Question Question about replacing brake pads and possible problem

[rkircher]

I have a 2006 Sequoia Limited with the full anti lock VCS braking system and traction control etc. I recently replace the rear break pads and rotors. Everything went well and the brakes have been working fine as far as I can tell.

Took the truck in for state inspection yesterday and they tell me that my driver side front wheel isn't braking properly and according to the chart is hardly grabbing at all. Front pads and rotors look fine to me. The thing still seems to have plenty of braking power and it doesn't seem to pull but the pedal does seem a but softer than it did even right after I did the rears.

Is there something I may have missed when I did the back brakes that could cause this problem? Does the VCS system requires some sort of reset or something? Did I do something wrong? There are no warning lights on in the dash...

Is there anywhere I can find the proper procedures for replacing pads and rotors for this truck?

The resivour has plenty of fluid and none of the brake line or bleaders were cracked open to let any air into the system.

Any help would be greatly appreciated.

Thanks,
Rob

[MEvang]

Rob,
I don't believe you have a problem at all. If your left front brake was not "grabbing" at all you would definitely have a hard pull to the right when you stop.
My thought is it is their equipment. I don't know what they are using to test the braking, but I would guess it's some kind of drive over slip plate system like this one by Hunter Inspection Lane: Computerized Vehicle Inspection
If you can confirm they are using this unit we can maybe find out for sure why it might read wrong. I have never used this type of equipment personally so I don't know for sure. My guess is they were somehow getting the ABS to kick in at that wheel. Part of a sensed wheel skid would be to first isolate that wheel from line pressure and then if the skid continues, bleed off the pressure.
These drive over testers can only point out a potential problem. A true test would be to install line pressure gauges and check the pressure at each wheel.
I hope they didn't flunk you for this!
Mike

[rkircher]

Originally Posted by MEvang

Rob,

Originally Posted by MEvang

I don't believe you have a problem at all. If your left front brake was not "grabbing" at all you would definitely have a hard pull to the right when you stop.
My thought is it is their equipment. I don't know what they are using to test the braking, but I would guess it's some kind of drive over slip plate system like this one by Hunter Inspection Lane: Computerized Vehicle Inspection
If you can confirm they are using this unit we can maybe find out for sure why it might read wrong. I have never used this type of equipment personally so I don't know for sure. My guess is they were somehow getting the ABS to kick in at that wheel. Part of a sensed wheel skid would be to first isolate that wheel from line pressure and then if the skid continues, bleed off the pressure.
These drive over testers can only point out a potential problem. A true test would be to install line pressure gauges and check the pressure at each wheel.
I hope they didn't flunk you for this!
Mike

Thanks Mike, to be honest I think you are correct and yes they do use a slip plate system like the one in your example. I was tempted to bring it back to the inspection station to day and have it retested but didn't have time.

As to pull there is the slights bit of pull if I take my hand off the wheel and apply firm pressure to the pedal. Who knows it may have always been this way but of course I've never looked for it so I wouldn't have noticed. You certainly can't feel any pull in the wheel when breaking.

My next concern is over the past 10 days or so the pedal does seem a bit spongier than it did before. Could just be that I didn't bleed the system after I did the back brakes but as I said nothing was cracked open so no air should have been introduced to the system.

My real worry is this is the first time I've done the brake pads and rotors on this vehicle or on a vehicle with this type of sophisticated braking system. So I was concerned I may have done something to damage the system when I did the back brakes. I did it the way i've alwasy done it, remove the caliper and apply steady pressure to the push the piston back in. Blow out all the brake dust and debris, replace the pads and reinstall the caliper. Put the cap back on the master cylinder and pump up the brakes until firm.

The front still have some wear on them as they were replaced a little more than a year ago (not by me) but I have rotors and pads so I was thinking about just replacing them tomorrow anyway.


One last question regarding bleeding. Can I bleed this system like older systems or do I need special tools due to the ABS. Any suggestions or tips?

Thanks again for you help.

