers to make it easier to bleed the system.  - Mark

Gars68Tux

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Re: 68 Brake issue. Input needed.
« Reply #14 on: May 29, 2022, 05:23:41 PM »
Just a thought, did you guys remember to push the button on the back of the metering valve http://camaros.org/brakevalve.shtml#mv when bleeding the brakes ??
Garth

68 RS L30 AA 749 Fred Gibb Chevrolet

 

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