RTH front brakes dragging hard

[dcguillory]

On trip to Oregon noticed sucky acceleration. Pulled over and came to hard stop without pressing brake pedal. After some fooling around I let the brake fluid pressure off by loosening the screw at the caliper. Drove fine for quarter mile with lots of test stops, now dragging hard again. Can barely move. Yes I confirmed it's both front brakes not one bad caliper. A few days ago my shop replaced front pads and turned the rotors. They didn't mention anything about booster/master but I noticed some parts up there look a bit too clean. Portioning valve? What you think. 1996 lx450

 

[inkpot]

Try shortening the pedal push rod a couple of turns.

 

[HAAANK]

May also be loose caliper bolts. If the the bottom bolts come loose and fall out they will end up jamming themselves into the rim making it near impossible to go forward. They can fall back into place too, which makes diagnosing difficult.

 

[HAAANK]

On trip to Oregon noticed sucky acceleration. Pulled over and came to hard stop without pressing brake pedal. After some fooling around I let the brake fluid pressure off by loosening the screw at the caliper. Drove fine for quarter mile with lots of test stops, now dragging hard again. Can barely move. Yes I confirmed it's both front brakes not one bad caliper. A few days ago my shop replaced front pads and turned the rotors. They didn't mention anything about booster/master but I noticed some parts up there look a bit too clean. Portioning valve? What you think. 1996 lx450

Any update? Hope you’re rollin smooth.

 

[dcguillory]

Had real bad service up there. I have NOT figured out the problem other than it is all 4 brakes sticking and they engage all on their own. Temp fix has been to pull over whenever it happens(average 5 times a day at random intervals) and loosen a screw at the caliper to let a couple drops of brake fluid squirt and release the extra pressure. I am then good for anywhere from 10 min to 10 hours. Super random. Just cruising down a straight and all of a sudden start slowing down. I will make it home at least.

 

[Tools R Us]

Had real bad service up there. I have figured out the problem other than it is all 4 brakes sticking and they engage all on their own. Temp fix has been to pull over whenever it happens(average 5 times a day at random intervals) and loosen a screw at the caliper to let a couple drops of brake fluid squirt and release the extra pressure. I am then good for anywhere from 10 min to 10 hours. Super random. Just cruising down a straight and all of a sudden start slowing down. I will make it home at least.

This is almost always master push rod adjusted too far out. It holds the pistons to far in, covering the return ports. Has the master or booster been messed with?

 

[jpoole]

I agree with above and just finished testing/adjusting my booster pushrod and had this same problem with it was adjusted out too much.

A quick test to confirm that the pushrod is adjusted out too far is to loosen the 4 12mm nuts that hold the master cylinder to the brake booster. If you loosen these enough for a gap to open up between the master and the booster you can release the booster pushrod and resolve the issue. You may be able to feel how far overextended the booster rod is by loosening the nuts and then sliding the master in and out of the booster to feel where the rod contacts the master plunger.

If the quick test confirms that the rod is in fact too long and keeping master depressed permanent adjustment is easy. Remove the 4 nuts completely and then press the brakes to push the master out/off of the studs (or just pull the master off by hand). Leave all of the lines connected and just pull the master out. You can then prop the brake pedal with something or have someone push it out a little for you until you can see/access the splined section of the pushrod. Grab that splined section firmly with a set of pliers (I used needle nose vice grips) or similar and then use a 7mm wrench to turn the screw on the end of the pushrod to shorten it the appropriate length. etc. After doing this a time or two you will find that you can adjust the pushrod start to finish in under 5 minutes, so it's quick/easy. You want a miniscule gap between the plunger and the rod, or no gap at all along with no pressure on the plunger.

You probably will need to correctly bleed your brakes/calipers after this as you may have let air back into the calipers unless you were very careful about it.