1989 F-250 7.3 Project

[DrCharles]

The rear ones are weird. When I have someone pump and stand on the brakes, when you crack the bleeders some fluid drips out but then it just stops. I'll have to hook up vacuum bleeders.

Ask yourself first, why doesn't standing on the brakes make fluid shoot out like Old Faithful? The pressure available from the master cylinder is far greater than anything you can do with vacuum (-14.7 psi is a perfect vacuum). Either there's a lot of air in the system, your RABS is defective and dumping the pressure to the rear brakes, the master cylinder is bad, etc.

 

[hacked89]

Ask yourself first, why doesn't standing on the brakes make fluid shoot out like Old Faithful? The pressure available from the master cylinder is far greater than anything you can do with vacuum (-14.7 psi is a perfect vacuum). Either there's a lot of air in the system, your RABS is defective and dumping the pressure to the rear brakes, the master cylinder is bad, etc.

Yea. New master cylinder, rabs I havent touched, from other vehicle experience i expected it to be steady flow out even farther from the master. I bled in the proper order for the truck, including the rabs. Vacuum can be 20psi. Also, I always thought if the pedal made it all the way to the floor that let's air in the system? Not sure if that's true or legend.
With the vacuum bleeding, dont need to worry about that. Anyway, that's the reasons I said I'm going to vacuum bleed next.

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[DrCharles]

No, it can't. Atmospheric pressure is 14.7 psi at sea level. So in a perfect vacuum, no air molecules at all, 0 psi (absolute) is -14.7 psi (gauge). You're probably thinking of inches of mercury which is how automotive vacuum numbers are frequently expressed. A perfect vacuum there is 29.92 inHg. or just about 2 inches per psi.

Pedal to the floor does NOT let air in the system. What it can do, however, is ruin the seals in a well-used master cylinder because the bore will be worn where the seals normally travel, and there can be a ridge there (just like piston rings leave a ridge near the top of a cylinder bore).

Every bleeder screw should move fluid (or air) whenever the pedal is stroked. If it's just large amounts of air, sure, vacuum bleeding at the screw (or pressure bleeding at the master) is easier. Let us know what you find.

 

[hacked89]

No, it can't. Atmospheric pressure is 14.7 psi at sea level. So in a perfect vacuum, no air molecules at all, 0 psi (absolute) is -14.7 psi (gauge). You're probably thinking of inches of mercury which is how automotive vacuum numbers are frequently expressed. A perfect vacuum there is 29.92 inHg. or just about 2 inches per psi.

Pedal to the floor does NOT let air in the system. What it can do, however, is ruin the seals in a well-used master cylinder because the bore will be worn where the seals normally travel, and there can be a ridge there (just like piston rings leave a ridge near the top of a cylinder bore).

Every bleeder screw should move fluid (or air) whenever the pedal is stroked. If it's just large amounts of air, sure, vacuum bleeding at the screw (or pressure bleeding at the master) is easier. Let us know what you find.

Thanks for the detailed explanation

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[Jimbanjer]

I'm also looking for a zf5 truck with a nice bed to swap onto my truck.
If anyone has a bedded truck that wants a flatbed, or a manual truck that wants a c6. Hit me up and come over. I'm in PA.

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I can’t even find anyone selling a zf5 for an idi down here in the Carolinas! Although I’d love to make the same trade!

 

[hacked89]

No, it can't. Atmospheric pressure is 14.7 psi at sea level. So in a perfect vacuum, no air molecules at all, 0 psi (absolute) is -14.7 psi (gauge). You're probably thinking of inches of mercury which is how automotive vacuum numbers are frequently expressed. A perfect vacuum there is 29.92 inHg. or just about 2 inches per psi.

Pedal to the floor does NOT let air in the system. What it can do, however, is ruin the seals in a well-used master cylinder because the bore will be worn where the seals normally travel, and there can be a ridge there (just like piston rings leave a ridge near the top of a cylinder bore).

Every bleeder screw should move fluid (or air) whenever the pedal is stroked. If it's just large amounts of air, sure, vacuum bleeding at the screw (or pressure bleeding at the master) is easier. Let us know what you find.

Here's what I found. I'm either doing something dumb and introducing air into the system or something is broken. More likely the former, cause I didnt have these problems before.
The PO said they replaced the master cylinder and booster. I definitely saw him buy and replace the booster cause it was something I asked for before I got the truck.

After my last round of brake bleeding, it now goes to the floor and needs to be "pumped up" to have pressure to stop.
Heres exactly what I'm doing. The order is RR,RL,RABS,FR,FL.
1. Crack open the bleeder
2. Put vacuum pump attachment into the bleeder.
3. Squeeze pump handle into theres about 2 inches of fluid in the catch can
4. Remove vacuum pump
5. Close bleeder



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[The_Josh_Bear]

Here's what I found. I'm either doing something dumb and introducing air into the system or something is broken. More likely the former, cause I didnt have these problems before.
The PO said they replaced the master cylinder and booster. I definitely saw him buy and replace the booster cause it was something I asked for before I got the truck.

