Brakes grabbing after startup

[The_Epsicle]

I drive a 1994 4.0 Extended Cab Ranger, auto 4x4, auto tranny, Dana 35 front Ranger 8.8 rear, 3.73 gears. This is a problem I've had since I've owned the truck but it just now is starting to annoy me. Right after startup my brake pedal will travel very easily without operating the brakes at all, until a certain point when it will grab and stop the car very roughly, this is at low speeds I haven't tried it at high speeds. After pumping the brakes a few times the problem disappears so I've just taken to pumping the brakes in the driveway before I leave. I have no brake light. I replaced the brake hoses on the front in December after they both exploded, I've repacked the wheel bearings, replaced all the ball joints, the front shocks, the rear shocks need to be replaced, the fluid level in the master cylinder has not gone down, and there is some rust on my power brake booster but it still has a vacuum.

EDIT: I'm pulling left under braking, and until the pedal hardens up a little the left rear tire locks but only the left rear tire. That's why I've been stopping rough at slow speeds.

 

[The_Epsicle]

I've done some searching and found out that Ford put out a TSB(Service Bulletin 985A36) for this. Unfortunately that TSB does nothing to tell me how to fix it or even what's wrong, when I find time I'll inspect the brakes and see what I find. In the mean time if anybody has more information about that TSB let me know.

 

[Mark_88]

Have you ever bled the brakes yourself? What colour is the brake fluid or has it been changed since you've owned the truck (completely changed, not just bled when the lines were replaced)?

Even if you have bled them till they bleed...it sounds like either there is air in the lines or the fluid is degraded to the point of needing changing.

 

[RonD]

Vacuum assisted Power brake booster works like this:

Inside the booster there is a rubber diaphragm, on the front side of this diaphragm is the check valve and the vacuum hose to the intake manifold.
Check valve holds vacuum at highest level regardless of current intake vacuum.
So the front side has a constant negative pressure while engine is running.

On the back side of the diaphragm, where the brake pedal push rod goes into the booster, there is the Atmosphere valve.
When you press on the brake pedal the Atmosphere valve is opened a little and the 15psi air pressure(at sea level) comes in, since the other side of the diaphragm has 18" vacuum(-9psi) the outside air pressure "assists" you in pushing down the brake pedal.
If your Atmosphere valve was failing it could be over assisting you, lol, before it starts working again.

You could also have a failing return spring so the resistance is less than normal, but I would think this would be an all the time thing, not just on start up.

 

[Mark_88]

Vacuum assisted Power brake booster works like this:

Inside the booster there is a rubber diaphragm, on the front side of this diaphragm is the check valve and the vacuum hose to the intake manifold.
Check valve holds vacuum at highest level regardless of current intake vacuum.
So the front side has a constant negative pressure while engine is running.

On the back side of the diaphragm, where the brake pedal push rod goes into the booster, there is the Atmosphere valve.
When you press on the brake pedal the Atmosphere valve is opened a little and the 15psi air pressure(at sea level) comes in, since the other side of the diaphragm has 18" vacuum(-9psi) the outside air pressure "assists" you in pushing down the brake pedal.
If your Atmosphere valve was failing it could be over assisting you, lol, before it starts working again.

You could also have a failing return spring so the resistance is less than normal, but I would think this would be an all the time thing, not just on start up.

AhA~! I was right...I just gave the booster advice to the wrong person...it should have been here...and the other guy gets to bleed brakes...

 

[RonD]

After re-reading OP I no longer think it's power booster, I think you have a bad slave or spring on left rear drum.
It is leaking but you may not see where, it is returning to closed all the way when it sits.
So when you first start off it has to refill and that causes the long pedal push, it has to re-expand so shoes are touching drum again, which is also causing the lock up on the left rear.

Can't explain the pulling though, that's front brake issue, and the front and rear brakes should be separate.
The reason hydraulics are used for brakes is because the pressure will be equal at both front wheels, pulling is generally the sign of a bad caliper.
If vehicle pulls to the left then the right caliper is not transferring enough/equal braking

 

[adsm08]

Ron, I have seen rear brakes cause a pull too. It's not as common because the difference in performance has to be drastically different, but it can happen.

I agree, it seems to sound like an issue in the hydraulics is causing your problem. Check the rear brakes for leakage.

 

[The_Epsicle]

Thanks for the help everyone, the steering pull is hardly noticeable but that is also because my steering is loose because of a sloppy gearbox and I've associated weird steering issues to that for awhile. The front brakes ought to be good since the pads and rotors are wearing evenly. When I replaced the hoses I bled the front but not the rear and the fluid looked new, so far I haven't looked at the rear brake system and I wouldn't be surprised if those hoses were about to go as well, I've been in my chiltons a lot since I don't have a lot of experience with drum brakes and the spring would make sense too. I'll check both, thanks!

 

[InsaneBroncoII]

Is the pushrod mis adjusted?

 

[96firephoenix]

I experienced this same issue the other day, and was surprised to find this very recent thread on the topic...

I can attest to the "pull". Mine pulls the ass end out like it's going into an oversteer condition, and then the wheel locks up. I'm thinking that there has to be some differential pressure between the rear brake drums.

I did notice that with about 300 lbs (fridge) in the bed, the problem did not appear. I did a deliberate test to see if this would occur, rather than find out suddenly with extra weight in the mix... I'm wondering if perhaps it is originating in the suspension, or if that is merely a coincidence (leaning towards the latter).

 

[scrapper]

Mine does that but only once. It seems to do it after it rains, heavy dew. I remember somewhere reading a lot of rangers have this problem.

 

[ranger1997]

Front pads could have brake fluid on them from the blown hoses, will cause grabbing and uneven braking. Moisture will exaggerate the problem.

Cheap pads and shoes can also cause grabbing. I had a set of cheap pads on my 97 ranger from auto zone that just plain sucked and would lock up easy when cold or wet until they warmed up a bit.
They almost got me in a wreck in the rain.

Possible the rear also. You need to do a good inspection of your brakes front and rear.

Me personally would replace rear wheel cylinders and shoes, springs as needed, turn the drums. If the drums have fluid on them replace them. If the front calipers are old replace them also.
Flush the brake fluid and bleed.
It will cost a lot more if you hit something.

If you have anti lock special procedures apply for proper bleeding.

Anti lock can cause strange issue also if the module has air in it.

My 97 only has rear anti lock and there is a valve under the truck that must be held open to properly bleed the rear brakes.

I use bendix thermoquiet brakes and very pleased with them. No fade or rapid wear or grabbing.

There was a TSB on the ranger brakes for grabbing and a believe replace of pads or shoes was the fix, don't remember front back or both.

I would think a booster problem would be all the time. Usually the diaphragm goes bad and they would be hard to push be cause it doesn't hold vacuum.


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