[MEvang]

The change in pedal feel could be from the brand of pad your using. I'm an advocate for using OEM pads on Toyotas. Also be aware that Toyota has made some shim changes on some models and pad part numbers. If you buy OEM pads look at them and see if the shims are in the box or attached. Also have the parts department check for a upgraded shim pack for your aplication. The old shims have been causing low pedal issues for Toyota.
You can bleed your brakes as normal, just don't allow the master cylinder to go dry. If air enter the ABS unit you may need a bidirectional scan tool to activate the ABS valves to get the air out.
I have asked DJ to take a look at this thread. He was a engineer for Hunter and I hope he can tell us about the testing equipment and what may have gone wrong.
Mike

[DJ]

Mike, you are correct that things can go wrong when using a plate brake tester. The two biggest problems are: 1) the technician who performs the test might not know what can go wrong or how to detect it when it happens; and, 2) the test apparatus can detect some, but not all, of the conditions which can invalidate a test.

To understand this, consider what the tester is and how it is used. The link you provided earlier explains much of the system.

The test apparatus has four flat plates which sit in a framework that is bolted to the floor. Each plate is mounted such that it could move fore-and-aft if it weren't constrained by a force measuring transducer. Each plate also uses force transducers to measure the downard force exerted by the weight of the corresponding vehicle wheel as it sits on the plate.

In use, the operator simply drives the vehicle onto the plates and steps on the brakes to bring the vehicle to a quick stop. This should be a hard stop, as the vehicle has to stop within the length of the plates. The four force measurement transducers measure the braking force exerted on the plates when the brakes are applied, after which the computer which controls the system analyses the results.

As the displays shown here illustrate nicely, the system compares the braking forces exerted left v. right and front v. rear. In Rob's case, the results resemble those shown at the lower right of that page, wherein the left front wheel shows much less braking force than it should.

The guiding principle behind evaluating the situation when the test shows that braking is not quite correct is this: It is extremely unlikely (if it is possible at all) that something will go wrong during the test such that the results will show everything is just dandy. So, the number one rule in using the equipment is this: If the test shows a problem, test it again to make sure the cause was not a test that was performed incorrectly. The difficulty in following this rule when it is used at an inspection facility is that they are often designed for a fast throughput of vehicles, and so the operators might balk at a quick re-test. A slow retest is easy; just go to the back of the line and wait your turn.

Now, just what might have gone wrong in this case to produce the stated result? Without knowing any details of the situation, we can list the following possibilities (but without assigning a probability to any of them):

If the tires and/or plates are wet, then friction can be considerably reduced. This varies greatly from tire to tire and depends on tire design, age, temperature, and air pressure. The plates are designed to minimize the problem, but it can still be present. The effect is that a tire can skid when the brakes are applied, which greatly reduces the braking effect of the skidding tire. The system will faithfully and accurately measure that reduced braking force, but it will not know that the tire has skidded; it generally cannot tell the difference between an ineffective and/or failed brake and skidding tire due to a slick surface.

If a patch of snow, ice, slush, mud, or even a patch of dry, dusty, or sandy dirt, is present on the plate, the same problem as with wet tires can occur. Such a condition might not be noticed, as the offending dirt might have been dropped onto the plate by a previous vehicle. In particular, this can effect a single plate, whereas wet plates due to rainy weather more likely affect all plates together.

Because the stop is a quick, hard stop, it is possible that only a single tire skids.

If a skid occurs for any reason, even if ABS is involved, the operator might not know it, and thus not be aware the problem occurred.

I notice that the Washington, DC, area had rain yesterday. Anyone want to bet that the tires and plates were wet?

So, Rob, I suggest a re-test. In particular, I suggest waiting until the roads and such have been dry for a couple of days (yeah, right; in February?). If you can, you might even consider a different test facility.

Mike is right. The results of the test should correlate with what you experience driving the vehicle. It's easy to find out what's wrong if they don't, and that's what you ought to focus on.

[rkircher]

Thanks again guys this truly has been an education.

Mike, I'm using Centric pads and rotors. I have no clue where they my fit on the good - bad scale. If you think they are bad than I’ll replace them with better. What brand would you suggest? One thing I can say is the front pads did not come with a shim kit. Any suggestions? I looked it up on the website where I bought the pads but nothing is listed. I know this isn’t' ideal but can I reuse the old shims?