After my last round of brake bleeding, it now goes to the floor and needs to be "pumped up" to have pressure to stop.
Heres exactly what I'm doing. The order is RR,RL,RABS,FR,FL.
1. Crack open the bleeder
2. Put vacuum pump attachment into the bleeder.
3. Squeeze pump handle into theres about 2 inches of fluid in the catch can
4. Remove vacuum pump
5. Close bleeder



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Are you still getting air to bleed at this point? If not then air isnt your problem.

The booster and master were changed yes? If the installer didnt match the pushrod length correctly you will have this problem or the opposite-- brakes dragging.

Page 4 of this file explains how to check if its working within parameters. Takes two people but only about 1 minute to check, thankfully.

 

[hacked89]

Are you still getting air to bleed at this point? If not then air isnt your problem.

The booster and master were changed yes? If the installer didnt match the pushrod length correctly you will have this problem or the opposite-- brakes dragging.

Page 4 of this file explains how to check if its working within parameters. Takes two people but only about 1 minute to check, thankfully.

Thanks I'll have to grab a friend, even though I dont think that's the problem right now it will be good to adjust and check.

So theres always some air bubbles coming through because I didnt grease around the bleeder screw, which i will do and bleed again. The RR I'm able to pump the fluid out at a decent smooth pace. The LR I'm pumping the vacuum pump a long time continuously just to get the 2 inches of fluid. Same for the RABS. The Front brakes I can get the 2inches quickly.
Maybe the rabs is messed up. Brake lights were always on this truck, but I assumed it was the sensor in the axle. I also did the diagnostic test where you ground the pin and count the flashes and it backed that up. I didnt get to swap it get because I tried today and it was like stuck in the axle.
Plus the weather sucks here. I hate the cold and its rapidly dropping to 5 degrees tomorrow in PA.

Edit: what I'm saying is I only got these new symptoms after I changed the caliper and lost all the fluid. So I assume I'm bleeding wrong or something.

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[The_Josh_Bear]

Thanks I'll have to grab a friend, even though I dont think that's the problem right now it will be good to adjust and check.

So theres always some air bubbles coming through because I didnt grease around the bleeder screw, which i will do and bleed again. The RR I'm able to pump the fluid out at a decent smooth pace. The LR I'm pumping the vacuum pump a long time continuously just to get the 2 inches of fluid. Same for the RABS. The Front brakes I can get the 2inches quickly.
Maybe the rabs is messed up. Brake lights were always on this truck, but I assumed it was the sensor in the axle. I also did the diagnostic test where you ground the pin and count the flashes and it backed that up. I didnt get to swap it get because I tried today and it was like stuck in the axle.
Plus the weather sucks here. I hate the cold and its rapidly dropping to 5 degrees tomorrow in PA.

Edit: what I'm saying is I only got these new symptoms after I changed the caliper and lost all the fluid. So I assume I'm bleeding wrong or something.

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Ok gotcha. I dont use vac bleeders so I have no advice-- tried it once and didnt like it so never tried again. But grease on the threads is a good idea and sounds like it could make it work. Make sure to crack the bleeder only as much as you need to pull fluid and no more.

I don't think the RABS can actuate the brake lights. AFAIK its strictly the brake pedal switch. I'm sure someone that knows more will chime in, maybe the switch is bad?

 

[hacked89]

Ok gotcha. I dont use vac bleeders so I have no advice-- tried it once and didnt like it so never tried again. But grease on the threads is a good idea and sounds like it could make it work. Make sure to crack the bleeder only as much as you need to pull fluid and no more.

I don't think the RABS can actuate the brake lights. AFAIK its strictly the brake pedal switch. I'm sure someone that knows more will chime in, maybe the switch is bad?

Yea thanks that's why I bought the switch.
This is my first time using a vacuum bleeder which is why I'm unsure too. I'm not too impressed but it could be user error.
What method do you use?

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[79jasper]

Yea thanks that's why I bought the switch.

You mean the brake lights at the back of the truck? Or the dash lights.
Need to clarify.
I prefer pressure bleeders. Speed bleeders are the cats meow.

I don't think the RABS can actuate the brake lights. AFAIK its strictly the brake pedal switch. I'm sure someone that knows more will chime in, maybe the switch is bad?

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[The_Josh_Bear]

You mean the brake lights at the back of the truck? Or the dash lights.
Need to clarify.

Good call

 

[hacked89]

You mean the brake lights at the back of the truck? Or the dash lights.
Need to clarify.
I prefer pressure bleeders. Speed bleeders are the cats meow.





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Dash

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[79jasper]

Then that is a issue with the RABS system. Personally, I would bypass the rabs valve.

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[hacked89]

I've been real busy hopefully closing on a house with a good size 3 car garage end of March.

Enjoying my last days laying in the dirt and cold.
For the truck, I first pulled the rabs off and the rear brake fitting was completely seized. I had to cut the line. I suggest taking the whole line off or atleast dropping it. I took it off.
Here are some flaring pictures. If you have any questions on sizes of anything let me know.

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Let's not forget the most important piece to bolt right in..

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Then just re run the rear line.
I also picked up a power bleeder. It's great.

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