Not happy with brakes

[rangerbassman]

My 05 dcab 4x4 6500 miles, will start creeping at a stop if the engine idle changes, like when the a/c compressor kicks in or out. Also when coming to a long stop it seems like it takes an unusual amount of pressure on the pedal to get it stop. I can lift my foot up slightly and reapply the same amount of pressure and it will stop rappidly. I know it sounds like the system needs bleeding. I am an 25 yr exp. ASE Master import tech. I Bled the brake just a little, no air in the lines and still feels about the same. Next I will try to adjust the rear shoes to see if this helps. REAR SHOES!!! come to the 21st century Toyota. Discs all around is the only way to go.

[wylcat]

rears adjust with the use of the parking break, but if they are way off then adjust manually. If you are a master tech then you already know to jube the landings of the backing plate and star adjuster with waterproof antiseize. also if you have any lift on it then you may need to adjust the BVP on the rear axle.

[rangerbassman]

I have never had any expirence with a BVP. I have no lift. I have noticed it back there and I have seen them on some other trucks but never had any problem with one. I know most brake shoes adjust off of the use of the parking brake. The brake problem has been there since day one and I never us the parking brake. Maybe I will go out and engage and disengage the park brake several time and see if that helps any. If I help or correct the problem I will post what I did to solve the problem. Thanks

[MEvang]

Rangerbassman,
You say it "creeps at a stop" are you getting any pedal drop, or just having trouble maintaining pedal pressure? Here's a fact, I always felt the brakes on my '01 are too sensitive. One thing I noticed on my friends '05 is the brakes are less sensitive and the brake feel is much better. Something had been changed in the brake booster between these years.
Back to your problem, most people have noticed when sitting at a stop the pedal will drop slightly any time the A/C compressor kicks on and off. This is do to a change in engine vacuum from the extra load cause by the compressor. Vacuum brake booster are very sensitive to these changes. If the pressure required to maintain locked brakes change to a degree that the truck starts creeping and you feel that stopping is unusually difficult I would look at the booster as a problem. Simple test, engine off pump the brakes to make sure there is no reserve in the booster. Start the engine with your foot on the brake, you should get a drop in pedal height. If you do get some drop, try and compare the amount of drop to another Tundra, same year. No or little drop, you've got a problem.
Second test, With it very quite in the cab push down on pedal and listen. You should here a wosh of air and then nothing. This is normal. If you continue to here a hiss after the wosh, you have a problem. Now this may be hard to hear since manufactures tend to try and cover this noise up with insulation.
One other thing to check, and this is a big problem on many Japanese vehicles, and that is brake fluid intrusion into the booster. If the rear seal has a slight leak, brake fluid can be drawn into the booster over a length of time. As the booster fill it's efficient drops off considerably. The only way to test for this it to remove the master from the booster and check for fluid. I use a piece of vacuum hose as a dip stick. Dropping it into the booster through the master cylinder hose and looking for sighs of fluid. If this is the problem first replace the master cylinder of course, the fluid in the booster can be sucked out but most time it damages the rubber diaphragm.
If all this is ruled out we can look at some other possible causes.
Fellow ASE Master Tech
Mike

[shall36]

On adjusting the rear brakes....an old trick is to get a feel for pedal pressure and height on engagement, then fully apply the parking brake and re-check pedal pressure and height. If engagement is more firm and higher up on the pedal, rear brakes need to be adjusted.

On general pedal feel, I think the brakes work better when the truck is loaded, indicated that I need to adjust the rear proportioning valve. Just haven't got around to it.

Bleeding is likely not the culprit. If you think bleeding will help, get a pressure bleeder. They're awesome. I use one and it make flushing and bleeding a snap. those with Corvettes know it's the only way to go!

