Odd Braking Issue - Advice Requested

[bdrlgion]

I've had my rig for about 3 years now. Previously, braking was normal. I could slam the brakes, and it'd come to an abrupt stop.

I knew I needed a right rear axle seal (done), rear shoes/drums from wear and tear + gear oil saturation, and front pads/rotors from wear and tear.

After another shop screwed up a bunch of work, they threw up their hands and sent it to the nearby Yota dealership at the shop's expense, which just installed new master cylinder, front calipers, rotors, pads, and rear drums/shoes on my '97 4wd SR5.

However, i'm now experiencing intermittent brake lockup upon hard braking, even as low as 10mph. I don't feel any rapid pumping, hear the ABS pump, or experience anything else that feels like ABS engaging prior to lockup. It just locks up when I brake hard, and the rig "slides" to a stop. The tires aren't locking up and skidding - it's the front brakes that are.

This model does have ABS installed. I don't think I ever experienced lockup previously on the old, worn-down brake system.

The dealership claims this is a result of the ABS system just being old/shitty, and that the new brake components are actually giving me unprecedented braking power, leading to lockup. "This is normal and good, actually. You now have more braking power than you've ever had," is what they said.

I find that really suspect. I'm struggling to understand how the heck that makes sense. I've essentially got a brand new brake system (excluding lines), and the braking experience is hands-down less than the old one.

Whatcha think? Am i being fed some BS, and something's up? My gut tells me it's still got a little air in the system, but i'm no pro.

 

[jgue467]

...It just locks up when I brake hard, and the rig "slides" to a stop. The tires aren't locking up and skidding - it's the front brakes that are...

So if the tires are not locking up under a hard brake effort and it stops, isn't that OK? Its hard to understand what the symptom is. Are you saying it nearly locks up with even the slightest brake pedal pressure?

 

[bdrlgion]

Currently, the brakes require fairly aggressive braking to lock up. They won't do so merely under light/moderate pressure.

My concern is that it's a different feel than previously. The handful of times i've had to brake aggressively prior to this round of maintenance, i'd feel ABS engage, and never once felt the front brakes lock up.

Do your brakes lock up under aggressive braking? I'd have thought ABS would kick in prior to that happening, which seemed to be the case previously.

 

[gamefreakgc]

I've had my rig for about 3 years now. Previously, braking was normal. I could slam the brakes, and it'd come to an abrupt stop.

I knew I needed a right rear axle seal (done), rear shoes/drums from wear and tear + gear oil saturation, and front pads/rotors from wear and tear.

After another shop screwed up a bunch of work, they threw up their hands and sent it to the nearby Yota dealership at the shop's expense, which just installed new master cylinder, front calipers, rotors, pads, and rear drums/shoes on my '97 4wd SR5.

However, i'm now experiencing intermittent brake lockup upon hard braking, even as low as 10mph. I don't feel any rapid pumping, hear the ABS pump, or experience anything else that feels like ABS engaging prior to lockup. It just locks up when I brake hard, and the rig "slides" to a stop. The tires aren't locking up and skidding - it's the front brakes that are.

This model does have ABS installed. I don't think I ever experienced lockup previously on the old, worn-down brake system.

The dealership claims this is a result of the ABS system just being old/shitty, and that the new brake components are actually giving me unprecedented braking power, leading to lockup. "This is normal and good, actually. You now have more braking power than you've ever had," is what they said.

I find that really suspect. I'm struggling to understand how the heck that makes sense. I've essentially got a brand new brake system (excluding lines), and the braking experience is hands-down less than the old one.

Whatcha think? Am i being fed some BS, and something's up? My gut tells me it's still got a little air in the system, but i'm no pro.

If you had air in the system, the brakes would feel 'mushy' and it would be easy to push them very close to the floor. Is this the case at all?

If not, the shop does have a point. From the factory the brake booster and ABS pump are set to allow certain brake pressure. Once an ABS sensor shows slip or wheel lockup the ABS pump will kick in and reduce brake pressure so that the tires do not lock up like what you are experiencing. When I say brake lockup, I mean tires squealing, burnt rubber and smoke on the road as your tires have stopped spinning. If the brakes are locked, the tires are locked. There's not one without the other.

If you replace with all new parts top to bottom but having aging ABS sensors on all 4 wheels and an aging ABS pump it may not be accurately seeing the brake fluid pressure and allowing the brakes to lock up.

I would recommend starting with pulling all 4 ABS sensors and look for debris, oil, or damage. They are held in place with one 10mm bolt and look like black plugs about the size of a cigarette lighter and are located right behind the wheels. Be gentle with them and use the small groove to pry them out with a screwdriver. Once out, clean off the magnets and look down the hole into the axles and make sure the ABS rings are clean without contamination - this is a bigger deal on the rear axle than the CV axles up front. Replace and see if braking behavior is improved. This shouldn't take more than 30 minutes with no rust. If rust, add several more hours and a lot of cursing and holes being punched in your garage walls.

 

[spartacus]

Currently, the brakes require fairly aggressive braking to lock up. They won't do so merely under light/moderate pressure.

