1995 Ford Taurus 6 cyl Front Wheel Drive Automatic 112500 miles
My '95 Taurus has a rear disc brake drag problem, as indicated by excessive heat and odor, smoke and/or pad/rotor wear/discoloration (and likely mileage), obvious when driven more than a few miles, right (R)side is more noticable than left (L), but both sides are similarly affected. I have seen very few posting on web about such a serious/annoying performance problem.
I have replaced the following without any effect: L& R side flexible brake lines (new), R side caliper (rebuilt), caliper bracket and slide pins (new), parking brake return spring (new), L& R rotors and pads, as well as the load sensing proportioning valve (salvaged). All with no change.
When jacked up and the road wheel removed, the rotor hub may be turned by hand with slight drag (deemed 'normal'), however if foot brake is depressed
the brakes are 'locked' (deemed 'excessive') until caliper is wriggled by hand.
What can account for this, how do I debug it and what is the cure? The car will soon be used for two new drivers about to enter the driving world so safety/reliability is a primary concern, but cost is also a consideration.
o-Brake fluid flush/replace?
o-Master Cylinder test procedures?
o-ABS test procedures?
o-TSB or known issues?
Are you saying when the service brake is applied then released, the rear brakes stay locked? Does the piston noticeablr retract? If yes the slide pins need to be replaced and thoroughly greased with silicone brake grease.
May, 29, 2008 AT 10:12 AM
Thanks for your reply. Per my original post, all pins are *new* (and properly lubed). Yes, when testing with rear end jacked up and road wheel(s) removed, after the service brake is depressed, the rear brakes continue to drag, even after foot pressure is released - unless the caliper is manipulated. (During regular operation it is difficult to detect drag unless car is driven long/far enough to heat up and/or cause odor/smoking, and even more difficult to manipulate caliper to see if doing so helps eliminate the drag).
Your response raises two additional questions, however: One about the pins, in that they fit quite loosely in the pin guides (which are part of - pressed into - the fixed bracket.) This is very noticable when test fitting the pins into the guides dry, and they still seem 'loose' to me when properly lubed with (silicone) grease. Since my pins and R side bracket are all new, should this be the case? (I.E, Have you verified this to be the case on functioning rear disc brakes?)
Another question about brake pad movement. Since the amount of movement a brake pad makes when going from 'applied' to 'released' is minimal, should you even be able to notice it (i.E, should the brake pad pull *visibly* away from the rotor)? If so, what causes this retraction (internal master cylinder return spring, fluid pressure)? I cannot say I have ever seen this to be the case in any disc brake application I've worked on in the past.
Thanks again. Please advise.
May, 29, 2008 AT 1:16 PM
If your calipers have the parking brake levers, make sure the notched in the inner pad sits in the groove in the piston, or drag will occur, second, the pins should be snug, and there should be a thin 1/2 wide plastic strip wrapped around them. And the lever for the parking brake should be fully relaxed. Now if all these are OK make sure the front calipers pads and hoses are good, this car as in all front drives, has diagonal braking system meaning left front and righr rear are paired off the master cylinder. The same is true for the opposite side.
May, 29, 2008 AT 2:53 PM
Thanks, good info! I'm as sure as I can be when sliding the caliper/piston assy over the pads that the notches/bumps line up (check visually before, wiggle afterwards to feel).
Now, your reference to a " 1/2 thin plastic strip wrapped around them" has me puzzled, it was not on any of the [original] pins I removed, was not included with the new bracket and pins I purchased from a local parts jobber, nor does it seem to appear in the drawings I referenced online (gif hopefully attached). All I see are the pins (#12) and the collapsible rubber boots (#10). Is the plastic strip intended as a sleeve? (The pins I have are all metal, with grooves for the rubber boots at the outer end, and three machined 'flats' [presumably to prevent hydraulic or pneumatic lock?] Running for some length along the inner end.) Should I go to the dealer for a more accurate parts list/drawing?
Thanks again. Please advise.
May, 29, 2008 AT 2:59 PM
Here's gif I referenced in previous reply:
May, 29, 2008 AT 3:59 PM
These will be an extra if your pins are loose! If they are too loose get new calipers, the holes have spread, and may be allowing the caliper to cock and missalign itself.
May, 29, 2008 AT 4:08 PM
Never mind on the plastic, thats a different model, you pins slide into the mount, and altho they should move freely, they should not be loose, the mounting brackett may be worn out...
June, 1, 2008 AT 10:58 PM
So, I've had a busy weekend. After reading a post about problems with the master cylinder [orifices being blocked], I replaced it with a rebuilt master cylinder from a local auto parts store, and while there, swapped the rebuilt right side caliper [which was still dragging] for another rebuilt one.
Upon reassembling and bleeding the system all seemed fine. Initial testing, with the rear end jacked up and road wheels off, indicated no brake drag after releasing the service brake pedal. My first road test however, was horrible. After only a five mile trip down a highway and back the smell of overheated brakes was evident, and now the LEFT wheel is the one affected, too hot to work on and visibly smoking.
So now what? Should I have the entire system flushed before proceeding further? If this were a common problem, I'm sure I would have read about it elsewhere. I'm seriously considering dumping the car, even after all this work and expense.
June, 2, 2008 AT 5:17 AM
You still havent said if you looked at the fronts. Diagonal brake system. And if the ride hieght valve is set wrong you can get this, the is a pressure gauge used to measure the rear brake pressures, your must be too high, try re-adjusting the valve. Open the bleefer on that left caliper, does it spin? Three things back there that can cause drag, Hose, caliper, and parking brake cablee too tight, (pulling lever)And in your case, the hieght valve.
June, 3, 2008 AT 12:00 PM
The front brakes (pads and rotors) have always looked and operated fine, no discernable heating, dragging, or abnormal wear. Despite 'diagonal' braking circuits, only the rear brakes have ever been problematic (dragging/heating), both similary affected at about the same time(?).
My latest endeavour was to replace the only items on the rear I had not; the Left Rear caliper and its bracket. This " seems" to have fixed the Left Side dragging for the time being, and I am now running cool on both sides so far.
I still do not understand the failure mechanism which affected only the rear brakes (never the front), gradually, over time - manifesting itself as heat and drag - with the only visible defects initially being the aging rear flexible brake lines (softened, outer layers cracking, but never leaking). Brake fluid, while bleeding lines throughout all this, always ran clean, never appeared to be discolored or to contain any foriegn particles of any kind.
In summary, I replaced both rear side pads, rotors, calipers, brackets, pins, flex lines, and parking brake return springs in order to " cure" this problem. In addition (and I suspect it was not absolutely necessary to), I replaced the load height proportioning valve and the master cylinder (out of frustration and desperation).
Thanks again for your input[s]. (And for keeping your fingers crossed over the next few weeks). I would still be interested how extreme, or common, the steps I took were to fix this, from someone with more experiance in these matters.