Author Topic: PLEASE PLEASE HELP, NO REAR BRAKES 2  (Read 5088 times)

kcandc

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PLEASE PLEASE HELP, NO REAR BRAKES 2
« on: May 28, 2006, 12:25:29 AM »
PLEASE PLEASE HELP, NO REAR BRAKES 2, I converted from manual drum to power disc/drum and the rears do not work. I have replaced the booster/master cyl, combo/porportion valve, front and rear flex hose's, rear brake tubing, wheel cylinders and the rear brakes just will not work, period. No air is present in the system, the front calipers work perfect. What is going on??? Any help would be greatly appreciated. Thanks, Karl

JohnZ

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #1 on: May 28, 2006, 12:33:50 AM »
Did you bench-bleed the new master cylinder before installing it?
'69 Z/28
Fathom Green
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Steve68

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #2 on: May 28, 2006, 01:00:36 AM »
Do you get any movement of the rear pads at all when the brake is applied?

kcandc

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #3 on: May 28, 2006, 04:38:50 AM »
Yes, Master Cylinder was bench bled before installed. Rear brake shoes do not move at all when pedal pushed. With both feet firmly planted on brake pedal, you can turn the rear drums by hand. Funny thing is, when you drive it, the pedal feels normal and it stops excellent. I just don't think the rear drums should be able to turn with the brakes applied. I installed the exact same system on my 56 Nomad and you can't turn them???? Thanks for you imput, Karl

Steve68

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #4 on: May 30, 2006, 12:21:28 AM »
Karl

Since you have fluid at the wheel cylinders then there must be a mechanical problem with the brake set-up within the wheels.  Do you have a shop manual to reference?  If so I would suggest looking at the pictures closely to see if there might be something reversed....such as a spring or the star wheel etc.  There has to be something mechanical wrong or something in the "workings" or the mechanical part of the brake in the wheel and not the new wheel cylinders.  I know this may seem obvious but it would not be the first time a part was installed backwards or upside down.   :)

Steve

kcandc

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #5 on: May 30, 2006, 02:39:37 AM »
Thanks for the input, Steve. I have checked all the mechanics and everything is correct. I have come to the conclusion that the porportioning valve limits the system in a static mode. Once driven, the brakes work great and the rear drums are hot, so I believe they are working while driving, just not while up on jack stands. I may be wrong, but the car stops perfect now. Thanks again, Karl

My68SS

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #6 on: May 30, 2006, 05:18:57 PM »
Doesn't sound right to me, rear drums should apply even stationary, otherwise you could never bleed them. The prop. valve knows nothing of vehicle motion.
Sounds like the pistons in the slave cylinders are stuck???  My steps would be, crack drivers side bleed nipple open and check that the pedal now goes down a long way and fluid is ejected from the nipple.
If that's ok, tighten up the nipple and remove the drum. Press the pedal with gradual increasing pressure. With only moderate pressure you should feel that the pedal is soft and see the brake shoes move outwards. If not, something is stuck.

Does the park brake work? If yes then it can't be jammed shoes - not much left then but the cylinders.
Rob
1968 12C SS
L34/M40
12 bolt posi 3.55

kcandc

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #7 on: June 04, 2006, 03:08:52 AM »
The parking brake works good. The wheel cylinders are new and I have checked the pistons and they are free. I have checked the whole system at least 3 times and everything is correct. After I bled all the air out of the system, (several times to make sure) I removed one of the rear drums and my wife pressed  the pedal as hard as she could and there was no movement at all. The pin on the front of the porportion valve still pops out when the brakes are pushed, so there is still a pressure difference from front to rear. I am going to take it in and have the brakes pressure bled and see what that does. Thanks for all your help, Karl

Steve68

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #8 on: June 04, 2006, 11:23:05 PM »
Karl

If you have the capability of taking a close-up picture of the back brakes post it so we can examine them and see if another set of eye might spot something for you.

Steve

DanZ10

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #9 on: June 05, 2006, 02:10:30 PM »
Karl, I'm betting one of three things is wrong. Either you have the front and rear outlets on the master reversed (feeding the wrong wheels), the rear section of the master cylinder is bad (pinched or split rubber cup), or the proportion valve you are using is stuck or installed reversed. Since you have NO brakes AT ALL on the rear, but you did get enough fluid through the system to bleed the rears, I'm betting on a proportion valve problem.

good luck


kcandc

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Re: PLEASE PLEASE HELP, NO REAR BRAKES 2
« Reply #10 on: June 11, 2006, 05:13:10 AM »
Thanks for everyones help! We bled these brakes so much and no air was coming out, so I thought it was all out! Wrong!, I drove the car over to a local brake shop, and with their vacuum pump they removed so much more air it's obvious why they were not working. I have since invested in one of those vacuum pumps. Never again will I pump to bleed. My lesson for the week I guess.
Thanks again and remember this little trick. $50.00 and 20 minutes and your done. ;D ;D