I put new rotors and pads up front and new shoes and hardware in the rear about 4 months (5000miles) ago when I moved up to 33s. Rear drums looked good so I didnt have them turned. Blead all four corners in the proper order. Anyway...

Everything was good until recently. As of late I will jump into the truck some mornings and back out of my space and hit the brakes to shift to forward and I have nothing at the brake pedal. The pedal goes to the floor and I do not stop. I pump the pedal a couple times and I am good. This is RANDOM. Does not happen all the time.

On the trails I've been noticing that on decent declines the brakes will not hold and the truck continues to roll forward slightly. Can't really pump the brakes in such situations as the decline is too great to do so without some risk so I don't know if pumping would bring them back in these instances.

Other than that everything seems fine. No leaks, etc. Once I'm going the truck stops fine and the pedal feels as good as I can recall. I was/am planning on changing out the fluid in the entire system because it was looking a little dark when I blead and there is no guarantee that it isn't the same fluid it came off the lot with, but it didn't seem bad enough to be concerned.

Any ideas? After a search I though maybe master cylinder or booster, but not sure either of those would work/not work randomly. Just wondering what you guys think. Thanks.

 

C'mon brake guys

 

I am sticking to my guns here!
replace the booster first, then try bleeding put a 2x4 under the pedal so it doesn't go to the floor when bleeding. If you get good fluid out of all 4 then see how the brakes act for a few days. If you don't get good fluid out of the front then replace the master and follow the bleeding steps again.

I have seen too many brake problems popping up that are so similar to mine! I think this will be the solution

 

Yes, it's possible for the master cylinder to have intermittent problems, particularly if the fluid hasn't been flushed as it should.

Questions-
-if you stab the brake pedal sharply, does it go to the floor?
-if you apply the brake pedal slowly, does it go to the floor?

 

Ok with the truck running...

stabbing the brake pedal, pedal does not go to floor
apply the brake pedal slowly, pedal does go to floor

Turned off...
makes no difference, pedal does not go to floor

 

sounds like master cylinder to me.
stabbing the brakes doesn't give the fluid time to leak around the pistons and that sudden buildup of pressure would flare the seals out to the bore of the mc.

 

i had a similar issue with my runner a few weeks back. if i hit the pedal hard i had brakes, if i went smooth and slow it would go nearly to the floor, replaced my mc and everything is good to go.

 

Alright then. You think there would be anything to gain by doing the fluid exchange?

I don't want to be risking anything with my brakes, but I really need to get another couple three weeks out of it right now. I just ordered CV shafts and a diff drop that I am going to install this weekend. That had been at the top of the priority list and kinda blew the budget for this month.

If it isn't going to make any difference then I'll probably just wait until I can get the MC in there and do it then.

 

Master cylinder. That IS one of the tests, to my knowledge. If you hit the pedal normally and hold it, and it gradually goes to the floor: master cylinder.

 

Flushing out the fluid may help some, particularly if the fluid has absorbed a lot of moisture. You've said that you've had a few instances where you've had no brakes, so it comes down to what you are comfortable with doing. Chances are it'll last a few more weeks, but don't quote me on that.

 

i replaced my mc and i still have no breaks at all goes to the floor everytime i got back to bleed once then nothing and nothing out of the front

 

new or remanufactured master cylinder?
oh, and you bled the LSPV valve too?

 

From what I understand you need to flush the brake system once in a while to get rid of moisture. I think it's that same moisture that eats at the seals in the MC. Don't quote me on that since it's just a theory.

The "slow pedal to the floor" indicates that seals are leaking. Replace the MC and bleed the system until you have healthy looking fluid coming out. If it looks black and nasty just keep bleeding until it looks like it does when it comes out of the container.

 

brake fluid: DOT 3, 4 and 5.1 (not 5) are alcohol based and are hygroscopic- they absorb water from the air.
Everyone knows that water contributes to rust... so if the brake fluid absorbs water it can contribute to rust (if the fluid isn't flushed and replaced regularly). Oh, and there's that issue regarding water, when it gets hot, it boils and water vapor takes up more space than liquid water... and since vapor can be compressed whereas liquids [generally] cannot be compressed, water in the brake fluid can cause a spongy brake pedal that gets worse the more you use it....
sorry...
...back to topic....

 

I like what Abe said, when my MC was going bad it woud creep to floor when depressed for a minute.

For myself. Whats the indicators of the booster going bad? Don't mean to hijack, thought it might be of interest.

 

well its the 2nd reman mc ive put in it in 2 weeks im still new to doing alot of this stuff but, i have rear antilock as well, i also took it to LES Schwab tire factory and they put it on a machine and couldnt bleed it either so my hands are in the air

 

Put a new MC on last week and couldn't get the thing blead for the life of me. Proper order and all that. So I made an appointment with a shop that has a power bleeder. I'm told my new "reman" MC is bad (can't swing the +$100 dif for a new one right now)

Anyway, went back to the parts house and collected on my lifetime warranty after 7 days and put the new one on in their parking lot, with the help of one of their lacky weekend helpers on the bleeding. Still doesn't seem to be 100% so I have another appointment with the power bleeder tomorrow.

I'll let you know how that turns out. Hoping this doesn't turn out to be like the 3 alternator jobs in 4 months routine i went through a few years back!!! Wish they could afford a little quality control at the reman factory, haha!