Soft brakes

toyota
brakes
sienna

#1

I brought our 2005 Toyota Sienna (FWD) in for new tires and a routine oil and lube in April of 2011. The car has 100,000 miles on it and is up to date on service. In May of 2010, we had new brake pads put in with no problems since. However, at the recent tire change the local garage said that 1 brake pad on one of the front brakes was worn and grabbing more than expected and that the caliper on that side was “frozen”. He had to “heat” up the caliper to release it and replaced the pad. Since then, the brakes have been very soft. We returned the car and he bled them twice. This helped a bit but they became softer within a week. We returned the car and the mechanic said it might be the master cylinder, the pushrod, or later after speaking to Toyota a problem with the brake booster which was under recall. We called Toyota who said there was no such recall. Can someone suggest to myself ( a non-mechanical type guy) what might have happened to our car.


#2

It’s possible that if he heated the caliper too long, he boiled the fluid. Once you do that, it’s usually easier just to flush the system with all new fluid rather than just doing a normal bleed. It’s also possible that he heated the wrong area and damaged a brake line (generally mechanics heat with a torch), and you have a slow leak - when he bled them, he added fluid up top which would have replenished what you lost.

It’s also possible that you have a bad master cylinder. Easy to test: When they go soft, come to a complete stop, put the car in neutral, and then let up on the brake pedal completely, then slam on the brakes. If the pedal feels firm, you have a bad master cylinder seal. If it still feels soft, you either have air in the lines or are low on brake fluid.


#3

Thanks for the answer and advice


#4

One thing to consider at this age & mileage is breakdown of the flexible brake lines at the wheels. This could have been hastened by the heating. Basically, if those lines get old & soft the pressure of the fluid can more or less go toward ballooning the walls of the brake line rather than applying pressure at the caliper.

If you do just sit and hold pressure on the brake pedal does it eventually settle and stop sinking? Or will it slowly just sink to the floor under pressure? If it just keeps sinking then you probably have a master cylinder problem.


#5

Thanks for your advice


#6

Yeah…flex line breakdown…especially if you take a propane torch to the adjacent hardware.


#7

I’d strongly recommend against returning to any shop that opens the calipers with localized heat and then replaces simply one stuck pad.

First off, callipers stick for a reason. Replacing the pad does nothing to correct the reason. A caliper stuck that bad should be replaced.

Secondly, excess heat can not only boil the fluid, it can also destroy the seals and O-rings inside the caliper.

Thirdly, pads should be replaced in sets. There is never a reason to replace only one. The frictional coefficient should be shared equally between all four pads on the front or rear (two pads per side). The only way to effect this is a new set.

Forthly, if you were driving with a stuck caliper, you may have damage to the disc, either warping or certainly glazing. The discs should be looked at and probably either turned (machined) or replaced.

If there were no direct and immediate connection between the actions he took and the symptoms, then we could suspect perhaps an MC (I’d ask more questions about the symptoms).

A booster is way too easy to check to suspect…and a failed booster makes the brakes hard, not soft.To check it, simply pump the brakes without the engine on until they turn hard, then hold your foot on the pedal and turn on the engine. The pedal should soften and drop a bit.

The rod…he’s guessing at the rod that goes from the pedal lever through the booster to the MC. It ain’t the rod. No way.

You may want to bring the vehicle to a reputable independant, tell him the story (or print this thread), have him check the system out, and have him flush the system with fresh fluid…not an expensive or difficult process.


#8

Thanks for your helpful advice. We indeed plan on taking the car for another opinion tomorrow.