Author Topic: help troubleshooting brakes  (Read 1783 times)

Offline kpurser

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help troubleshooting brakes
« on: June 14, 2015, 09:19:21 PM »
I have a 78 Scottsdale k20. The brake light came on and then a couple weeks later the brakes went out. I only drive it a little on the weekends. Probably drove less than 20 miles with the light. With the truck running, the brake pedal will push full travel with almost no resistance till the last inch. The pedal comes back up very slowly. I can't pump the brakes up. The emergency/parking brake also does not work. The break fluid reservoir is about half full. I would appreciate any help. Also, any suggestions on resources to learn about the mechanics of this truck like books or other websights?

Offline Don5

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Re: help troubleshooting brakes
« Reply #1 on: June 14, 2015, 10:12:40 PM »
You need to look at the rear wheel cylinders. Look on the back for any leaks. You will probably have to pull the drum off to check inside. The rubber seals break down after a while and the leak inside the drum. Do you still have the original rubber lines? They will corrode on the inside and you can't tell by looking at them. That is another area to replace. I would also follow your brake line down the passenger frame looking for any wet spots too. You might have a small leak due to rust. That should help find any problems with the rear brakes.

You can check the front rubber hoses by opening the brake fitting on the back of the caliper. If fluid comes out, especially if someone puts pressure on the pedal, then the front lines are ok.   
It's been a LONG time since I have been called a newbie. Just sayin....

1979 GMC K15 355, SM 465, 205, 3.73 Dana 44 with a Spartan Locker, 12 bolt Eaton limited slip and 6 inch lift with 36 x 12.50 Super Swamper TSL's.

Offline jg1977c20

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Re: help troubleshooting brakes
« Reply #2 on: June 15, 2015, 02:41:43 AM »
check the brakes but im leaning more towards a blown master cylinder by your description ,
1977 c20 cheyenne camper special 8200gvw

Offline philo_beddoe

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Re: help troubleshooting brakes
« Reply #3 on: July 17, 2015, 07:54:23 AM »
Or you could do a full brake system re-placement. This is a sure fix with peace of mind, but it'll cost ya.
Behold, the day of the LORD cometh, and thy spoil shall be divided in the midst of thee.  Zechariah 14:1

Offline roundhouse

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Re: help troubleshooting brakes
« Reply #4 on: July 17, 2015, 06:28:19 PM »
I'd swap the master cylinder and the rubber flex lines front and rear and check the calipers and rear wheel cylinders for leaks

The light comes on when the fluid pressure is unbalanced between the front and rear


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