Brakes-Help: Mine don't work well (uncommon problem)

So I've notice my brakes aren't working as they should and I think its limited towards the rear drum brakes. I have a 2000 4WD V6 Manual. I cannot stop/stall the car with the truck in gear and idling while pushing the brake pedal! A big problem obviously... I've went to inspect the brakes and readjusted the drum brakes and bled the entire system with new brake fluid. No visible leaks, the brake pedal feels normal, and I can stop the truck using the parking brake. That leads me to believe there is something wrong with the hydraulics. The brake fluid didn't look too bad when I bled it.
Any ideas?

 

I would suspect the booster.
When you hold the brake pedal down, while starting the truck, the pedal should go down a bit when the motor fires up.

 

also you cant rule out the Master cylinder

 

Thanks for the suggestion! I went out this morning to test it, and the brake booster seems to be okay. Brake Pedal sits at 5.5 inches. With Engine off, the brake pedal can only go to 4 inches. With Engine on, brake pedal can go to 3 inches. I recorded a video when I was testing the brake booster.

Last night I was thinking maybe the master cylinder was bad? Im not sure how to diagnose, and everything seems to be working fine (other then the fact that the brakes are weak). Everything Feels normal otherwise. I think I may have a new AISIN brake cylinder in the basement... Perhaps I should just slap it on.

Any other ideas?

 

does the brake pedal feel normal when you apply the brakes or does it seem to take a lot of pressure to apply the brakes?

 

disregard last post...the master cylinder could be bypassing the pressure applied to the brakes...ie internal failure of seals.

 

Just checked the basement and I only have the CLUTCH cylinder....Dang! Is there a way to diagnose the master cylinder before I replace it? Searches online only talk about spongy brakes or the pedal sinking to floor, which is not what I have. Could a Wheel cylinder on the rear brakes cause the problem? I replaced one (yes, only one, I know I shouldve done both) in 2010.

If I replace the wheel and master cylinder, is it okay to not go with an AISIN part? I mean, I know its okay, but would you guys go with something other then OEM for hydraulics?

 

I have always verified master cylinder operation by applying brakes on a downhill grade. Apply moderate brake pressure going downhill: if the pedal fades while on that downhill grade, i.e., travels further down than you had pressed, your master cylinder is probably defective. With a bad master cylinder and a fading brake pedal you will find you can regain braking strength by pumping the brake pedal, a sure sign of bad master cyl. Good luck and keep us posted with what you find out!

 

Try this, with trane in park engine running slam on the brake pedal and hold firm, if the pedal continues to travel to the floor that indicates the seals in the master cylindrler are bad, as some else stated fluid can leak internally causing it not to be able to apply full pressure.

 

Condition of the front rotors/pads - calipers ?

Factory rotors/pads or what ?

The front brakes perform approx. 75 - 80 % of the stopping power
whereas the rear brakes generally offer less stopping power at around 20 - 25%.
Bed load weight and the proportioning valve setting can alter the Rr brake
bias slightly, if the proportioning valve is incorrectly set. (lift - adj. ?)

Because you say the rear brakes grab/hold using the manual parking cable.
I'd suspect the problem lay primarily with the front brakes.

I might suspect that the front rotors /or pads are glazed due to escessive heat
or may be simply be worn and the rotors are not in good condition
causing the pads not to embed or seat on the rotors fully.
tho' no pictures are included that I see... so cannot say for sure.

If the rotors are grooved like an old skool record...
that could be of issue.

Of course sticking calipers may also not allow the hydraulics to compress
the caliper pistons fully, which need clamp down on the rotors tightly.

The MC/booster/hydraulics could be of fault...
But IMO, the condition/function of the rotors/pads/calipers need be ruled out first
before assuming the failure may be otherwise.

 

How about the load sensing brake adjuster? Any changes to your suspension lately? any damage to the pushrod that runs to the axle?

 

When you bled the brakes, what method did you use?

 

i wonder is it a clutch problem not a brake problem

 

Sorry for the late reply guys. I got busy... shame on me I know. Anyhow, I do believe it is the Master Cylinder. I took the truck off the jack stands and took it for a drive, and once I started to look for it, there was a considerable amount of brake fade. I inspected the front pads and rotors and they are serviceable - though I plan on replacing those aswell. I was going to do it earlier but it appears the pads I bought a year ago are for a gen 2 Tacoma (Thanks Amazon....). The Brembo rotors I have will be installed when I get the right pads. I will also be replacing the rear wheel cylinder for symmetry and I have some new shoes i got cheap too. I'll resurface the drums aswell.

When I bled the brakes, I had my wife push the brake pedal while i had the bleeder open, then closed the bleeder and told her to release the brake pedal. Did that a few times all while keeping an eye on the level of the reservoir and went in the order of RR-->RF-->LR-->LF

I replaced the clutch myself 2 years ago so i dont think that is the problem. It works fine. No complaints there. It was slipping prior. Now it bites....HARD.

I'll be ordering the parts from RockAuto so it'll be awhile before I install them. Then i get to rebleed the system.....Wife will like that...

I'm not sure what/where the proportioning valve is -- or the load sensing brake adjuster. No changes to the suspension since 2010. Not sure about the pushrod that runs to the axle. I'll look at those things now though.

 

bleeding manually should start first with the brakes
that are farthest away from the MC.

ie: Pass rear, Driver rear, Pass front, Driver front

a power bleeder works best.

a hydraulic pressure test should determine
if the MC is to blame.

 

Do this, and then if you have LSPV in the rear...bleed that last. I still had air in the system after only doing the wheels

 

The LSPV is easy to find if you have it: Find the rubber brake line feeding into the hard lines for your rear wheels, follow that up and you should have a funny looking contraption bolted to the frame right up above the left wheel, the bleeder will be facing towards the rear bumper.

Its a pain in the ass BTW, and I plan to rid my truck of that nonsense the first chance I get

 

Ive always been told to bleed brakes from the furthest from the MC...so like it was said Passenger rear, drivers rear, passenger front, drivers front. The proportion valve typically is below the MC mounted on the frame.

 

Well shiver me timbers, I never realized or remembered that the first gen LPSV had a bleeder on it. I gotta suspect that even more now.