Brakes acting up. Some times good......some times shhht (1 Viewer)

[ScotyDosentKnow]

Drove our cruiser 2500 miles on a road trip and everything was great. Have been home for several weeks and all of a sudden the brakes are acting up. Push the brake peddle and its fine. Drive it for several minutes with out hitting the brakes and then all of a sudden they engage much lower on the peddle than they should. Hit them again immediately and they are engage at the top. Hit them several times in a row and at the top. Drive for 5 minutes and engagement is very low again.

Im guessing this is a master cylinder/booster issue. I have not noticed that the fluid is low at all. I remember a thread on here describing a test sequence for the electric motor on the master but cannot find it again. Can someone link it or describe how to diagnose exactly what part is failing? This is my wifes daily driver and she is scared to drive it (dont blame her!)

 

[AlpineAccess]

Drove our cruiser 2500 miles on a road trip and everything was great. Have been home for several weeks and all of a sudden the brakes are acting up. Push the brake peddle and its fine. Drive it for several minutes with out hitting the brakes and then all of a sudden they engage much lower on the peddle than they should. Hit them again immediately and they are engage at the top. Hit them several times in a row and at the top. Drive for 5 minutes and engagement is very low again.

Im guessing this is a master cylinder/booster issue. I have not noticed that the fluid is low at all. I remember a thread on here describing a test sequence for the electric motor on the master but cannot find it again. Can someone link it or describe how to diagnose exactly what part is failing? This is my wifes daily driver and she is scared to drive it (dont blame her!)

I rebuilt the master with a new piston and bled the brakes with Toyota brake fluid and it's been good for the last year. My understanding is the pressure will build in the accumulator when you depress the pedal; so if you brake again quickly after the system functions as designed.

If you wait, the built up pressure slowly bleeds past the bad piston seal.

 

[nukegoat]

Wheel bearings

 

[ScotyDosentKnow]

I rebuilt the master with a new piston and bled the brakes with Toyota brake fluid and it's been good for the last year. My understanding is the pressure will build in the accumulator when you depress the pedal; so if you brake again quickly after the system functions as designed.

If you wait, the built up pressure slowly bleeds past the bad piston seal.

Thank you, this seems like what I have going on. I will probably give re building it a shot. Seems like a cheap alternative to try versus replacement of the whole unit.

 

[snide]

Wheel bearings

Interesting. What is the connection here? I've also had similar problems and a couple of garage's have said the braking system looks fine, so I would like to believe it will fix it but would like to understand how this is linked.

 

[Biga27110]

Interesting. What is the connection here? I've also had similar problems and a couple of garage's have said the braking system looks fine, so I would like to believe it will fix it but would like to understand how this is linked.

Pretty sure he is just trolling dont get your hopes up.

 

[snide]

Thank you, this seems like what I have going on. I will probably give re building it a shot. Seems like a cheap alternative to try versus replacement of the whole unit.

I just did some googling and, yes, I think that is what is going on with mine. Can't believe that more than one shop didn't look at that. I also recently changed the tires to KO2s and the steering has felt 'loose' ever since. I just thought it was the heavier tires and offroad tread pattern playing a little more with a pretty well worn suspension (almost 300k miles) but now I'm thinking wheel bearings are probably the culprit there as well.

 

[Biga27110]

I just did some googling and, yes, I think that is what is going on with mine. Can't believe that more than one shop didn't look at that. I also recently changed the tires to KO2s and the steering has felt 'loose' ever since. I just thought it was the heavier tires and offroad tread pattern playing a little more with a pretty well worn suspension (almost 300k miles) but now I'm thinking wheel bearings are probably the culprit there as well.

Wheel bearings, bushings, tie rod ends upper and lower ball joints it could be a million things.

 

[Eyedaho]

Pretty sure he is just trolling dont get your hopes up.

I think he's referring to wheel bearing play causing rotor runout, which pushes the brake pads/pistons into the calipers. Then it takes more brake pedal travel before the pads contact the rotor. If @nukegoat is trolling it will probably involve nightview or door mounted fuel bladders or other marvels of engineering prowess.

 

[nukegoat]

I think he's referring to wheel bearing play causing rotor runout, which pushes the brake pads/pistons into the calipers. Then it takes more brake pedal travel before the pads contact the rotor. If @nukegoat is trolling it will probably involve nightview or door mounted fuel bladders or other marvels of engineering prowess.

This is correct. The fact that it only gets bad after some driving is a good indicator. Another test might be (while parked) to pump the brakes, verify, they're firm, then cycle the steering wheel back and forth (foot off brakes) and then see if the pedal is soft again. If so, wheel bearings.

 

[nukegoat]

Pretty sure he is just trolling dont get your hopes up.

I am not

 

[ScotyDosentKnow]

This is correct. The fact that it only gets bad after some driving is a good indicator. Another test might be (while parked) to pump the brakes, verify, they're firm, then cycle the steering wheel back and forth (foot off brakes) and then see if the pedal is soft again. If so, wheel bearings.

