1990 F150 Brake Woes

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Air could only be drawn in when the pedal is released while the bleeder screw is loose.. I never had to use teflon tape on any bleeder screw.
yes, just typing about attempting a gravity bleed with the tube end immersed in brake fluid, like in a single operator bleed operation,
even with the tube in clean fluid, air can leak through the threads. Leading to small amounts of air trapped.
 
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yes, just typing about attempting a gravity bleed with the tube end immersed in brake fluid, like in a single operator bleed operation,
even with the tube in clean fluid, air can leak through the threads. Leading to small amounts of air trapped.
Huh? Once the fluid is through the threads and past the caliper, what difference does it make?
 
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I still don’t get how air can get in. It would have to have some place for fluid to shoot out. Calipers on wrong side is possible, but it must have some massive air bubble in it otherwise.
 
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Air can get past the treads and make it appear air is in the system. Particularly if the blender is backed out too far.

Some blenders have sealant applied to help Russles for example.
 

cbrf3

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So we found a few minor leaks, got them sealed and bled the MC then the corners in the correct order. A bit of air removed at every turn. Pedal feels pretty good when the truck is not running. With a short test crash around the neighborhood the pedal goes down too far for comfort, feels like mush and has a slow pedal return. When the brakes engage they are grabby and have no feel.

The truck is not safe to drive and is a bit terrifying on minor hills. Please help. 🤪
 
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If air is getting in, fluid is coming out. Where is it leaking?

sometimes the MC tank can leak where it attaches to the MC. If it’s dry, then you’ll pump in air the first time you go the next morning.

if there’s no leak, is there a drum brake with a messed up tightener? Is the first pump of the pedal just shoes or pads moving in? Are there improperly weighted springs in the drums? Too strong?

m
 
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Is there a proportioning valve in this system somewhere? Could it also be enabling rear brakes to send fluid back to the MC, causing a gap between shoes and drum in the am?
 
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They have a seat like a valve in a head. Wrapping the threads does not do a thing for sealing.
Right but it does prevent false air bubbles being drawn in past the bleeder threads. This false air does not prevent proper bleeding but in this case where he is getting bubbles at all four corners it doesn't hurt to determine if it is air really in the system of coming from the threads.
 
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cbrf3

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If air is getting in, fluid is coming out. Where is it leaking?

sometimes the MC tank can leak where it attaches to the MC. If it’s dry, then you’ll pump in air the first time you go the next morning.

if there’s no leak, is there a drum brake with a messed up tightener? Is the first pump of the pedal just shoes or pads moving in? Are there improperly weighted springs in the drums? Too strong?

m
Replaced with MotorCraft MC from RockAuto. MC dry at the lines and at the 2 lines going out. Also dry on the rear seal at the booster. The rear brakes were totally rebuilt using the kit from Summit.

But...We found a leak at reservoir seals/o-ring. MC came with the reservoir installed.
Is this just a return item or can we do anything about it? It seems aftermarket parts are not so good currently.
 

cbrf3

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Is there a proportioning valve in this system somewhere? Could it also be enabling rear brakes to send fluid back to the MC, causing a gap between shoes and drum in the am?
Proportioning valve is on the rear outlet of the MC, threaded in as an addition. Some MC we see do not have one and some do not have a tank.

Are there any brands worth trying? Dorman and Cardone seem to get decent reviews on Amazon otherwise, there is no feedback at all.
 
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It seems aftermarket parts are not so good currently.
Were they ever?

Usually anything Dorman is bottom of the heap, but by now, you’ll be able swap out parts and bleed brakes in your sleep—got nothing to lose by trying yet another MC.
 
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I bet the problem's in your master cylinder.

Bench bleeding is important because there's a dead space on the forward (headlight) side that points up and will get an air bubble that won't come out when it's installed. You may have done it right, you may have done it wrong, but you're not going to have a good feel for how you did until you assemble everything else.

If it's stubborn (and it is), I'd get a dishpan and a gallon of DOT-3 and dunk the whole thing and bench bleed it that way.

Or just get another MC. They're $35 on Rockauto. If you just bought this truck with spongy brakes, not knowing its maintenance history, what would you do? Sweet, so do it again.

When you bleed it, do the pump, stomp and hold method with a helper. It shakes more bubbles loose from random dead ends in the line. Pump the pedal 5x quickly and aggressively, hold it, have the helper crack a bleeder then close it after 1/2 second before your pedal sinks more than an inch or two. Repeat a few times on each corner.
 
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Bench bleeding is important because there's a dead space on the forward (headlight) side that points up and will get an air bubble that won't come out when it's installed.
So that‘s why on bench bleeding, never knew that. Thanks.
 

cbrf3

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Son replaced the new leaking Master Cylinder, bled all corners but still lousy brakes.
Pedal moves almost to the floor, the brakes are grabby and have no power nor feel and the pedal is sluggish to return.

Back to its position in the garage as it is unsafe to drive. ☹️
 
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cbrf3

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Safe to drive again! We had to bypass the old, clogged ABS system with a coupler and learned how to bend and flare some new brake line.
It was the fix as my son has been driving for a week now and the brakes are pretty good.

I did a few passes in front of the house and worked hard but was able to lock all 4 wheels evenly. 🚴‍♂️
 
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