The front brakes on my 2000 Toyota Sienna are dragging occasionally. I have replaced the front calipers (one of them twice), the master cylinder, and the ABS unit (with a junk yard unit). I have also shortened the master cylinder push rod to see if that would make a difference. The brakes still drag occasionally as indicated by the front hubs becoming excessively hot. Any ideas regarding what the root problem is?
It may be that the inner linings on the flex lines at the calipers are collapsing and closing the lines off. It is a known, albiet not common, phenominon in old lines.
I sincerely respect your willingness to do the repair work and diligence in chasing the problem, but would respectfully suggest that finding the cause up front would be a lot less expensive that changing parts and hoping for the best. The MC might have been a possibility, but the ABS unit would not likely cause these symptoms. The chances of all four solenoid-operated valves hanging up in this manner are remote.
Are the brake pad shims properly installed? Most require a bit of rubbery goo between them and the pad and some high temperature grease where the pads touch the brackets.
Replace the flex lines as directed by the poster above, especially if they look cracked and/or swollen. You will need lots of PB Blaster (soak the fittings overnight) and a set of high quality flare nut wrenches. If you damage the flare on the end of the metal brake line you will find yourself wishing you had let a mechanic do it.
I replaced the flex lines but there was no improvement in the brakes. Any other good ideas?
“brakes still drag occasionally as indicated by the front hubs becoming excessively hot.”
The next time you feel the hubs are hot, jack up the wheels and see if the BRAKES are actually dragging…
On the caliper mounting brackets look at the slide pins with the little rubber boots surrounding them. Those pins should easily slide/rotate in and out of the caliper mounting brackets. If they don’t it can prevent the brake pads from releasing from the brake rotors when the brakes are released.
I will agree with Tester about checking those slider pins. They’re 13 years old and should be serviced when doing any brake work.
I agree that the slides should be checked.
You might want to check the bearings too. Bad bearings can easily be mistaken for a hung up brake. The easiest way to do this IMHO is to remove the wheels and turn the hubs by hand. If there’s any roughness, suspect the bearings. There should also be no play when trying to wobble the wheel radially by hand with it suspended.
Another possibility is a sticking proportioning valve such that hydraulic pressure is not being fully supplied to the rear brakes or perhaps there is a brake line restriction to the rear brakes. If so, the front brakes could be carrying more load than they are designed to and thus are overheating. Some years ago a couple of early 1990s Ford Explorers I worked on had this particular issue with bad proportioning valves. Interestingly, only factory authorized remanufactured valves were available from the dealer not brand new ones. I realize your Toyota is different from those Fords but it might be worth checking into.