[MEvang]

On load sensing valves:
Just for my own information, does any one know if they used load sensing valve all the way to '06. Many manufacture drop these when ABS is used. I have no information on whether Toyota continued to use this valve with ABS or let the ABS do the job.
GM's use of rear ABS all the way back into the '80s was to eliminate the need for a load sensing valve. Chrysler did the same on the Caravan and dropped their load sensing valve once ABS became standard.
Mike

[nhparrot]

Originally Posted by MEvang

On load sensing valves:
Just for my own information, does any one know if they used load sensing valve all the way to '06. Many manufacture drop these when ABS is used. I have no information on whether Toyota continued to use this valve with ABS or let the ABS do the job.
GM's use of rear ABS all the way back into the '80s was to eliminate the need for a load sensing valve. Chrysler did the same on the Caravan and dropped their load sensing valve once ABS became standard.
Mike

Th '06 Tundra has a LOAD SENSING PROPORTIONING AND BY−PASS VALVE (LSP & BV)

[rangerbassman]

My 05 has abs and the load senseing valve.

[cupidstoy]

my understanding is that abs and the lsb and pv valve accomplish two very seperate and necessary functions and both are needed.

abs: modulates the braking pressure either on or off to the wheel it is controlling thus allowing the wheel to still turn under maximum braking to give some steering control

lsb and pv: actually adjusts brake bias between front and rear based on available traction to the rear wheels as a function of weight in bed (over rear axle). can also be adjusted within a narrow range to accomplish bias adjustment to compensate for changes in front or rear pad material, rotor type/size and different types of tires.

unless the ABS system allows for continuously variable pressure applied to each wheel, you would still need some type of bias valve. i believe most production vehicles have a bias valve built in to the braking system at some point but most are not user adjustable. toyota does us a huge favor by making ours easy to find and adjust on the tundra.

abs not to be confused with VSC or the other types of traction control devices available on some later models.

[MEvang]

Your right to some degree. Here's the scoop.
Proportioning valves, as they are called are used to merely slow down the pressure to the rear drum brakes. If you have the same line pressure going to the front as to the rear, the rears drums, which are self energizing they will always lock up before the front discs.
Load sensing valves take this a step further. Used mostly on utility vehicles, they are used to drop this line pressure even more when the vehicle is unloaded. Applying more pressure as the load increases. It does this by measure ride height. So changes to the suspensions ride height mean you must readjust this valve to compensate.
Most manufactures will still use a proportioning valve along with the load valve, but not always.
ABS is used to keep one wheel or a full axle from locking up individually. This is actually what the load sensing valve does, but ABS uses electronics to sense a lock up instead of relying on a static chassis height reading. ABS is much more sophisticated. ABS can do this very quickly, it has the ability to not just cut off brake pressure but to hold a pressure if need be. All in the name of no lock up. Bad thing about ABS is once the action starts it's out of your hands. Or Foot!
Now here is some history of how things progressed. Proportioning valves have been around and used since disc and drum combos have been used. On trucks, and vans of old, it was found that in wet condition with no load the rear brakes would easily lock up and create an unsafe condition. As more trucks where used for noncommercial use, this issue became a big concern. The big three began using the proportioning valves to bias out the rear brakes more and more (about early '80s). Now trucks that worked, burnt up the front brake constantly. GM truck of the early '80 where known for bad brakes because of this. Late '80 the big three added rear ABS to their truck lines, many import followed. The idea was to turn up the rear brake bias and let the ABS keep the rear brake from locking in wet slippery conditions. Toyota and a few others went a different way the used a load sensing valve to cut the bias and never offered a rear ABS alone.
Now in a sense the load sensing valve is not needed with ABS since it can be used to keep the rears under control. But a well working load valve is a better way to control the pressure issue and keep the ABS from kicking in unnecessarily.
Now Sorry for this long drawn out post, but hopefully you will understand that when you drive you truck unloaded the front brake do most of the work. If you chose to set more brake bias on the rear you could create an unsafe condition that you may not know about until you get in to a bad situation. And further more lift kit can render the rear brakes usless unless if this valve is not readjusted.
MIke

[cupidstoy]

thanks for the extra info, mike. very helpful and imformative as usual.

on my tundra, i don't believe i have an ABS that allows any more than the basic pulsating off and on behavior when it is activated. i don't think it is sophisticated enough to apply partial braking to any one wheel like some of the trucks with VSC or TRAC or whatever they are called.

