89 f-350 dually 4x4 with 460 and c6
just remedied a fuel problem I was having, and started driving the truck again.
suddenly the “rear antilock brakes” light came on and my front brakes started dragging. Bad.
every time I turn the truck off for a short period of time, the front brakes release, and then once I start driving again, they gradually start dragging more and more.
the RABS shows code 11 “stop lamp switch malfunction” when the light comes on.
but my brake lights seem to work just fine. Lol
this thing has me confused as heck.
I know it only has abs in the rear.
I have no idea why my fronts are the ones acting up.
they only act up if the rear abs light comes on. If I never exceed 35 mph they won’t lock up. I understand code 11 for the rabs only activated above 35mph

so I’m pretty much concluding that my FRONT brakes dragging is related to the rear antilock light coming on.

anybody have some insight for this? Does it make you guys scratch your head just as much as me?

 

That doesn't make much sense. The front brakes are completely independent from the rear, except for the master cylinder. And the rear abs system can't create pressure; it can only reduce pressure.
There is no pressure sensor in the brake system, so the abs computer doesn't know what the line pressure is. The only thing I can think of is your master cylinder may not releasing fully. This is caused the the brake booster rod being extended too far out.

 

Not sure myself if the 89 f350 had hydroboost. But, it sound like when a hydroboost unit is going bad and applies the brakes. Then bleeds off after not running. The RABS is another story.

 

Kindve my thoughts, that it doesn’t make much sense. Especially since the rear brakes are the only ones associated with the ABS.
it’s just ironic that the fronts only seem to act up after 35mph and the rear antilock light comes on.

Would you guys say that it a coincidence?

question for you guys, why would “all the sudden” the brake booster rod become out of adjustment? Or how rather would the brake rod become out of adjustment?

 

Post a picture of the brake master cylinder and lines, I wonder could a PO have mistakenly switched the front and rear lines?

 

Not likely. Truck didn’t give me any brake issues last fall when it was last drove.

 

I’ve got the truck on jack stands and can’t replicate the problem. Can’t get it to drag the fronts on jack stands. I’m gonna go drive it again I guess.

 

Still dragging after my drive.
doesn’t seem as bad as previously but is still dragging

 

The only thing the front and rear brakes have in common is the master cylinder. So I would suspect that. Don't know how it could cause that, but something is going on.

 

it is not the driving that makes the front brakes start dragging, it is the times you step on the brake pedal while driving that does it.
you can duplicate the issue by jacking it up, and step on the brakes around 20 times or so. then check the fronts and you will not be able to turn the wheel.
to check to see if it is the master cylinder push rod, loosen the master at the booster and pull it out. if it is the rod, the brakes will release.
to check master cylinder, loosen line out of master to brakes. if they release, the master is bad.
if they still stick, loosen the line going into the caliper. if the brakes release, replace the rubber lines between steel lines and caliper.
if they do not release, replace calipers.
i replace rubber lines every time i replace calipers.
they deteriorate inside and eventually collapse holding pressure in the caliper.
than when they sit, they slowly release the pressure until you step on the brakes again. the more times you hit the brakes, the more pressure they hold into the caliper.
my bet is you will find the rubber lines are collapsed inside.

 

I used to see malfunctioning hydro boost units over center themselves and do that same type of brake sticking thing
I think in your case I would replace the master cylinder
Unless you mucked with the pushrod length, that will not be your issue IMO
Same with the rubber hoses, pretty hard to get them to collapse and still hold pressure
Deteriorating rubber inside the brake lines could theoretically cause a chunk of rubber to plug the return port in the master cylinder
To me, those F350s always did have a slight amount of front brake drag
Rebuilt about a thousand calipers replacing pistons and seals on those dual piston calipers back in the day at the dealer
If you know how to overhaul calipers and replace the pistons, I'd possibly do that first
Ford changed their minds about three times on the pistons in those calipers, Phenolic and steel, settled on steel after a few years IIRR
The phenolic pistons were the ones that would stick

 

Thank you guys. Tied up a bit this weekend so as soon as I can get back in the shop Monday evening after work I’m gonna do some more playing around with it and let you know what I come up with.

 

Manicmechanic007 any chance you could come up with a link or some part numbers for me for a caliper rebuild? I’m pretty handy, I have repaired sticky calipers and rebuilt calipers before. In my experiences the rubber soft lines were most common cause for sticky fronts.
however, this scenario is definitely a little different. Both calipers are dragging the same… I’m inclined to believe the problem is not the calipers themselves or suddenly BOTH front soft lines.
but will do some more looking into it and let you guys know what I come up with if anything

 

https://www.oreillyauto.com/detail/c...uild+kit&pos=0
I was gonna rebuild mine, and my instructor told me this would do the job
This is for my 88 f150 though so it m not sure if yours would be different

 

Well, I pulled the master from the booster. Brakes didn’t release.
Pulled the lines off of the master, brakes didn’t release.
Got a new master since it was affordable for a decent unit at Napa. Bench bled her all up, got her installed. Cracked the bleeders on each wheel and the rabs in proper sequence. Wife got a good workout.
The brake pedal now feels firmer and better than ever, but the front calipers are now dragging worse than ever before too.
Gonna throw some new front rubber hoses at her and cross my fingers.
Even when I crack the bleeders on the calipers, I get a little stream out of them but they will sit and dribble as long as I’ve got the bleed screw open. Mind you this is without any brake pedal pressure applied.
But, I’m gonna start with the hoses and bleed them again. Rather not replace calipers if I can avoid it but I’ve got a pretty good feeling they’re gonna have to be replaced.