Having braking issues with my '99 E-150. Some background:

Approx 2 months ago replaced:

Front rotors/pads
Rear drums, brakes and hardware

Gravity bled until no bubbles.

Issue: Brakes are good under normal around town braking. Good firm pedal with not much travel. However upon having to slam on the brakes occasionally, I experience less than full braking force immediately, then after about a 1 second delay, the remainder of braking force is supplied. I would guess 60% initial force followed by the additional 40% after the delay. There is also a slight pull to the right when the remainder of braking force is experienced, and then a little more pedal travel
I cannot tell if the problem is the front or rear, only that I would guess that the rears are delaying. Any ideas? Thanks

 

In order to remove any doubt about brake fluid I'd re-bleed them with someone behind the wheel pushing the brake pedal, aka "old school way". One of those check valve thingys from the cheapy auto parts places work remarkably well all things considered. The no bubble gravity way is good in some situations but nothing beats bleeding brakes properly.

My guess is your vacuum booster chamber isn't working properly. This could be a failing booster unit or the plumbing from the engine intake to the booster could be at fault too. The check valve mounted to the booster could also be an issue.

If your steering changes with brake pedal application then your issue is probably related to the front calipers. Assuming the slides are properly lubricated and the calipers are moving properly, the pistions not hanging up, the pads not unevenly worn then I'd suspect the flexible brake lines are or have collapsed.

HTH

 

Thanks JWA I will check out what you suggested. May have two separate issues happening

 

From what I'm reading.........your experiencing a delay in the rear brakes on a panic stop?

This would be some-what normal with ABS brakes.
You wrote that you have drums on the rear?
Is this van Rear ABS only? or 4 wheel ABS?

Also, if you have at least rear only ABS, did you bleed the ABS unit, after the right rear - left rear - ABS unit - right front - left front.

I'll agree that gravity bleed is not a really good way to bleed the system, I've always have pressured bleed brakes, using a rubber hose on the bleeder, into a container with fluid, open the bleeder, pumped brake pedal by hand, closed bleeder, and removed hose.
Sometimes it take 2-3 rotations to get the system expelled of any air, out of the system, specially if you had to replace a brake line in the system.

And, Always keeping an watch on the master cylinder, and adding fluid after each wheel was bleed, you do not want the master to run dry of fluid, as you need to start over and redo the system several times.

 

This van has rear only ABS. The brakes were gravity bled in the order you suggested but I did not bleed the ABS unit separately. Do you suggest bleeding the ABS unit when I re-bleed the system?

 

I'm not sure about Ford vans but......some vehicles require a Tech II to properly bleed the ABS. It cycles the ABS system

 

Yes, you'll need to bleed the ABS unit after the rear wheels, then the front wheels, it's mandatory that the unit is bleed.

You'll find this info in any repair manual.

 

This could be right, on some "newer" model years, or 4WABS.

I know on the '90's era, bleeding the ABS unit is not required for a Tech.

Someone with the right answer can jump in on this??

 

Just sounds like a hanging prop valve to me. Might have a bubble in it but likely just gummy. Not unheard of for them to hang shut momentarily when you hit em hard then it'll slam open and rapidly apply.

 

So I was able to re-bleed them last night even in the cold Chicago weather. Used my trusty bleeder buddy and pedal pushed 'em. The rears had no air bubbles but was surprised to see how dark the fluid was as I had just bled them several weeks ago. Both front calipers had a little trapped air. Kept bleeding until all was clear.
Took it for a drive and used some aggressive braking and found that there is no more pull to the right. Will have to wait for the next person who pulls in front of me to really test them but for the time being I believe they are better.