Mine sounds more like booster issue. I will do this from the time you start driving, immediately out of the neighborhood. Pads and rotors were done maybe 6K miles ago and I put a lift on it 3K miles ago and didnt note any issues when wheels were off and it was off the ground.

 

[TreatSmash]

This is correct. The fact that it only gets bad after some driving is a good indicator. Another test might be (while parked) to pump the brakes, verify, they're firm, then cycle the steering wheel back and forth (foot off brakes) and then see if the pedal is soft again. If so, wheel bearings.

This is almost certainly what's happening to me, I just replaced my front bearings a couple days ago and now I am having the first push soft-then hard brake pedal. I did your test and after I cycle the steering wheel a couple times the pedal goes almost all the way to the floor then works fine.

So its probably the bearings...is there a way to determine which one? Can it be the races seated poorly? I can take them apart and put them back together, but I can't imagine doing it any different than I did the first time.

Do you have any further advice?

 

[nukegoat]

This is almost certainly what's happening to me, I just replaced my front bearings a couple days ago and now I am having the first push soft-then hard brake pedal. I did your test and after I cycle the steering wheel a couple times the pedal goes almost all the way to the floor then works fine.

So its probably the bearings...is there a way to determine which one? Can it be the races seated poorly? I can take them apart and put them back together, but I can't imagine doing it any different than I did the first time.

Do you have any further advice?

Just gotta figure out which one is loose and tighten it. Or all of em

 

[TreatSmash]

Just gotta figure out which one is loose and tighten it. Or all of em

Hey man, wanted to say thanks, you hit the nail on the head. I had never done some of this work before and the video I was following gave some bad advice. You saved me a lot of time, I just went back and tightened the axle nuts appropriately and problem solved.

 

[nukegoat]

Hey man, wanted to say thanks, you hit the nail on the head. I had never done some of this work before and the video I was following gave some bad advice. You saved me a lot of time, I just went back and tightened the axle nuts appropriately and problem solved.

Glad to hear it! Also an easy way to tell if they're loosening up in the future

 

[harshjay]

So, where did this thread wind up?

Random pedal engagement = wheel bearings? Which I get sort of, since the front brakes are four piston, opposing, no slide pins.

I have a pseudo similar problem.

I will apply a constant pedal pressure, and can feel the entire vehicle slowing, releasing, slowing, releasing. And, much less frequent that the wheels rotating, so not likely any rotor warp. Also, it happens intermittently.

I really don’t feel lime the brakes are great either, as in I would doubt they would lock, unless I stood both feet on rhem.

Pads are thick, no uneven wear. Rotors are clean, no heavy grooves / corrosion, full spec thickness.

60,000 miles on 2002.

Was thinking wheel bearing check, but also perhaps the electronic booster due to the pressure modulation. I do not feel any foot pedal modulation when that happens either.

Any extra thoughts? Insights?

A new Toyota booster can be found for $400, and the dealer wants $2700 for same part. So, I would be swapping myself, or providing independant shop with parts.

It floors me, how buying a Toyota part internationally, usually saves me 300-400% from local dealer.

 

[Biga27110]

So, where did this thread wind up?

Random pedal engagement = wheel bearings? Which I get sort of, since the front brakes are four piston, opposing, no slide pins.

I have a pseudo similar problem.

I will apply a constant pedal pressure, and can feel the entire vehicle slowing, releasing, slowing, releasing. And, much less frequent that the wheels rotating, so not likely any rotor warp. Also, it happens intermittently.

I really don’t feel lime the brakes are great either, as in I would doubt they would lock, unless I stood both feet on rhem.

Pads are thick, no uneven wear. Rotors are clean, no heavy grooves / corrosion, full spec thickness.

60,000 miles on 2002.

Was thinking wheel bearing check, but also perhaps the electronic booster due to the pressure modulation. I do not feel any foot pedal modulation when that happens either.

Any extra thoughts? Insights?

A new Toyota booster can be found for $400, and the dealer wants $2700 for same part. So, I would be swapping myself, or providing independant shop with parts.

It floors me, how buying a Toyota part internationally, usually saves me 300-400% from local dealer.

Dealers are a scam. Booster might be the problem. Well known. Where can you find the booster for 400? Ive heard of places rebuilding them.

 

[TexLexican]

I’ve recently changed the front and rear pads as the old ones had maybe a quarter of life left. The brake pedal travel isn’t any better, it’s actually the same. Can’t say it’d be due to the bearings since I did use a fish scale and torqued past 6 ft/lb. Also flushed the brake fluid.

Compared to my 4 runner where I felt an instant difference in pedal travel, I’m wondering if it’s master cylinder related in the 100.

 

[harshjay]

Dealers are a scam. Booster might be the problem. Well known. Where can you find the booster for 400? Ive heard of places rebuilding them.

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