1986 F150 soft brake pedal only when running
01-19-2018, 08:20 AM
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1986 F150 soft brake pedal only when running
I have a 1986 F150 regular cab short bed 4x4 4 speed with the 4.9.
Okay, here is the issue:
I have been bleeding the brakes on my truck (starting with the passenger side rear, then going to the driver side rear, then the passenger side front, and finally the driver side front). I can get the pedal to be firm, but as soon as I start the truck it goes to the floor when I push it. It will still stop the truck, but the pedal feels very spongy. I have tried bleeding the brakes multiple times, but with no avail.
The truck has a new brake booster, master cylinder (which was bench bled correctly), calipers, and all three rubber lines are new. I have checked and there are no leaks at any of the lines. Also, the wheel cylinders are not leaking. Oh, and the master cylinder has brake fluid in it. I am sure that someone is going to say that there is still air trapped in there, but instead of just saying that please explain how this can be when there is no air coming out of the bleeder screws. On the driver side towards the front of the truck there something that all the lines run into. I have attached some pictures of one in unknown condition from another truck. Is there something that I am supposed to do with this? I know on newer trucks you have to bleed the rear antilock brake system valve, but I didn’t think they had that on 86. I could be wrong though.
Any advice will be greatly appreciated. Thanks in advance.
Okay, here is the issue:
I have been bleeding the brakes on my truck (starting with the passenger side rear, then going to the driver side rear, then the passenger side front, and finally the driver side front). I can get the pedal to be firm, but as soon as I start the truck it goes to the floor when I push it. It will still stop the truck, but the pedal feels very spongy. I have tried bleeding the brakes multiple times, but with no avail.
The truck has a new brake booster, master cylinder (which was bench bled correctly), calipers, and all three rubber lines are new. I have checked and there are no leaks at any of the lines. Also, the wheel cylinders are not leaking. Oh, and the master cylinder has brake fluid in it. I am sure that someone is going to say that there is still air trapped in there, but instead of just saying that please explain how this can be when there is no air coming out of the bleeder screws. On the driver side towards the front of the truck there something that all the lines run into. I have attached some pictures of one in unknown condition from another truck. Is there something that I am supposed to do with this? I know on newer trucks you have to bleed the rear antilock brake system valve, but I didn’t think they had that on 86. I could be wrong though.
Any advice will be greatly appreciated. Thanks in advance.
01-26-2018, 09:27 PM
#2
Senior Member
That's your proportioning valve. There should be a small pin on the top that you have to pull up a little to bleed the rear brakes correctly. Some people say you have to pull it, some say you don't if there's fluid to the rears. I always just pull it to be safe.
My guess for your problem though is there is still air in the master. Pick a side nut and loosen it a small amount and see if any air bubbles come out. Tighten it then try the other one.
My guess for your problem though is there is still air in the master. Pick a side nut and loosen it a small amount and see if any air bubbles come out. Tighten it then try the other one.
01-27-2018, 12:24 PM
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WHY did you start bleeding the system? Was there some problem before you started?
HOW "new" is each of the parts you mentioned? As new as this problem, or more than a few days older? What's the brand/PN/source for each part? Why was each one replaced? Did each one pass the same test that the original failed? WHO installed each part? Has he done this job many times before, or did he follow the instructions in some shop manual? Are the caliper bleed screws pointing up, or down? (I've seen it many times before.)
Have the REAR brakes been checked/serviced properly? Does the emergency brake work properly? Is the tension limiter still good, and adjusted?
It would probably help us help you if you upload several good pics of the truck, the calipers, the rear brakes, the tension limiter, and the MC. And you should put ALL the truck's details into your signature here. This caption explains how:
(phone app link)
HOW "new" is each of the parts you mentioned? As new as this problem, or more than a few days older? What's the brand/PN/source for each part? Why was each one replaced? Did each one pass the same test that the original failed? WHO installed each part? Has he done this job many times before, or did he follow the instructions in some shop manual? Are the caliper bleed screws pointing up, or down? (I've seen it many times before.)
Have the REAR brakes been checked/serviced properly? Does the emergency brake work properly? Is the tension limiter still good, and adjusted?
It would probably help us help you if you upload several good pics of the truck, the calipers, the rear brakes, the tension limiter, and the MC. And you should put ALL the truck's details into your signature here. This caption explains how:
(phone app link)