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1992 Ford F-350 - icky brakes

7.3 diesel
Crew Cab

I have ICKY brakes. I say that because I don’t know what word is technically correct.

Typically I down-shift, so no real problem, but had to make an emergency stop, and took to the ditch. An alignment being much cheaper than repairs to 3-4 vehicles!!

I now know how to demonstarte a part of the problem to the mechanic.

On a level road, if I put it in 1st gear, and let the clutch out, and idle it up just a little to keep the engine from stalling, then with my left foot I smash down on the brake pedal hard, it takes 20 feet of travel before stopping.

Pressing on the brake is like trying to move a shock absorber.

A mechanic plugged the master cylinder, and with the back (drum) brakes (only) the pedal has a hard “stop.”

With the rear barkes pluged at the master cylinder, the pedal has no hard stop. Can keep pushing, and it will go almost to the floor.

With the back brake port still plugged, The mechanic clamped the front hoses at the lines, and there was a hard stop. Same test, but at the calipers, there again was a hard stopping point with the brake pedal.

The front calipers were replaced with Ford OEM parts (in case it was a poor Chinese copy, or “springy” steel).

Mechanic bled the p($& out of it.

Booster was replaced a long time ago.

Vacuum is good.

Mater cylinder was replaced w/ an oversize piston. About 1 year old.

Front calipers and hoses are new. 3 days old.

Rear brakes are newish, and “set up.” [by blocking the front brakes, the rear seem fine.]


Check the front brake calipers, the bleed screw should be at the top of the caliper, if it is on the bottom the calipers are on the wrong side of the vehicle.

HUGE mistake. A larger piston does not make MORE brake pressure, a smaller one does. Change it back and find better mechanics before you kill someone!

If the front brakes don’t work, it isn’t rocket science. Chase the lines from the master to the combo valve to the calipers and as Nevada said, make sure the calipers aren’t upside down.

But find better mechanics, these guys you a re working with are clueless!

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Thanks for the Really Nice photo, and suggestion. I’ve heard of this problem. :slight_smile:
I will crawl under and check, but I doubt that this is the problem as they are quite competent mechanics.
They (and the others) have just been thrown something really weird.
I’ve checked many (Ford) forums, with a multitude of suggestions, but there does not seem to be a high-probability answer.

Oh, should I respond to these e-mails? Not quite sure how this works.

No, they aren’t competent mechanics. The proof is that they haven’t fixed your brake problem AND they put in a larger bore master.

No you don’t have to respond to every post. When you respond, we can all see it.

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You didn’t specify, but if they’re the ones that put in the oversized master cylinder, then you need to re-evaluate that statement.

The rear brake shoes have to be properly adjusted for good pedal feel and good overall brake performance.

If he runs the test now (new front calipers, rear port plugged) and gets good results, then we know the problem is in the rear.

Thank you for your concern. My current brakes do apply. I can “lock them up” but only after the pedal has
traveled a considerable distance (almost to the floor). If it gets to the point where there is not so much travel,
Then I can probably evaluate if I need more pressure, thus switch back to a smaller bore.

One mechanic is on a paid service where he can look up problems - solutions. So far, it has not helped.

Larger bore master cylinder was one recommendation. The thought was that it was taking more volume of
fluid to…take up the slack? By having more volume, the brakes WOULD apply without the pedal going all the
way to the floor. But, thinking about this, it would probably be more of a volume of fluid problem. Say if it had to move
1 cc (cubic centimeter) of fluid, then it really wouldn’t matter. The same volume of fluid would need to be moved,
so it would “take the same amount of time” more or less.

CALIPERS ARE RIGHT-SIDE UP. I crawled under, and the bleeder is on the top.

Does this truck have a hydraulic brake booster?

No, unfortunately a different service did the master cylinder, so no “free” switch back.
This was also back before I discovered (?) the stall test. Back then is was just a
I say "the pedal “FEELS” the same
They say "the pedal “FEELS” better, and it stops better.
So, it was an impase. I pull out the plastic, then drive down the road.
It has been a LONG TIME PROBLEM. No one has time to keep hammering away at a problem
when typically it works acceptably. There has been over 7 mechanics I’ve had look at it in the past 4(?) years.

Correct. They are adjusted well. I can somewhat tell b/c my emergency brake will hardly move when applied.
If they are badly out of adjustment, then the emergency brake pedal will also go the the floor, and I need to carry
bricks to put behind the wheel.

But, at this time, the mechanic plugged the front brakes at the master cylinder, and with the rear brakes
Only connected, the pedal had minimal travel, and quick application. Well, at least that is what I was told.
It’s just that he is befuddled at the real problem.

This does raise another problem. The TRUST/truthfullness of the mech. I went to a nationally known shop for them
to bleed the brakes (thinking the problem was air in the line). They “used the machine.” They told me that
the master cylinder had an air leak (air leaking IN) and I needed a new master. Mainly for time, and possibly
that “little voice” I decided to not do that. The next mechanic said he could not bleed the brakes b/c a
rear bleeder had to be removed, and all the dirt/rust drilled out of the bleeder holes before he could bleed it.

Good point. I’ll put this on my 2 Do list.
I’m sure he would put a clamps on the hoses to the front calipers for me for no charge.

No, This truck has the old-style vacuum booster.
The vacuum pump is belt-driven. Mechanic said that the vacuum (pressure) was within spec.
Booster holds vacuum (don’t know how long it takes to leak down, but I’d guess close to 1/2 hour)
Not that it may matter, but rear brakes are drum.

**I’m attaching a photo of my $$$$ new calipers. Hope you can see it?
Let me know if I need to post it or other.**Drivers side, front axle. Calipers are on the back/rear of the axle.
I’ve clipped on a piece of string with a weight, so you can “see down/gravity.”