i think the most important thing about the lsp and bv is to know it is there and that mods you make to your truck can and will affect how it operates. i've ready many posts on TS about folks who have lifted their trucks and not even checked their brake bias and adjusted their lsb and pv valve. then they wonder why they go through front pads every 20000 miles and have black dust problems on the front wheels! this is a basic MUST DO anytime you mess around with the ride height (distance between axles and frame) or the pad materias on the brakes.

the factory settings are a starting point based on the way the truck comes stock. i would even go so far as to say that the factory settings might not be quite right in the real world driving conditions of a stock truck. on my truck, i ended up making a minor adjustment to get the rear brakes to participate a little more during normal around town driving. made a HUGE difference in my braking confidence and the pad wear on the fronts as evidenced by no longer having a bad brake dust problem in the front. this is after i adjusted the rear pads correctly and drove several thousand miles to make sure the front and rear pads were working as well as possible before messing around with the lsb and pv adjustment.

if you're going to try to adjust the lsb and pv on your truck it is very important you know what you are doing and do it in a safe, controlled manner to avoid the kind of nasty surprises mike is talking about. if you don't know or aren't sure, take it to a professional who understands the complete tundra braking system and how to improve your performance in a safe way.

rangerbassman, did you bleed the little bleeder balve on the lsb and pv? there is one up there as well as on each of the four wheels as usual. others have reported this is a difficult place to bleed and that air trapped in the valve can be hard to get rid of. you won't be able to do it by just bleeding the wheel locations. if you suspect air in the lines, that is the first place i would start. make sure you bleed it several times and tap lightly on the valve body to help dislodge air bubbles and then do all the wheels again. you should get a better pedal.

while not impossible, i doubt your 05 has a bad master cylinder or vacuum assist already, but maybe you got a bad one from the factory? i find mike usually has good advice, so check out what he says, too.

don't worry, you'll get this problem fixed. just hang in there!

[jmiele4]

Back to the original issue of the truck creeping and the brakes feeling inadaquate. I have the exact same problem with my '05 Tundra DC 4x4 TRD. Thought it was just me, first new truck but maybe it is something to look at. Its been that way since day 1 and at 15000 miles it still does it.

[NiveK]

i have it in my truck as well, and we just got my wife a trd sport dbl cab taco and it does the same thing, just not as bad

[longwoodklon]

I'm trying to get info. on this as well, since I've put on new Powerslot rotors and still have vibration. My thinking was the rear brakes, bled them again and no air bubbles.

** So the question I have is, how much braking are the rears suppose to have?
--'01 Tundra, I can press the ebrake quite hard, I can feel the rears braking(no vibration) but not enough to lock them up.
--'05 Sienna, I touch the ebrake and the rears lock up INSTANTLY. I actually tried this in the parking lot and everyone looked at me.

So there is a BIG difference in the Tundra vs. Sienna rear brakes, both use drums. Is this what's causing my front rotors to get too hot and warp?
/Mike

[MEvang]

Here's a little more information on the Tundra brake system, now I only have an '01 service manual so things may be different on newer trucks.
Toyota does not use a conventional proportioning valve at all. All rear brake pressure change is done through the LSP&BV (Load Sensing Proportioning and By-Pass Valve) I am not sure what the by pass part is. It seem that in '01 they did use this with ABS. (My truck does not have ABS so I can't look at this on mine)
The factory recommend adjustment proceeders starts by setting the rear axle load on scales at 2094 lb for the standard can and 2205 lb AC V6, 2315 AC V8. It does not say but I would have to assume this is an unloaded weight, this means nothing in or on the bed, no tool boxes no cap no bed cover, with the vehicle weight on the axles.
Next you install a set of brake pressure gauges on the front and rear bleeders. (Most techs don't even have these. I do have a set since I use to do a lot of ABS work.)
You bring the front brake pressure up to 1138psi the rears should be at 741 + - 71 psi.
If off, adjust the shackle length, one turn should change the pressure 11psi. lengthen the shackle to increase pressure shorten it to decrees pressure.

Now back to the problem at hand, can anyone elaborate more on the brake creep? Does this mean that the pedal seems to be dropping, or does the pedal hold steady and pressure on the brakes seem to give out? This is important to know.
Also does everyone experiencing this problem have ABS on their truck?
Mike