Dangerous brake issue. They go out on bumpy roads.

Figures this would happen on a holiday weekend. Yesterday evening I was driving down a dirt road and the brakes seemed soft when I stepped on the pedal. I pumped them a couple times and then they seemed fine for a while. This morning I was driving on a bumpy paved road and I pressed on the brake pedal when coming to an intersection and it went to the floor. The only way I was able to stop was to step on the parking brake. Very scary. Even when driving through town, if I hit a few bumps, the brakes would be soft the next time I stepped on them. Dangerous when driving in heavy traffic.

I checked the fluid level and it's filled to the max line. Anything I could check now before getting it to the mechanic on Monday?

 

I would bleed your brakes, butnit sounds like the abs is kicking in. Was there a grinding noise or pulsing feel? Did any dash lights come on?

 

Check your front wheel bearings for play it it's only happening on rough road.

 

Good idea. Wasn't someone have this issue before and chased his tail for quite a while before finding a bad wheel bearing on the passenger side.

 

Maybe the brake master cylinder went for a dump.

 

While you're at home.... parked, truck running. Press on the brake pedal as hard as you can. Does the pedal ever stop moving? If it doesn't stop moving... even slightly...You probably have a leak. It could be a hairline leak...still not good. System should be completely sealed.

Start looking around for 'wet' areas around the brakes lines....master cylinder, booster, rear drum wheel cylinders, and all the brake lines.

 

I did have a pulsing feel one time on the dirt Rd, but it happened so fast this morning I couldn't say for sure if there was pulsing. I will check tomorrow morning for any relevant trouble codes and for leaks (I am working late tonight). How would I know if the master cylinder is broken?

 

Subscribing for more info. I'm having similar issues and still trying to track down the issue.

-B

 

Have you jacked up the front end and checked the wheel bearings?

 

So I bled my brakes on Monday. I wanted to drive a proper distance before posting. Seems like that fixed the issue. I just had a shop do some suspension work. I didn't think they had to take off the caliper, but maybe they did and didn't bleed the brakes.

The wheel bearings are fairly new. But just out of curiosity, how would those affect braking?

 

All six lug Tacomas use 4 piston fixed calipers on the front brakes. When wheel bearing play allows the brake rotor to move radially, the rotor pushes the individual pistons back into the caliper. On the next brake application, a lot more fluid flow is required to push the caliper pistons back out against the pads and rotor, which causes the pedal to drop far more than normal. This is more noticeable on fixed caliper systems like our trucks have, rather than a sliding caliper system. Either worn/pitted bearings or improperly torqued axle nuts can be the cause, and rough roads or cornering is what aggravates the issue as it causes the movement of the hub in relation to the spindle allowed by the bearing play.

 

glad I popped in to check out this thread, very usefull information, thanks!

 

Excellent explanation. Thank you.

 

I'm glad it made sense.

 

I've been having some recent issues with my brakes going soft. I'll depress the pedal and it'll go nearly to the floor before actually stopping. If I pump the pedal twice the actual travel of the pedal is much higher and it'll get the brakes to instantly engaged.


Things that I've done to try and remedy this issue:


1) Bleed brakes, topped off the master cylinder with basic DOT 3 fluid which resulted in marginally better braking.... but it's still spongy
2) Completely drained master cylinder, refilled with DOT 4 synthetic fluid, bled the system on all 4 corners, went through 32 oz. of fluid.
3) Re torqued the CV axle nut to 175ft/lbs
4) Bled the front with a mighty vac and used the brake pedal for the rears.


Things that I've checked:
1) No obvious leaks from around the bleeder valves or connections under the fenders
2) Both front wheel bearings are brand new and installed last week.
3) I'm running stainless braided lines front and rear.
4) Front pads are at 70% and the rears are 1 month old.


Things I still need to check:


1) Re torque the brake caliper bolts
2) Take off the rear drums and check for leaks on the spreader piston
3) Check the master cylinder for obvious leaks.
4) Double check and re tighten all brake line fittings.


Any clue as to whats going on?


-B

 

Blown 383 - have you manually adjusted your rear shoes with the star wheel adjusters?

 

Yup! I cranked them down tight and backed them off 3 clicks. This allows for the e-brake to fully engage at 7 clicks up.

 

Blown 383 - I'm curious how your issue started - if all on it's own, I'd suspect that the master cylinder is bypassing internally at times. If it started after the hydraulic brake system was opened and allowed to drain, I'd say there is still air trapped in the system - probably within the ABS modulator pump.

 

I didn't have any issues till after I installed a new set of wheel bearings in the front.

Spent some time on the truck this weekend and I bled the system again, re torqued the CV axle nuts to 175lbs, inspected all of the brake fittings, and tested all 10 of the caliper pistons individually. So it seems that the next step would be to test the master cylinder. Does anyone locally have access to an Intelligent tester to bleed the master cylinder?

-B

 

maybe it is this

when on any of my toyotas

1999 4runner
2010 yaris
2013 tacoma

if I am hitting --washboard or rippling bumps and braking--

when the tire is in the air the wheels obviously come close to lock for that fraction of a
second so ABS drops pressure and if the speed is just right and the bump frequency is just right
ABS does make you lose your brakes and it is quite scary. the only fix is to get past the washboard
section and hope the rears are braking

just going slower on washboard gravel fixes the issue, but if you are jamming along and suddenly
have to brake -and it is washboard- it's like no brakes at all for a moment