I'm glad to hear I can bleed like normal I was afraid I might need speacial tools to bypass the anti lock stuff.

DJ
Very interesting description and the inspection station used a test unit almost identical to the one in the link. One thing I can tell you is there was no rain however I did run the car through the car wash about 30 minutes before the inspection and drove it the 7 or so miles from the car wash to the station. I can also say that after looking at the results the printed and the graph on the site you linked my results are exactly like the one pictured in the very last FAIL example except my dotted like running from back to front is just outside the margin.

Where I'm confused is what does this indicated exactly. That the right front is slipping or grabbing? I can also tell you that I just replaced the right front with my spare (warn but not as bad as the tire it replaced.)

Could improperly torque lugs cause this?

I'm going back for inspection early this week before I do anything alse to the car. If it fails again I'll replace the fronts and try once more. If that fails its off to the deal for a look-see.

Thanks
Rob

[MEvang]

I would not reuse old shims at this time without checking with Toyota. Since you are having a low pedal problem you may need upgraded shims. The parts department should know this right away since there will be a replacement part numbers if it applies.
I think DJ will agree, if your tires are not in good shape, this will affect the your brake test. Consider your tires are the only contact between you and the road. If they are not the same left to right or more worn left or right this will have an effect on the way the brakes can grab traction from the surface the tires are on.
ABS, traction control and stability control systems all rely on proper brake bias, the tires, and pads ability to deliver this as designed. First off the tires need to be in good condition and aired to the proper specification. Second brake formulation must be as designed by the factory or very close to it. I don't know about the pads you are using, but you can usually trust name brand as Raybestos, Wagner, ect as being close. But only one manufactures pad has been tested by the NHTSA to work properly with your system and that is Toyota's pads.
Mike

[rkircher]

Thanks Mike,

I think I may go pick up the Toyota parts from my local dealer on Monday. that way I can make sure I have the right shims.

[DJ]

Originally Posted by rkircher

[...]

Where I'm confused is what does this indicated exactly. That the right front is slipping or grabbing? I can also tell you that I just replaced the right front with my spare (warn but not as bad as the tire it replaced.)

The display indicates, via a scale superimposed over each wheel, the braking forces exerted by each tire on the plates of the test apparatus. In the last example shown at the link I provided, the scales are the same for the rear wheels, indicating identical braking forces by each. Note the "bar graph", vertically oriented, to the left of the rear wheels, showing that the braking forces are nearly the same left-right for the rear wheels.

On the front, however, it shows low braking force at the left wheel and high braking force for the right wheel. The bar graph to the right of the front wheels shows the front braking force is biased toward the right side. This indicates that, either the left front tire slipped during the test, or the left front brakes didn't work well.

Originally Posted by rkircher

Could improperly torque lugs cause this?

Nope.

Originally Posted by rkircher

I'm going back for inspection early this week before I do anything alse to the car. If it fails again I'll replace the fronts and try once more. If that fails its off to the deal for a look-see.

Good plan. If it fails again the same way, I'd suspect the left front brakes are bad.

Originally Posted by rkircher

Thanks
Rob

Happy to help.

[rkircher]

Thanks again DJ for your helpful replies. As you know its snowed here over the weekend so I've put everything on hold until the weather gets a bit better. When it does I plan to take the truck back to the inspection station and have it retested. If it fails again I will replace the front brakes with Toyota parts and try again. I'll keep you posted.

Thanks,

[rkircher]

Just an Update...

So I did finally bring the truck back for inspection. As expected it passed. Here's what I noticed at the inspection station. DC has one 8 lane facility for inspections. Each lane is similarly equipped except for the lane where the truck was first inspected. In that lane the brake test unit is much like the one in the links provided. A raised plate device that uses smooth metal plates. All the other lanes have inset grates which would greatly reduce the chance of tire skid when doing the test. I suspect that the smooth plates were the culprit in the failure.

In any event the truck made it through the second time w/o any work before hand.

Thanks again for everyone's help. Now I can wait until the weather gets better to do the front brakes.