My concern is that it's a different feel than previously. The handful of times i've had to brake aggressively prior to this round of maintenance, i'd feel ABS engage, and never once felt the front brakes lock up.

Do your brakes lock up under aggressive braking? I'd have thought ABS would kick in prior to that happening, which seemed to be the case previously.

Take it out on ice and apply the brakes see if the abs kicks in.

 

[bdrlgion]

If you had air in the system, the brakes would feel 'mushy' and it would be easy to push them very close to the floor. Is this the case at all?

If not, the shop does have a point. From the factory the brake booster and ABS pump are set to allow certain brake pressure. Once an ABS sensor shows slip or wheel lockup the ABS pump will kick in and reduce brake pressure so that the tires do not lock up like what you are experiencing. When I say brake lockup, I mean tires squealing, burnt rubber and smoke on the road as your tires have stopped spinning. If the brakes are locked, the tires are locked. There's not one without the other.

If you replace with all new parts top to bottom but having aging ABS sensors on all 4 wheels and an aging ABS pump it may not be accurately seeing the brake fluid pressure and allowing the brakes to lock up.

I would recommend starting with pulling all 4 ABS sensors and look for debris, oil, or damage. They are held in place with one 10mm bolt and look like black plugs about the size of a cigarette lighter and are located right behind the wheels. Be gentle with them and use the small groove to pry them out with a screwdriver. Once out, clean off the magnets and look down the hole into the axles and make sure the ABS rings are clean without contamination - this is a bigger deal on the rear axle than the CV axles up front. Replace and see if braking behavior is improved. This shouldn't take more than 30 minutes with no rust. If rust, add several more hours and a lot of cursing and holes being punched in your garage walls.

I really appreciate the thorough response.

Pedal's not mushy, booster's fine (ran self-diagnostic there). I will certainly pop those ABS sensors and inspect shorty. Fortunately, there's no rust in the area. Fingers crossed for myself + the garage walls.

I suppose what i'm experiencing isn't brake lock as you'd define it - no tires skidding, burnt rubber, etc... But at a certain point in the hard brake, i hear/feel a loud clunk and then hear loud, noticeable grinding in the front brakes combined with a sliding feel when coming to a stop. It's very different and distinct from normal braking sound and feel and only evidences itself at the end of a hard braking cycle - like a second or two into it.

 

[bdrlgion]

Maaaaaaybe it's actually just my ABS and i'm a dummy.

 

[brillo_76]

The only thought I can add as a possibility then the abs unit. Is how old are your flex lines? As these have been known to slightly collapse and cause issues of locking up the brakes from them as well as not function properly. May not be the issue just a thought.

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[gamefreakgc]

I really appreciate the thorough response.

Pedal's not mushy, booster's fine (ran self-diagnostic there). I will certainly pop those ABS sensors and inspect shorty. Fortunately, there's no rust in the area. Fingers crossed for myself + the garage walls.

I suppose what i'm experiencing isn't brake lock as you'd define it - no tires skidding, burnt rubber, etc... But at a certain point in the hard brake, i hear/feel a loud clunk and then hear loud, noticeable grinding in the front brakes combined with a sliding feel when coming to a stop. It's very different and distinct from normal braking sound and feel and only evidences itself at the end of a hard braking cycle - like a second or two into it.

That sounds a lot like the ABS pump kicking in. A drop in braking ability with a grinding, almost popping sound? Vehicle becomes hard to stop and will brake only gradually, leaving you sitting halfway into the intersection because you couldn't stop in the space provided? Definitely check the ABS sensors to make sure all is well.

A fresh set of tires makes a world of a difference. My old Cooper tires that were on when I bought it would engage the ABS all the time in the rain. New tires and it never happened again.

 

[cahilc]

I'm going to assume you've pulled check engine light (CEL) codes and no hard codes which set the check engine light.

How about the next level down in OBD2 diagnostics? Any persistent or pending codes? May not set the visible check engine light but would be recorded.

Also the ABS on our 3rd gens is nicely functional but still pre-historic compared to the current tech out there. Point being made is to correctly pull ABS codes you not only should pull codes from the OBD2 port under the dash but also pull codes using the manual diagnostic port under the hood. This implies using a jumper cables on the diagnostic plug and reading the flashing light on the dash. Then going to an ABS diagnostic chart to interpret.

I would first pull coded from OBD2 and the manual diagnostic plug as good diagnostic.
Let's say to get the complete electrical diagnostic.

There have been some excellent writeups on this forum on that procedure.

 

[19963.4lsr5]

I too think he’s hearing the abs activate.


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[gamefreakgc]

Still check your ABS sensors though regardless. Then check your tire tread with a quarter and see if they need replacing. Some A/T tires lose braking ability very quickly when they have low tread.

 

[bdrlgion]

Still check your ABS sensors though regardless. Then check your tire tread with a quarter and see if they need replacing. Some A/T tires lose braking ability very quickly when they have low tread.

Thanks a bunch! I'll definitely check the sensors shortly. The tires are practically new + high quality + 95% tread left.