Odd Brake Issue -- Half soft, half firm (lol)

Before a couple weeks ago, the brakes on my 03 felt typical Tacoma -- a little spongy, but worked fine.

Last week, I did a bunch of work to the rear end of the truck. New wheel bearings/seals, added Firestone airbags.

In the process discovered that one of the brake line nuts to the wheel cylinder was cross-threaded, so I replaced the nut with a new one after cutting a new flare.

On the other side, the bleeder was rusted solid to the cylinder so I replaced the cylinder.

Now, my brakes feel really different.

The top couple inches of travel are really soft -- enough braking to stop the truck at slow speeds, but much softer than before.

Then, a few inches in, the braking is much firmer and the truck stops normally. The pedal does not sink to the floor, but it's pretty deep at that point.

It feels like there are 2 stages -- the light one at first and then real braking.

Here's what I've done:

1) Bled the brakes several times w/ a pressure bleeder. No air in the lines, no leaking anywhere I can see. (my replacement fitting seems fine). Bled the LSPV too.
2) Replaced the master cylinder with a reman from NAPA.
3) Adjusted the rear drums.
4) Took all the pressure out of the airbags in case the extra lift was messing up the LSPV.

Feel is still the same and I'm stumped. Wondering if i got a bad MC or if I messed it up during the bench bleed -- accidentally pushed the pushrod into the cylinder pretty far. But that seems pretty damn unlikely.

Any thoughts?

 

Dual breaking systems behave that way due to fluid loss somewhere in the system. A damaged or poorly rebuilt master cylinder could do it also. If you are sure no fluid is escaping while braking swap a NEW master cylinder in.

 

Rear brake adjustment can be tricky sounds like they are still loose

How much drag do you have ??

Unless your flare is bad and your sucking air .

You also bleed the front brakes ?

Just poor timing rubber hoses ballooning ?

Do you have Access to a brake pressure tester?? Rebuilt part quality has gone Down Hill .

Good luck.

 

Welp, just replaced the MC with a brand-new NAPA unit. Still feels similar, though maybe a little bit better.

Rear brakes are adjusted with a little bit of audible drag.

Re-checked all the fittings for tightness, and I can't see anywhere where fluid is escaping. No puddles or anything on the ground.

Weird thing is that the truck seems to brake just fine, it's just that I have to push through that first part to get hard braking.

Not sure if maybe my brakes were badly-adjusted for a long time and I got used to it, or what.

Maybe the LSPV is out of whack, causing the rear brakes to kick in a lot earlier than the front?

 

Just re-adjusted the rear brakes to what I believe is the factory procedure (Tighten drums to where the wheel can't spin freely, then back off 15 clicks on the star wheel).

Brakes definitely are feeling more like they used to. Still a bit of a 2-stage thing going on. Wondering if the airbags are part of it, as even totally deflated, I think they still provide a little lift.

Also noticed that my LSPV rod is bent, probably by the PO, who installed a lift. Maybe I need to bend it a little more?

One thing I tried is jacking up the rear axle, then letting the wheels spin while the engine ran (not in gear, just from the fluid friction).

I watched the rear wheels spin while I pressed the brake. During the first, soft part of brake travel, they didn't stop, but at the lower part, when the pedal started getting hard, I could see the rears lock up.

 

Is the BPV Bar bent up or down?

 

Bent upwards so that the angle of the bar going into the valve is more horizontal than if it were straight. Makes sense, adding a lift probably threw the LSPV off.

 

Turns out the solution of my problem was to just bleed the shit out of the brakes. Set up the pressure bleeder (homemade one with a weed sprayer), then cracked the bleeder on each wheel for several minutes, until I'd gotten a couple cups of brake fluid out.

 

Having the exact same issue after having my brake guy replace all springs, the cylinders, turn drums, and replace pads with toyota on the rear. And then I asked him to purge the brake system.
Then my brakes felt exactly like you stated at the start, two stages. Everything was new. Intuition and experience made me think break fluid but he said it was fine.
I’ll bleed the breaks - thank you.

 

like the previous comments mentioned, the LSPV could be thrown off. Or there could just be air still in there. The LSPV has a line that returns fluid back to the master cylinder. It’s very possible that air could be trapped in there.

i had the same issue where my brakes were soft then firm. My truck spent many years up north so the LSPV was rusted shut. I removed it and the return line, replaced with a manual prop valve and the brakes have never been better. If you’re interested I can link the parts I used.

 

Also noticed ny LSPV rod is bent probably by the PO, who installed the lift...

^^^ this is important^^^

https://www.offroadwarehouse.com/pr...__pWkPkJu_YNiXFDiIpv48PEKvWNOH9CKcOYTENap5S-t

 

If the LSPV rod is bent, that means the LSPV is seized up. The rod should be able to go in and out of the LSPV (to actually perform the load sensing).